Edge strength test method and equipment

Abstract

The present invention discloses an apparatus for testing a thin sheet of brittle material. The apparatus may include a plurality of assemblies configured to selectively apply a 3-point bending load to the edge of the thin sheet of material in a test region of the apparatus; a detection mechanism that optically measures the strain in the thin sheet of material in the region; and a processor that determines the stress in the thin sheet of material based on the measured strain by calculating the stress that would be required to produce the measured strain in the thin sheet of material.

Description

Technical Field

[0001] Cross-reference to related applications

[0002] This application claims the benefit of priority under the patent laws of U.S. Provisional Application No. 62 / 848091, filed on May 15, 2019, U.S. Provisional Application No. 62 / 852677, filed on May 24, 2019, and U.S. Provisional Application No. 62 / 959559, filed on January 10, 2020, the contents of each of which are relied upon and incorporated herein by reference in their entirety.

[0003] The present disclosure generally relates to apparatus for testing glass and / or glass ceramics and methods of testing glass and / or glass ceramics. Background Art

[0004] High performance display devices such as liquid crystal displays (LCDs) and plasma displays are commonly used in a variety of electronic devices such as cell phones, laptop computers, electronic tablets, televisions, and computer monitors. Currently marketed display devices may use one or more high precision glass sheets, for example, as substrates for electronic circuit components, or as color filters, to name just a few applications. The leading technology for making such high quality glass substrates is the fusion draw process, which was developed by Corning Incorporated and described, for example, in U.S. Pat. Nos. 3,338,696 and 3,682,609, which are incorporated herein by reference in their entirety; however, the embodiments described herein are applicable to any forming process, including slot draw, re-stretch, float, and the like.

[0005] For each of these applications, the glass sheets are typically cut to size, and the resulting sharp edges of the glass sheets are then beveled by grinding and / or polishing. Cutting, edge processing, grinding, and other processing steps can introduce defects, such as chips or cracks, to the surface and edges of the glass sheets. These defects can act as a source of breakage and thereby reduce the strength of the sheet, especially when the glass is flexed so that the defects are subjected to tensile stress. The display device undergoes some flexure, so the presence of these defects can be worthy of attention. Flexible display devices, by their nature, can generate significant stresses in the display substrate (s) during the manufacturing process or in use. Thus, when the glass sheets are subjected to sufficiently large stresses, residual defects that may exist in the glass sheets can cause cracks in the glass sheets. Because typical display manufacturing involves cutting glass to form individual displays, and it is known that cutting produces multiple defects in the glass along the cut edges, flexible display devices based on glass substrates can have an unacceptably high probability of breakage after the glass sheets are made into final products.

[0006] Attempts to mitigate defects at the edges of glass sheets have included laser cutting, grinding, polishing, and the like, all in an attempt to remove or minimize defects that occur when glass sheets are cut to size. However, many of these methods are unsatisfactory because the techniques are unable to remove defects down to the size required for the expected stresses or because the techniques are difficult to apply to such thin glass sheets (less than about 0.4 mm thick). Acid etching of the glass edges may be used, but this may degrade the display device disposed on the substrate. Thus, some level of defects will continue to exist in manufactured glass sheets, especially at the edges of the sheets, and there is a need in the industry to accurately test the edge strength of such glass sheets, as well as the edge strength of panels or laminate structures using such glass sheets, in order to screen out glass sheets having less than the desired edge strength.

[0007] Conventional inspection methods utilize over one hundred full-time employees who specialize in V4PTB measurements of glass edge samples. Even with this large manpower commitment, only a tiny fraction of the total output can be tested. This results in quality leakage in the form of bad products that reach consumers, which originates from low testing frequencies. In addition, because almost all allocated resources are guaranteed to keep up with quality requirements, there is almost no opportunity for process optimization research to help improve product quality. Conventional methods therefore create uncertain situations in which one person may be making a bad product but does not have the bandwidth to intercept this product before it leaves or find out how to fix the problem. However, exemplary embodiments result in a significant reduction in the amount of time devoted to edge quality control, a significant increase in the total glass tested versus produced glass, a significant increase in the percentage of edge perimeters tested, and a means for simultaneous process feedback used in the pursuit of product improvement. Summary of the invention

[0008] Exemplary embodiments will be described that are directed to methods for continuous measurement of the fracture strength of glass edges by placing the edges under stress such that the stress away from the edges is significantly less than the fracture strength at their respective locations. Additionally, using the exemplary embodiments, both sides of the edge can be subjected to substantially the same tensile stress during measurement. Additionally, the exemplary embodiments provide continuous high speed properties that result in at least a 30x increase in processing rate, at least a 3x increase in the number of sample edges tested, and several orders of magnitude in the population size of glass sheets covered by the samples of the tested edges. This increase in statistical sampling can thus ensure that fewer defects are leaked to the consumer and can be suitable for in-line configurations.

[0009] In some embodiments, an apparatus for testing the edge strength of a thin sheet of material is disclosed. The apparatus includes a plurality of assemblies configured to selectively apply a 3-point bending load along the edge of a thin sheet of material in a test region of the apparatus, whereby these assemblies can establish a load condition on the thin sheet of material in the test region by applying the 3-point bending load, and establish a no-load condition on the thin sheet of material in the test region by not applying the 3-point bending load. The apparatus also includes a detection mechanism configured to optically measure the strain in the thin sheet of material in the test region when the thin sheet of material is in a no-load condition and when the thin sheet of material is in a load condition. The load condition is generated by the 3-point bending load. The apparatus also includes a processor configured to determine the stress in the thin sheet of material based on the measured strain.

[0010] In another embodiment of an apparatus for testing a sheet of material, the apparatus may include a plurality of assemblies configured to continuously advance the sheet of material along the edge of the sheet through a test area of ​​the apparatus. The assemblies are further configured to selectively apply a 3-point bending load to the edge of the sheet of material passing through the test area. The apparatus also includes a detection mechanism configured to optically measure the strain on the surface of the sheet passing through the test area, wherein the strain is generated by the applied load. The apparatus also includes a device for determining the stress in the sheet passing through the test area generated by the applied load, wherein the stress is determined based on the measured strain. The applied load on the test area generates a strain on the surface of the test area because the load causes the test area of ​​the sheet of material to bend.

[0011] A method of testing the edge strength of a sheet of material along an edge of the sheet is also disclosed. The method includes: applying a surface pattern of visual indicia on the surface of the sheet in a region of interest along the edge of the sheet; obtaining a first optical image of the surface of the sheet in the region of interest without any 3-point bending load applied to the region of interest; applying a 3-point bending load to the region of interest along the edge of the sheet; obtaining a second optical image of the surface of the sheet in the region of interest while the 3-point bending load is being applied to the region of interest; and determining the stress on the surface in the region of interest along the edge of the sheet resulting from the application of the 3-point bending load based on the first optical image and the second optical image.

[0012] According to some embodiments, another method of testing the edge strength of a sheet of material along an edge of the sheet using a testing apparatus including a testing area is disclosed. The method includes: applying a surface pattern of visual indicia on a surface of the sheet in an area of ​​interest along the edge of the sheet; continuously advancing the sheet of material through the testing apparatus, wherein the edge of the sheet is advanced through the testing area while a 3-point bending load is applied to a portion of the sheet passing through the testing area; obtaining a first optical image of the surface of the sheet in the area of ​​interest while the edge of the sheet is continuously advancing through the testing area before the area of ​​interest reaches the testing area; obtaining a second optical image of the surface of the sheet in the area of ​​interest when the area of ​​interest advances into the testing area while the 3-point bending load is being applied; and determining a stress on the surface of the area of ​​interest along the edge of the sheet resulting from the application of the 3-point bending load based on the first optical image and the second optical image.

[0013] Other features and advantages of the present disclosure will be set forth in the following detailed description, and in part, those skilled in the art will readily understand these features and advantages from the description, or recognize these features and advantages by practicing the methods described herein (including subsequent embodiments, claims, and drawings).

[0014] It should be understood that the foregoing general description and the following detailed description set forth various embodiments of the present disclosure and are intended to provide an overview and framework for understanding the nature and character of the invention claims. The accompanying drawings are included to provide a further understanding of the present disclosure and are incorporated into and constitute a part of this specification. The accompanying drawings illustrate various embodiments of the present disclosure and, together with the description, serve to explain the principles and operation of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The following detailed description may be best understood when read in conjunction with the following drawings, in which like structures are designated by like reference numerals where possible, and in which:

[0016] 1A-1D are schematic diagrams of some examples of hardware configurations in a standard edge strength measurement system (ESMS) for performing a 3-point or 4-point bend test on the edge of a glass sheet for edge strength.

[0017] Figure 1E Schematic diagram of the 3-point bend test setup used to test the edge strength of the test specimen.

[0018] Figure 2 is a graph showing the change in load-stress at the tension side of the test panel with a change in the bonding position between the panels.

[0019] Figure 3 Graph showing the change in load-stress at the tension side of the test panel with changes in roller engagement position.

[0020] Figure 3A FIG. 1 is a schematic diagram of the basic principle of the digital image correlation (DIC) process used in the edge strength testing method described herein.

[0021] Figure 3B Graph showing stress versus time for a repeatability study of DIC at the same location during load cycling.

[0022] Figure 3C Shown is the stress distribution along the top edge during 3-point bending.

[0023] Figure 3D Shown is the overall load-stress curve for the test sample used in the repeatability study of DIC.

[0024] Figure 4 is an isometric view of one embodiment of an ESMS as disclosed herein.

[0025] Figure 5A for Figure 4 Side view of the ESMS.

[0026] Figure 5B For meshing the tested sheet Figure 5A A close-up view of the bow-shaped component of the device.

[0027] Figure 6 for Figure 4 and Figure 5A A top view of the device shown in FIG.

[0028] Figure 7 An embodiment according to the present disclosure is a specific view illustration of one configuration of an assembly for making 3-point contact with an edge of a test sheet to bend the test sheet for testing edge strength.

[0029] Fig. 8A is the sample strain field obtained at a load of 6N.

[0030] Figure 8B is a graph showing the maximum stress of a penetration test in static mode.

[0031] Figure 8CPlotted is a comparison of stress fields generated using a digital image correlation (DIC) apparatus disclosed herein compared to stress field results generated using finite element analysis (FEA).

[0032] Fig.8D Plotted are graphs showing maximum stress and displacement calculated using the digital image correlation apparatus disclosed herein and using finite element analysis.

[0033] Fig. 9A is a schematic diagram illustrating the dynamic mode of the device as disclosed herein.

[0034] Fig. 9B Schematic diagram showing a sequence of regions imaged as a sheet of material advancing through a plurality of assemblies without load.

[0035] Fig. 9C Schematic diagram showing a sequence of regions imaged as a sheet of material advancing through a plurality of assemblies with an applied load.

[0036] Fig.9D Schematic diagram showing two ways of using DIC for stress measurement of a test sheet: measuring stress on the top surface of the test sheet and measuring stress on the vertical edge surface.

[0037] Fig.9E 3D stress graphs on the edge and top surface of a glass test sheet are shown.

[0038] Fig. 10A A digital image correlation strain map of a 11 N load with 60 steps in between is shown.

[0039] Fig. 10B Shown are strain graphs from the same test with only one step confirming that they are identical.

[0040] Fig.11A On the top part of the figure a first schematic diagram of a sample configuration for use in the calibration of an ESMS is shown, and on the bottom part a top view of the test wafer depicted in the schematic diagram is shown.

[0041] Fig. 11B On the top part of the figure a second schematic diagram of a sample configuration for use in the calibration of an ESMS is shown, and on the bottom part a top view of the deflected lamella depicted in the schematic diagram is shown.

[0042] Fig. 11COn the top part of the figure a third schematic diagram of a tilted sample configuration for use in the calibration of an ESMS is shown, and on the bottom part a top view of the lamella depicted in the schematic diagram is shown.

[0043] Fig.11D On the top part of the figure a schematic diagram of a fourth sample configuration for use in the calibration of an ESMS is shown, and on the bottom part a top view of the skewed lamella depicted in the schematic diagram is shown.

[0044] Fig.12 A schematic diagram showing belt rollers that may be used in embodiments disclosed herein.

[0045] Fig.13 A schematic diagram showing a ball roller that may be used in embodiments disclosed herein.

[0046] Fig.14 Another embodiment of a DIC system according to the present disclosure shows schematic side and top view illustrations of a configuration of cameras for monitoring both the horizontal top surface of a test slide along the edge and the vertical edge surface of the test slide.

[0047] Fig.15 A schematic diagram showing the position of the force gauge relative to the position of the arch member and the test sheet 204.

[0048] Fig.16 Graphs of applied load and sample edge position showing the improved load control achieved with the improved aggregates of the ESMS disclosed herein.

[0049] Fig.17 A graph of load versus time is shown measured on ten sample sheets at a faster speed where the test sample sheet 204 moves on the rollers at a speed of 10 mm / s.

[0050] Fig.18 A graph of load versus time is shown measured on ten sample sheets at a slower speed where the test sample sheet 204 moves on the rollers at a speed of 1 mm / s.

