A device for measuring the shear modulus of a surface shear stress sensitive membrane

Abstract

The application discloses a device for measuring the shear modulus of a surface shear stress sensitive film, and relates to the field of shear modulus measurement. The device comprises a water platform, a tilting device module and a test piece platform. The tilting device module is installed on the water platform, and the test piece platform is installed on the tilting device module. The tilting device module is used for adjusting the inclination angle of the test piece platform. The test piece substrate, the inclination sensing module and the image acquisition module are all fixed on the test piece platform. The test piece substrate is used for mounting and fixing the surface shear stress sensitive film to be measured, which is provided with marked particles. The mass block is used for being placed on the surface shear stress sensitive film to be measured to provide shear stress for the surface shear stress sensitive film to be measured. The inclination sensing module is used for measuring the inclination angle data of the test piece platform. The image acquisition module is used for acquiring a plurality of images before and after the mass block is placed on the surface of the surface shear stress sensitive film to be measured to obtain image data. The data acquisition and processing module is used for calculating and obtaining the shear modulus of the surface shear stress sensitive film to be measured. The device can accurately measure the shear modulus of the surface shear stress sensitive film.

Description

Technical Field

[0001] This invention relates to the field of shear modulus measurement, and more specifically, to a device for measuring the shear modulus of a surface shear stress-sensitive membrane. Background Technology

[0002] The drag of aircraft, high-speed trains, and underwater vehicles is mainly composed of wave drag and surface friction, with surface friction accounting for more than half of the total drag. Surface shear stress is the friction per unit area, and its distribution characteristics are an important basis for surface flow state analysis and drag reduction effect evaluation. The prediction and measurement of surface shear stress and its distribution characteristics have always been a challenging problem in aerodynamics.

[0003] Surface shear stress sensitive membrane sensing technology is a novel technology promising for accurately measuring the distribution characteristics of surface shear stress. The surface shear stress sensitive membrane is a transparent or semi-transparent, homogeneous, and incompressible elastic membrane with randomly distributed marker particles embedded in its surface. The shear modulus G and thickness h of the membrane are precisely determined beforehand. When surface shear stress is applied to the membrane surface, the marker particles on the membrane surface undergo corresponding displacement; when the surface shear stress disappears, the marker particles return to their original positions. Under conditions where the shear strain γ is very small, the average surface shear stress τ and the average shear strain γ within a certain area exhibit a linear relationship, with the shear modulus G serving as the conversion coefficient between the two. Measuring surface shear stress is difficult and precise quantification is challenging. Shear strain γ, however, is determined by measuring the membrane's shear direction displacement d and the local membrane thickness h. Both d and h are length measurements, and the measurement methods are mature, relatively simple, and offer relatively higher accuracy. Therefore, utilizing this sensitive characteristic of the surface shear stress sensitive membrane, the measurement of surface shear stress can be converted into the measurement of shear strain.

[0004] The prerequisite for this technique is the accurate prior measurement of the shear modulus G of the surface shear stress-sensitive membrane, i.e., the conversion factor between shear stress and shear strain. Traditional methods for measuring the shear modulus of elastomers employ the American Society for Testing and Materials (ASTM) method for testing the tensile strength of vulcanized rubber and thermoplastic elastomers (ASTM D412). The specimen is prepared as a C-type specimen according to ASTM D412, with an overall elongated shape, a thickness of 3 mm, and cup-shaped ends for clamping. After clamping, the change in length produced when the specimen is stretched by a certain tensile force is measured, thereby obtaining the elastic modulus / shear modulus of the specimen. However, the ASTM D412 test method is not well-suited for soft elastomers with low shear moduli because soft elastomers will experience a certain stretching length under their own weight, and the clamping ends are also prone to significant deformation, all of which introduce errors.

[0005] If the shear modulus of a surface shear stress-sensitive membrane is less than 10,000 Pa, it is a relatively soft elastic body. If its shear modulus is measured using the ASTM D412 method, there will be a large error, and the smaller the shear modulus, the greater the error. How to accurately measure the shear modulus of the prepared surface shear stress-sensitive membrane is a current challenge. Summary of the Invention

[0006] The purpose of this invention is to accurately measure the shear modulus of a surface shear stress-sensitive membrane.

