Stress luminescence measurement method and stress luminescence measurement system

Abstract

To provide a stress light emission measurement method and a stress light emission measurement system which can simultaneously measure the stress and the distortion generated in an object.SOLUTION: A stress light emission measurement method comprises steps of: forming a stress light emission film 1 having a plurality of stress light emitters arrayed in a two-dimensional pattern on a surface of an object 2; exciting the stress light emission film 1; applying a load to the object 2; imaging the stress light emission film 1 when the load is being applied; and measuring the stress and the distortion generated in the object 2 on the basis of a light emission image of the stress light emission film 1. The step of measuring the stress and the distortion comprises steps of: measuring the stress generated in the object 2 on the basis of the light emission intensity of the stress light emission film 1; and measuring the distortion in the object 2 on the basis of the displacement amounts of the plurality of stress light emitters before and after the load is applied.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a stress luminescence measurement method and a stress luminescence measurement system.

Background Art

[0002] A stress luminescent body is a member that emits energy and emits light when its energy state is enhanced, and emits light according to the stress generated inside when a load is applied from the outside. Since there is a correlation between the luminescence intensity of the stress luminescent body and the stress, a technique for measuring the stress generated in an object coated with the stress luminescent body based on the luminescence phenomenon of the stress luminescent body has been put into practical use (for example, see Japanese Patent Application Laid-Open No. 2015-75477 (Patent Document 1)).

[0003] On the other hand, as a technique for measuring the strain of an object with respect to an external load, it is common to use a strain gauge. However, since the strain gauge measures local strain, it is difficult to measure a wide range of strain distributions. Therefore, in recent years, as a method代替 the strain gauge, the digital image correlation method (DIC: Digital Image Correlation) and the moire method have been put into practical use. The DIC method is a method for measuring the displacement and strain distribution of an object by analyzing the change in a pattern called a random pattern applied to the surface of the object by spraying or the like. The moire method is a method for measuring the deformation and shape of an object using the phenomenon (moire) in which a pattern different from the original pattern appears when two geometric patterns are superimposed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Both the DIC method and the moiré method are performed in a bright environment to photograph changes in patterns drawn on the surface of an object. On the other hand, stress luminescence is performed in a dark environment to photograph the light emitted by a stress luminescent material. Therefore, even if a stress luminescent material and a pattern are formed on the surface of an object, it is not possible to photograph them simultaneously, making it difficult to simultaneously measure the stress and strain generated in the object.

[0006] In the elastic deformation region, where the object deforms linearly and elastically in response to the load, a proportional relationship exists between stress and strain. Therefore, even if stress and strain cannot be measured simultaneously, if either stress or strain can be measured, the other can be determined from that measurement.

[0007] In contrast, in the plastic deformation region, where the material does not return to its original state even after the load is removed and remains deformed, a proportional relationship does not exist between stress and strain. Therefore, it is not possible to determine one from the other, and it becomes necessary to measure stress and strain separately. Thus, the aforementioned problem of not being able to measure stress and strain simultaneously can be a concern in the plastic deformation region.

[0008] This disclosure provides a stress luminescence measurement method and a stress luminescence measurement system capable of simultaneously measuring stress and strain occurring in an object. [Means for solving the problem]

[0009] A stress emission measurement method according to a first aspect of this disclosure comprises the steps of: forming a stress emission film having a plurality of stress emission elements arranged in a two-dimensional pattern on the surface of an object; exciting the stress emission film by irradiating it with excitation light from a light source; applying a load to the object; using an imaging device to image the stress emission film while the load is applied; and measuring the stress and strain generated in the object based on the captured emission image of the stress emission film. The steps of measuring stress and strain include measuring the stress generated in the object based on the emission intensity of the stress emission film, and measuring the strain generated in the object based on the displacement of the plurality of stress emission elements before and after the load is applied.

[0010] A stress emission measurement system according to a second aspect of this disclosure is a system for measuring the stress and strain generated in an object when a load is applied to it. A stress emission film having a plurality of stress emission elements arranged in a two-dimensional pattern is formed on the surface of the object. The stress emission measurement system comprises a testing machine for applying a load to the object, a light source for exciting the stress emission film, an imaging device for photographing the stress emission film when the load is applied, and a control device for measuring the stress and strain generated in the object based on the captured emission image of the stress emission film. The control device measures the stress generated in the object based on the emission intensity of the stress emission film, and measures the strain generated in the object based on the displacement of the plurality of stress emission elements before and after the load is applied. [Effects of the Invention]

[0011] According to this disclosure, it is possible to simultaneously measure the stress and strain generated in an object to which a load is applied. [Brief explanation of the drawing]

[0012] [Figure 1] This is a block diagram showing an example configuration of a stress luminescence measurement system according to an embodiment. [Figure 2] This is a schematic diagram showing an example of a test specimen. [Figure 3]It is an enlarged view showing a part of the stress luminescence film. [Figure 4] It is a schematic diagram showing an example of the hardware configuration of the control device. [Figure 5] It is a diagram showing an example of the time transition of the test force applied to the specimen. [Figure 6] It is a diagram schematically showing the state of atoms in the elastic region. [Figure 7] It is a diagram schematically showing the state of atoms in the plastic region. [Figure 8] It is a diagram showing an example of the luminescence intensity-stress curve. [Figure 9] It is an enlarged view showing a part of the stress luminescence film. [Figure 10] It is a flowchart for explaining the processing procedure of the stress luminescence measurement method according to this embodiment. [Figure 11] It is a diagram for explaining the stress luminescence measurement method according to the first modification example of this embodiment. [Figure 12] It is a flowchart for explaining the processing procedure of the stress luminescence measurement method according to the second modification example of this embodiment. [Figure 13] It is a diagram showing an example of the luminescence image. [Figure 14] It is a diagram showing the first modification example of the stress luminescence film. [[ID=3৪]] [Figure 15] It is a diagram showing the second modification example of the stress luminescence film. [Figure 16] It is an enlarged view showing a part of the stress luminescence film. [Figure 17] It is a diagram showing the third modification example of the stress luminescence film. [Figure 18] It is an enlarged view showing a part of the stress luminescence film. [Figure 19] It is a flowchart for explaining an example of the processing procedure of the stress luminescence film forming step (S20 in FIG. 10).

Embodiments for Carrying Out the Invention

[0013] The embodiments of this disclosure will be described in detail below with reference to the drawings. The same or corresponding parts in the drawings will be denoted by the same reference numerals, and their descriptions will not be repeated.

[0014] <Stress-induced luminescence measurement system> First, the configuration of the stress luminescence measurement system according to this embodiment will be described.

[0015] Figure 1 is a block diagram showing an example configuration of a stress luminescence measurement system according to an embodiment. The stress luminescence measurement system 100 according to this embodiment is a system that measures the stress and strain generated in an object when a load is applied to the object by utilizing the luminescence phenomenon of a stress luminescent body. The stress luminescence measurement system 100 can be used to measure the stress and strain when a tensile load is applied to a test specimen 2, as described below.

[0016] As shown in Figure 1, the stress luminescence measurement system 100 comprises a tensile testing machine 4, a control device 6, an imaging device 8, a light source 10, a drive device 12, a control device 14, and a storage device 16. At least the tensile testing machine 4, the imaging device 8, and the light source 10 of the stress luminescence measurement system 100 are installed in a darkroom.

[0017] The tensile testing machine 4 is a device for applying a tensile load to the test specimen 2 and measuring its mechanical properties such as tensile strength, yield point, elongation, and reduction of area. The test specimen 2 corresponds to one embodiment of the object being tested. In the example in Figure 1, the tensile testing machine 4 is a precision universal testing machine (product name: Autograph AG-Xplus, manufactured by Shimadzu Corporation). The tensile testing machine 4 corresponds to one embodiment of the "testing machine".

[0018] The tensile testing machine 4 comprises a table 40, a crosshead 42, a pair of screw rods 44, 46, an upper grip 48, a lower grip 50, and a load cell 52. The pair of screw rods 44, 46 are rotatably mounted on the table 40 in a vertical orientation. The pair of screw rods 44, 46 consist of ball screws.

[0019] The crosshead 42 is connected to each screw shaft 44, 46 via nuts (not shown). The crosshead 42 is configured to move vertically along the pair of screw shafts 44, 46. A load mechanism (not shown) for raising and lowering the crosshead 42 is installed inside the table 40.

[0020] The upper grip 48 is connected to the crosshead 42 and grips the upper end of the test specimen 2. The lower grip 50 is connected to the table 40 and grips the lower end of the test specimen 2. The distance L1 between the upper grip 48 and the lower grip 50 is 120 mm. During a tensile test, the tensile testing machine 4 applies a tensile force to the test specimen 2 by raising the crosshead 42 in accordance with the control of the control device 14, while gripping both ends of the test specimen 2 with the upper grip 48 and the lower grip 50.

[0021] The load cell 52 is a sensor for detecting the test force, which is the tensile load applied to the test specimen 2. The load cell 52 outputs a signal indicating the detected test force to the control device 6.