[0051] Fig.19A is a diagram of an ESMS testing system according to one embodiment showing a test wafer mounted on a sample stage.

[0052] Fig.19B is a detailed close-up illustration of the desired roller engagement location along the edge of the test sheet 204 at a distance D from the edge E of the bottom roller 218.

[0053] Fig.19C To illustrate the beginning of the test procedure with ESMS, the front edge E of the test sheet is LIllustration of the positioning of the test sheet 204 resting above the apex of the bottom roller 218.

[0054] Fig. 20 An illustration of an example of a test wafer 204 for identifying a fly-in zone, measuring a length, and a fly-out zone.

[0055] Fig.21 Graph showing an example of load distribution from the initial cycle during lowering, flying into the zone, measuring length, and flying out of the zone of the upper rollers 220a, 220b.

[0056] Fig. 22 A schematic diagram of an example of a test sheet 204 identifying a new crack location being detected.

[0057] Fig.23A A schematic diagram illustrating the application of Phantom Motor technology to improve load control in ESMS according to an embodiment of the present disclosure.

[0058] Fig. 23B Graph of measured load counts obtained without Phantom Motor technology modification.

[0059] Fig.23C A graph of measured load counts obtained using Phantom Motor technology.

[0060] Fig.24 Graph illustrating the effect of roller diameter / polymer thickness on load and stress correlation as determined by finite element analysis.

[0061] Fig.25 Graph of stress (MPa) versus load (N) comparing two groups of panels of two different thicknesses, 0.2 mm and 0.3 mm, measured by DIC and modeled by FEA.

[0062] Fig.26A Graph of Stress (MPa) versus Load (N) showing modeled load and stress correlation for panels with different overall thicknesses.

[0063] Fig.26B is a graph of normalized change in stress versus load (N) showing normalized change in stress with respect to a change in thickness of a panel.

[0064] Fig.27A Graph of force over time measured by dynamic ESMS for 0.1 mm, 0.15 mm, 0.2 mm, and 0.5 mm thick glass sheets.

[0065] Fig.27BGraph of displacement over time measured by dynamic ESMS for 0.1 mm, 0.15 mm, 0.2 mm, and 0.5 mm thick glass sheets.

[0066] Fig.28 Schematic diagram of a test panel / sheet showing the distance d from the center of the test panel / sheet to the test location.

[0067] Fig.29 Graph showing the effect of roller mesh on load and stress correlation as determined by FEA and DIC measurements.

[0068] Fig. 30A are photographs showing examples of off-apex fractures in test panels / sheets during edge strength testing.

[0069] Fig. 30B is a graph of normalized stress versus distance from the roller apex for off-apex fracture in the test panel / sheet.

[0070] Fig.31 It is a curve diagram of ESMS stress distribution.

[0071] Fig.32 Probability versus stress graphs showing the strength distribution of a batch of panels analyzed by either the "simplified method" or the "direct" method.

[0072] Fig.33 Schematic diagram showing different panel surface nominations.

[0073] Fig.34 Schematic diagram showing the propagation of a pre-existing crack on a long edge interfering with the measurement of a short edge.

[0074] Fig.35 The stress distribution on the surface 1 and the surface 3 when the gap between the sealant and the glass edge is 0 mm is shown.

[0075] Fig.36 The stress distribution on the surface 1 and the surface 3 when the distance between the sealant and the glass edge is 2 mm is shown.

[0076] Fig.37 Schematic diagram of a machine learning neural network used to identify cracks in a test panel / sheet.

[0077] Fig.38 Schematic diagram of the panel and its design parameters.

[0078] Fig.39 Schematic diagram of the terminal and non-terminal edges of a panel engaged with rollers in the ESMS of the present disclosure.

[0079] Fig.40A flowchart illustrating a method according to an embodiment of the present disclosure is provided.

[0080] Fig.41 Another embodiment according to the present disclosure is a flow chart illustrating a method. DETAILED DESCRIPTION

[0081] For example, in the production of glass sheets for display applications, the glass sheets cut to size are subjected to a trimming process to remove sharp edges and make beveled edges by grinding and / or polishing. During these trimming processes, handling or other handling steps, residual stresses may remain on the edges of the glass sheets. These residual stresses and improper handling may cause subsequent breakage of the glass sheets. If the breakage occurs before the glass sheets are shipped to the consumer, the breakage reduces the glass manufacturing yield and interrupts the glass manufacturing process. If the breakage occurs in the possession of the consumer, typically the manufacturer of the display device that utilizes the glass sheets, the breakage will cause yield loss and interruption in the consumer's manufacturing process. Regardless of when this subsequent breakage occurs, the breakage is undesirable.

[0082] For this reason, the edge strength of glass sheets is tested in the glass manufacturing plant before the glass sheets are shipped to the consumer. A conventional method for edge strength testing is the vertical four point bending (V4PTB) method. The V4PTB test is performed on a small test coupon sample of glass cut from the glass sheet at the end of production. The size of the coupon is approximately 150 mm x 10 mm and the coupon is tested individually. Because the glass sheets are destroyed to cut out the test coupons, only a small number of glass sheets are tested and it is assumed that these glass sheets are statistically representative of the entire population of glass sheets being manufactured.

[0083] Testing sample coupons by V4PTB is a manually intensive process that takes about a day to process a sample from one glass sheet, and thus very few glass sheets are tested, e.g., about three sheets for every 22,000 sheets produced. Furthermore, such methods cannot evaluate laminate structures or panels. Such shortcomings can result in significant leaks in the form of bad products that reach consumers.

[0084] In Corning's U.S. patent application Ser. No. 15 / 557,991, published as US 2018 / 0073967 A1, an edge strength measurement system (ESMS) and related methods for non-destructively testing the edge strength of glass sheets without cutting out test specimens are disclosed. The ESMS system performs a 3-point bend test or a 4-point bend test directly on the edge of the glass sheet, thereby providing the ability to test glass sheets in production without cutting, so that a larger portion of the entire glass sheet production can be tested.

[0085] 1A-1D are schematic diagrams of some examples of hardware configurations in a conventional ESMS system for performing a 3-point or 4-point bend test on the edge of a glass sheet for edge strength. FIG. 1A and FIG. 1B are perspective and plan views, respectively, of an exemplary configuration for enabling a 3-point bend test on an edge 205 of a glass sheet 204. Roller assemblies 207b and 213b provide a 3-point bend test configuration via three rollers 215 associated with these roller assemblies, which are top sides 226 of the glass sheet 204 (see FIG. 1A ). Figure 1E ) and two rollers on the bottom side of the glass sheet 204. The roller assemblies 207c and 213c provide a 3-point bend test configuration with three rollers 215 associated with these roller assemblies, two rollers on the top side of the glass sheet 204 and one roller on the bottom side of the glass sheet 204. As described in FIG. 1B , the vertical load that bends the glass sheet 204 is applied using the rollers on the top side. As shown in FIG. 1D , the rollers 215 and glass sheet 204 are positioned so that the rollers 215 grip the edge 205 of the glass sheet 204 between the top and bottom rollers so that the vertical load force is applied to the edge 205.

[0086] 1C is a side view of an exemplary configuration for enabling a 4-point bend test on edge 205 of glass sheet 204. Roller assemblies 207d and 213d provide a 4-point bend test configuration with four rollers 215 associated with the roller assemblies, two rollers on the top side of glass sheet 204 and two rollers on the bottom side of glass sheet 204. A vertical load that bends glass sheet 204 is applied using roller assembly 207d on the top side.

[0087] The ESMS system can be useful for testing glass sheets used in the manufacture of flat panel displays, because such glass sheets must meet stringent surface quality requirements in the display area, which is typically in the central portion of the glass sheet away from the edge. Contacting the serviceable or "quality" area of ​​the glass sheet can impart surface defects that render the glass sheet unusable. The configuration of the rollers 215 in the exemplary configuration shown in FIGS. 1A-1D protects the surface quality on both sides of the glass sheet 204.

[0088] The ESMS system can be utilized to test sheet materials other than the glass sheet 204 shown in the illustrated example. For example, the ESMS system can be used to test the strength of laminated structures (also referred to as panels) of other rigid or semi-rigid materials. The laminated structure or panel may include multiple glass sheets laminated with one or more intermediate polymer layers, or in an alternative embodiment, may also include a structure having a thin film transistor glass substrate and a color filter glass substrate, the thin film transistor glass substrate and the color filter glass substrate having one or more films between or adjacent to either or both substrates. For the purposes of the present disclosure of the ESMS system and the method of using the ESMS system, the terms "sheet(s)" and "panel(s)" will be used interchangeably. Unless specifically distinguished, whether sheet(s) or panel(s) is being tested by the ESMS system will not fundamentally change the edge strength testing methodology using the ESMS system.

[0089] The structure of an example of a panel that can be tested on an ESMS will be described. Panels with different designs can be tested. Fig.38 Schematic diagram of a panel showing identification of some design parameters. W and L are the width and length of the panel, respectively. (1) is the protruding length of the terminal edge, (2) is the distance between the sealant and the panel edge, (3) is the sealant width, and (4) and (5) are the CF and TFT glass thicknesses, respectively.

[0090] There are some preferences regarding the size of the panel and the properties of the sealant in order to be tested on the ESMS. These preferences are as follows: Small-sized rectangular panels with a length (L) and / or width (W) of 600mm or less can be tested. Larger-sized panels are also measurable. Preferably, the protruding length (1) of the terminal edge is longer than the roller engagement, which can range from 0.5mm to 2mm. Preferably, the distance (2) between the sealant and the panel edge is less than 1mm. Preferably, the sealant width (3) is equal to or wider than 500um. Preferably, the thickness of the sealant is ≤10um and has a Young's modulus of 1Gpa or greater. Preferably, the interfacial bonding strength between the brittle material and the seal should be sufficient so that no delamination occurs during the edge strength test. Preferably, the total thickness of the CF glass thickness (4) + TFT glass thickness (5) is ≥0.2mm but ≤0.5mm. The CF glass thickness (4) and the TFT glass thickness (5) can be equal or different. Preferably, the mechanical rigidity of the display layers deposited on the TFT surface is negligible.

[0091] Both the non-terminal edges and the terminal edges of the panel can be tested. Fig.39 Side and top views of a panel are shown engaging rollers on both the non-terminal side edge and the terminal side edge. The terminal edge of the panel is where the TFT glass protrudes relative to the CF glass edge.

[0092] One of the drawbacks of the ESMS system described in US 2018 / 0073967 A1 cited above is that stress measurements during edge strength testing are performed using a dynamometer attached to the top side roller assemblies 207b, 207c that are used to apply the test load to the glass sheet. This is an indirect way of detecting stress in the edge. A more direct way of measuring the stress experienced by the test subject glass sheet is needed.

[0093] The aforementioned techniques for measuring edge stress and strength of ultra-thin glass sheets using a three-point bending configuration produce highly variable results. These results are subject to substantial levels of variability based on various factors, including but not limited to (a) failures prior to testing, (b) residue or dust in the system, (c) product variability (e.g., changes in panel thickness, adhesive properties / positions), and (d) alignment, among others. These sources of variability result in incorrect strength measurements and lead to unexpected product failures in the field. Figure 2 and Figure 3 Note how changes in bond location and roller meshing result in variability in stress values. Figure 2 is a graph showing the change in load-stress at the tension side of the test panel with a change in the bonding position between the panels. Figure 3is a graph of the variation of load-stress at the tension side of the test panel with changes in the roller engagement position.An additional source of variability is the fact that the three-point bending configuration described above is based on a model of the glass sheet and not on direct measurements of strain on the surface of the region of the glass sheet in question.

[0094] In contrast, the measurement apparatus and methods disclosed herein use direct image correlation (DIC) full-field imaging technology to provide real-time information about the stress distribution in the thin film 204 being tested. Using DIC, one can measure the strain on the surface of the thin film 204 in two orthogonal directions in two planes simultaneously as a function of time. Subsequently, the stress can be determined based on the measured strain and a stress field map of the thin film is generated. The direct measurement technology disclosed herein is more accurate than the previous technology and avoids the need to develop new calibration equations and models each time the glass thin film / panel is redesigned or reconfigured.

[0095] Examples of uses of the ESMS described herein include, but are not limited to: (a) calibrating currently existing edge strength testers that do not have DIC capabilities; (b) exploring failure modes of new glass sheet / panel designs since the test system has the flexibility to vary various test parameters such as roller engagement, sheet / panel angle, roller diameter, load rate, etc.; and (c) optically performing direct strain measurements during dynamic & continuous edge strength testing suitable for manufacturing plants.

[0096] Examples of benefits and advantages of the devices described herein include, but are not limited to:

[0097] Direct full-field (optical) strain measurement on ultra-thin glass panels.

[0098] Optical imaging for inspection together with full-field stress mapping provides insight into failure modes.

[0099] Real-time stress visualization during dynamic, continuous edge testing suitable for deployment in manufacturing plants.

[0100] Improved analytical equations for deriving stress from measured strain.

[0101] • Providing a novel material handling assembly that enables enhanced optical visibility of the stress measurements mentioned above.