[0007] To achieve the above objectives, the present invention provides an apparatus for measuring the shear modulus of a surface shear stress-sensitive film, the apparatus comprising:

[0008] Water platform, tilting device module, specimen substrate, specimen platform, image acquisition module, mass block, tilt angle sensing module and data acquisition and processing module;

[0009] The tilting device module is installed on a horizontal platform, and the specimen platform is installed on the tilting device module. The tilting device module is used to adjust the tilt angle of the specimen platform. The specimen substrate, tilt angle sensing module, and image acquisition module are all fixed on the specimen platform. The specimen substrate is used to install and fix the shear stress sensitive membrane of the surface to be tested. The surface of the shear stress sensitive membrane of the surface to be tested is marked with particles. The mass block is used to place on the shear stress sensitive membrane of the surface to be tested to provide shear stress to the shear stress sensitive membrane of the surface to be tested. The tilt angle sensing module is used to measure the tilt angle data of the specimen platform. The image acquisition module is used to acquire several images before and after the mass block is placed on the surface of the shear stress sensitive membrane of the surface to be tested to obtain image data. The data acquisition and processing module is used to calculate the shear modulus of the shear stress sensitive membrane of the surface to be tested based on the tilt angle data and the image data.

[0010] The principle of this device for measuring the shear modulus of a surface shear stress-sensitive membrane is as follows: A mass block is placed on the surface of the shear stress-sensitive membrane to be tested. When the test platform is tilted, the gravitational component of the mass block in the tilt direction acts on the surface of the shear stress-sensitive membrane, causing shear strain in the membrane and corresponding displacement of the marked particles on the surface. The tilt angle sensing module can accurately measure the tilt angle of the test platform. The camera captures particle images before and after the mass block is placed on the shear stress-sensitive membrane. The data acquisition and processing module records data such as the mass of the mass block, the thickness of the shear stress-sensitive membrane, and the tilt angle, as well as the corresponding particle images. The data and images are processed according to a certain procedure to obtain the corresponding shear strain of the surface shear stress-sensitive membrane under different surface shear stresses. Finally, the shear modulus of the surface shear stress-sensitive membrane specimen is calculated.

[0011] This device avoids the use of the traditional ASTM D412 method, avoids the influence of the weight of the shear stress-sensitive membrane on the test surface, and eliminates the need to clamp the shear stress-sensitive membrane. The device is stable and reliable, capable of applying precise shear stress to the surface of the shear stress-sensitive membrane while simultaneously measuring the corresponding displacement and shear strain of the marked particles on the membrane surface. The accurate shear modulus of the surface shear stress-sensitive membrane specimen is obtained by fitting the shear stress-shear strain data. This device is particularly suitable for the accurate measurement of low shear modulus in softer elastomers.

[0012] Furthermore, the image acquisition module includes a camera and a light source module. The light source module illuminates the marked particles, and the camera can then capture clear images of the marked particles, facilitating subsequent image analysis and processing.

[0013] Furthermore, the image acquisition module also includes: an optical lens, a right-angle bracket, an optical flat plate, an adapter plate, and a two-dimensional displacement platform; one right-angle side of the right-angle bracket is fixed to the specimen platform, the optical flat plate is fixed to the other right-angle side of the right-angle bracket, the two-dimensional displacement platform is fixed on the optical flat plate, the camera is fixed on the two-dimensional displacement platform through the adapter plate, the camera is equipped with an optical lens, and the two-dimensional displacement platform is used to adjust the position of the camera.

[0014] The right-angle bracket can stably fix the optical plate on the test piece platform and make the two perpendicular to each other, so that the camera fixed on the optical plate can take a frontal picture of the sensitive film fixed on the test piece platform.

[0015] Among them, optical imaging can be performed using an optical lens, and the camera and two-dimensional displacement platform can be easily installed and fixed using an optical flat plate. The position of the camera can be precisely adjusted using the two-dimensional displacement platform.

[0016] Furthermore, in order to accurately obtain the thickness of the shear stress sensitive film on the surface to be tested, a groove is formed on the substrate of the specimen for fixing the shear stress sensitive film on the surface to be tested. The depth of the groove is the same as the thickness of the shear stress sensitive film on the surface to be tested.