[0022] The control device 6 communicates with the tensile testing machine 4 and controls the tensile operation performed by the tensile testing machine 4. The control device 6 receives user operations such as setting various parameters, including the test conditions for the tensile test, and issuing execution instructions, and controls the loading mechanism according to the received user operations. Furthermore, the control device 6 receives various signals from the tensile testing machine 4, including the output signal from the load cell 52 and a signal indicating the displacement of the crosshead 42, and analyzes data such as the detected value of the test force.

[0023] The control device 6 includes a processor such as a CPU (Central Processing Unit), memory such as ROM (Read Only Memory) and RAM (Random Access Memory), an interface circuit for connecting peripheral devices, and a display unit 62. The various functions described above are realized when the processor executes the tensile test program stored in the memory.

[0024] The display unit 62 displays various information based on signals input to the control device 6. For example, during the execution of a tensile test, the display unit 62 displays the test force detected by the load cell 52. The display unit also displays the displacement amount indicating the displacement (stroke) of the crosshead 42.

[0025] The light source 10 is positioned opposite the test specimen 2 and is configured to irradiate the stress-emitting film 1 on the test specimen 2 with excitation light. The light source 10 is, for example, a blue LED (Light Emitting Diode). Upon receiving excitation light from the light source 10, the stress-emitting film 1 transitions to an excited state. The number of light sources 10 is not limited. For example, multiple light sources 10 may be arranged to irradiate the test specimen 2 with excitation light from multiple directions.

[0026] The drive unit 12 supplies power to drive the light source 10 and controls the on / off state of the light source 10. The drive unit 12 can control the amount of excitation light emitted from the light source 10 and the irradiation time of the excitation light.

[0027] The imaging device 8 is positioned so as to include at least a predetermined area of ​​the test specimen 2 in its field of view. The imaging device 8 includes an optical system such as a lens and an image sensor. The image sensor is implemented by, for example, a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide Semiconductor) sensor. The image sensor generates an image by converting light incident from the test specimen 2 through the optical system into an electrical signal. In the example in Figure 4, the imaging device 8 is installed at a distance of approximately 30 cm from the test specimen 2.

[0028] The control device 14 controls the shooting operation by the shooting device 8 and the driving of the light source 10 by the drive device 12. The control device 14 is connected to the control device 6 of the tensile testing machine 4 by a communication line 15. By exchanging data with the control device 6 via the communication line 15, the control device 14 can comprehensively control the tensile testing machine 4, the shooting device 8, and the light source 10. Communication between the control device 14 and the control device 6 may be achieved by wireless communication.

[0029] In this embodiment, the control devices 14 for the light source 10 and the imaging device 8, and the control device 6 for the tensile testing machine 4 are provided separately, but the control devices 14 and 6 may be integrated into a single unit.

[0030] The display unit 142 displays various information based on signals input to the control device 14. For example, the display unit 142 can display data input from the control device 6 via the communication line 15 (such as the test force detected by the load cell 52 and the displacement amount indicating the displacement (stroke) of the crosshead 42).

[0031] Furthermore, the display unit 142 can display an image (luminescence image) of the stress-emitting film 1 captured by the imaging device 8. Specifically, the display unit 142 can display the luminescence image captured by the imaging device 8 in real time.

[0032] <Specimen> Figure 2 is a schematic diagram showing an example of test specimen 2. Test specimen 2 is made of a metallic material. For example, a test specimen 2 specified in Japanese Industrial Standard (JIS) Z-2201 "Tensile Test Specimen for Metallic Materials" can be used. In this embodiment, the mechanical properties of the metallic material are measured by applying strain to test specimen 2 until fracture occurs due to tensile load.

[0033] In the example shown in Figure 2, specimen 2 is a plate-shaped test piece conforming to JIS No. 13B, with a total length L = 220 mm, gauge length Lo = 50 mm, parallel section length Lc = 75 mm, width W = 25 mm, parallel section width D = 12.5 ± 0.04 mm, shoulder radius R = 25 mm, and plate thickness t = 1 mm.

[0034] A stress-emitting film 1 is formed in a predetermined area on the surface of specimen 2. The predetermined area is positioned to cover the parallel portion of specimen 2 and has a rectangular shape with a width of 80 mm and a length of 12.5 mm. The thickness of the stress-emitting film 1 is several micrometers. In this specification, the thickness of the stress-emitting film refers to the height of the stress-emitting film in the direction perpendicular to the surface of the specimen.

[0035] The stress-luminescent film 1 is obtained by molding a stress-luminescent material alone or in combination with another material (such as resin). A stress-luminescent material is a material that emits light in response to mechanical stimuli such as external forces (tension, compression, displacement, friction, impact, etc.).

[0036] Stress-induced luminescence materials are constructed by solid-solving a luminescent element within the framework of an inorganic crystal (matrix). A typical example is europium-doped strontium aluminate. Other examples include zinc sulfide, barium titanate-calcium, and calcium aluminate-yttrium, which are doped with transition metals or rare earth elements. Known stress-induced luminescence materials can be used.

[0037] The luminescence intensity of the stress-emitting film 1 increases in proportion to the magnitude of the applied force. Furthermore, since the stress-emitting film 1 is strongly adhered to the surface of the specimen 2, both the stress-emitting film 1 and the specimen 2 deform equally. Therefore, the stress distribution generated on the surface of the specimen 2 due to deformation can be imaged (visualized) by the luminescence of the stress-emitting film 1.

[0038] Figure 3 is an enlarged view showing a portion of the stress-emitting film 1. As shown in Figure 3, the stress-emitting film 1 is composed of a plurality of stress-emitting elements 3. The plurality of stress-emitting elements 3 are arranged in a two-dimensional pattern in a predetermined region (parallel section) on the surface of the specimen 2. In this specification, a two-dimensional pattern refers to the arrangement structure of the plurality of stress-emitting elements 3. In the example of Figure 3, each stress-emitting element 3 has a square shape and is arranged periodically at predetermined intervals d0 in both the length and width directions of the specimen 2. That is, the plurality of stress-emitting elements 3 are arranged to form a checkerboard pattern as a two-dimensional pattern.

[0039] Each stress-emitting element 3, which is square in shape, has a side length of several to tens of micrometers, and the predetermined interval d0 is also several to tens of micrometers. The size of each stress-emitting element 3 and the predetermined interval d0 can be set to any value depending on the resolution of the imaging device 8, etc. Note that the outer shape of each stress-emitting element 3 is not limited to a square shape; for example, it may be circular.

[0040] Because the stress-emitting film 1 has a two-dimensional pattern, the stress-emitting measurement system 100 can simultaneously measure the stress and strain generated in the test specimen 2 from the intensity of the light emitted by each stress-emitting element 3 and the amount of displacement of each stress-emitting element 3 as the test specimen 2 deforms. In order to quantify the stress and strain generated in each part of the test specimen 2, it is desirable that the two-dimensional pattern be uniform throughout the entire stress-emitting film 1, as shown in Figure 3.

[0041] <Control device hardware configuration> Figure 4 is a schematic diagram showing an example of the hardware configuration of the control device 14. Referring to Figure 5, the control device 14 includes a processor 140 such as a CPU, memory 141 such as ROM and RAM, a communication interface 146, an input / output interface 145, a display interface 143, and a non-volatile storage device 16. These components are connected to each other via an internal bus 147 so as to be able to communicate with one another.

[0042] The various functions described above are realized when the processor 140 loads the stress measurement program 160 stored in the storage device 16 into memory 141 and executes it. In addition to the stress measurement program 160, the storage device 16 also stores data exchanged with the control device 6 (data such as detected test force values) and image data captured by the imaging device 8. The storage device 16 further stores pre-created calibration curve data 162.

[0043] The communication interface 146 exchanges data with other devices. These other devices include the control unit 6 and external devices (not shown). The communication interface 146 may be configured to allow downloading of various data, such as the stress measurement program 160 and calibration curve data 162, from these external devices.

[0044] The input / output interface 145 is connected to the control unit 144 and receives signals indicating user operation from the control unit 144. The control unit 144 typically consists of a keyboard, mouse, touch panel, touchpad, etc., and accepts user input. The control unit 144 may be configured integrally with the control device 14 or separately from the control device 14.

[0045] The display interface 143 is connected to the display unit 142 and outputs image signals to the display unit 142 for displaying images, according to commands from the processor 140 or the like. The display unit 142 is composed of an LCD (Liquid Crystal Display) or an organic EL (Electro Luminescence) display, and displays various information to the user.

[0046] Figure 4 shows an example configuration in which the processor 140 provides the necessary functions by executing a program. However, some or all of these provided functions may be implemented using dedicated hardware circuits (for example, an ASIC (Application Specific Integrated Circuit) or an FPGA (Field-Programmable Gate Array)).

[0047] <Testing machine> Returning to Figure 1, a tensile load is applied to the specimen 2 by driving the tensile testing machine 4. Figure 5 shows an example of the time transition of the test force applied to the specimen 2. Figure 5 shows the time transition of the test force (corresponding to the tensile load) and stroke (corresponding to the displacement of the crosshead 42). The test force is the value detected by the load cell 52.