[0102] • Ability to serve as a calibration station for existing edge strength testing equipment.

[0103] Ability to vary test parameters such as roller diameter, engagement area, roller thickness, etc. to develop new panel designs.

[0104] Accurate stress measurement with ±10% accuracy on measured stress.

[0105] Refer to Figure 4-7. Fig. 9B and Fig. 9C , discloses an apparatus 200 for testing the edge strength of a thin sheet 204 of material. The structure of the apparatus 200 described herein is an exemplary embodiment configured to optically measure strain in a thin sheet 204 when the thin sheet is in an unloaded condition and when the thin sheet 204 is in a loaded condition. The loaded condition is generated by a 3-point bending load.

[0106] The apparatus 200 may include a plurality of assemblies 206a, 206b configured to selectively apply a 3-point bending load along an edge of a material sheet 204 in a test area 208. Selectively applying a 3-point bending load means that the plurality of assemblies 206a, 206b are configured to apply or not apply a 3-point bending load as desired and also to control the amount of load applied. The apparatus 200 also includes a detection mechanism configured to optically measure strain in the sheet 204 in the test area 208 when the material sheet 204 is in an unloaded condition and when the material sheet 204 is in a loaded condition. The strain in the loaded condition is generated by the applied 3-point bending load. The apparatus 200 also includes a processor 214 (see FIG. 214 ) for determining stress in the sheet 204 based on the measured strain. Fig. 9C ). The applied 3-point bending load on the sheet 204 generates strain on the surface of the sheet 204 because the applied 3-point bending load causes the sheet 204 to bend.

[0107] Multiple assemblies 206a, 206b (see Figure 7 ) includes two opposing assemblies 206a and 206b, wherein the first of the two opposing assemblies 206a includes a single arcuate member 218 for engaging a first side of the sheet 204. The second of the two opposing assemblies 206b includes two spaced-apart arcuate members 220a, 220b for engaging a second side 230 of the sheet 204 opposite the first side. The two spaced-apart arcuate members 220a, 220b define a test area 208 between the two spaced-apart arcuate members.

[0108] The arched members 218, 220a and 220b may be rotatably mounted rollers (eg, Fig. 9A ), belt rollers, bearing rollers, or fixed bushings. Fixed bushing (e.g., non-rotating) structures are shown in Figure 4 and Figure 5BThe fixed bushing is configured to have an arcuate surface formed of a material having a low coefficient of friction (e.g., a fluoropolymer resin). In a preferred embodiment of the test apparatus 200 of the present disclosure incorporating the DIC feature, two spaced-apart arcuate members 220a and 220b are fixed bushing structures for engaging the second side 230 of the sheet 204, such as Figure 4 and Figure 5B The non-rotating bushing structure is configured to have a narrower width than the rotating roller so that when two contact points on the surface of the test sheet 204 are the same distance apart, the bushing structure provides a wider space between the two arcuate members.

[0109] In some embodiments, the detection mechanism includes a first optical system 222 for determining strain on the surface of the test sheet 204 in the test area 208. The first optical system 222 utilizes DIC technology to determine strain. The DIC technology is described in more detail below, but in essence, DIC determines strain by acquiring two images of a region of interest of the test sheet 204: a first image taken under no-load conditions, and a second image taken of the region of interest of the test sheet under load conditions, i.e., 3-point bending load in the context of the present disclosure. The surface of the region of interest is provided with some visual landmarks, so that when the two images are compared, any displacement of the visual landmarks in the load condition image caused by strain (deformation) can be detected.

[0110] As mentioned, the sheet 204 may be a brittle material such as glass or glass ceramic. The 3-point bending load is sufficient to deform the sheet 204 of material. Figure 4-5B and Figure 7 As shown in FIG. 1 , in some embodiments, the plurality of assemblies 206a, 206b include a first assembly 206a positioned below the sheet 204 including a single arched member 218 for engaging a first side (lower side) of the sheet 204 and a second assembly 206a positioned above the sheet 204 including a single arched member 218 for engaging a second side (top / upper side) of the sheet 204 opposite the first side (see FIG. 1 ). Fig.11A , Fig. 11B ). The two arch members 220a, 220b are separated by a minimum spacing S to provide a clear view of the test area 208 for the optical system. The actual size of the minimum spacing S will depend on the specific type of camera and the size of the test area 208 determined by the specific configuration of the arch members 220a, 220b and 218 selected.

[0111] The arched members 218, 220a and 220b are preferably structures that contact the sheet 204 when the arched members and the sheet are moving relative to each other while giving low friction at the contact surfaces. Some examples of such arched members are as follows: Figure 7, Figures 9A-9C and Figures 11A-11D The cylindrical roller shown in Fig.13 The bearing roller shown in .

[0112] In such Fig.12 In the belt roller embodiment shown in , the arcuate members 218, 220a, 220b can be belt rollers 240c, 240a, 240b. In the belt roller embodiment, the belt 240a, 240b, 240c extends around the drive shaft 242a, 242b, 242c and the arcuate tensioner 244a, 244b, 244c. In some embodiments, the arcuate tensioner can be a cylindrical roller or a static arcuate tensioner (such as a polished metal finger with an arcuate portion that contacts the belt). In an embodiment such as Fig.13 In the bearing roller embodiment shown in , the arcuate members 218, 220a, 220b are bearing rollers 246a, 246b, 246c. In such embodiments, the bearing rollers 246a, 246b, 246c are formed by roller balls 248a, 248b, 248c placed and held in sockets 250a, 250b, 250c.

[0113] In some embodiments, Fig. 9A As shown in FIG. 2 , a single arcuate member 218 is vertically aligned between two spaced apart arcuate members 220a, 220b. As used herein, "longitudinally" refers to the direction of movement of the sheet 204 through the test apparatus 200 (eg, the machine direction).

[0114] refer to Fig. 9B In some embodiments, the optical system 222 includes a first set of stereoscopic (i.e., a pair of) CCD cameras 222a, 222b positioned above the second side 226 of the sheet 204 to inspect the surface of the sheet 204 in the test area 208 between the two separated arch members 220a, 220b. The test area 208 is the area between the arch members 220a, 220b below the two cameras 222a, 222b, where the two cameras 222a, 222b are used for the purpose of capturing digital images for optical measurement. In other words, the test area 208 represents the field of view of the two cameras 222a, 222b. In addition, the test area 208 is the area where the three arch members 221, 220 and 218 can apply the 3-point bending test load. Thus, the test area 208 represents the target area of ​​the test equipment for applying the 3-point bending test on the test sample. The test sheet 204 to be tested needs to be brought into the test area 208 for edge strength testing.

[0115] In some embodiments, the test apparatus 200 may be operated in a dynamic mode. In the dynamic mode, edge strength testing of the sheet 204 is performed by passing the sheet 204 through the test area 208 of the test apparatus 200. Alternatively, the test apparatus 200 may be configured such that edge strength testing of the sheet 204 is performed by holding the sheet 204 stationary and traversing the test apparatus across the sheet 204.

[0116] A plurality of assemblies 206a, 206b may be included that are configured to continuously advance a sheet of material along an edge of the sheet 204 through a test area 208. The plurality of assemblies 206a, 206b are further configured to apply a 3-point bending load to the edge of the sheet of material passing through the test area 208. The apparatus 200 also includes a detection mechanism configured to optically measure strain on a surface of the sheet passing through the test area 208, wherein the strain is generated by the applied 3-point bending load. The apparatus 200 also includes a processor 214 for determining a stress generated by the application in the sheet 204 passing through the test area 208. The stress is determined based on the measured strain. The applied load on the test area 208 generates strain on the surface of the test area 208 because the applied 3-point bending load causes the sheet 204 in the test area 208 to bend.

[0117] [Digital Image Correlation (DIC)]

[0118] Now refer to Fig. 9B and Fig. 9C The DIC feature of the test apparatus 200 is described in more detail. DIC involves point tracking. Point tracking is a full-field optical technique for obtaining displacement and thereby strain. In some embodiments, the surface of the second side 226 is applied with a surface pattern 230 as a visual marker to facilitate strain measurement in both the unloaded state and the loaded state. In the loaded state measurement mode, the load imposed on the thin sheet 204 in the test area 208 deforms the surface of the second side 226 of the thin sheet 204, which in turn distorts and displaces the surface pattern 230 on the second side 226 of the thin sheet 204. The surface pattern 230 can be an array of dots or points applied on the surface being monitored, which will serve as a visual marker for measuring strain in the thin sheet 204. The array of dots or points can be in any pattern, regular or random. The image of the surface pattern 230 on the sheet 204 taken under no-load conditions serves as a reference point for determining the displacement of those reference points caused by the distortion of the surface pattern 230 produced by the subsequent application of the 3-point bending load. The first set of stereo cameras 222a, 222b in the optical system 222 observes the distortion of the surface pattern 230 and the image data can be used to determine the amount of strain in the sheet 204.

[0119] In order to make a determination of the amount of strain in the sheet 204 based on the distortion of the surface pattern 230, the amount of distortion needs to be quantified. This is accomplished by comparing an image of the distorted surface pattern 230 on the top surface 226 of the test sheet 204 with a reference / registration image of the second side 226 in an unloaded state where the surface pattern 230 is not distorted.

[0120] Whether the device 200 is operated in a static mode or a dynamic mode, an image of the surface pattern 230 in the unloaded state is recorded using the optical system 222 as a reference or baseline state. The reference image is used to record the original positions of various points in the surface pattern 230. Subsequently, the new positions of the recorded points are tracked in the loaded state image. If the top surface 226 is distorted due to the applied load stress, many of the recorded points on the top surface 226 will have been displaced from their original positions. By correlating the recorded points in the two image data, the processor 214 can determine and quantify the deformation, i.e., strain. The algorithms used to perform this digital image correlation are well known in the art and are not necessary to be discussed in more detail here.

[0121] The surface pattern 230 may be printed on the top surface 226, or projected as an image on the top surface 226, or sprayed on the top surface 226 as a random pattern, or etched on the top surface 226 using a chemical treatment, or affixed as a fabricated film having a pattern on the top surface 226. The nanoparticles may be sprayed on the top surface 226 using a spray gun. The pattern 230 may be a spot pattern or a grid pattern.

[0122] In some embodiments, the surface pattern 230 may include a coating of a mixture or blend of black dots and white dots to form a spot pattern. Stereo cameras 222a, 222b and / or 224a, 224b with appropriate lenses are used to record images of the surface pattern 230 during the test. The coating of the spot pattern 230 can be made using an oil-based black spray and a white spray that produce a fine mist that causes each spot to cover a spot of 5-7 μm. Ensure that the paint layer is less than a few microns so that the paint layer does not affect the results. White light LED lamps are used to illuminate the area of ​​interest for optical inspection by a stereo camera.

[0123] There are two ways to use DIC for edge strength measurement: one is to measure the strain on the top surface of the sample and the second is to measure the strain on the edge surface. Fig.9D The diagram in identifies the top surface 226 and the edge surface 204e on the test sheet 204. The edge strength measured according to both methods should be the same because the stress is continuous at the edge boundary. This example is shown in Fig.9E, this figure shows a 3D stress graph on the edge and top surfaces of a test sheet. The gradient in the image, represented by the dark differences in shading, shows that the stress on the top and edge surfaces is continuous. The dark shading in the gradient represents different stress levels, but the actual stress values ​​are not important for the purposes of this disclosure.

[0124] [Alternative methods of spot coating and methods for performing dynamic DIC thereof]

[0125] If the test sheet 204 is coated with a visible speckled dot surface pattern 230, then that glass sheet cannot be used in consumer applications, even if the glass sheet survives the edge strength test screening. To prevent this, technicians can use invisible speckles that are only visible to the specialized optical system utilized by the equipment (e.g., ultraviolet light, fluorescent imaging, infrared light, or another invisible portion of the electromagnetic spectrum). Alternatively, technicians can use a laser to project speckled dots onto the test sheet 204, and these speckled dots can be tracked by a camera during testing. The dot pattern can be random.

[0126] Exemplary embodiments have been described which are directed to methods for continuous measurement of the fracture strength of a glass edge by placing only the edge under stress such that the stress away from the edge is significantly less than the fracture strength at its respective location. Additionally, using the exemplary embodiments, both sides of the edge can be subjected to substantially the same tensile stress during measurement. One method for providing this continuous stress has been described in detail (e.g., reverse and offset rollers), but the claims appended hereto should not be so limited as it is contemplated that acoustic energy and / or infrared energy (coherent and non-coherent) can also be used for the same purpose to induce stress at the edge of a glass sheet. For example, focused ultrasound can be used to induce stress at the glass edge and measurements taken from the glass edge using the apparatus and methods disclosed herein. Furthermore, IR irradiation using a laser or other means (at a frequency spectrum where the respective glass material may have significant absorption) can also be used to induce stress at the glass edge and exemplary measurements taken from the glass edge using the apparatus and methods disclosed herein. Additionally, the exemplary embodiments provide continuous high speed properties that result in at least a 30x increase in processing speed, at least a 3x increase in the amount of margin tested, and orders of magnitude more wafers processed and tested relative to conventional methods. This increase in statistical sampling thus ensures less leakage to the consumer and is suitable for online configuration.

