A test method, device and computer-readable storage medium for Poisson's ratio

Abstract

The present invention relates to the technical field of material testing, and specifically discloses a method, device and computer-readable storage medium for testing Poisson's ratio. By performing a deformation test on a sample to be measured and measuring a plurality of stress data of the sample to be measured that change with the test time during the deformation test; according to the plurality of stress data, a longitudinal strain-stress value curve of the sample to be measured is calculated, and the elastic deformation stage is distinguished according to the change of the curve slope, and the elastic modulus value is calculated; based on the plurality of stress data and the elastic modulus value, the longitudinal plastic strain value is calculated, and the elastic Poisson's ratio value, the elastic-plastic Poisson's ratio-longitudinal strain relationship curve and the plastic Poisson's ratio-longitudinal plastic strain curve are calculated and output. The present invention combines theory with actual testing to establish a direct testing method for elastic Poisson's ratio, elastic-plastic Poisson's ratio and plastic Poisson's ratio, improves the testing efficiency and accuracy, and is easy to realize automated testing and operation.

Description

Technical Field

[0001] The present invention relates to the technical field of material testing, and particularly to a method and device for testing Poisson's ratio and a computer-readable storage medium. Background Art

[0002] Poisson's ratio is a material parameter that must be involved in industrial design. It refers to the ratio of the absolute value of the lateral normal strain to the axial normal strain when the material is subjected to unidirectional tension or compression. It is also called the lateral deformation coefficient. The commonly used one in production and life is the elastic Poisson's ratio, which is an elastic constant reflecting the lateral deformation of the material. At present, there are mature testing methods and devices for measuring the elastic Poisson's ratio of materials. By measuring the longitudinal and lateral strain values of the material during tension and then calculating the ratio, the value can be obtained.

[0003] However, when the material enters the plastic deformation stage from the elastic deformation, Poisson's ratio is no longer a constant but becomes a function curve of strain. Moreover, after the material enters the plastic deformation, accompanied by severe deformation, the "necking" phenomenon will occur, resulting in uneven edges of the measured material. Especially for polymer materials, after the material enters the plastic deformation stage, the "necking" of some materials will be very severe and obvious. This makes the calculation of the elastic-plastic Poisson's ratio and the plastic Poisson's ratio a difficult problem.

[0004] In the current Poisson's ratio measurement methods or devices, in the Poisson's ratio measurements carried out in various industries based on the existing measurement technologies, generally only the elastic Poisson's ratio is measured, and rarely involves the measurement of the elastic-plastic Poisson's ratio or the plastic Poisson's ratio after entering the plastic deformation stage. The elastic-plastic Poisson's ratio and the plastic Poisson's ratio can usually be indirectly obtained by theoretical derivation or simulation, but it is impossible to accurately predict the changes in various parameters during the "necking" stage when the material changes from elastic deformation to plastic deformation. It is difficult to simulate or deduce the actual deformation situation of the measured material. Therefore, there is an urgent need for a direct testing method for the elastic-plastic Poisson's ratio and the plastic Poisson's ratio of materials at present. Summary of the Invention

[0005] Embodiments of the present invention provide a method and device for testing Poisson's ratio and a computer-readable storage medium, which overcome the problem that it is difficult to directly measure and calculate the elastic-plastic Poisson's ratio and the plastic Poisson's ratio.

[0006] The present invention provides a method for testing Poisson's ratio, including:

[0007] Performing a deformation test on a sample to be measured, and measuring a plurality of strain force data of the sample to be measured that change with the test time during the deformation test; wherein, the plurality of strain force data includes a stress value, a lateral strain value, and a longitudinal strain value;

[0008] Based on the multiple stress-strain data, calculate the longitudinal strain value-stress value curve of the sample to be measured, calculate the elastic modulus value, and calculate the longitudinal plastic strain value based on the multiple stress-strain data and the elastic modulus value;

[0009] Obtain the elastic Poisson's ratio according to the transverse strain value-longitudinal strain value curve;

[0010] Obtain the Poisson's ratio measurement result of the sample to be measured according to the elastic Poisson's ratio and the longitudinal plastic strain value.