[0017] Among them, the groove can be used to facilitate the preparation of shear stress sensitive membranes on the surface to be tested. The sensitive membrane substrate is formed by mixing and solidifying two liquid raw materials. The groove can effectively control the shape and thickness of the sensitive membrane.

[0018] Furthermore, to eliminate errors caused by rigid displacement, a reference area is set at the edge of the substrate. The surface of the reference area also has marked particles to indicate the possible rigid displacement of the shear stress sensitive film on the surface under test relative to the camera.

[0019] Furthermore, the mass block is a transparent mass block, and there is no relative sliding between the mass block and the shear stress sensitive membrane on the test surface when the test platform is tilted. The transparent design aims to avoid obstructing the view of the marked particles, and the absence of relative sliding between the mass block and the shear stress sensitive membrane ensures accurate reflection of the displacement data of the marked particles in the tilt direction, preventing inaccurate calculation results.

[0020] Furthermore, to achieve better contrast in the particle image, the color at the bottom of the groove is different from the reflective color of the marked particles.

[0021] Furthermore, the labeled particles are reflective particles, such as hollow glass microspheres.

[0022] One or more technical solutions provided by this invention have at least the following technical effects or advantages:

[0023] This invention enables accurate measurement of the shear modulus of a surface shear stress-sensitive membrane. Attached Figure Description

[0024] The accompanying drawings, which are provided to further illustrate embodiments of the invention and constitute a part of this invention, are not intended to limit the scope of the invention.

[0025] Figure 1 A schematic diagram of a device for measuring the shear modulus of a surface shear stress-sensitive membrane;

[0026] The components are as follows: 1-Water platform; 2-Tilt device module; 2-1-Tilt angle adjustment knob; 3-Support rod; 4-Specimen platform; 5-Specimen substrate; 6-Shear stress sensitive membrane of the surface to be tested; 7-Mass block; 8-Data acquisition and processing module; 9-Tilt angle sensing module; 10-Right angle bracket; 11-Optical flat plate; 12-Light source module; 12-1-Light source brightness adjustment knob; 13-Two-dimensional displacement platform; 14-Adapter plate; 15-High resolution camera; 16-Optical lens. Detailed Implementation

[0027] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, where there is no conflict, the embodiments of the present invention and the features thereof can be combined with each other.

[0028] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0029] Example 1

[0030] Please refer to Figure 1 , Figure 1 This invention provides a device for measuring the shear modulus of a surface shear stress-sensitive membrane. The device includes a horizontal platform 1, an tilting device module 2, a specimen substrate 5, a specimen platform 4, a high-resolution camera 15, a light source module 12, a mass block 7, a tilt angle sensing module 9, and a data acquisition and processing module 8.

[0031] A surface shear stress sensitive film of a certain thickness is pre-cured on a specimen substrate as the test specimen; the test specimen and the tilt sensing module are horizontally fixed on the test specimen platform, a high-resolution camera is fixed at a certain height directly above the test specimen, and a light source module is fixed at a certain height to the side above the test specimen; the test specimen platform is fixed to the tilting device module by four or more support rods, and the tilting device module is fixed to the horizontal platform, which enables the test specimen platform and the test specimen, mass block, high-resolution camera and light source module fixed on the test specimen platform to tilt at the same angle relative to the horizontal platform.

[0032] A mass block is gently placed on the central surface of the specimen. When the specimen platform is tilted, the gravitational component of the mass block in the tilt direction acts on the surface shear stress sensitive membrane, causing shear strain in the membrane and corresponding displacement of the marked particles on its surface. The tilt angle sensing module can accurately measure the tilt angle of the specimen platform; the light source module can uniformly and stably illuminate the marked particles; the high-resolution camera can clearly capture particle images; the data acquisition and processing module can record data such as the mass block mass, membrane thickness, tilt angle, and corresponding particle images, and process the data and images to obtain the corresponding shear strain of the surface shear stress sensitive membrane under different surface shear stresses. Finally, the shear modulus of the surface shear stress sensitive membrane specimen is obtained using a fitting method.