[0127] [Top surface DIC]

[0128] The basis of optical methodology DIC is shown in Figure 3ABy comparing the images at each time interval (during incremental load or before and while load is applied), the displacement of the spots can be tracked. This provides a displacement map that can be differentiated to obtain strain. This 3D DIC technique can be used to obtain a 3D strain field. Using the two (x-direction and y-direction) in-plane strain fields, the bending stress can be determined using equation (1)

[0129] Where E is the elastic modulus, ε xx is the strain along the bending direction (x), ε yy is the strain along the principal axis (y) in the other plane, and v is the Passon's ratio. Previous practice of stress conversion ignores the biaxial stress ratio of the stress state and applies Hooke's law to the uniaxial stress condition. This provides less information than the DIC technique described herein and oversimplifies the results.

[0130] [Vertical edge surface DIC]

[0131] refer to Fig.14 , a series of 3-point bending tests are performed on the test sheets 204 while the vertical edge surface 204e of each test sheet 204 is monitored using DIC. In these tests, the test sheets 204 have a laminated structure such as a display panel. The thickness of the test sheet is about 200 μm. A spot pattern 230 is made on the vertical edge surface 204e of the test sheet 204. When testing certain types of test sheets 204 such as those having a laminated structure, it may be more desirable to implement optical monitoring on the vertical edge surface 204e rather than the top (horizontal) surface of the test sheet 204.

[0132] Fig.14 A schematic diagram of an embodiment of a camera configuration of an optical system 222 of a test apparatus 200 for enabling DIC, which can optically measure strain along a vertical edge surface 204e during a 3-point bend test, is shown according to one embodiment. In this embodiment of the test apparatus 200, a second set of at least one camera 222c, 222d is provided, and the at least one camera is aimed at the vertical edge surface 204e of the test sheet 204. The at least one camera 222c, 222d is aimed at the vertical edge surface 204e in the test area 208 between the two spaced-apart arch members 220a, 220b. In a static operating mode of the test apparatus 200, the at least one camera 222c, 222d can be used to obtain an optical image of the vertical edge surface 204e under both no-load conditions and loaded conditions. Although the pair of cameras 222c, 222d observing the vertical edge surface 204e in the test area 208 is shown in FIG. Fig.14However, when viewing the vertical edge surface 204e, a single camera can be used because the vertical edge surface 204e is flat even when a 3-point bending load is applied. Because the vertical edge surface 204e is flat, a 3D view using two cameras is not necessary.

[0133] Fig.14 Also shown is a second set of at least one camera 224c, 224d aimed at the vertical edge surface 204e but at a location away from the test area 208. Similar to the camera pair 224a, 224b, the second set of at least one camera 224c, 224d can be used to obtain an optical image of the vertical edge surface 204e under no-load conditions when the test apparatus 200 is operating in the dynamic mode. Again, although in Fig.14 A pair of cameras 224c, 224d is illustrated, but a single camera can be utilized to view the vertical edge surface 204e. The processor 214 is connected to the cameras 222c, 222d, 224c and 224d, and the processor 214 can control the cameras and receive and process optical images from the cameras.

[0134] The inventors have developed two ways to make fine spot patterns. In the first way, the inventors use a fine brush with liquid paint to make a paint layer on the edge surface. Subsequently, lens tissue is used to make a pattern on the edge surface. The lens tissue has a fine random pattern on a micro scale, and the areas with fibers absorb the paint, and the areas without fibers leave the paint on the edge surface. This technology provides a good spot pattern for imaging. Another technology for making fine spot patterns is to use nanoparticles for spot pattern manufacturing. However, soft coagulation affects the quality of the spot pattern. The quality is not very reliable and stable.

[0135] Figure 3B Repeatability study of DIC for the same position during load cycles is plotted. This figure shows that the repeatability of DIC on the edge is stable. As we can see in the no-load state, the accuracy of DIC is within ±10 MPa. Using edge surface DIC, the failure mode of the panel was observed to be mainly due to stress concentration. Figure 3C The stress distribution along the top edge during 3-point bending is shown. The separate curves are the stress distribution along the top edge at different loads. Figure 3C The stress distribution is plotted from the loading to the point where the test sheet 204 breaks. From those curves, it can be seen that defects along the edge affect the stress distribution. Figure 3DThe overall load-stress curve of the test sample is plotted. It should be noted that edge surface DIC is performed at high magnification. The resolution of one pixel is about 0.5 μm, and the stress is localized at the vertex position. Variations are due to edge defects, accuracy of vertex position, and sample variations such as thickness, intrusion, layer differences, sealing level, etc.

[0136] In some embodiments, conventional acrylic paint may be used to form a very thin (a few microns) coating of the speckled surface pattern 230 on the glass sheet 204. Because the modulus of the paint is at least an order of magnitude smaller than the glass sheet 204 and its thickness is several orders of magnitude lower than the glass sheet 204, the effect of the pattern on the measurement is negligible. The use of such surface patterns in digital image correlation is well known in the art and a more detailed discussion is not necessary here.

[0137] Top surface and edge surface DIC can be performed statically or dynamically. Static DIC measures the load and stress correlations at a fixed position along the edge of the test sheet 204. Dynamic DIC measures the load and stress correlations along the entire length of the edge of the test sheet 204. Static DIC is easy to perform, but can only measure a single position at a time. Dynamic DIC is more complicated to perform, but can measure the entire length of the edge of the test sheet 204. Static DIC works best for samples such as whole pieces of glass, where the correlations do not change relative to the edge position. Dynamic DIC works best for samples such as panels with laminated structures, where the correlations can vary.

[0138] [ESMS static mode - edge strength tester with real-time stress measurement]

[0139] In a static mode embodiment, a first set of stereo cameras 222a, 222b is used to obtain both no-load measurements and loaded measurements in a step-by-step manner. A surface pattern 230 of visual indicia is provided on the top surface 226 of the test sheet 204. The test sheet 204 is moved through the test area 208 of the test apparatus in a step-by-step manner, stopping when a particular area of ​​the sheet 204 to be tested is brought into the test area 208 so that both no-load measurements and loaded measurements can be obtained.

[0140] In this example, four different areas (areas 1, 2, 3, and 4) along the edge of the sheet 204 are to be tested by Fig. 9B 204 is brought into test area 208 in the right-to-left motion illustrated in FIG. 20. To test test area 1 on the leftmost portion of the bottom edge of the sheet 204, this test area is brought into test area 208. To test test area 2, which is slightly to the right of area 1, the sheet 204 is moved to the leftmost portion of the bottom edge of the sheet 204. Fig. 9B204. The first optical system 222 includes at least two cameras 222a, 222b to optically inspect and detect deformation of the sheet in both no-load and load measurements.

[0141] The load conditions of the test equipment used for each of the test areas 1-4 are shown in FIG. Fig. 9C In the loaded state, the vertical load is applied by the two top arch members 220a, 220b or by the single lower arch member 218. In either case, the applied load causes the sheet between the arch members to bend. Each of the four loaded states corresponding to regions 1-4 is labeled Deformation 1, 2, 3, and 4, respectively.

[0142] In static mode, no-load measurements and load measurements may be performed back-to-back at each of the four test areas. Alternatively, no-load measurements for the four areas 1-4 may be performed first, then the sheet 204 may be moved back to the initial position and then load measurements may be performed for each deformation 1, 2, 3, 4 state by moving the sheet 204 across the test area 208.

[0143] Combining the 3-point bending based edge strength testing technique with the optical method of DIC with appropriate design modifications makes it possible to perform real-time stress measurements when strength testing the edges of ultra-thin monolithic or laminated glass structures (eg, thin sheets of material).

[0144] Any form of optical measurement including DIC features requires a clear direct optical view of the region of interest on the test sheet 204 in the test area 208 for measurement. In earlier systems (e.g., U.S. Patent Application Publication No. 2018-0073967), direct stress measurement did not exist and its design did not allow clear optical access to the region of interest because the rollers blocked the path. In accordance with the present disclosure of an embodiment of a DIC implementation for the test apparatus 200, the arched members 220a, 220b are modified to allow clear optical access to the region of interest for the camera. See Figure 4-7 , Figures 9A-9C ,and Figures 11A-11D This modification and resulting improvement also applies to the test apparatus 200, whether the apparatus is operated in static DIC mode or dynamic DIC mode. The key design considerations are:

[0145] • The top rollers (bow members) 220a, 220b are changed from wheels to local segments. Specifically, the local segment width is minimized for maximum optical access while maintaining the required contact area on the glass sheet 204 of the full roller. See Figure 5A and Figure 5B .

[0146] Fine micrometer level adjusters 232 are incorporated for x, y, z axis control to enable precise alignment of glass to roller / upper local section for studying the effects of meshing. Figure 5A and Figure 5B .

[0147] Fine micron-level adjustments 234 are incorporated for axis control to enable precise alignment of glass to rollers / upper local sections for studying the effects of deflection. Figure 5A and Figure 5B .

[0148] The two halves and partial sections of the fixture are all pinned together with dowel pins 236a, 236b to ensure initial test alignment. Figure 5A and Figure 5B .

[0149] With clear optical access now available to the test area 208, an optical system is designed that utilizes the technique of DIC to make real-time direct stress measurements. Two 4 megapixel commercial monochrome cameras equipped with a specialized lens system are used to observe a 7 mm x 7 mm test area 208 near the edge of the glass sheet 204. The sample is coated with a random black and white dot surface pattern 230 such that the dot size is approximately 5-7 pixels and the thickness of the coating does not exceed a few microns. Using a stereo camera system, a series of images (150-200 pairs of images at 4 frames per second) are recorded during the edge testing experiment. This series of images is correlated to obtain the strain field and thereafter, using equation (1), the stress is obtained. An example of the stress field obtained at a load step of 6 N is shown together with the maximum stress history throughout the test. Figure 8C It is believed that such stress visualization / measurement has not been done before. The results are correlated with numerical simulations (e.g., finite element analysis) and good agreement is seen, as shown in Figure 8C as shown in .

[0150] refer to Fig.40500 in Figure 5, an example of a method for testing the edge strength of a material sheet along the edge of the material sheet 204 can be summarized as follows: the method includes: (a) applying a surface pattern of a visual mark 230 on the surface 226 (second side) of the sheet 204 in the area of ​​interest along the edge of the sheet 204 (see box 510); (b) obtaining a first optical image of the surface of the sheet 204 in the area of ​​interest along the edge of the sheet without any 3-point bending load applied to the area of ​​interest (see box 520); (c) applying a 3-point bending load to the area of ​​interest along the edge of the sheet (see box 530); (d) obtaining a second optical image of the surface of the area of ​​interest along the edge of the sheet while the 3-point bending load is being applied to the area of ​​interest (see box 540); and (e) determining the stress on the surface of the area of ​​interest along the edge of the sheet resulting from the application of the 3-point bending load based on the first optical image and the second optical image (see box 550).

[0151] In some embodiments of the method of flowchart 500, step (e) of determining the stress on the surface of the region of interest along the edge of the sheet includes: measuring the strain in the material sheet 204 in the region of interest under no-load conditions based on the first optical image; measuring the strain in the material sheet in the region of interest under load conditions based on the second optical image, wherein a 3-point bending load is applied; and comparing the measured strain under no-load conditions with the measured strain under load conditions to determine the strain in the sheet induced by the applied 3-point bending load.

[0152] In some embodiments of the method, the step of measuring the strain in the sheet of material in the region of interest under the load condition based on the second optical image includes the step of determining the displacement of the visual marker 230 in the second optical image compared to the position of the visual marker in the first optical image. In some embodiments, the step of determining the stress on the surface of the region of interest along the edge of the sheet includes the step of calculating the stress that would be required to produce the measured strain in the sheet of material in the region of interest.

[0153] In some embodiments of the method, the step of applying a surface pattern of visual indicia comprises the step of printing, coating, spraying, etching, adhering or projecting an image onto the surface of the sheet.

[0154] In some embodiments of the method, the first optical image and the second optical image are obtained using an optical system including at least one camera 222a, 222b.

[0155] [Dynamic Mode - Edge Strength Tester with Algorithm for Real-time Stress Measurement]

[0156] refer to Fig. 9CIn some embodiments, the apparatus 200 may be operated in a dynamic mode, wherein the apparatus 200 may obtain both no-load measurements and loaded measurements while the test sheet 204 is continuously moving through the test apparatus 200 without pausing. In a preferred embodiment, both no-load measurements and loaded measurements are performed during a single pass of the test sheet 204 through the test apparatus 200. To accomplish this, the optical system 222 may further include a second set of stereo cameras 224a, 224b positioned in front of the test area 208 for obtaining no-load condition measurements by recording images of the test sheet 204 without a 3-point bending load applied to the test sheet.

[0157] The second set of stereo cameras 224a, 224b is positioned above the second (top) side 226 of the test sheet 204 and because the second set of stereo cameras looks at the section of the test sheet 204 in front of the test area 208 as the test sheet 204 passes by before moving into the test area 208, the second set of cameras 224a, 224b can record images of the section of the test sheet 204 under no-load conditions. Fig. 9C The leftmost illustration is an example.