[0011] Preferably, the method for performing a deformation test on the sample to be measured includes:

[0012] Install the sample to be measured on a test device and input test parameters into the test device; wherein, the test device is used to deform the sample to be measured and record the real-time stress value;

[0013] Start the test device and the deformation recognition device simultaneously to perform a deformation test on the sample to be measured; wherein, the deformation recognition device is used to measure the transverse strain and longitudinal strain of the sample to be measured in real time.

[0014] Preferably, before installing the sample to be measured on the test device, it further includes:

[0015] Make the sample to be measured into a standard specimen;

[0016] Set speckles with randomly varying grayscales on the surface of the standard specimen for the deformation recognition device to obtain the transverse strain value and longitudinal strain value data of the standard specimen through image recognition.

[0017] Preferably, the method for obtaining the elastic Poisson's ratio according to the transverse strain value-longitudinal strain value curve is:

[0018] Combine the transverse strain value and the longitudinal strain value to obtain a transverse strain value-longitudinal strain value relationship curve, perform a regression linear fit on the elastic section of its starting line, and the obtained linear slope is the elastic Poisson's ratio.

[0019] Preferably, the method for obtaining the Poisson's ratio measurement result of the sample to be measured according to the elastic Poisson's ratio and the longitudinal plastic strain value is:

[0020] Based on the multiple stress-strain data, calculate the elastic Poisson's ratio and the elastic modulus value, and further calculate the longitudinal true strain;

[0021] Obtain a transverse strain value-longitudinal true strain value relationship curve, establish a first fitting equation for it based on an exponential relationship, and take the derivative of the fitting curve of the first fitting equation to obtain the curve slope, which is the elastic-plastic Poisson's ratio-longitudinal strain value curve;

[0022] By using the longitudinal strain value and calculating the longitudinal plastic strain value, a longitudinal plastic strain value - transverse strain value relationship curve is obtained, and the slope of the curve is calculated, that is, the plastic Poisson's ratio - longitudinal strain value curve is obtained;

[0023] Based on the elastic Poisson's ratio, the longitudinal true strain value is calculated, the relationship curve of the transverse strain value - longitudinal true plastic strain value is obtained, a second fitting equation is established for it according to the exponential relationship, and the derivative of the fitting curve of the second fitting equation is obtained to get the curve slope, which is the plastic Poisson's ratio - longitudinal true plastic strain value curve;

[0024] Furthermore, the plastic Poisson's ratio - longitudinal plastic strain value curve is calculated.

[0025] The present invention provides a Poisson's ratio testing device, including: a deformation testing module, a first calculation module, a second calculation module, and a Poisson's ratio calculation module;

[0026] The deformation testing module is used to perform deformation testing on the sample to be measured and measure a plurality of strain force data of the sample to be measured that change with the testing time during the deformation testing process;

[0027] The first calculation module is used to calculate the elastic modulus value and the longitudinal plastic strain value of the sample to be measured according to the plurality of strain force data;

[0028] The second calculation module is used to obtain the elastic Poisson's ratio according to the transverse strain value - longitudinal strain value curve;

[0029] The Poisson's ratio calculation module is used to obtain the Poisson's ratio measurement result of the sample to be measured according to the elastic Poisson's ratio and the longitudinal plastic strain value.

[0030] The present invention provides a terminal device, including a processor and a storage device, and the storage device is used to store one or more programs; when the one or more programs are executed by the processor, the processor implements the above-mentioned Poisson's ratio testing method.

[0031] The present invention provides a computer-readable storage medium, and the computer-readable storage medium includes a stored computer program, wherein when the computer program runs, it controls the device where the computer-readable storage medium is located to execute the above-mentioned Poisson's ratio testing method.

[0032] The embodiments of the present invention have the following beneficial effects:

[0033] The present invention provides a method and device for testing Poisson's ratio and a computer-readable storage medium. By performing a deformation test on a sample to be measured and measuring multiple stress data that change with the test time during the deformation test, calculating the elastic modulus value and the longitudinal plastic strain value, and finally obtaining the measurement result of Poisson's ratio of the sample to be measured; through the combination of theory and actual test, a direct test method and data processing method for elastic Poisson's ratio, elastoplastic Poisson's ratio, and plastic Poisson's ratio are established, improving the test efficiency and accuracy, being easy to apply to automated testing and operation, and having high versatility. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a schematic flowchart of an embodiment of the method for testing Poisson's ratio provided by the present invention;