[0033] The present invention has a robust and reliable structure, which can apply precise shear stress to the surface of the surface shear stress sensitive membrane specimen and simultaneously measure the corresponding displacement and shear strain of the marked particles on the surface of the surface shear stress sensitive membrane specimen. The accurate shear modulus of the surface shear stress sensitive membrane specimen can be obtained by fitting the shear stress-shear strain data. This device is particularly suitable for the accurate measurement of low shear modulus of softer elastomers.

[0034] In this embodiment of the invention, the substrate of the test specimen has a regularly shaped groove at its center. A shear stress-sensitive film for the surface to be tested is solidified in the groove. The shear stress-sensitive film is a transparent or semi-transparent elastomer with randomly distributed marker particles on its surface. A high-resolution camera captures images of the marker particles. To ensure good contrast in the particle images, the color at the bottom of the groove is set to the opposite of the color reflected by the particles, such as a matte dark color at the bottom of the groove. To determine the thickness of the shear stress-sensitive film for the surface to be tested, the film thickness is consistent with the groove depth. To eliminate errors caused by rigid displacement, a reference area is set at the edge of the substrate. The surface of the reference area also has marker particles to indicate possible rigid displacement of the test specimen relative to the camera.

[0035] In this embodiment of the invention, the tilting device module can fix and support the test specimen platform, the test specimen, the high-resolution camera, the light source module, the mass block, the tilt angle sensing module, etc., and can make these supports tilt smoothly at a certain angle along the same direction.

[0036] In this embodiment of the invention, the mass block is a material with uniform mass, high transparency, regular shape, and smooth surface (surface roughness Ra≤10 micrometers), such as optical glass or transparent acrylic material. The mass block is gently placed on the surface shear stress sensitive film without any gap between them. The area of ​​the contact surface between the two can be calculated simply and accurately. When tilted, the mass block does not slip relative to the surface shear stress sensitive film. Its gravitational component in the tilting direction acts on the surface shear stress sensitive film, providing shear stress input.

[0037] In this embodiment of the invention, the light source module is a DC stable light source, fixed at a certain height above the test piece, and can adjust the brightness within a certain range to illuminate the marked particles on the surface of the shear stress sensitive film and the substrate reference area with an appropriate and constant brightness.

[0038] In this embodiment of the invention, the high-resolution camera is fixed at a certain height directly above the surface shear stress sensitive film specimen using a combination of a right-angle bracket, an optical plate, an adapter plate, and a two-dimensional displacement platform. One right-angle side of the right-angle bracket is fixed to the specimen platform, and the other right-angle side is fixed to the optical plate, making the specimen platform and the optical plate perpendicular to each other. The optical plate provides ample screw holes for easy fixing of the light source module and the high-resolution camera. Since the mounting holes of the high-resolution camera and the optical plate are not the same size, they are connected by an adapter plate. The two-dimensional displacement platform is used to fine-tune the position of the camera. An optical lens with a certain focal length is installed at the front of the camera, which can adjust parameters such as height, left and right position, lens focal length, exposure time, and gain within a certain range, enabling clear and high-resolution imaging of the marked particles on the surface of the shear stress sensitive film and the substrate reference area.

[0039] The tilt sensing module is horizontally mounted on the specimen platform, and the angle sensing direction is consistent with the tilt direction, which can accurately measure the tilt angle of the specimen platform.

[0040] In this embodiment of the invention, the data acquisition and processing module can record data such as the mass of the mass block, the thickness and tilt angle of the surface shear stress sensitive membrane, and the corresponding particle images and the actual distance corresponding to each pixel of the image. The module processes the above data and images according to a certain procedure to obtain the corresponding shear strain of the surface shear stress sensitive membrane under different surface shear stresses. Finally, the shear modulus of the surface shear stress sensitive membrane specimen is obtained by fitting method.