[0158] In the illustrated 3-point bend test configuration imposed by the arch members 220a, 220b, and 218, the second side 226 of the test sheet 204 experiences tension as the sheet passes under the top arch members 220a, 220b and over the bottom arch member 218. In some embodiments, as Fig. 9A , Fig. 9B and Fig. 9C As shown in FIG. 1 , the arcuate members 218 , 220 a , 220 b are rollers.

[0159] A method for testing the edge strength of a sheet of material 204 along the edge of the sheet using a test apparatus 200 operating in a dynamic mode may use Fig.41600 in . The method includes: (a) applying a surface pattern of visual indicia 230 onto a surface of a sheet in a region of interest along an edge of a sheet 204 (see block 610); (b) continuously advancing a sheet of material through a testing apparatus 200, wherein the edge of the sheet is advanced through a test area 208 while a 3-point bend load is applied to a portion of the sheet passing through the test area (see block 620); (c) obtaining a first optical image of a surface of the sheet in the region of interest as the edge of the sheet continuously advances through the test area 208 but before the region of interest reaches the test area (see block 630); (d) obtaining a second optical image of a surface of the region of interest of the sheet as the region of interest advances into the test area while the 3-point bend load is being applied (see block 640); and (e) determining a stress on a surface of the region of interest along the edge of the sheet resulting from the application of the 3-point bend load based on the first optical image and the second optical image (see block 650).

[0160] In some embodiments of the method summarized in flowchart 600, the step of determining the stress on the surface of the region of interest along the edge of the thin film 204 includes: measuring the strain in the material thin film in the region of interest under no-load conditions based on the first optical image; measuring the strain in the material thin film in the region of interest under load conditions based on the second optical image, wherein a 3-point bending load is applied; and comparing the measured strain under no-load conditions with the measured strain under load conditions to determine the strain in the thin film induced by the applied 3-point bending load.

[0161] In some embodiments of the method of flowchart 600, measuring strain in the material sheet in the region of interest under load conditions based on the second optical image includes determining a displacement of the visual marker 230 in the second optical image compared to a position of the visual marker in the first optical image.

[0162] In some embodiments of the method, the step of determining the stress on the surface of the region of interest along the edge of the sheet includes the step of calculating the stress that would be required to produce the measured strain in the sheet of material in the region of interest.

[0163] In some embodiments of the method of flowchart 600, the first optical image and the second optical image are obtained by an optical system including at least two cameras 222a, 222b, 224a, 224b. In some embodiments, the step of applying the surface pattern 230 of the visual mark includes the step of printing, coating, spraying, etching, pasting or projecting the image on the surface of the sheet.

[0164] In some embodiments of the methods described above, stress is determined in at least two dimensions. The two-dimensional stress is displayed as a surface graph. Fig. 8A2D surface strain on a thin sheet when loaded by 3 point contact is shown. 216 indicates the peak strain location with high stress and 217 indicates the far field location with low stress. Figure 8B is an exemplary graph showing applied load versus maximum stress on a test sheet for multiple measurements. Figure 8C Also the 2D surface stress field on the sheet when loaded by 3-point contact. The left image is measured by DIC and the right image is modeled by FEA. Fig.8D Normalized stress values ​​are shown in relation to the perpendicular distance from the peak stress location to the inward sheet direction (shown as black arrows). Stress increases according to the applied load.

[0165] In one embodiment of this system, in addition to being a calibration unit in static conditions, it can also be used in a manufacturing environment (or other) with continuous edge testing in a dynamic mode. As discussed throughout, direct optical access to the surface of the material being tested facilitates more accurate direct strain measurements relied upon herein.

[0166] The ability to perform dynamic mode measurements is a design improvement to existing edge measurement techniques and also adds the ability to perform real-time direct stress measurements. In some embodiments, the setup described above can be modified by exchanging the partial rollers (e.g., bow members) with 3 full-function rollers that can introduce samples that are continuously fed into these full-function rollers, as shown in Figures A-9C and Figures 11A-11D . This system will have the rollers in the proper position so that the input glass edge will continuously experience the required bend / load. In this system, the spacing between the rollers and their diameters is controlled to provide a minimum spacing S between the two rollers 220a, 220b so that there is a clear optical path for camera inspection.

[0167] Figure 9B-9C The methodology used to achieve real-time stress measurement in this dynamic type of edge strength test setup is described. The edge strength tester requires pre-inspection of the edge prior to testing (the sample is passed over rollers without any load / bending) so that a pre-existing fracture can be detected. If this fracture is not detected, the system will fail or overestimate the edge strength. During this inspection, the stereo cameras 222a, 222b can capture a sequence of images along the length of the edge, such as Fig. 9B Then, when the load is applied to the edge of the sample, the camera captures the precise position on the edge as shown in Fig. 9C In a second pass of another set of images of the first sequence of images shown in , by pairing corresponding images from the same location and then correlating, one can obtain the strain field and thereby the stress, as previously described, i.e., by using Fig. 9B and Fig. 9C Images with the same number in are related.

[0168] Alternatively, an embodiment of the test apparatus 200 having two sets of stereo cameras 222a, 222b and 224a, 224b can be used to perform dynamic measurements in a single pass. An example of this embodiment is shown in Fig. 9C The system includes a first set of stereo cameras 222a, 222b and a second set of stereo cameras 224a, 224b. In such a system, the two sets of stereo cameras are connected to a processor 214, which controls the cameras 222a, 222b, 224a, 224b and also processes the image data from the cameras. The system may also include a display 228 for displaying any of the analytical information about the measured stress in the sheet 204 and displaying the images seen by the cameras.

[0169] The obvious problem that arises is that the algorithm and image correlation can obtain the strain from zero stress to peak stress without any intermediate images (150-200 images for static testing). Fig. 10A and Fig. 10B Results obtained from testing a proof of concept of this are shown and confirm that it is possible to obtain accurate results without intermediate images. A sequence of 150-200 images taken during a static test at a 11N load was correlated to obtain Fig. 10A On the other hand, Fig. 10B The stress distribution map obtained by correlating the first image with the 200th image without any intermediate images is shown. The two stress distribution maps are identical, showing that the lack of an intermediate step does not affect the results. Thus, this embodiment describes a dynamic system for edge strength measurement of ultra-thin monolithic and laminated glass samples with real-time stress visualization.

[0170] The test apparatus 200 described herein can be used to perform the method. This is referred to as the dynamic DIC method. Dynamic DIC is when it is taking strain measurements in real time as it "rolls" along an edge at 3 points. In such cases it is necessary to take the strain after a no-load measurement.

[0171] An example of a dynamic method for testing the edge strength of a sheet of material 204 along the edge of the sheet using a test apparatus 200 including a test area 208 can be summarized as follows. The method includes: providing a surface pattern 230 of visual indicia on a surface 226 of the sheet 204 including the edge of the sheet; continuously advancing the sheet of material through the test apparatus, wherein the edge of the sheet is advanced through the test area 208 of the test apparatus while a 3-point bend load is applied to the portion of the sheet passing through the test area; obtaining a first optical image of the surface of the area of ​​interest along the edge of the sheet as the edge of the sheet is continuously advanced through the test area 208 of the test apparatus but before the area of ​​interest reaches the test area 208; obtaining a second optical image of the surface 226 of the area of ​​interest of the sheet as the area of ​​interest has advanced within the test area 208 while the 3-point bend load is being applied; and determining the stress on the surface of the area of ​​interest along the edge of the sheet resulting from the application of the 3-point bend load by comparing the first optical image and the second optical image.

[0172] In some embodiments, stresses may be determined in the time-resolved domain, i.e., a stress evolution history is obtained. This may be true in a static mode, where measurements are taken at locations along the edge of the test sheet 204 when the test sheet 204 is stationary, or in a dynamic mode, where measurements are taken along the length of the edge of the test sheet 204 as the test sheet 204 is continuously fed through the test apparatus 200 while a predetermined load is applied.

[0173] It should be noted that while some embodiments are described with reference to a sheet 204 formed of glass, the claims appended hereto should not be so limited, as the test apparatus 200 described hereto may be used to accept or accommodate and analyze a laminated structure or panel. Suitable laminated structures may include multiple glass sheets with one or more intermediate polymeric layers, or in alternative embodiments, may also include structures having a thin film transistor glass substrate and a color filter glass substrate with one or more films interposed therebetween or adjacent to either or both substrates. Thus, where reference is made to a sheet 204 or glass sheet herein, reference may also be made to glass, glass-ceramic, plastic, and laminated structures and other panels. For the sake of brevity, reference will only be made to the sheet 204 herein.

[0174] The test apparatus 200 can test thin sheets of various sizes. For example, the length / width dimension of the test thin sheet 204 can range from about 5mm / 5mm, to about 100mm / 100mm, to about 600mm / 600mm, to about 1000mm / 1000mm, to about 2300mm / 2600mm, to about 4000mm / 4000mm and all sub-ranges therebetween. The length / width dimension of the glass thin sheet in the panel or laminated structure can also range from about 5mm / 5mm, to about 100mm / 100mm, to about 600mm / 600mm, to about 2300mm / 2600mm, to about 4000mm / 4000mm and all sub-ranges therebetween. In addition, adjacent glass thin sheets in the panel or laminated structure can have different length / width dimensions, which can result in overlapping of one thin sheet on another thin sheet and on one or more sides of such thin sheets. Exemplary glass thicknesses for single glass sheet testing or separate glass sheets contained in a panel or laminate structure can be less than 0.1 mm (e.g., down to 10 microns) to greater than 5 mm, between 0.1 mm and 3 mm, between 0.4 mm and 2 mm, between 0.5 mm and 1 mm, between 0.5 mm and 0.7 mm.

[0175] The platform 202 may include a plurality of drive mechanisms configured to move the glass sheet 204 into a predetermined position to initiate a measurement cycle or to continuously advance the glass sheet 204 through the testing area 208 for dynamic mode testing.

[0176] The predetermined portion of the edge of the glass sheet 204 can be tested. The width range of this predetermined portion can be from about 1mm to about 5mm, from about 1.5mm to about 3.5mm, from about 2mm to about 3mm, and all sub-ranges therebetween. Because the main purpose of testing the glass sheet 204 is to test the strength of the sheet material along the edge of the sheet material, it is usually desirable to test the area as close to the edge as possible. For this reason, for glass sheets with the size mentioned above, the last 2mm of the surface of the glass sheet 204 along the edge of the glass sheet is meshed with the arched members 220a, 220b and 218, which will usually ensure that stress concentration is at the edge of the glass sheet. This arrangement is also beneficial in minimizing the capture of foreign particles (such as dust) between the glass sheet 204 and the arched members 220a, 220b and 218, thereby any opportunity for introducing unwanted surface cracks. In embodiments where sheet 204 is a panel or laminate structure being measured for edge strength and the adjacent glass sheets in such panel or laminate structure are different (e.g., one or more edges of the structure have overlapping features), the predetermined portion is measured with respect to the smaller of the glass sheets in the structure (i.e., the non-overlapping sheets).

[0177] In some embodiments, the arch members 220a, 220b, and 218 in each or any of the assemblies 206 may be made of a compliant material to minimize the risk of creating cracks in the glass sheet 204 during non-destructive testing (e.g., not evaluating maximum stress). The arch members or rollers may be selected to have sufficient compliance while providing long life to minimize maintenance and downtime, and sufficient friction to allow the rollers to roll freely on the glass surface. Exemplary arch member materials may include hardened steel rollers, steel rollers, urethane rollers, polyetheretherketone (PEEK) rollers, 80 Shore A urethane rollers, polycarbonate (PC) rollers (e.g., polycarbonate plastics, etc.), high-density polyethylene (HPDE) rollers, 90 Shore A urethane rollers, urethane-coated rollers, etc. The exemplary urethane rollers may also be utilized to reduce rolling noise that may contaminate any signals, feedback or otherwise used by the system. Additionally, urethane rollers or urethane coated rollers may be used to accommodate debris in the roller path and provide a y-direction stress profile without inboard stress concentrations. In embodiments used to measure edge strength of panels and laminate structures, it has been found that less compliant rollers (e.g., PC, HPDE, etc.) are required to achieve adequate edge strength test results.

[0178] Exemplary dimensions for each arch member or roller may vary depending on the particular embodiment of the present invention. For example, roller sizes may range from 5 mm to 15 mm outside diameter (OD), from 7 mm to 12 mm OD, from 9 mm to 10 mm OD. In some embodiments, exemplary roller sizes may be about 9 mm OD so that stress may be applied almost all the way to the corners of the glass sheet, which is important because many consumer problems occur in this area. The exemplary system may also traverse the glass edge at speeds ranging from 5 mm / s to 500 mm / s or greater, or from 2 mm / s to 400 mm / s or greater. The exemplary system is robust and may be used on glass having a thickness as small as 0.1 mm to a thickness as large as 1 mm, depending on the durability of the polymer material used for the rollers.