[0048] As shown in Figure 5, when the test force is applied at time 0 (seconds), the stroke increases monotonically according to the preset tensile speed (10 mm / min in Figure 5).

[0049] The test force increases linearly immediately after the start of the test. This region corresponds to the elastic deformation region (hereinafter also referred to as the "elastic region") in which specimen 2 deforms linearly and elastically. After 4 to 6 seconds from the start of the test, the increase in the test force stops, and thereafter the test force is kept almost constant. This region corresponds to the plastic deformation region (hereinafter also referred to as the "plastic region") of specimen 2. In the example in Figure 5, in the plastic region, the test force remains less than the maximum load of 1500 N as the stroke increases. Then, approximately 80 seconds from the start of the test, fracture occurs in specimen 2.

[0050] Figure 6 schematically shows the state of atoms in the elastic region. Attractive and repulsive forces act between two atoms. As shown in Figure 6(A), normally, two metal atoms remain at rest, maintaining a distance where the attractive and repulsive forces are balanced. When a tensile load is applied to these atoms, as shown in Figure 6(B), the interatomic distance is stretched, and the attractive force becomes dominant. According to Hooke's Law, a stress proportional to the elongation of the interatomic distance is generated. This ratio of elongation of the interatomic distance corresponds to the strain generated in specimen 2. Strain is the ratio of the elongation ΔL of specimen 2 to the length L before the tensile load is applied to specimen 2, and is expressed as ε = ΔL / L.

[0051] The relationship between the stress σ and strain ε generated between atoms by a tensile load is given by the equation σ = Eε (where E is Young's modulus). The region in which stress is proportional to strain is called the "elastic deformation region (elastic region)." In the elastic region, when the tensile load is removed, the interatomic distance returns to its original state.

[0052] However, when the tensile load exceeds a certain threshold, the stress is no longer proportional to the strain, and the material does not return to its original state even when the tensile load is removed, but remains deformed. This region is called the "plastic deformation region (plastic zone)." Figure 7 schematically shows the atomic state in the plastic zone.

[0053] As shown in Figure 7, plastic deformation occurs when line defects called dislocations move in a specific slip direction on a specific slip plane while maintaining the bonds between atoms. In the plastic region, irreversible strain (permanent strain) progresses. From the perspective of this disclosure, in the plastic region, specimen 2 is in a state where stress originating from the elongation of interatomic distances and strain mainly based on the movement of dislocations are present.

[0054] In the plastic region, a proportional relationship does not hold between stress and strain, making it necessary to measure stress and strain separately. Here, methods such as digital image correlation (DIC) and moiré patterns have been put into practical use for measuring strain. The DIC method measures the displacement and strain distribution of an object by analyzing changes in a random pattern applied to its surface using spray paint or other methods. The moiré pattern method uses the phenomenon (moiré) where a different pattern appears when two geometric patterns are superimposed, to measure the deformation and shape of an object.

[0055] Both the DIC method and the moiré method are performed in a bright environment to photograph changes in patterns drawn on the surface of the specimen. On the other hand, stress luminescence is performed in a dark environment to photograph the light emitted by stress-luminescent materials. Therefore, even if a stress-luminescent film and a pattern are formed on the surface of the specimen, it is difficult to photograph them simultaneously.

[0056] In the stress emission measurement system 100 according to this embodiment, a stress emission film 1 having a two-dimensional pattern is formed on the surface of the test specimen 2, and the stress emission of the stress emission film 1 is captured. With this, even in a dark environment, stress can be measured from the intensity of the light emitted by the two-dimensional pattern of the stress emission film 1, and strain can be measured from the deformation of the emitting two-dimensional pattern. As a result, it becomes possible to simultaneously measure the stress and strain generated in the test specimen 2, even in the plastic region.

[0057] <Stress-induced luminescence measurement method> Next, the measurement principle of the stress luminescence measurement method according to this embodiment will be described.

[0058] (1) Calibration curve data In the stress luminescence measurement system 100, calibration curve data 162 stored in the memory device 16 is used to measure the stress generated in the test specimen 2. A "calibration curve" is a function that shows the relationship between the luminescence intensity of the stress luminescence film and the stress. The calibration curve can be created using the luminescence image captured by the imaging device 8 when a tensile force is applied by the tensile testing machine 4 to a standard test piece on which a stress luminescence film has been formed on its surface.

[0059] Specifically, a stress-luminescent film is formed on the surface of the standard test specimen, having at least the same thickness and composition as stress-luminescent film 1. Note that "the stress-luminescent film has the same composition" means that at least the composition and density of the stress-luminescent material contained in the stress-luminescent film are the same.

[0060] This is based on the fact that the thickness and composition of the stress-emitting film affect its luminescence intensity. Specifically, even with the same composition of the stress-emitting film, the luminescence intensity for the same stress increases as the thickness of the stress-emitting film increases. Furthermore, the color and intensity of the luminescence differ depending on the composition of the stress-emitting material. In addition, even with the same composition of the stress-emitting material, the luminescence intensity for the same stress increases as the density of the stress-emitting material increases.

[0061] Using the emission image of the stress-emitting film and the tensile force detected by the load cell 52, an emission intensity-stress curve (see Figure 7) is created, plotting the relationship between the emission intensity of the stress-emitting film and the stress. If the standard test specimen is made of a metallic material, image data corresponding to the elastic region of the standard test specimen is used. Specifically, for each frame of the image data (dynamic image data) corresponding to the elastic region, the emission intensity within the region of interest (ROI) of the emission image and the stress generated in the stress-emitting film are calculated. The stress can be determined by dividing the tensile force detected by the load cell 52 by the cross-sectional area of ​​the standard test specimen. Then, by plotting the emission intensity and stress for each frame on a two-dimensional coordinate system with emission intensity on the horizontal axis and stress on the vertical axis, an emission intensity-stress curve is created.

[0062] Figure 8 shows an example of a luminescence intensity-stress curve. By performing a simple linear regression analysis on the luminescence intensity-stress curve shown in Figure 8, the regression equation can be obtained. Linear regression or polynomial regression can be used for the simple linear regression analysis. The obtained regression equation is stored in the storage device 16 as calibration curve data 162. Calibration curve data 162 includes information on the composition and thickness of the stress-emitting film, along with the regression equation data.

[0063] (2) Stress measurement The stress generated in specimen 2 can be measured using the emission image of the stress-emitting film 1 on specimen 2 and calibration curve data 162. Specifically, image data (moving image data) captured by the imaging device 8 is extracted frame by frame. Then, for each frame of emission image, the emission intensity within a pre-set ROI is calculated. The emission intensity within the ROI can be calculated by statistically processing the emission intensity within the ROI. For example, the average emission intensity within the ROI is calculated. Note that the stress emission amount, which is the increase in emission intensity due to stress emission, depends on the film thickness of the stress-emitting film 1, so it is necessary to normalize the stress emission amount by dividing it by a correction coefficient corresponding to the film thickness of the stress-emitting film 1.

[0064] Next, the stress generated in the ROI is calculated using the calculated luminescence intensity within the ROI and the calibration curve data 162. By substituting the calculated luminescence intensity within the ROI into the independent variable of the regression equation, which is the calibration curve, the stress, which is the dependent variable, is calculated.

[0065] Furthermore, if multiple ROIs are set on the surface of specimen 2, the stress distribution on the surface of specimen 2 can be measured based on the positional information and calculated stress values ​​of each ROI by calculating the stress for each ROI.

[0066] (3) Strain measurement The strain generated in the specimen 2 can be measured based on the displacement of the multiple stress-emitting elements 3 that make up the stress-emitting film 1 before and after the application of a tensile load.

[0067] Figure 9 is an enlarged view showing a portion of the stress-emitting film 1. Figure 9(A) is the same as Figure 3 and shows the stress-emitting film 1 when no tensile load is applied to the specimen 2. Multiple stress-emitting elements 3 are arranged periodically at predetermined intervals d0 in both the length and width directions of the specimen 2. That is, the multiple stress-emitting elements 3 are arranged to form a checkerboard pattern as a two-dimensional pattern.

[0068] When a tensile load is applied to specimen 2, the stress-emitting film 1 deforms in accordance with the elongation of specimen 2. Figure 9(B) shows the stress-emitting film 1 when a tensile load is applied to specimen 2 in the direction of the arrow in the figure. Each stress-emitting element 3 moves from its original position. Therefore, in a portion of the stress-emitting film 1 (region RGN in the figure), the distance d1 between two adjacent stress-emitting elements 3 is greater than the original distance d0. The difference between this distance d1 and the distance d0 (d1-d0) represents the local elongation in that portion.

[0069] Therefore, by dividing a single frame of light emission image into multiple ROIs and calculating the change in the spacing of the stress-emitting elements 3 due to the tensile load (d1-d0) for each ROI, it is possible to measure the local strain in each part of the specimen 2. Then, from the change calculated for each ROI, it is possible to measure the strain distribution occurring on the surface of the specimen 2.