[0041] It should be noted that the surface shear stress sensitive membrane 6 prepared in this embodiment is a surface shear stress sensitive membrane with different shear moduli prepared based on different component ratios. In one embodiment, the raw materials for this surface shear stress sensitive membrane are two types: DC184 silicone rubber base liquid and its curing agent provided by Dow Corning, both of which are transparent liquids. After being mixed evenly according to different ratios, they are poured into the central groove of the horizontally placed test specimen substrate 5 until it is full. The groove has dimensions of 55mm × 75mm × 5mm. After curing at a certain temperature for a certain time, transparent elastomers with different shear moduli can be obtained. The smaller the proportion of the curing agent, the smaller the shear modulus of the resulting elastomer. The membrane surface is uniformly distributed with marker particles, specifically a type of marker particle with a core diameter of 10μm to 14μm and a density of 1.1g / cm³. 3 Hollow glass microspheres.

[0042] The prepared surface shear stress sensitive membrane test specimen and tilt angle sensing module 9 are horizontally fixed on the specimen platform 4. A high-resolution camera 15 is fixed at a certain height directly above the specimen, and a light source module 12 is fixed at a certain height to the side. The specimen platform 4 is fixed to the tilting device module 2 by four support rods 3. The tilting device module 2 is fixed on the horizontal platform 1, which enables the specimen platform 4 and the specimen, mass block 7, high-resolution camera 15 and light source module 12 fixed on the specimen platform to tilt at the same angle relative to the horizontal platform 1. Mass block 7 is gently placed on the center surface of the specimen. When the specimen platform 4 is tilted, the gravitational component of mass block 7 in the tilt direction acts on the surface shear stress sensitive membrane, causing shear strain in the surface shear stress sensitive membrane and corresponding displacement of the marked particles on the surface of the surface shear stress sensitive membrane. The tilt angle sensing module 9 can accurately measure the tilt angle of the specimen platform 4. The light source module 12 can uniformly and stably illuminate the marked particles. The high-resolution camera 15 can clearly capture particle images. The data acquisition and processing module 8 can record data such as the mass of the mass block, the thickness of the surface shear stress sensitive membrane, and the tilt angle, as well as the corresponding particle images. The above data and images are processed according to a certain procedure to obtain the corresponding shear strain of the surface shear stress sensitive membrane under different surface shear stresses. Finally, the shear modulus of the surface shear stress sensitive membrane specimen is obtained by fitting method.

[0043] The tilting device module in this device can be a corner platform or other angle-adjustable mechanism, equipment or device. The corner platform can be an electric corner platform or a manual corner platform. The tilting angle of the corner platform can be adjusted by rotating the angle adjustment knob on the corner platform.

[0044] The tilting device module is preferably an angle stage. The angle stage can form a relatively stable measurement system with the specimen substrate 5, specimen platform 4, high-resolution camera 15, light source module 12, mass block 7 and tilt angle sensing module 9, which facilitates the adjustment of the tilt angle and makes the device more stable as a whole.

[0045] The test substrate is a rigid body with a certain rigidity. When tilted or subjected to fluid impact, only the sensitive membrane deforms, while the test substrate remains unchanged. The test substrate can be made of materials such as acrylic, glass, polyetheretherketone, aluminum, or steel.

[0046] In one embodiment of the device of this invention, almost all components are optical precision parts with standard threads / screw holes for secure connection and assembly. The maximum tilt angle of the entire device is 45°, with a resolution of 0.005°. When used with a transparent mass block weighing 0.2g and measuring 24mm × 24mm × 0.1mm, it can provide a minimum shear stress of 0.0003Pa, thus providing a verification function with a minimum resolution of 0.0003Pa for the surface shear stress sensitive film. When used with a transparent mass block weighing 40g and measuring 24mm × 24mm × 20mm, it can provide a maximum shear stress of 481.2Pa. Assuming that the shear strain generated by the maximum shear stress does not exceed 5% of the film thickness, the shear modulus range that this device can measure with the two mass blocks is 48Pa to 9624Pa, which can meet the requirements for accurate measurement of the shear modulus (<10000Pa) of the developed surface shear stress sensitive film.

[0047] The measurement methods based on this device include:

[0048] S1: The calibration measurement device obtains calibration information based on the length corresponding to each pixel;

[0049] S2: Based on the calibration information and the measuring device, the test piece is tilted multiple times in a preset angle sequence. Each time, the first displacement data of the marker particle in the tilting direction under the action of the shear direction component of its own gravity is measured. Multiple first displacement data are accumulated, and the multiple first displacement data correspond one-to-one with the tilting angle in the preset angle sequence.