[0179] In some embodiments, a high-speed dead-loop stress control mechanism can be utilized to detect cracks and ensure that the applied external force is within a target predetermined value, for example, within 2 MPa of a target. For example, a load can be applied to the glass sheet 204 using a single bow member 218, whereby a load cell signal can be sent to a high-speed controller (not shown) that continuously monitors for cracks. This load cell signal can also be used to control the applied load when traversing across the edge at a predetermined speed (e.g., 5 mm / sec to 100 mm / sec or greater).

[0180] The use of the edge strength testing apparatus 200 is not limited to the interrogation of only edge features. It is contemplated that embodiments may interrogate surface features and be used to implement defect screening in a manufacturing line. For example, some features on the surface of a glass sheet such as particle contamination and / or visible types of surface defects such as pits, debris, or scratches may be utilized with embodiments of the present subject matter. However, in such embodiments, the embodiments will utilize size, shape, and / or depth distributions, i.e., dimensional metrics, of such surface defects rather than providing intensity distributions. Exemplary and non-limiting surface features include surface proximity regions (e.g., approximately 20 mm inward from the edge) and interface regions (where the surface meets the edge) and any size, shape, or depth characteristics of surface defects. Such dimensional metrics may be used alone or in conjunction with intensity metrics obtained from edge features.

[0181] In some embodiments, the test length may span the entire edge of the glass sheet or may be performed on a portion (or portions) of the edge of the glass sheet. Thus, the test length may span from as little as about 1 mm to 5 mm to as much as about 2600 mm, 3000 mm, 4000 mm, or more, depending on the length of the glass edge.

[0182] Edge strength test based on 3-point bending

[0183] Figure 4-7 B. Figures 9A-9C and Figures 11A-11D A schematic diagram of an edge strength test apparatus 200 using a three-point bending method is shown. In a destructive failure test mode, a test sample glass panel 204 is placed under increasing loads until failure and the peak load at the failure point is recorded. This peak load is mapped to stress based on a previously empirically developed calibration curve from strain gauges. This technique provides strain / stress along two directions (x-axis and y-axis), which is a significant improvement over the current practice of using only strain along the bending direction by strain gauges.

[0184] [Optical system (camera) calibration]

[0185] refer to Figures 11A-11D, the system calibration is done before performing actual tests on the glass panels. By doing this, the image correlation software knows the angle and distance at which the camera is positioned relative to the test sample. This will help translate the movement of the dot pattern in terms of image pixels and physical dimensions in 3D space. This calibration step is schematically described in Figures 11A-11D middle. Fig.11A The relative positions of the cameras (222a, 222b), rollers and test panel are shown. Before the test begins, the top roller is farther away from the panel. Now, we swap the test panel with a predetermined (known to the image correlation software) pattern printed on a flat surface. The camera takes a series of pictures of this pattern while it is rotating in 3D space but within the camera's focus area, as shown in FIG. Figures 11B-11D A series of images and appropriate software can be used to develop a calibration file that will be used to obtain the strain during actual testing on the panel.

[0186] [Static test setup capabilities]

[0187] The static mode has the following design features that help it serve as a calibration device (or benchmark device) for studying panel / laminate designs along with other parametric studies.

[0188] Interchangeable rollers (roller material and diameter)

[0189] Ability to change feed angle. This helps solve edge testing for non-rectangular display panels.

[0190] Adjustment of the roller assembly closer or further away from the test edge. This enables inspection of specific areas of the edge together with testing of smaller panels (mobile devices).

[0191] The roller can be replaced by a local roller profile, which increases the observable area especially near the contact point and enables the stress distribution in that area to be studied without additional stresses from the roller.

[0192] It incorporates alignment techniques, such as alignment pins 236a, 236b, which accurately align the various components, which is extremely critical for the test to be accurate.

[0193] [Improvement of stress measurement accuracy in non-DIC ESMS testing]

[0194] [Dynamometer Location] In the prior art ESMS, the dynamometer is attached to the top side roller assembly and positioned. The inventors have discovered that an improvement in load control can be achieved by moving the dynamometer below the bottom side roller 218. Fig.15 Schematic diagram showing the new position of the dynamometer. No dynamometer drift was observed in the new configuration.

[0195] [Speed ​​Control] The stress on the sheet 204 varies with the load applied to the sheet. Thus, stress measurement accuracy depends on load measurement accuracy. One factor in accuracy in non-DIC ESMS testing in which a modified test sample sheet 204 is continuously fed into the test area 208 of the tester is the speed at which the test sheet 204 is moved through the test area 208. Transport of the test sheet 204 is achieved by using rollers for the arch members 218, 220a, 220b. Thus, the material used for the rollers can affect the friction between the rollers and the test sheet, which can affect the ability of the rollers to move the test sheet 204. The compliant rollers contract and expand as they rotate against the test sheet 204 and can induce changes in the load applied by the bottom roller 218. When the test sheet is moving rapidly through the rollers, the ESMS test system 200 has very little time to adjust for load changes. The inventors used a commercially available load frame Instron to investigate the effect of the speed at which the test sheet 204 moves on the rollers on load control. Fig.17 and Fig.18 The data were generated with ten (10) samples. Fig.17 The graph in the middle shows the measured load over time at a speed of 10 mm / s. Fig.18 The graph in shows the measured load over time at a speed of 1 mm / s. Load control is significantly improved when the speed is reduced from 10 mm / s to 1 mm / s. Load control also depends on the speed and accuracy with which the software of the ESMS test system can adjust for load changes. Therefore, the optimal speed should be selected to take these factors into account. With the current improved ESMS setup, the inventors were able to achieve good load control at speeds between 1 mm / s and 40 mm / s. Using a speed of 5 mm / s, for a 0.2 mm piece of glass, the inventors were able to achieve a load change of ±0.1 N or less for a 2N target, which is equivalent to a 100 ± 5 MPa stress change. Although faster speeds will result in shorter test times, some maximum limits are required so as not to compromise the ability to control the load.

[0196] [Polymer coating on rollers] In embodiments where the arched members 218, 220a, 220b are rollers, the rollers preferably have a polymer coating on the rolling surface that contacts the test sheet 204 to help move the test sheet 204. Because polymers are viscoelastic, the material can shrink and expand during rolling. Therefore, the inventors had expected that a thinner polymer coating on the rollers would be better for controlling the load applied to the test sheet 204. However, the inventors unexpectedly discovered that a thicker polymer coating provides better load control with less variability in the applied load. The overall diameter of the roller (roller bearing + polymer coating) is 9 mm. The thickness of the polymer coating is 1.32 mm.

[0197] The inventors further explored the influence of roller diameter and polymer coating thickness on the load-stress correlation to understand the possible variability of dynamic measurements. Modeling results show that for a given roller inner diameter L2 and outer diameter L1, when the roller inner diameter changes from 4 mm to 14 mm and the polymer thickness changes from 0.5 mm to 2.5 mm, the correlation changes up to 400 MPa are negligible. Fig.24 Figure 2 is a graph of the load and stress correlation as determined by FEA for roller outer diameter L1 / roller inner diameter L2. The correlation is invariant up to 400 MPa for a wide range of L1 and L2. From research, the inventors were able to understand that the possible variability of the load and stress correlation is minimal for dynamic measurements.

[0198] [Software Improvement]

[0199] Improvements were made to the control software for the ESMS system 200 to fully automate the system operation in order to make the testing operation more reliable. The system targets small ~200 x 130 x 0.2 mm test sheets / panels. Test samples as thin as 0.2 mm require more accurate load control to accurately measure stress because even small changes in load induce relatively large changes in stress. Therefore, improvements were made to the control software by improving the control loop to maintain better load control. The control software allows the ESMS to perform the following automatic procedures. One of the initial steps in the edge strength test procedure is the alignment of the test sheet 204. The desired roller engagement is at a distance D from the edge E of the test sheet 204 (typically at about 2 mm). This roller engagement position is at Fig.19B Shown in.

[0200] Before edge strength testing can begin, some pre-scan routines are performed. Such routines include generating a thickness profile of the edge of the test sheet 204 to be tested. Fig.19A, slowly moves the length of the test sheet 204 through a pair of thickness sensors 410a, 410b, which measure the thickness of the test sheet 204 and generate a thickness profile distribution of the edge of the test sheet 204 to be tested. If the test sheet 204 cracks, the thickness data allows accurate post-measurement analysis of the failure stress. This routine also finds the front edge E of the test sheet 204. L and rear edge E T and sample sheet length so that actual dimensions can be used during edge strength testing rather than link library dimensions. The test sheet 204 is positioned so that the front edge E L Position over the apex of the bottom roller 218 at the start of the edge strength test procedure. Fig.19C This configuration is shown.

[0201] Next, the ESMS drives the test sheet 204 in the direction indicated by the arrow M until the top of the bottom roller 218 is aligned with the starting offset position. Fig.19C The horizontal edges shown in are aligned. Fig. 20 Illustration of an example of a test sheet 204 identifying a fly-in zone, measuring length, and a fly-out zone. To begin the edge strength test procedure, the ESMS slowly drives the top roller assembly 220a, 220b downward toward the top surface of the test sheet 204 until a small force is detected, which means that the top rollers 220a, 220b have contacted the test sheet 204.

[0202] Next, the load force and glass test sheet speed are synchronously ramped up over the specified fly-in distance through the fly-in zone within the specified time frame. The load force is maintained along the measuring length until the fly-out zone is reached. The length of the fly-out zone is defined by the fly-out distance and the load force and glass test sheet speed are ramped down to complete the test procedure. Fig.21 Graph showing an example of load distribution from the initial cycle during lowering, flying into the zone, measuring length, and flying out of the zone of the upper rollers 220a, 220b.

[0203] [Crack Detection] Under the updated control software, the ESMS performs the following crack detection procedure. The user specifies the critical values ​​around the target load. If the critical values ​​are violated, the ESMS immediately disengages the rollers 218, 220a, 220b and stops the test sheet 204. With the test sheet 204 under the applied stress, the position of the lower roller 218 (i.e., the apex of the roller 218) is defined as the new crack location. If enough space is left along the edge of the test sheet 204 to account for the user-defined crack offset, the edge strength test continues. Fig. 22Schematic diagram of a test sheet 204 showing the location of the detected crack location. Crack offset refers to the distance the roller will move away from the detected crack before the roller can re-engage with the edge of the test sheet to restart dynamic testing. If the crack offset is too short, the crack will propagate and interfere with the measurement. If the crack offset is too large, the testable edge real estate can be wasted. Based on the modeled size and shape of the stress field, the inventors used a minimum distance of 25 mm for the crack offset.

[0204] After reengaging the test sheet 204, the ESMS cycles through all user-defined load forces as long as sufficient length of the edge region of the test sheet remains to be tested. The ESMS applies a constant force as it traverses along the edge. When rupture occurs, the strength of the test sheet 204 can be any stress between 0 and the stress corresponding to the applied force. Therefore, to accurately determine the strength of the sheet, one must apply multiple step loads in an incremental manner to better understand the lower limit of the strength. The user can define these step forces based on the level of measurement accuracy he desires. The system must cycle through all user-defined step loads until rupture occurs.

[0205] [Load Control] For controlling the 3-point bending stress load applied to the test sheet 204 by rollers 218, 220a, 220b, Phantom Motor technology (also known as Cascading Servo Loop) is incorporated into the ESMS control software. Phantom Motor technology is applied to the dynamometer analog input. The technology allows the ESMS to read the dynamometer input signal and make changes to move the sample platform 202 to control the load being applied to the test sheet 204 in real time.

[0206] Fig.23A Schematic diagram illustrating Phantom Motor technology. Delta Tau's Power PMAC motion controller can be configured in such a way that the output of a separate servo loop can be used as the input of another. This allows the system to combine the capabilities of two loops on a single actuator and allows engineers to take full advantage of the controller tuning parameters for a device that is not specifically intended to control motion. In this case, the output of the dynamometer is integrated into the motion system so that the analog output of the dynamometer is directed to the output of the servo loop inside the controller. This is called the "inner loop." The servo loop that actually controls the physical motion of the actuator then feeds the inner loop output to command physical motion. By calibrating the relationship between the two loops with the motor tuning parameters provided by the Delta Tau system, an optimal balance is achieved that allows the motion controller to respond to real-time deviations from the target load and apply necessary corrections, thereby facilitating stable load application across the sample.

[0207] Fig. 23B and Fig.23C A graph of measured load readings from the dynamometer versus time is shown to compare the dynamometer readings from the test run. Fig. 23B The graphs are for measured load readings obtained without Phantom Motor technology modification, and Fig.23C The graph in the middle is for measured load readings taken with Phantom Motor technology. Fig.23C The graph in Figure 2 shows substantially less variation in dynamometer readings when Phantom Motor technology is implemented.