[0070] Furthermore, by calculating the sum of the changes (d1-d0) calculated for each ROI along the length of specimen 2, the strain of the entire specimen 2 due to tensile load can be measured based on the calculation results.

[0071] In this way, the stress generated in each part of the specimen 2 and the strain generated in that part can be measured simultaneously from a single frame of light emission image. The control device 14 associates the measured stress and strain values ​​obtained from the light emission image with the light emission image of the single frame and stores them in the storage device 16. This makes it possible to observe the temporal changes in stress and strain in response to tensile load.

[0072] (4) Processing flow Figure 10 is a flowchart illustrating the processing procedure of the stress luminescence measurement method according to this embodiment. As shown in Figure 10, the stress luminescence measurement method mainly consists of a specimen preparation step (S10), a stress luminescence film formation step (S20), a measurement step (S30), and a calculation step (S40).

[0073] First, the specimen preparation process (S10) is carried out. In this embodiment, a specimen 2 (see Figure 2) made of a metallic material is prepared.

[0074] Next, the stress-emitting film formation process (S20) is carried out. In this process (S20), a stress-emitting film 1 is formed on a predetermined area (parallel portion) of the surface of the specimen 2. As shown in Figure 3, the stress-emitting film 1 has a plurality of stress-emitting elements 3 arranged in a two-dimensional pattern.

[0075] Methods for forming the stress-luminescent film 1 include applying a paint containing a stress-luminescent material (stress-luminescent paint) to the surface of the test specimen 2 to print a two-dimensional pattern on the surface. Screen printing or inkjet printing can be used to print the two-dimensional pattern.

[0076] Next, the measurement process (S30) is performed. In this process (S30), the stress and strain generated in the test specimen 2 are measured by utilizing the luminescence phenomenon of the stress-luminescent film 1 when a tensile load is applied to the test specimen 2. The luminescence of the stress-luminescent film 1 can be captured using the imaging device 8.

[0077] The measurement process (S30) includes a step of irradiating with excitation light (S31), a step of quenching (S32), a step of applying a tensile load (S33), and a step of photographing stress luminescence (S34).

[0078] In the excitation light irradiation step (S31), excitation light is irradiated from the light source 10 onto the surface of the test specimen 2. By irradiating the stress-emitting film 1, which is placed in a predetermined region (parallel section) of the test specimen 2, with excitation light, the stress-emitting film 1 is brought into an excited state.

[0079] In the quenching process (S32), the light source 10 is stopped and the system waits until the emission intensity of the stress-emitting film 1 stabilizes after excitation. For example, the irradiation time (excitation time) of the light source 10 is set to 1 minute, and the waiting time after irradiation (quenching time) is set to 2 minutes.

[0080] Next, the process of applying a tensile load (S33) is carried out. In this process (S33), a tensile load is applied to the test specimen 2 by driving the tensile testing machine 4. The tensile speed and maximum load are set as conditions for the tensile test.

[0081] In the step of photographing stress luminescence (S34), a predetermined area of ​​the test specimen 2 is photographed by the imaging device 8. That is, the luminescence of the stress luminescence film 1 is photographed by the imaging device 8. The imaging device 8 uses, for example, an industrial camera, and the frame rate is set to 1 fps to photograph the stress luminescence film 1.

[0082] Next, the calculation process (S40) is performed. In this process (S40), the stress and strain generated in the test specimen 2 are measured using the light emission image captured by the imaging device 8 in the measurement process (S30).

[0083] Specifically, the calculation process (S40) includes a step of acquiring the luminescence intensity of the ROI (S41), a step of calculating the stress generated in the ROI (S42), a step of calculating the amount of displacement generated in the ROI (S43), a step of calculating the strain (S44), and a step of saving the measured values ​​(S45).

[0084] In the process of acquiring the luminescence intensity of the ROI (S41), the image data (moving image data) captured by the imaging device 8 is extracted frame by frame. Then, the luminescence intensity within the ROI is calculated for each frame of the luminescence image. For example, the ROI contains light emitted by two or more stress emitters 3. The luminescence intensity within the ROI is calculated by statistically processing the luminescence intensities of the two or more stress emitters 3.

[0085] In the step (S42) for calculating the stress generated in the ROI, the stress generated in the ROI is calculated using the calculated luminescence intensity within the ROI obtained in step (S41) and the calibration curve data 162 (regression equation) stored in the memory device 16. If multiple ROIs are set on the surface of the specimen 2, steps (S41) and (S42) are performed for each ROI to calculate the stress generated within each ROI. Then, based on the position information of each ROI and the calculated stress values, the stress distribution on the surface of the specimen 2 is calculated.

[0086] In the step of calculating the amount of displacement occurring in the ROI (S43), the amount of displacement within each ROI is calculated for each frame of the luminescence image. Specifically, for each ROI, the spacing d1 between adjacent stress luminescent elements 3 is calculated along the length and width directions of the specimen 2. Then, by subtracting a predetermined spacing d0 from the calculated spacing d1, the amount of displacement in the length and width directions is calculated.

[0087] In the strain calculation step (S44), the strain generated in specimen 2 is calculated using the displacement amounts within each ROI calculated in step (S43). Specifically, the total strain of specimen 2 is calculated by summing the displacement amounts of multiple ROIs arranged in the longitudinal direction of specimen 2. Furthermore, the strain distribution on the surface of specimen 2 can be calculated based on the positional information and calculated displacement values ​​of each ROI.

[0088] In the step of saving the measured values ​​(S45), the calculated stress values ​​within the ROI calculated in step (S42) and the calculated strain values ​​within the ROI calculated in step (S44) are associated with each frame of the luminescence image and stored in the storage device 16. In other words, the storage device 16 stores data showing the stress and strain generated in the specimen 2 by the tensile load at the time when each frame of the luminescence image was obtained. By observing the data at each timing in the order in which it was obtained, the temporal changes in stress and strain due to the tensile load can be evaluated.

[0089] As described above, according to the stress emission measurement method of this embodiment, a stress emission film having a two-dimensional pattern is formed on the surface of the test specimen, and the stress emission of the stress emission film is photographed. This allows for the measurement of stress from the intensity of light emitted by the two-dimensional pattern of the stress emission film 1, and the measurement of strain from the deformation of the emitting two-dimensional pattern. This makes it possible to simultaneously measure the stress and strain generated in the test specimen, even in the plastic region.

[0090] [Other configuration examples] (1) First modified example of stress luminescence measurement method A stress-emitting film releases energy by emitting light after the excitation light irradiation ends. Therefore, the emission intensity (afterglow) gradually decreases over time. In response to the application of a tensile load, the emission intensity peaks at a certain point. This peak represents emission caused by stress due to the tensile load (stress emission).

[0091] The stress emission amount, which is the increase in emission intensity due to stress emission, corresponds to the peak height. The stress emission amount can be determined by subtracting the afterglow from the total emission intensity. Note that the thinner the film thickness of the stress emission film, the less energy is stored, and therefore the smaller the stress emission amount becomes.

[0092] As described above, while the excitation light irradiation is stopped and the tensile load is applied, the luminescence intensity (afterglow) of the stress-emitting film gradually decreases. During this time, the elongation of the specimen 2 continues to progress under the tensile load. Since the displacement of the multiple stress-emitting elements 3 can be tracked from the afterglow emitted by the multiple stress-emitting elements 3, the temporal change in strain can be observed.

[0093] On the other hand, as the afterglow of the multiple stress-emitting elements 3 gradually decreases, the stress-emitting amount also decreases, resulting in a narrower dynamic range of emission intensity. Therefore, there is a concern that it will become difficult to observe the stress distribution based on emission intensity. This concern may become more pronounced as the thickness of the stress-emitting film decreases, as the amount of energy that can be stored decreases.

[0094] Therefore, the stress-emitting film 1 may be re-excited by irradiating it with excitation light while a tensile load is being applied. Figure 11 is a diagram illustrating a stress-emitting measurement method according to a first modified example of this embodiment.

[0095] Figure 11 shows an example of the timing of excitation light irradiation in accordance with the time transition of the test force applied to specimen 2. The time from t0 to t1 corresponds to the time when excitation light is irradiated onto the stress-emitting film 1 before the test force (tensile load) is applied. At time t2, the tensile test is started and the test force is applied to specimen 2, causing light emission (stress emission) in the stress-emitting film 1 due to the stress generated by the tensile load. In the example in Figure 12, the emission intensity peaks at the elastic limit of specimen 2 (the limit of stress at which specimen 2 elastically deforms) (time t3).

[0096] From time t1 onward, the amount of energy stored in the stress-emitting film 1 gradually decreases due to the release of energy through luminescence, and therefore the luminescence intensity (afterglow) also gradually decreases. During the time t4-t5 while the tensile load is applied, the stress-emitting film 1 is irradiated again with excitation light. As a result, the stress-emitting film 1 is excited again, and the luminescence intensity (afterglow) increases. From time t5 onward, when the irradiation of excitation light ends, the luminescence intensity (afterglow) decreases again.