[0050] S3: Based on the calibration information and the measuring device, the test piece is tilted multiple times in a preset angle sequence. Each time, the second displacement data of the marker particle in the tilting direction is measured under the combined action of the applied external shear stress and the shear direction component of its own gravity. Multiple second displacement data are accumulated, and the multiple second displacement data correspond one-to-one with the tilting angle in the preset angle sequence.

[0051] S4: For each tilt angle in the preset angle sequence, based on the second displacement data and the first displacement data corresponding to the tilt angle, calculate the third displacement data of the marker particle of the test piece under the applied external shear stress corresponding to the tilt angle in the tilt direction, and accumulate multiple third displacement data.

[0052] S5: Based on each third displacement data and the calibration information, calculate the shear strain data generated under the applied external shear stress when the test piece is tilted at the corresponding angle, and accumulate multiple shear strain data.

[0053] S6: Calculate the magnitude of shear stress applied to the surface of the test piece at each tilt angle in the preset angle sequence, and accumulate multiple shear stress magnitude data. The shear stress magnitude data corresponds one-to-one with the shear strain data.

[0054] S7: The shear modulus of the surface shear stress sensitive membrane is obtained by fitting and calculating based on multiple shear strain data and their corresponding shear stress magnitude data.

[0055] The principle of this method is as follows: First, the measuring device is calibrated to obtain calibration information, which facilitates the calculation of subsequent displacement data. Then, under the condition of no external force, the first displacement data of the marker particle in the tilt direction under the action of the shear component of gravity of the test piece is measured. The purpose of calculating the first displacement data is to prepare for the subsequent calculation of the true displacement data, calculating the displacement data affected by its own weight in advance, and then discarding it when calculating the true displacement data to ensure the true displacement data. Then, the second displacement data of the marker particle in the tilt direction under the action of external shear stress and the shear component of gravity of the test piece is measured. The first displacement data is subtracted from the second displacement data to obtain the third displacement data under the actual action of external shear stress. Based on the third displacement data and calibration information, the shear strain data generated by the test piece under the action of external shear stress when tilted is calculated. Finally, the shear modulus of the surface shear stress sensitive film is calculated based on the shear strain data and the magnitude of the shear stress. This method indirectly obtains shear strain data based on calibration information and image processing, avoiding the traditional method of using ASTM. The D412 method has a large measurement error problem. This invention can accurately measure the shear modulus of surface shear stress sensitive films.

[0056] Furthermore, step S1 specifically includes:

[0057] Make the surface of the calibration plate flush with the surface of the test piece;

[0058] A calibration image is obtained by capturing an image of the calibration plate using a measuring device;

[0059] Select a line segment in the calibration image, with a line segment length of L, and obtain the number of pixels N occupied by the line segment. The length corresponding to each pixel of the measuring device is then obtained as L / N.

[0060] The above calibration method can accurately calibrate the measuring device.

[0061] Furthermore, during the measurement process, the reference area at the edge of the specimen is a rigid body, and the displacement of the marked particles on it is the rigid displacement of the camera relative to the specimen when tilted. If the influence of the rigid displacement is ignored, the measurement results will be inaccurate. In order to further ensure the accuracy of the measurement results, the preferred scheme of this method considers the rigid displacement and performs a rejection process. The method for obtaining the first displacement data in step S2 includes:

[0062] The test piece is tilted at 0 degrees, and the measuring device captures the marked particles on the surface of the test piece and the reference area at the edge of the test piece to obtain the first particle image.

[0063] The test piece is tilted at several angles, and the angle value of each tilt is recorded. The measuring device captures the marked particles on the surface of the test piece and the reference area at the edge of the test piece at each tilt to obtain several second particle images.

[0064] Based on calibration information, a single second particle image, and a first particle image, first displacement distribution data of particles on the surface of the test piece and second displacement distribution data of particles in the edge reference area of ​​the test piece are obtained at a single tilt angle. Several first displacement distribution data of particles on the surface of the test piece and several second displacement distribution data of particles in the edge reference area of ​​the test piece are accumulated. The second displacement distribution data of particles in the edge reference area of ​​the test piece are averaged respectively. A first average displacement data is obtained for each tilt angle. Several first average displacement data are accumulated.