[0208] [Method for estimating the strength of a panel batch]

[0209] According to some embodiments, methods of measuring the average strength of identically manufactured panels having the same design but different manufacturing tolerances are disclosed. There can be two ways of measuring the strength of multiple panels to obtain the average strength of the batch:

[0210] Directly measure the strength of all individual panels by using the optical strain measurement technique disclosed in this invention;

[0211] · Estimate the strength of all remaining panels making up the batch using nominal load-stress correlation determined by measuring a small number of samples using optical strain measurement techniques;

[0212] The first method has the advantage of being more accurate than the second method, but can be time consuming because all samples must be measured using an optical strain measurement technique, which can have multiple processing steps and a long time. The second method involves less processing time because this method can directly use the load to estimate the strength, but will have an error bar in the estimate because the same nominal correlation is used for panels with certain manufacturing tolerances. However, the second method is preferred in practice because the less testing time has the advantage of additional accuracy obtained from using the first method. Here, we describe the second method in more detail.

[0213] The nominal load and stress correlation can be obtained by performing multiple optical strain measurements (i.e., DIC) on multiple panels using static or dynamic DIC methods. A higher number of measurements will provide a more accurate estimate of the nominal correlation. As the number of measurements increases, the error bar will also increase due to manufacturing tolerances of the panels.

[0214] For example, Fig.25Load and stress graphs are shown for two different batches of panels with average thicknesses of 0.2 mm and 0.3 mm measured by DIC and modeled with FEA. While the DIC measurement results have a spread due to panel manufacturing tolerances, the FEA model shows only a single result because the nominal panel design parameters are used for the calculations.

[0215] To minimize the error from using the nominal load and stress correlation for all panels, a correction factor may be applied to the nominal load and stress correlation on each panel based on the measurement variability of each panel.

[0216] [Panel correction factor]

[0217] Thickness - For example, if a nominal load and stress correlation from a panel batch with an average thickness of 0.3 mm is applied to a panel with a thickness of 0.29 mm, the stress may be underestimated. Therefore, a correction factor may be applied based on a measured thickness of 0.29 mm. In this case, the correction factor is related to the measured panel thickness and the average thickness of the panel batch. The mathematical form of the correction factor may be obtained from sensitivity studies performed by DIC and / or FEA modeling.

[0218] If the tolerances are small, it may be difficult to characterize the effects of panel manufacturing tolerances using experimental methods such as DIC. In such cases, FEA modeling can be used to understand the sensitivity and derive correction factors. Fig.26A The modeled load and stress correlations for panels with different thicknesses of 0.1 mm, 0.2 mm, 0.21 mm, 0.22 mm and 0.25 mm are shown, and Fig.26B The normalized variation of stress and load (N) for different thicknesses is shown. By using these graphs and measuring the thickness variation of each panel, one can apply the appropriate correction factor to the nominal load and stress relationship.

[0219] Similarly, correction factors may be applied to other panel design parameters that have certain manufacturing tolerances.

[0220] [Measurement process correction factor]

[0221] The measurement location-measurement process may also involve measurement variability which should be interpreted as a correction factor. For example, Fig.27A and Fig.27BForce and displacement curves versus time are shown for 0.1 mm, 0.15 mm, 0.2 mm, and 0.5 mm thick glass sheets when the glass sheets are tested on a dynamic ESMS with a constant load. Although the force remains constant for all thicknesses, the displacement curves show significantly different behavior as the roller gets closer to the corners, as shown by the rising behavior as time progresses. This indicates that as the thickness of the glass becomes thinner, the stiffness at the corners becomes lower, a condition that means that the load and stress correlations must be corrected for the measurement locations along the edges. Reference Fig.28 , the position d measured along the edge of the panel is measured from the center C of the edge of the panel 204 to the point through Fig.28 The “X” in the figure marks the center of the test area 208 .

[0222] Roller engagement - The variability of roller engagement can also be accounted for as a correction factor. Roller engagement refers to the length of engagement between the roller and the edge of the panel. Although roller engagement is typically set to a nominal value, the nominal value can vary depending on the straightness of the edge and the alignment process. Fig.29 An example of the effect of roller engagement on the load and stress correlation is shown. When the engagement varies between 0.7 mm and 1.7 mm, it has a 10% effect on the load and stress correlation.

[0223] Off-apex Failures (Static ESMS only) - For a static ESMS, the off-apex failure location must be considered as a correction factor for accurate stress measurements because stresses drop dramatically as the off-apex failure location becomes farther away from the roll apex. Fig. 30A is a photograph of an example of off-apex cracking in a test panel, and Fig. 30B is a graph of stress distribution with respect to the fracture position offset from the apex.

[0224] Mathematically, for example, a correction factor can be applied to the nominal load and stress as follows:

[0225] Stress = F(N)x C1(t)x C2(x)xC3(R)r C4(L)x...

[0226] Here, F is the nominal load related stress, and C1-C4 are correction functions that account for each individual variable, thickness (t), measurement location (x), roll engagement (R), and offset apex fracture location (L).

[0227] Error Bars - Variability in certain panel design parameters or measurement processes that may not be easily measured for practical reasons may be interpreted as error bars. For example, variability in sealant width, position, or individual glass thickness comprising the panel may be interpreted as error bars. Additionally, measurement process variability such as errors from the dynamometer, operator, etc. may also be interpreted as error bars. The following shows the final load and stress correlation that explains both the correction factor and the error bar:

[0228] Stress J=F(N)x C1(t)x C2(x)x C3(R)x C4(L)x...±error bar

[0229] [Method for estimating the probability of panel failure]

[0230] [1. Derive strength distribution and predict product reliability based on ESMS]

[0231] The traditional way of predicting the reliability of glass in a specific application involves deriving a strength distribution based on strength testing, and then calibrating the failure probability for a given reference size to the entire production size. This method has been used successfully for many years, however, it relies on the strength distribution being referenced to a given size. Traditional means of testing glass strength, such as 4-point bending and ring-to-ring, performed on glass specimens of appropriate thickness, have the benefit that the stress field in the test area is constant. Therefore, if the strength distribution is obtained from this data, the resulting distribution is referenced to the tested area (inside the inner ring for ring-to-ring testing, and inside the inner knife for four-point bending testing). Using these distributions for reliability prediction is straightforward in this case because the reference size of the strength distribution relative to the product size is known, and therefore the failure probability can be easily calibrated to the product size by utilizing the Weibull calibration (or closure) property. To utilize this method, the reference size to which the Weibull strength distribution is applied must be known.

[0232] Various new test methods such as ESMS are being used to measure the strength of thin glass. Although ESMS is very suitable for thin glass edge strength assessment, it does not have a constant stress field. In static ESMS testing, the stress field is symmetrical around the center roller and Fig.31 , which illustrates the stresses along the edge of a panel / sheet. Here, the failure site location and stresses are shown as stars. A common mistake is to generate a strength assignment based only on the stresses at the failure site. The problems with this process are:

[0233] Since the stress is maximum at the center roller position and decreases monotonically away from this position, the obtained strength is specified by the weakest location within the position "center ± fault location to center distance". Therefore, the distribution is the distribution of the weakest defect within the fault location. Since the location of this weakest defect varies, the test length based on which the distribution is obtained also varies. Therefore, the distribution does not refer to a specific length.

[0234] • The length of the edge subjected to stresses above the failure stress can significantly affect the strength distribution and must be accounted for.

[0235] Therefore, distribution based solely on stress at the fault site cannot be used for product reliability prediction. Therefore, special methods are needed to derive effective strength distribution. In order to adequately determine the strength distribution for ESMS, the effects of length and stress must be expanded and convolved, and the distribution must be referenced to a specific unit length. A methodology has been developed to achieve this. This methodology includes defining a small reference length (or reference area in the case of surface reliability), identifying the specific reference length (or area) of the failure, the stress at which it fails, and the stress exposed by the remaining reference length (or area). The obtained data is then statistically analyzed to derive an effective strength distribution relative to the known length (or area). This distribution can then be used for reliability prediction purposes. The details of this method are not provided here.

[0236] [A “Simplified Method” for Data Analysis of Dynamic ESMS]

[0237] For dynamic ESMS, the inventors also implemented a simplified method to derive the strength distribution by using the first failure data. The simplified method assumes that the stress distribution is constant across the entire test area for a dynamic ESMS. Fig.32 Probability vs. stress graphs are plotted showing the strength distribution of a batch of panels analyzed by either the "simplified method" or the "special" method outlined in the previous section above. The results from both methods are not significantly different because at each step load, the stresses in the gauge area at the entire test length are nearly the same and the step stresses are small. This enables the inventors to use conventional Weibull statistics and not rely on the "special" method for dynamic ESMS data analysis.

[0238] [Panel failure mode]

[0239] Panel failure modes describe the different ways or locations that a panel can break when tested on an ESMS. It is generally preferred to have a consistent or predictable break location on a panel in order to classify the break. However, due to complications in panel structure and defect population, identification of the break location and understanding the precise failure stress can be challenging. Here, we provide examples of failure modes found in panels and methods used to estimate their failure stresses.

[0240] Edge failure - Edge failure is when an edge on a surface 1 breaks under tension ( Fig.33). Edge failure on surface 1 under tension is the predetermined failure mode to be obtained from the ESMS test. However, to obtain this failure mode, it is required that the two glass sheets comprising the panel behave collectively as a single glass sheet. In the case where the two glass sheets comprising the panel behave as two separate glass sheets, edge failure can also occur at the edge on surface 3, which will complicate the identification of the fracture location. Single-piece glass behavior of the panel can be achieved by ensuring that the sealant bonding the two glass sheets is well cured, sufficiently wide, and sufficiently close to the edge of the panel being measured. For example, the sealant must not delaminate due to the shear stress applied by the test, the modulus of the sealant should be sufficiently high, typically exceeding 1 GPa, and the sealant must bond well to the area around the edge where the load is being applied.

[0241] This behavior of the panel with respect to sealant properties can be better explained by the variation of the stress distribution on surfaces 1 and 3 with respect to different sealant-to-edge distances. Fig.35 The stress distribution on surface 1 and surface 3 is shown when the gap between the sealant and the glass edge is 0 mm. The sealant width is about 1 mm and the rigidity is 3 GPa. The peak stress is at the edge of surface 1, while the edge stress on surface 3 is less than half, which means that the crack will only occur on surface 1. Fig.36 The stress distribution on Surface 1 and Surface 3 is shown as the distance between the sealant and the glass edge increases to 2 mm. As the sealant moves away from the load area, the peak stress is now located on both edges of Surface 1 and Surface 3. The probability of having a failure on the edge of Surface 3 is now the same as that on Surface 1.

[0242] In some cases, it may be preferable to test both edges on surfaces 1 and 3 simultaneously. If so, one can design panels where the sealant does not have the aforementioned properties. The failure stress for both edges will be calculated based on the same correlation, since the glass will behave like two identical sheets of glass, such as Fig.36 as shown in .

[0243] Surface failure - Surface failure is near the edge, usually within 3mm of the edge ( Fig.33 ) occurs at the surface of surface 1 under tension of 20°C. Failure can also occur at the surface of surface 3 in cases where the panel behaves like two separated sheets of glass. Similar to edge failure, if it is preferred to test both surfaces 1 and 3 simultaneously, one can design the panel with a sealant that does not have the aforementioned properties and use the same correlation to estimate stress.

[0244] Failure from the compression side surface - Failure from the compression side surface refers to the failure caused by the two outer rollers ( Fig.33) due to the small tensile stress applied by the center roller. Due to the force balance, the tensile stress under each outer roller is half of that applied by the center roller. Despite the smaller stress on surface 4, if a large flaw is present, a crack can still occur at the edge or surface of surface 4. Although it is still generally desirable to have a crack only on surface 1, others can take advantage of this method and test flaws on both surface 1 and surface 4 at the same time. This may eliminate the need to have two sets of rollers to test both the A side and the B side.

[0245] Adjacent cracks - Adjacent cracks are cracks that occur when a pre-existing crack extends into the load zone ( Fig.34 ). In practice, the pre-existing crack propagates into the adjacent test area and subsequently becomes the origin of the failure. This failure mode usually occurs when the distance between the test areas is too close. A way to mitigate this failure mode is to ensure that sufficient distance is provided between the adjacent fracture and the test location.

[0246] [Gauge Failure Modes] Gauge failure modes describe ways in which a gauge may fail to detect a crack or falsely detect a crack on a panel.

[0247] Missed Crack Detection - A missed crack detection is when the ESMS fails to detect a crack on a panel. The inventors have found that this usually occurs when the crack energy from the crack is small relative to the sensitivity of the dynamometer. In some cases, the crack may still be bonded by the underlying sealant that bonds the two glass sheets together.

[0248] False rupture detection - A false rupture detection is when the ESMS detects a rupture without an actual rupture occurring. The inventors have found that this usually occurs when the sensitivity of the dynamometer is too high relative to the noise from the environment.

[0249] Machine learning to identify fractures

[0250] In ESMS crack detection, panel samples are captured with cameras with different illumination and magnification. Manually crafted features are difficult to identify to define panel cracks from image frames. The captured video samples have the majority of image frames as crack-free glass. There are very limited cracked glass image frames from the collected data. This problem is addressed as anomaly detection using unsupervised learning. In other words, the machine learning model is trained with normal images and finds shared features. Subsequently, encoders and decoders are used to detect outliers, and outlier images are considered abnormal images. Crack images will be detected as abnormal images in this case. Fig.37 Instantiate a machine learning model.