[0097] By restoring the energy stored in the stress-emitting film 1 while applying the tensile load, the amount of stress emission increases, thus widening the dynamic range of emission intensity. As a result, it becomes possible to observe the stress distribution on the surface of the specimen 2 with high sensitivity based on the emission intensity of the stress-emitting film 1.

[0098] The time (time t4 to t5) for irradiating the stress-emitting film 1 with excitation light again can be arbitrarily set to match the timing at which you want to observe the stress distribution. For example, if you want to observe the stress distribution that occurs just before the specimen 2 fractures in the plastic region, you can irradiate it with excitation light at the same time. Normally, if a tensile load is continuously applied to the specimen 2, a neck will form in a part of the specimen 2, and the deformation will concentrate in the neck. Finally, the specimen 2 will fracture from the neck. By irradiating it with excitation light at the time the neck forms, you can observe the stress distribution during the process of neck growth with high sensitivity.

[0099] Furthermore, during the time when the excitation light is irradiated (time t4 to t5), the movement of the crosshead 42 may be stopped to temporarily halt the tensile operation, or the movement of the crosshead 42 may be continued to allow the tensile operation to continue.

[0100] By configuring the system to temporarily halt the tensile motion during excitation light irradiation, the stress is kept constant during the excitation light irradiation time, interrupting the process leading to fracture of the specimen 2. This allows for reliable observation of the stress distribution at the interrupted moment. In contrast, by continuously moving the crosshead 42 during excitation light irradiation, it is possible to observe the temporal changes in the stress distribution during the fracture process.

[0101] (2) Second modified example of stress luminescence measurement method Figure 12 is a flowchart illustrating the processing procedure for the stress luminescence measurement method according to a second modified example of this embodiment. The stress luminescence measurement method according to the second modified example is obtained by adding a display step (S50) to the flowchart shown in Figure 10.

[0102] As shown in Figure 12, the display step (S50) is performed after the calculation step (S40). The display step (S50) includes the steps of reading the light-emitting image stored in the storage device 16 (S51), reading the measured stress and strain values ​​stored in the storage device 16 (S52), and superimposing the measured values ​​onto the light-emitting image (S53).

[0103] In the process of reading out the light emission image (S51), one frame of the light emission image is extracted and read out from the video data captured by the imaging device 8 in the measurement process (S30) and stored in the storage device 16.

[0104] In the step of reading the measured values ​​(S52), data indicating the stress and strain calculated in the calculation step (S40) for the one frame of light emission image read in step (S51) is read from the storage device 16. As described above, in the calculation step (S40), the calculated stress and strain values ​​calculated in steps (S42) and (S44) are associated with one frame of light emission image and stored in the storage device 16. Therefore, by reading one frame of light emission image from the storage device 16 in step (S51), the calculated stress and strain values ​​associated with that light emission image can also be read at the same time.

[0105] In the superimposed display process (S53), the luminescent image of one frame read in process (S51) is displayed on the display unit 142 of the control device 14. At this time, the calculated stress and strain values ​​read in process (S52) are superimposed on the luminescent image and displayed. Figure 13 shows an example of a luminescent image displayed on the display unit 142 of the control device 14 in process (S53).

[0106] In the example shown in Figure 13, the display unit 142 displays an image of the stress-emitting film 1 formed in a predetermined area of ​​the test specimen 2, along with a table 164 showing the measured stress and strain values ​​at multiple points P1 to P9 set in the predetermined area.

[0107] In the emission image, the magnitude of the emission intensity is represented by brightness on a two-dimensional plane. Areas with high brightness indicate areas of high emission intensity (i.e., areas of high stress), while areas with low brightness indicate areas of low emission intensity (i.e., areas of low stress). Therefore, the distribution of stress generated in specimen 2 can be qualitatively detected from the emission image. Furthermore, by superimposing the measured values ​​of stress and strain onto the emission image, it becomes possible to quantitatively detect the magnitude of stress and strain at each point in the distribution.

[0108] (3) First modified example of a two-dimensional pattern of a stress-emitting film The two-dimensional pattern formed by multiple stress-emitting elements 3 is not limited to the checkerboard pattern shown in Figure 3. Figure 14 shows a first modified example of the stress-emitting film 1. A portion of the stress-emitting film 1 is shown in magnified view in Figure 14.

[0109] In the example shown in Figure 14, the stress-emitting film 1 has a two-dimensional pattern consisting of a grid. The grid pattern can be formed by intersecting linear stress-emitting elements 3 in the length and width directions of the specimen 2.

[0110] In the example shown in Figure 14, the strain generated in the specimen 2 can be measured based on the displacement d0 of the distance between two adjacent stress-emitting elements 3 in the longitudinal or lateral direction. Simultaneously, the stress generated in the specimen 2 can be measured based on the luminescence intensity of each stress-emitting element 3.

[0111] (4) Second modified example of a two-dimensional pattern of a stress-emitting film Figure 15 shows a second modified example of the stress-emitting film 1. A portion of the stress-emitting film 1 is shown in magnified view in Figure 15. As shown in Figure 15, the stress-emitting film 1 according to the second modified example is composed of a plurality of first stress-emitting elements 3A and a plurality of second stress-emitting elements 3B.

[0112] The first stress-emitting body 3A is formed from a stress-emitting material that emits light in a first wavelength range. The second stress-emitting body 3B is formed from a stress-emitting material that emits light in a second wavelength range different from the first wavelength range. By selecting the inorganic matrix material and the element of the light-emitting center, stress-emitting bodies that emit light at various wavelengths from ultraviolet to visible to infrared can be formed. By making at least one of the inorganic matrix material and the element of the light-emitting center contained in the stress-emitting material different between the first stress-emitting body 3A and the second stress-emitting body 3B, the wavelength of stress emission of the first stress-emitting body 3A and the wavelength of stress emission of the second stress-emitting body 3B can be made different.

[0113] The first stress-emitting element 3A and the second stress-emitting element 3B are arranged in a two-dimensional pattern in a predetermined region (parallel section) on the surface of the specimen 2. In the example shown in Figure 15, both the first stress-emitting element 3A and the second stress-emitting element 3B have a square shape and are arranged alternately in the length and width directions of the specimen 2, maintaining a predetermined interval d0. The multiple first stress-emitting elements 3A and the multiple second stress-emitting elements 3B together form a two-dimensional pattern.

[0114] The length of one side of each of the first stress-emitting element 3A and the second stress-emitting element 3B is several to several tens of micrometers, and the predetermined interval d0 is several to several tens of micrometers. The first stress-emitting element 3A and the second stress-emitting element 3B do not necessarily have the same shape and size; they may have different shapes and sizes.

[0115] Alternatively, as shown in Figure 14, the first stress-emitting element 3A and the second stress-emitting element 3B may each be made into a linear shape, and they may be arranged alternately in the length and width directions of the specimen 2 while maintaining a predetermined interval d0, thereby forming a two-dimensional pattern consisting of a grid pattern as a whole.

[0116] In this modified example, the stress luminescence measurement system 100 can simultaneously measure the stress and strain generated in the test specimen 2 from the intensity of the light emitted by the first stress luminescent body 3A and the second stress luminescent body 3B, respectively, as the test specimen 2 deforms, and from the amount of displacement of the first stress luminescent body 3A and the second stress luminescent body 3B, respectively.

[0117] Specifically, when a tensile load is applied to specimen 2, the stress-emitting film 1 deforms in accordance with the elongation of specimen 2. Figure 16(A) shows a magnified view of a portion of the stress-emitting film 1 when a tensile load is applied to specimen 2 in the direction of the arrow in the figure. The first stress-emitting element 3A and the second stress-emitting element 3B have each moved from their original positions.

[0118] The stress generated in specimen 2 can be measured using the emission image of the stress-emitting film 1, a first calibration curve data showing the relationship between emission intensity and stress for the first stress-emitting element 3A, and a second calibration curve data showing the relationship between emission intensity and stress for the second stress-emitting element 3B.

[0119] Specifically, the imaging device 8 captures light in a first wavelength range from the emission of stress-emitting film 1 to acquire a first emission image (see Figure 16(B)), and also captures light in a second wavelength range from the emission of stress-emitting film 1 to acquire a second emission image (see Figure 16(C)). The imaging device 8 can be a camera equipped with a wavelength-selective filter.

[0120] Based on the calculated luminescence intensity of each first stress emitter 3A and the first calibration curve data for the acquired first luminescence image (see Figure 16(B)), the stress generated at the location of each first stress emitter 3A is calculated. Similarly, based on the calculated luminescence intensity of each second stress emitter 3B and the second calibration curve data for the second luminescence image (see Figure 16(C)), the stress generated at the location of each second stress emitter 3B is calculated. Based on the positional information and calculated stress values ​​of the first and second stress emitters 3A and 3B, the stress distribution on the surface of the specimen 2 can be measured.