[0065] A single first displacement data is calculated based on the first displacement distribution data and the first average displacement data corresponding to a single tilt angle, and multiple tilt first displacement data are accumulated for multiple tilt angles.

[0066] Specifically, by performing cross-correlation processing on the second particle image and the first particle image, the displacement distribution is obtained by performing cross-correlation calculation on the two particle images. This allows us to obtain the displacement data of the particle's offset in the image, and then calculate the particle's true displacement data based on the calibration information.

[0067] At different tilt angles, the magnitude of the gravitational shear component of the sensitive membrane is different, resulting in different deformation displacements. The two are not strictly linearly related. Therefore, it is impossible to measure the deformation displacement of the sensitive membrane under the action of its own gravitational shear component at all angles by tilting once. It is necessary to tilt at multiple angles for measurement.

[0068] When adjusting the tilt angle of the test piece, the adjustment method is to gradually increase the initial angle from 0 degrees to the maximum angle, and then gradually decrease the maximum angle back to the initial angle.

[0069] The purpose of using the above-mentioned angle adjustment method is that as the tilt angle increases, the component of the sensitive membrane's own gravity in the shear direction also increases, thereby obtaining the shear deformation of the sensitive membrane under different gravity components. When the mass block is tilted at different angles, the deformation caused by the sensitive membrane's own gravity component is deducted. The angle increases from 0 to the maximum angle and then returns to 0. The purpose is to examine whether the shear deformation law of the sensitive membrane is consistent when the force increases and decreases.

[0070] Furthermore, the surface shear stress sensitive film near its edge is also affected by the tensile force of the substrate edge, making the stress at the edge of the sensitive film more complex and unable to reflect the relationship between the external shear stress and shear strain. Therefore, to further ensure the accuracy of the measurement results, when calculating the first displacement data, the displacement data of the marked particles in the central region of the first particle image is selected for averaging, and then the first average displacement data at the corresponding angle is subtracted to obtain the first displacement data. Furthermore, to ensure the accuracy of the second data measurement, step S3 involves multiple measurements at various tilt angles to calculate the average, and the influence of rigid displacement is eliminated. Step S3 includes:

[0071] The mass block is placed on the surface of the central region of the shear stress-sensitive membrane on the surface of the test piece, with no gap between them;

[0072] The test piece is tilted at 0 degrees, and the measuring device captures the marked particles on the surface of the test piece and the reference area at the edge of the test piece to obtain a third particle image.

[0073] The test piece is tilted at several angles corresponding to step S2. During the measurement process, the mass block does not slip relative to the shear stress sensitive membrane on the surface of the test piece. The measuring device captures several fourth particle images of the marked particles on the surface of the test piece and the reference area at the edge of the test piece at each tilt.

[0074] Based on calibration information, a single third particle image, and a fourth particle image, the third displacement distribution data of particles on the surface of the test piece and the fourth displacement distribution data of particles in the edge reference area of ​​the test piece are obtained at a single tilt angle. Several third displacement distribution data of particles on the surface of the test piece and several fourth displacement distribution data of particles in the edge reference area of ​​the test piece are accumulated. Several second average displacement data are obtained by averaging the several fourth displacement distribution data of particles in the edge reference area of ​​the test piece.

[0075] A single second displacement data point is obtained by calculating the third displacement distribution data and the second average displacement data at a single tilt angle, and multiple second displacement data points are obtained by accumulating them.

[0076] Furthermore, when calculating the second displacement data, the displacement data of the marked particles in the central region of the third particle image are averaged, and then the second average displacement data at the corresponding angle is subtracted to obtain the second displacement data.

[0077] Furthermore, the third displacement data is equal to the second displacement data minus the first displacement data.

[0078] Furthermore, in step S5, the shear strain data γ τ (θ i The calculation method for ) is as follows:

[0079] γ τ (θ i ) = arctan(D τ (θ i )2×(L / N) / h)

[0080] Among them, D τ (θ i )2 represents the third displacement data, and h represents the thickness of the shear stress sensitive film on the surface of the test piece.