[0251] There are three convolutional neural networks. Two of the networks G and D are adversarial and unsupervised learning using training data, which only constitutes the self-target class. Specifically, G learns to reconstruct positive samples and attempts to deceive the detector D with feature weights z and G (z). However, D learns to distinguish the original (positive) sample from the reconstructed sample. In this way, D only learns the concept of featuring the space of all positive samples, and therefore it can be used to distinguish between the positive class and the novel class. There is another neural network E, which has been trained to reflect the behavior of G, and this behavior will be able to extract feature weights from the image. On the other hand, G learns to effectively reconstruct positive samples, and for negative (or novel) samples, it cannot accurately reconstruct the input, and therefore, for negative samples, it acts as a decimator (or informally a distorter). In the test phase, D operates as an actual novel detector, and G improves the performance of the detector by fully reconstructing the positive or target sample and decimating (or distorting) any given negative or novel sample.

[0252] For our ESMS case, if our input image is x(image), it goes to neural network E and produces feature weights E(x). We then define Z equal to E(x), and Z passes through neural network G and it becomes G(z)(image). If (G(z),z) and (x,E(x)) achieve similar scores through neural network D, and (G(z),z) achieves a high score through D, then input x is a normal / positive case. Otherwise, it is an abnormal / negative case.

[0253] The embodiments and functional operations described herein may be implemented in a digital electronic circuit system, or in computer software, firmware, or hardware including the structures disclosed in this specification and their structural equivalents, or in a combination of one or more thereof. The embodiments described herein may be implemented as one or more computer program products, that is, one or more modules of computer program instructions encoded on a tangible program carrier for execution by a data processing device or for controlling the operation of the data processing device. The tangible program carrier may be a computer readable medium. The computer readable medium may be a machine readable storage device, a machine readable storage substrate, a memory device, or a combination of one or more thereof.

[0254] The term "processor" or "controller" may encompass all devices, apparatuses, and machines for processing data, including, by way of example, a programmable processor, a computer, or multiple processors or computers. In addition to hardware, a processor may include code that creates an execution environment for the computer program in question, for example, code constituting processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more thereof.

[0255] A computer program (also called a program, software, software application, script, or code) may be written in any form of programming language, including compiled or interpreted languages, or declarative or procedural languages, and may be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file in a file system. A program may be stored in a portion of a file that stores other programs or data (e.g., one or more scripts stored in a markup language file), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., a file that stores one or more modules, subroutines, or portions of code). A computer program may be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communications network.

[0256] The processes described herein may be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows may also be performed by, and apparatus may be implemented as, special purpose logic circuitry such as an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit), to name a few.

[0257] By way of example, processors suitable for the execution of a computer program include general-purpose and special-purpose microprocessors, and any one or more processors of any kind of digital computer. In general, the processor will receive instructions and data from a read-only memory or a random access memory, or both. The essential components of a computer are a processor for executing instructions and one or more data storage devices for storing instructions and data. In general, a computer will also include one or more mass storage devices for storing data, or be operatively coupled to receive data from or transfer data to such one or more mass storage devices, or both, such as magnetic, magneto-optical, or optical disks. However, a computer need not have such devices. In addition, a computer may be embedded in another device, such as a mobile phone, a personal digital assistant (PDA), to name a few.

[0258] Computer-readable media suitable for storing computer program instructions and data include all forms of data storage, including non-volatile memory, media and memory devices, including, by way of example, semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks, such as internal hard disks or removable disks; magneto-optical disks; and CD ROM and DVD-ROM disks. The processor and memory may be supplemented by, or incorporated into, special purpose logic circuitry.

[0259] To provide interaction with a user and as shown in the figures included herein, the embodiments described herein may be implemented on a computer having a display device for displaying information to a user, such as a CRT (cathode ray tube) or LCD (liquid crystal display) monitor, etc., and a keyboard and pointing device, such as a mouse or trackball, or a touch screen through which a user can provide input to the computer. Another type of device may also be used to provide interaction with a user; for embodiments, input from a user may be received in any form, including acoustic input, voice input, or tactile input.

[0260] The embodiments described herein may be implemented in a computing system that includes a back-end component, such as a data server, or a computing system that includes a middleware component, such as an application server, or a computing system that includes a front-end component, such as a client computer having a graphical user interface or a web browser through which a user can interact with an implementation of the objects described herein, or any combination of one or more such back-end components, middleware components, or front-end components. The components of the system may be interconnected by any form or medium of digital data communication, such as a communication network. Examples of communication networks include local area networks ("LANs") and wide area networks ("WANs"), such as the Internet.

[0261] A computing system may include clients and servers. Clients and servers are generally remote from each other and typically interact through a communication network. The client and server relationship arises by virtue of computer programs running on the respective computers and having a client-server relationship to each other.

[0262] It should be understood that various disclosed embodiments may relate to specific features, elements or steps described in conjunction with specific embodiments. It should also be understood that although specific features, elements or steps are described relative to a specific embodiment, they can be interchanged or combined with alternative embodiments in various undescribed combinations or permutations.

[0263] It should also be understood that, as used herein, the terms "the" or "an" mean "at least one" and should not be limited to "only one" unless clearly indicated to the contrary. Thus, for example, reference to a "component" includes instances having two or more such "components" unless the context clearly indicates otherwise.

[0264] Ranges may be expressed herein as from "about" one particular value, and / or to "about" another particular value. When expressing such a range, examples include from one particular value and / or to another particular value. Similarly, when a value is expressed as an approximation by using the antecedent "about," it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are meaningful relative to and independent of the other endpoint.

[0265] As used herein, the terms "substantially," "substantially," and variations thereof are intended to mean that the described feature and value or description is equal or approximately equal. Additionally, as defined above, "substantially similar" is intended to mean that two values ​​are equal or approximately equal. In some embodiments, "substantially similar" may mean values ​​within about 10% of each other, such as within about 5% of each other or within about 2% of each other.

[0266] Unless otherwise expressly stated, it is not intended that any method described herein be construed as requiring that its steps be performed in a specific order. Therefore, if a method claim does not actually recite the order in which its steps are to be followed or if it is not otherwise expressly stated in the invention claims or specification that the steps should be limited to a specific order, no specific order is intended to be inferred.

[0267] Although the transition phrase "comprising" may be used to disclose various features, elements, or steps of a particular embodiment, it should be understood that it implies alternative embodiments, including those that may be described using the transition phrase "consisting of" or "consisting essentially of. Thus, for example, implied alternative embodiments for an apparatus comprising A+B+C include embodiments in which the apparatus consists of A+B+C and embodiments in which the apparatus consists essentially of A+B+C.

[0268] It will be apparent to those skilled in the art that various modifications and variations may be made to the present disclosure without departing from the spirit and scope of the present disclosure. As modifications, combinations, sub-combinations, and variations of the disclosed embodiments incorporating the spirit and substance of the present disclosure may be contemplated by those skilled in the art, the present disclosure should be construed to include everything within the scope of the appended claims and their equivalents.

Claims

1. An apparatus for testing the edge strength of a sheet of material, the apparatus comprising: a plurality of assemblies configured to selectively apply a 3-point bending load along an edge of the sheet of material in a test area of ​​the apparatus, whereby the plurality of assemblies can establish a loaded condition on the sheet of material in the test area by applying the 3-point bending load and a no-load condition on the sheet of material in the test area by not applying the 3-point bending load; a detection mechanism configured to optically measure strain in the sheet of material in the test area when the sheet of material is in the no-load condition and when the sheet of material is in the loaded condition, wherein the strain in the loaded condition is produced by the 3-point bending load; as well as a processor configured to determine stress in said sheet of material based on said measured strain, Wherein a pattern provided on the surface of the sheet in the test area facilitates optically measuring the strain in the sheet of material.

2. The apparatus of claim 1, wherein the plurality of assemblies comprises two reverse assemblies, wherein a first of the two reverse assemblies comprises a single arcuate member for engaging a first side of the sheet and a second of the two reverse assemblies comprises two spaced-apart arcuate members for engaging a second side of the sheet opposite the first side, The two spaced apart arcuate members define the testing area between the two spaced apart arcuate members.

3. An apparatus as described in claim 2, wherein the single arch member is vertically aligned between the two spaced apart arch members.

4. The apparatus of claim 2, wherein the inspection mechanism comprises a first pair of cameras positioned to acquire one or more images of the surface of the second side of the sheet in the test area between the two spaced arcuate members, Wherein the detection mechanism optically measures the strain in the sheet of material from the image of the surface of the second side of the sheet acquired using the first pair of cameras.

5. The apparatus of claim 2, wherein the arcuate member is a non-rotating bushing, a cylindrical roller, a belt roller, or a bearing roller.

6. The apparatus of claim 4, wherein the inspection mechanism further comprises a second pair of cameras positioned to acquire images of the surface of the second side of the sheeting at an area other than the test area.

7. The apparatus of claim 2, wherein the detection mechanism comprises at least one camera positioned to acquire one or more images of a vertical edge surface of the sheet in the test area between the two spaced arcuate members, Wherein the detection mechanism optically measures the strain of the sheet of material from the image of the vertical edge surface of the sheet acquired using the at least one camera.

8. The apparatus of claim 7, wherein the inspection mechanism further comprises at least one additional camera positioned to acquire images of vertical edge surfaces of the sheet at areas other than the test area.

9. A method of testing the edge strength of a sheet of material along its edge, the method comprising: applying a surface pattern of visual indicia onto the surface of the sheet in an area of ​​interest along the edge of the sheet; obtaining a first optical image of the surface of the sheet in the region of interest without any 3-point bending load applied to the region of interest; applying a 3-point bending load to the region of interest along the edge of the sheet; obtaining a second optical image of the surface of the sheet in the region of interest while the 3-point bending load is being applied to the region of interest; as well as Stress on the surface of the region of interest along the edge of the sheet resulting from the application of the 3-point bending load is determined based on the first optical image and the second optical image, wherein the surface pattern facilitates optically measuring strain in the sheet of material.

10. The method of claim 9, wherein determining the stress on the surface of the region of interest along the edge of the sheet comprises: measuring strain in the sheet of material in the region of interest under no-load conditions based on the first optical image; measuring strain in the sheet of material in the region of interest under loading conditions based on the second optical image, wherein the 3-point bending load is applied; and The strain measured under the no-load condition is compared to the strain measured under the loaded condition to determine the strain in the sheet induced by the applied 3-point bending load.

11. The method of claim 10, wherein measuring the strain in the thin film of material in the region of interest under the load condition based on the second optical image comprises: A displacement of the visual marker in the second optical image compared to a position of the visual marker in the first optical image is determined.

12. The method of claim 11, wherein determining the stress on the surface of the region of interest along the edge of the sheet comprises calculating the stress that would be required to produce the measured strain in the sheet of material in the region of interest.

13. The method of claim 9, wherein applying the surface pattern of visual indicia comprises printing, coating, spraying, etching, affixing or projecting an image onto the surface of the sheet.

14. The method of claim 9, wherein the first optical image and the second optical image are obtained using an optical system comprising at least one camera.

15. A method of testing the edge strength of a sheet of material along an edge of the sheet using a testing apparatus, the testing apparatus comprising a testing area, the method comprising: applying a surface pattern of visual indicia onto the surface of the sheet in an area of ​​interest along the edge of the sheet; continuously advancing the sheet of material through the testing apparatus, wherein the edge of the sheet is advanced through the testing area while a 3-point bend load is applied to the portion of the sheet passing through the testing area; obtaining a first optical image of the surface of the sheeting in the region of interest as the edge of the sheeting is continuously advancing through the test region before the region of interest reaches the test region; obtaining a second optical image of the surface of the region of interest of the sheet as the region of interest advances into the test region while the 3-point bending load is being applied; and The stress on the surface of the area of ​​interest along the edge of the thin sheet resulting from the application of the 3-point bending load is determined based on the first optical image and the second optical image, wherein the pattern provided on the surface of the thin sheet in the test area facilitates optically measuring the strain in the thin sheet of material.

16. The method of claim 15, wherein determining the stress on the surface of the region of interest along the edge of the sheet comprises: measuring strain in the sheet of material in the region of interest under no-load conditions based on the first optical image; measuring strain in the sheet of material in the region of interest under loading conditions based on the second optical image, wherein the 3-point bending load is applied; and The strain measured under the no-load condition is compared to the strain measured under the loaded condition to determine the strain in the sheet induced by the applied 3-point bending load.

17. The method of claim 16, wherein measuring strain in the thin sheet of material in the region of interest under the load condition based on the second optical image comprises: A displacement of the visual marker in the second optical image compared to a position of the visual marker in the first optical image is determined.

18. The method of claim 17, wherein determining the stress on the surface of the region of interest along the edge of the sheet comprises calculating the stress that would be required to produce the measured strain in the sheet of material in the region of interest.

19. The method of claim 15, wherein the first optical image and the second optical image are obtained by an optical system comprising a pair of stereo cameras.

20. The method of claim 15, wherein applying the surface pattern of visual indicia comprises printing, coating, spraying, etching, adhering or projecting an image onto the surface of the sheet.

Images