[0121] The strain generated in specimen 2 can be measured based on the displacement of the first stress-emitting element 3A and the second stress-emitting element 3B before and after the application of a tensile load. Specifically, in a portion of the stress-emitting film 1, the distance d1 between adjacent first stress-emitting elements 3A and second stress-emitting elements 3B is calculated based on the positional information of each first stress-emitting element 3A and second stress-emitting element 3B. By calculating the change in this calculated distance d1 relative to the original distance d0, the local strain in that portion can be measured. Then, from the change calculated for each ROI, the strain distribution generated on the surface of specimen 2 can be measured.

[0122] To perform a high-level analysis of the stress and strain distribution on the surface of specimen 2, it is necessary to increase the resolution of the stress-emitting film 1. This can be effectively achieved by reducing the size of each of the multiple stress-emitting elements 3 (see Figure 3) arranged in a two-dimensional pattern on the surface of specimen 2, thereby narrowing the spacing d0 between adjacent stress-emitting elements 3.

[0123] However, if a single type of stress-emitting element 3 is densely arranged to form a two-dimensional pattern, there is a concern that it may become difficult to distinguish adjacent stress-emitting elements 3 in the emission image due to factors such as the resolution of the imaging device 8.

[0124] In this modified example, as described above, two stress emitters 3A and 3B with different stress emission wavelengths are arranged alternately to form a two-dimensional pattern (see Figure 15), and the stress emission at each wavelength is captured. This configuration makes it easy to distinguish between adjacent stress emitters 3A and 3B. Therefore, it becomes possible to perform a highly sophisticated analysis of the stress and strain distribution occurring on the surface of the specimen 2.

[0125] (5) Third modified example of a two-dimensional pattern of a stress-emitting film In the second modified example described above, a configuration was described in which the first stress-emitting element 3A and the second stress-emitting element 3B are arranged alternately on the surface of the specimen 2 while maintaining a predetermined interval d0. However, a configuration in which the first stress-emitting element 3A and the second stress-emitting element 3B are arranged offset from each other in a direction perpendicular to the surface of the specimen 2 is also possible.

[0126] Figure 17 is a schematic cross-sectional view showing a third modified example of the stress-emitting film 1. A portion of the stress-emitting film 1 is shown in magnified view in Figure 17. The basic structure of the stress-emitting film 1 according to the third modified example is the same as that of the stress-emitting film 1 according to the second modified example described above, but the arrangement of the multiple first stress-emitting elements 3A and the multiple second stress-emitting elements 3B is different.

[0127] Furthermore, the stress-emitting film 1 according to the third modified example has the same configuration as the stress-emitting film 1 according to the second modified example shown in Figure 15 when viewed from a direction perpendicular to the surface of the test specimen 2. That is, in the stress-emitting film 1 according to the third modified example, the plurality of first stress-emitting elements 3A and the plurality of stress-emitting elements 3B are arranged to form a two-dimensional pattern when viewed from a direction perpendicular to the surface of the test specimen 2. Figure 17 corresponds to a cross-sectional view of that two-dimensional pattern along the line XVII-XVII in Figure 15.

[0128] Multiple second stress-emitting elements 3B are arranged alternately in a predetermined region on the surface of the specimen 2, maintaining predetermined intervals in both the longitudinal and widthwise directions of the specimen 2.

[0129] A translucent (preferably optically transparent) film 5 is placed in a predetermined area on the surface of the test specimen 2. The film 5 is laminated to the surface of the test specimen 2, on which a plurality of stress-emitting elements 3B are arranged, via an adhesive layer (not shown). The film 5 is, for example, a flexible transparent resin film.

[0130] Multiple stress-emitting elements 3A are arranged alternately in a predetermined area on the surface of the film 5, maintaining a predetermined interval in both the length and width directions of the test specimen 2. Furthermore, stress-emitting elements 3A and 3B are arranged alternately in both the length and width directions of the test specimen 2, maintaining a predetermined interval d0.

[0131] In this modified example, as in the second modified example described above, the stress luminescence measurement system 100 can simultaneously measure the stress and strain generated in the test specimen 2 from the intensity of the light emitted by the first stress luminescent body 3A and the second stress luminescent body 3B, respectively, as the test specimen 2 deforms, and from the amount of displacement of the first stress luminescent body 3A and the second stress luminescent body 3B, respectively.

[0132] Figure 18 shows a magnified view of a portion of the stress-emitting film 1 when a bending load is applied to the specimen 2 along the direction of the white arrow in the figure. As shown in Figure 18, when a bending load is applied, both the specimen 2 and the film 5 deform in a curved shape. The first stress-emitting element 3A moves from its original position in accordance with the deformation of the film 5. The second stress-emitting element 3B moves from its original position in accordance with the deformation of the specimen 2.

[0133] Bending stress is generated in both specimen 2 and film 5. Specifically, compressive stress is generated on the inside of the curve, and tensile stress is generated on the outside of the curve. Therefore, as shown in Figure 18, stresses in opposite directions may be generated in specimen 2 and film 5, which may result in delamination between specimen 2 and film 5.

[0134] The stress generated in specimen 2 can be measured using a first emission image taken with light in a first wavelength range and first calibration curve data. The strain generated in specimen 2 can be measured based on the displacement of the first stress emitter 3A before and after the bending load is applied.

[0135] The stress generated in film 5 can be measured using a second emission image captured with light in a second wavelength range and second calibration curve data. The strain generated in film 5 can be measured based on the displacement of the second stress emitter 3B before and after the bending load is applied.

[0136] Based on these obtained stress and strain measurements, it becomes possible to evaluate, for example, the adhesion resistance of the film 5 to the test specimen 2 when subjected to a bending load.

[0137] In this modified example, two stress-emitting elements 3A and 3B, which have different stress emission wavelengths, are arranged so that their positions in the direction perpendicular to the surface of the specimen 2 are different from each other, and so that they form a two-dimensional pattern when viewed from that perpendicular direction. Based on the emission intensity and displacement of each of the stress-emitting elements 3A and 3B, the distribution of stress and strain in the horizontal and perpendicular directions on the surface of the specimen 2 can be measured. This makes it possible to measure the three-dimensional distribution of stress and strain.

[0138] In the second and third modified examples described above, the stress-emitting film was constructed from two stress-emitting elements with different stress emission wavelengths. However, the stress-emitting film may also be constructed from three or more stress-emitting elements. For example, in the stress-emitting film 1 shown in Figure 17, another film may be laminated on the surface of film 5, and stress-emitting elements with different stress emission wavelengths from stress-emitting elements 3A and 3B may be further arranged on the surface of this film. This makes it possible to measure the three-dimensional distribution of stress and strain generated within the multiple laminated films.

[0139] (6) Stress-induced light-emitting film formation process (S20 in Figure 10) Figure 19 is a flowchart illustrating an example of the processing procedure for the stress-luminescent film formation process (S20 in Figure 10). As shown in Figure 19, the stress-luminescent film formation process (S20) mainly consists of a step of generating stress-luminescent paint (S21), a step of applying the stress-luminescent paint (S22), and a step of drying the stress-luminescent paint (S23).

[0140] In the process of producing stress-luminescent paint (S21), a paint containing stress-luminescent material (stress-luminescent paint) is produced. In this process, first, a process of pulverizing the stress-luminescent material (S211) is carried out.

[0141] Stress-luminescent materials are constructed by solid-solving elements that act as luminescence centers within the framework of an inorganic crystal (matrix). Stress-luminescent materials are in powder form and consist of multiple ceramic particles. Ideally, to form a uniform stress-luminescent film with a thickness of several tens of micrometers, the particle size of the stress-luminescent material should be on the submicron order. However, the ceramic particles that make up typical stress-luminescent materials have an average particle size of 2-3 μm and a particle size distribution in the range of 1-10 μm. This is because, if stress-luminescent materials are produced with a submicron-order particle size from the outset, the crystal structure becomes a cubic crystal, which lacks stress-luminescence ability, rather than a monoclinic crystal, which does possess stress-luminescence ability. However, this makes it difficult to achieve a film thickness of several tens of micrometers in the stress-luminescent film.

[0142] In step (S211), these particles are pulverized to produce a stress-luminescent material with a particle size on the order of submicrons. This is based on the inventors' finding that even when monoclinic particles are pulverized, the crystal structure of the particles does not change, and the stress-luminescent ability is not impaired. Furthermore, the inventors have also found that aggregation of particles after pulverization is suppressed. This makes it possible to form a homogeneous stress-luminescent film.

[0143] Stress-luminescent materials can be pulverized using known pulverizing equipment. However, stress-luminescent materials have low water resistance and may deteriorate and lose stress-luminescence ability due to heating. Therefore, it is preferable to use a pulverizing equipment that can pulverize particles by causing them to collide at high speed. The pulverizing conditions are not particularly limited and should be set considering the particle size and particle size distribution of the stress-luminescent material before pulverization.

[0144] Next, a stress-luminescent coating is produced by mixing the crushed stress-luminescent material with a solvent in a step (S212). In this step (S212), the stress-luminescent material and the solvent are mixed by crushing the stress-luminescent material in a slurry state in which the stress-luminescent material is dispersed in the solvent. The solvent contains a film-forming resin. The solvent may optionally contain coating additives such as solvents, dispersants, fillers, and thickeners. The crushing method is not particularly limited, but for example, a roller mill or a ball mill can be used.