[0081] Furthermore, the method for calculating the shear stress magnitude data in step S6 is as follows:

[0082] A mass block of mass m is placed at the center of the test piece. The area of ​​the contact surface between the mass block and the test piece is A, and the tilt angle of the test piece is θ. i , i is the number of the tilt angle; the shear stress τ(θ) corresponding to each tilt angle i Size:

[0083] τ(θ i )=mgsin(θ i ) / A

[0084] Where g is the local gravitational acceleration.

[0085] Furthermore, the shear strain data and the corresponding shear stress magnitude data are fitted using the following functional relationship:

[0086] τ(θ i )=G×γ τ (θ i )

[0087] Where G represents the shear modulus of the shear stress-sensitive membrane on the surface to be measured, τ(θ) i ) represents the tilt angle θ i The corresponding shear stress magnitude data, γ τ (θ i ) represents the tilt angle θ i The corresponding shear strain data.

[0088] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0089] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A device for measuring the shear modulus of a surface shear stress-sensitive membrane, characterized in that, The device includes: Water platform, tilting device module, specimen substrate, specimen platform, image acquisition module, mass block, tilt angle sensing module and data acquisition and processing module; The tilting device module is mounted on a horizontal platform, and the specimen platform is mounted on the tilting device module. The tilting device module is used to adjust the tilt angle of the specimen platform. The specimen substrate, tilt angle sensing module, and image acquisition module are all fixed on the specimen platform. The specimen substrate is used to mount and fix the shear stress sensitive membrane of the surface to be tested. The surface of the shear stress sensitive membrane of the surface to be tested has marked particles. The mass block is used to place on the shear stress sensitive membrane of the surface to be tested to provide shear stress to the shear stress sensitive membrane of the surface to be tested. The tilt angle sensing module is used to measure the tilt angle data of the specimen platform. The image acquisition module is used to acquire several images before and after the mass block is placed on the surface of the shear stress sensitive membrane of the surface to be tested to obtain image data. The data acquisition and processing module is used to calculate the shear modulus of the shear stress sensitive membrane of the surface to be tested based on the tilt angle data and image data. When the specimen platform is tilted, there is no relative sliding between the mass block and the shear stress sensitive membrane of the surface to be tested.

2. The device for measuring the shear modulus of a surface shear stress-sensitive membrane according to claim 1, characterized in that, The image acquisition module includes a camera and a light source module.

3. The device for measuring the shear modulus of a surface shear stress-sensitive membrane according to claim 2, characterized in that, The image acquisition module also includes: an optical lens, a right-angle bracket, an optical flat plate, an adapter plate, and a two-dimensional displacement platform; one right-angle side of the right-angle bracket is fixed to the specimen platform, the optical flat plate is fixed to the other right-angle side of the right-angle bracket, the two-dimensional displacement platform is fixed on the optical flat plate, the camera is fixed to the two-dimensional displacement platform through the adapter plate, the camera is equipped with an optical lens, and the two-dimensional displacement platform is used to adjust the position of the camera.

4. The device for measuring the shear modulus of a surface shear stress-sensitive membrane according to claim 1, characterized in that, The mass block is transparent, of uniform mass, of regular size, and with a surface roughness Ra ≤ 10 micrometers.

5. The device for measuring the shear modulus of a surface shear stress-sensitive membrane according to claim 1, characterized in that, The labeled particles are reflective.

6. The device for measuring the shear modulus of a surface shear stress-sensitive membrane according to claim 1, characterized in that, The tilting device module is an angle stage.

7. The device for measuring the shear modulus of a surface shear stress-sensitive membrane according to claim 1, characterized in that, The specimen substrate is a rigid body, and a groove is formed on its surface to fix the shear stress sensitive film on the surface to be tested.

8. The device for measuring the shear modulus of a surface shear stress-sensitive membrane according to claim 7, characterized in that, The depth of the groove is the same as the thickness of the shear stress sensitive membrane on the surface to be measured.

9. The device for measuring the shear modulus of a surface shear stress-sensitive membrane according to claim 7, characterized in that, A reference area is provided at the edge of the specimen substrate, and marker particles are provided on the surface of the reference area.

10. The device for measuring the shear modulus of a surface shear stress-sensitive membrane according to claim 7, characterized in that, The color at the bottom of the groove is different from the reflective color of the marked particles.

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