[0145] Next, the process of applying stress-luminescent paint (S22) is carried out. In this process, stress-luminescent paint is applied to a predetermined area of ​​the test specimen 2. For applying the stress-luminescent paint, for example, a printing technique using a screen plate can be used. Specifically, process (S22) mainly consists of a process of filling the screen plate with stress-luminescent paint (S221), a process of transferring the stress-luminescent paint to the test specimen 2 (S222), and a process of isolating the screen plate (S223).

[0146] In step (S221), stress-luminescent paint is supplied to the screen plate while it is in contact with the surface of the test specimen 2. The screen plate has a two-dimensional mesh structure with multiple through-holes formed in a matrix. The size of each through-hole can be set according to the size of the stress-luminescent body 3 in the two-dimensional pattern (see Figure 3). The spacing between adjacent through-holes can also be set according to the spacing between the stress-luminescent bodies 3 in the two-dimensional pattern.

[0147] In this state, the lower end of the flat squeegee is brought into contact with the screen plate, and the squeegee is moved horizontally across the screen plate, thereby filling each through-hole of the screen plate with stress-luminescent paint. By repeatedly moving the squeegee horizontally in this state, the stress-luminescent paint that has filled each through-hole is transferred to the surface of the specimen 2 (S222). Then, by separating the screen plate from the surface of the specimen 2 (S223), the stress-luminescent particles are removed from the screen plate and transferred onto the surface of the specimen 2. This forms a stress-luminescent coating film with a two-dimensional pattern.

[0148] Next, a drying step (S13) is performed on the stress-luminescent coating. In this step (S23), the stress-luminescent coating hardens as the solvent and water in the solvent evaporate due to drying. As a result, a stress-luminescent film 1 (see Figure 3) is formed on the surface of the specimen 2, in which multiple stress-luminescent elements 3 are arranged in a two-dimensional pattern.

[0149] Furthermore, the film thickness of each stress-emitting element 3 after drying can be adjusted by changing the thickness of the screen plate and the boiling point and viscosity of the stress-emitting paint. In addition, the size of each stress-emitting element 3 and the spacing between them can be adjusted by changing the thickness of the screen plate, as well as the size of each through-hole and the spacing between them.

[0150] In the DIC method described above, a random pattern is generally formed on the surface of the specimen by spraying paint from a spray can onto the specimen's surface. In this method of spray painting, the paint film thickness formed with one spray is small, about 20 μm, but because the film thickness is non-uniform, it is necessary to spray the paint multiple times on the same area to ensure uniformity of the film thickness. Therefore, when a stress-emitting film is formed using spray paint, there is a concern that the film thickness of the stress-emitting film will become too thick. If the film thickness of the stress-emitting film becomes thick, the load applied to the stress-emitting film itself will become dominant, which could lead to measuring the stress of the stress-emitting film rather than that of specimen 2.

[0151] In contrast, in this embodiment, a stress-luminescent coating containing finely granulated stress-luminescent material is applied to the specimen 2 by printing using a screen plate to form a stress-luminescent film 1. This makes it possible to form a thin stress-luminescent film 1 with excellent film thickness uniformity. As a result, it is possible to capture minute changes in stress and strain occurring on the surface of the specimen 2, enabling highly sensitive measurement. It should be noted that a thin stress-luminescent film 1 with excellent film thickness uniformity can also be formed by using inkjet printing instead of printing using a screen plate.

[0152] [Aspect] Those skilled in the art will understand that the above-described exemplary embodiments are specific examples of the following embodiments.

[0153] (Section 1) A stress emission measurement method according to one embodiment comprises the steps of: forming a stress emission film having a plurality of stress emission elements arranged in a two-dimensional pattern on the surface of an object; exciting the stress emission film by irradiating it with excitation light from a light source; applying a load to the object; using an imaging device to photograph the stress emission film when the load is applied; and measuring the stress and strain generated in the object based on the captured emission image of the stress emission film. The steps of measuring stress and strain include measuring the stress generated in the object based on the emission intensity of the stress emission film, and measuring the strain generated in the object based on the displacement of the plurality of stress emission elements before and after the load is applied.

[0154] According to the stress emission measurement method described in paragraph 1, a stress emission film having a two-dimensional pattern is formed on the surface of the object, and the stress emission from this stress emission film is photographed. As a result, even in a dark environment, the stress generated in the object can be measured from the intensity of the light emitted by the two-dimensional pattern of the stress emission film, and the strain generated in the object can be measured from the deformation of the emitting two-dimensional pattern. Consequently, even in the plastic region where the proportional relationship between stress and strain does not hold, it is possible to simultaneously measure the stress and strain generated in the object.

[0155] (Section 2) In the stress emission measurement method described in Section 1, the step of measuring stress includes the step of detecting the emission intensity of each of a plurality of stress emission bodies, and the step of calculating the stress generated in the object from the detected emission intensity using a calibration curve that shows the relationship between the emission intensity of the stress emission bodies and the stress.

[0156] In this way, the stress generated in each part of the object can be measured from the intensity of light emitted by each part of the two-dimensional pattern.

[0157] (Article 3) In the stress emission measurement method described in Article 1 or Article 2, the step of measuring strain includes the step of calculating the displacement of each part of the stress emission film from the change in the distance between two adjacent stress emission bodies, and the step of measuring the strain occurring in the entire object based on the sum of the calculated displacements of each part.

[0158] In this way, the strain occurring in the entire object can be measured from the deformation of the luminescent two-dimensional pattern.

[0159] (Section 4) In the stress emission measurement method described in Section 3, the step of measuring strain further includes the step of measuring the strain distribution on the surface of the object based on the calculated displacement amounts of each part.

[0160] According to this method, it is possible to measure local strains occurring in an object from the deformation of each part of a two-dimensional pattern.

[0161] (Article 5) The stress luminescence measurement method described in Articles 1 to 4 further comprises the step of associating the measured values ​​of stress and strain obtained from the luminescence images taken at each timing when a load is applied with the luminescence images and storing them in a memory device.

[0162] In this way, by observing the measured values ​​at each timing in the order in which they were obtained, it is possible to evaluate the temporal changes in stress and strain under load.

[0163] (Section 6) The stress luminescence measurement method described in Section 5 further comprises the step of displaying luminescence images taken at each time the load is applied. The display step includes superimposing and displaying measured stress and strain values ​​obtained from the luminescence images onto the luminescence images.

[0164] In this way, it becomes possible to qualitatively detect the stress distribution generated in an object from the emission image, and at the same time, to quantitatively detect the magnitude of stress and strain at each point in that distribution.

[0165] (Section 7) The stress emission measurement method described in Sections 1 to 4 further comprises the step of a light source irradiating the stress emission film with excitation light when a load is applied to re-excite the stress emission film. The step of measuring stress includes measuring the stress distribution on the surface of the object based on the emission intensity of the re-excited stress emission film.

[0166] According to this method, by re-exciting the stress-emitting film while a load is applied and restoring its energy reserves, the amount of light emitted due to the stress generated by the load (stress emission) increases, thus widening the dynamic range of the emission intensity. Therefore, it becomes possible to observe the stress distribution on the surface of an object with high sensitivity based on the emission intensity of the stress-emitting film.

[0167] (Clause 8) In the stress emission measurement method described in paragraph 1, the step of forming a stress emission film includes forming a stress emission film having a two-dimensional pattern on the surface of an object in which a plurality of first stress emission bodies that emit light in a first wavelength range and a plurality of second stress emission bodies that emit light in a second wavelength range different from the first wavelength range are alternately arranged.

[0168] In this way, even when first and second stress-emitting bodies with different stress emission wavelength ranges are densely arranged to form a two-dimensional pattern, it becomes possible to easily distinguish adjacent first and second stress-emitting bodies by photographing the stress emission at each wavelength. This makes it possible to perform a highly sophisticated analysis of the stress and strain distribution occurring on the surface of the object.

[0169] (Section 9) In the stress emission measurement method described in Section 8, the step of forming a stress emission film further includes the step of arranging a plurality of first stress emission bodies and a plurality of second stress emission bodies on the surface of an object such that their positions in a direction perpendicular to the surface of the object are different from each other and that they form a two-dimensional pattern when viewed from a perpendicular direction.

[0170] In this way, it becomes possible to measure the three-dimensional distribution of stress and strain occurring in the object based on the luminescence intensity and displacement of each of the first and second stress-emitting elements.

[0171] (Clause 10) In the stress emission measurement method described in paragraph 8 or 9, the step of measuring stress includes detecting the emission intensity of each of a plurality of first stress emitters and a plurality of second stress emitters, and calculating the stress generated in the object from the detected emission intensity using a first calibration curve showing the relationship between the emission intensity of the first stress emitters and stress, and a second calibration curve showing the relationship between the emission intensity of the second stress emitters and stress.

[0172] According to this method, the distribution of stress generated on the surface of an object can be analyzed in a highly sophisticated manner from a two-dimensional pattern in which the first and second stress-emitting elements are densely arranged.

[0173] (Clause 11) In the stress measurement method described in paragraph 8 or 10, the step of measuring strain includes the steps of calculating the displacement of each part of the stress-emitting film from the change in the distance between a first stress-emitting body and a second stress-emitting body arranged adjacent to each other when viewed from a direction perpendicular to the surface of the object, and measuring the strain distribution occurring on the surface of the object based on the calculated displacement of each part.

[0174] According to this method, the distribution of strain generated on the surface of an object can be analyzed in a highly sophisticated manner from a two-dimensional pattern in which the first and second stress-emitting elements are densely arranged.

[0175] (Section 12) The stress emission measurement method described in Sections 1 to 11 further comprises the step of stabilizing the stress emission film by stopping the irradiation of excitation light from the light source.

[0176] According to this method, a load can be applied to a stress-emitting film in a state where the luminescence intensity is stable, allowing for accurate detection of luminescence caused by stress resulting from the load (stress luminescence).

[0177] (Section 13) In the stress luminescence measurement method described in Sections 1 to 12, the step of forming a stress luminescence film includes the steps of: finely granulating a stress luminescence material having monoclinic particles while maintaining the crystalline structure of the particles; mixing the finely granulated stress luminescence material with a solvent; applying the mixture of stress luminescence material and solvent to the surface of an object to print a two-dimensional pattern on the surface of the object; and drying the applied mixture.

[0178] In this way, the finely granulated stress-luminescent material retains its stress-luminescence ability, and particle aggregation is suppressed. By printing a two-dimensional pattern onto the surface of an object using a mixture containing this stress-luminescent material, a thin stress-luminescent film can be formed in which the stress-luminescent material is uniformly dispersed. As a result, it becomes possible to measure minute changes in stress and strain generated on the surface of an object under load with high precision.

[0179] (Section 14) A stress luminescence measurement system according to one embodiment is a system for measuring the stress and strain generated in an object when a load is applied to the object. A stress luminescence film having a plurality of stress luminescent elements arranged in a two-dimensional pattern is formed on the surface of the object. The stress luminescence measurement system comprises a testing machine for applying a load to the object, a light source for exciting the stress luminescence film, an imaging device for photographing the stress luminescence film when the load is applied, and a control device for measuring the stress and strain generated in the object based on the captured luminescence image of the stress luminescence film. The control device measures the stress generated in the object based on the luminescence intensity of the stress luminescence film. The control device further measures the strain generated in the object based on the displacement of the plurality of stress luminescent elements before and after the load is applied.

[0180] According to the stress emission measurement system described in Section 14, by configuring the system to capture the stress emission of a two-dimensional patterned stress emission film formed on the surface of an object, it is possible to measure the stress generated in the object from the intensity of the light emitted by the two-dimensional pattern of the stress emission film, even in dark environments, and to measure the strain generated in the object from the deformation of the emitting two-dimensional pattern. As a result, it is possible to simultaneously measure the stress and strain generated in the object even in the plastic region where the proportional relationship between stress and strain does not hold.

[0181] Furthermore, regarding the embodiments and modifications described above, it was intended from the outset that the configurations described in the embodiments could be appropriately combined, including combinations not mentioned in the specification, to the extent that no inconvenience or inconsistency arises.

[0182] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims rather than the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended. [Explanation of symbols]

[0183] 1 Stress-emitting film, 2 Test specimen, 3 Stress-emitting body, 3A First stress-emitting body, 3B Second stress-emitting body, 4 Tensile testing machine, 5 Film, 6, 14 Control device, 8 Imaging device, 10 Light source, 12 Drive device, 15 Communication line, 16 Storage device, 40 Table, 42 Crosshead, 44, 46 Screw rod, 48, 50 Grip, 52 Load cell, 62, 142 Display unit, 100 Stress-emitting measurement system, 140 Processor, 141 Memory, 143 Display I / F, 144 Operation unit, 145 Input / Output I / F, 146 Communication I / F, 160 Stress measurement program, 162 Calibration curve data.

Claims

1. The steps include forming a stress-emitting film on the surface of an object, having a plurality of stress-emitting elements arranged in a two-dimensional pattern, The steps include: exciting the stress-emitting film by irradiating it with excitation light from a light source, The steps include applying a load to the object, The imaging device takes a photograph of the stress-emitting film when the load is applied, The procedure includes the step of measuring the stress and strain generated in the object based on the captured light emission image of the stress light emission film, The step of measuring the stress and strain is as follows: A step of measuring the stress generated in the object based on the light emission intensity of the stress-emitting film, A stress emission measurement method comprising the step of measuring the strain generated in the object based on the amount of displacement of the plurality of stress emission elements before and after the load is applied.

2. The step of measuring the stress is as follows: The steps include detecting the light emission intensity of each of the plurality of stress-emitting elements, The stress emission measurement method according to claim 1, comprising the step of calculating the stress generated in the object from the detected emission intensity using a calibration curve showing the relationship between the emission intensity of the stress emission element and the stress.

3. The step of measuring the strain is as follows: A step of calculating the displacement of each part of the stress-emitting film from the change in the distance between two adjacent stress-emitting elements, The stress emission measurement method according to claim 2, comprising the step of measuring the strain occurring in the entire object based on the sum of the displacement amounts of each of the calculated parts.

4. The step of measuring the strain is as follows: The stress emission measurement method according to claim 3, further comprising the step of measuring the strain distribution on the surface of the object based on the calculated displacement amounts of each of the parts.

5. The stress emission measurement method according to any one of claims 1 to 4, further comprising the step of associating measured stress and strain values ​​obtained from the emission images with the emission images taken at each timing when the load is applied, and storing them in a storage device.

6. The method further includes the step of displaying the light-emitting image captured at each timing when the load is applied, The stress emission measurement method according to claim 5, wherein the display step includes a step of superimposing and displaying measured stress and strain values ​​obtained from the emission image onto the emission image.

7. The light source further comprises the step of irradiating the stress-emitting film with excitation light while the load is applied to re-excite the stress-emitting film, The stress emission measurement method according to any one of claims 1 to 4, wherein the step of measuring the stress includes measuring the stress distribution on the surface of the object based on the emission intensity of the stress emission film that has been re-excited.

8. The step of forming the stress-emitting film is, The stress emission measurement method according to claim 1, comprising the step of forming the stress emission film having the two-dimensional pattern in which a plurality of first stress emission bodies that emit light in a first wavelength range and a plurality of second stress emission bodies that emit light in a second wavelength range different from the first wavelength range are alternately arranged on the surface of the object.

9. The step of forming the stress-emitting film is, The stress emission measurement method according to claim 8, further comprising the step of arranging the plurality of first stress emitters and the plurality of second stress emitters on the surface of the object such that their positions in a direction perpendicular to the surface of the object are different from each other and that they form the two-dimensional pattern when viewed from the perpendicular direction.

10. The step of measuring the stress is as follows: A step of detecting the light emission intensity of each of the plurality of first stress-emitting elements and the plurality of second stress-emitting elements, A stress emission measurement method according to claim 8 or 9, comprising the step of calculating the stress generated in the object from the detected emission intensity using a first calibration curve showing the relationship between the emission intensity of the first stress emission element and stress, and a second calibration curve showing the relationship between the emission intensity of the second stress emission element and stress.

11. The step of measuring the strain is as follows: A step of calculating the displacement of each part of the stress-emitting film from the change in the distance between the first stress-emitting element and the second stress-emitting element, which are arranged adjacent to each other when viewed from a direction perpendicular to the surface of the object, A stress emission measurement method according to claim 8 or 9, comprising the step of measuring the strain distribution occurring on the surface of the object based on the calculated displacement amounts of each of the parts.

12. The stress emission measurement method according to claim 1, further comprising the step of stopping the irradiation of excitation light from a light source to stabilize the stress emission film.

13. The step of forming the stress-emitting film is, A stress-luminescent material having monoclinic particles is granulated while maintaining the crystalline structure of the particles. The steps include mixing the granulated stress-luminescent material with a solvent, The steps include printing the two-dimensional pattern on the surface of the object by applying a mixture of the stress-luminescent material and the solvent to the surface of the object, The stress luminescence measurement method according to claim 1, comprising the step of drying the coated mixture.

14. A stress measurement system for measuring the stress and strain generated in an object when a load is applied to the object, A stress-emitting film having a plurality of stress-emitting elements arranged in a two-dimensional pattern is formed on the surface of the object. A testing machine for applying a load to the aforementioned object, A light source for exciting the stress-emitting film, A photographic device for photographing the stress-emitting film when the aforementioned load is applied, The system includes a control device that measures the stress and strain generated in the object based on the captured light emission image of the stress-emitting film, The control device is Based on the light emission intensity of the stress-emitting film, the stress generated in the object is measured, A stress emission measurement system that measures the strain generated in an object based on the displacement of the plurality of stress emission elements before and after the load is applied.

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