[0035] Figure 2 is a schematic structural diagram of an embodiment of the testing device provided by the present invention;

[0036] Figure 3 is a schematic structural diagram of one embodiment of the standard specimen provided by the present invention;

[0037] Figure 4 is the lateral strain ε y and longitudinal strain ε x relation curve graph of the present invention in one embodiment;

[0038] Figure 5 is the engineering stress-strain curve graph of one embodiment of the present invention;

[0039] Figure 6 is the linear fitting curve graph of the elastic Poisson's ratio value of one embodiment of the present invention;

[0040] Figure 7 is the elastoplastic Poisson's ratio value curve graph of the direct calculation method of one embodiment of the present invention;

[0041] Figure 8 is the comparison graph of the elastoplastic Poisson's ratio value curves of the direct calculation method and the data volume reduction method of one embodiment of the present invention;

[0042] Figure 9 is the linear fitting curve graph of the elastoplastic Poisson's ratio when the deformation amount is relatively large (≥30%) in one embodiment of the present invention;

[0043] Figure 10 is the exponential fitting curve graph of the relationship between the lateral strain ε y and the longitudinal strain ε x when the deformation amount is relatively small (≤30%) in one embodiment of the present invention;

[0044] Figure 11The elastoplastic Poisson's ratio curve graph of the curve fitting method in one embodiment of the present invention;

[0045] Figure 12 The transverse strain ε y and the longitudinal plastic strain ε p relation curve graph;

[0046] Figure 13 The comparison graph of the plastic Poisson's ratio curves of the direct calculation method and the data reduction method in one embodiment of the present invention;

[0047] Figure 14 The linear fitting curve graph of the plastic Poisson's ratio when the deformation amount in one embodiment of the present invention is relatively large (≥30%);

[0048] Figure 15 The transverse strain ε y versus the plastic strain ε p relation curve exponential fitting curve graph when the deformation amount in one embodiment of the present invention is relatively small (≤30%);

[0049] Figure 16 The plastic Poisson's ratio curve graph of the curve fitting method in one embodiment of the present invention.

[0050] In the figure: 1. Tensile testing machine; 2. Tensile fixture; 3. Standard specimen; 4. Force value sensor; 5. Computer; 6. CCD camera. Specific implementation manner

[0051] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0052] Refer to Figure 1 , which is a schematic flowchart of a method for testing Poisson's ratio provided by an embodiment of the present invention, including the following steps:

[0053] S1. Perform a deformation test on the sample to be measured through a testing device, and measure a plurality of strain force data of the sample to be measured that change with the test time during the deformation test; wherein, the plurality of strain force data include stress values, transverse strain values, and longitudinal strain values;

[0054] S2. According to the plurality of strain force data, calculate the longitudinal strain value - stress value curve of the sample to be measured, and calculate the elastic modulus value; based on the plurality of strain force data and the elastic modulus value, calculate the longitudinal plastic strain value;

[0055] S3. Calculate and output the elastic Poisson's ratio according to the transverse strain value - longitudinal strain value curve;

[0056] S4. Obtain the elastic - plastic Poisson's ratio and plastic Poisson's ratio of the sample to be measured according to the elastic Poisson's ratio and longitudinal plastic strain value.

[0057] The Poisson's ratio testing method provided by the embodiment of the present invention combines theory with actual testing, establishes direct testing methods and data - processing methods for elastic Poisson's ratio, elastic - plastic Poisson's ratio, and plastic Poisson's ratio, improves testing efficiency and accuracy, is easy to apply to automated testing and operation, and has high versatility.

[0058] See Figure 2 and Figure 3 , which are schematic diagrams of a Poisson's ratio testing device and a standard specimen 3 provided by an embodiment of the present invention, including: The standard specimen 3 is a dumbbell - shaped spline. The testing device used includes a tensile testing machine 1, a tensile fixture 2, and a force - value sensor 4. The force - value sensor 4 is arranged at the connection of the tensile testing machine 1 and the tensile fixture 2. The deformation recognition device includes a CCD camera 6 and a computer 5. The computer 5 is respectively connected to the force - value sensor 4 and the CCD camera 6 through data lines. Software for data acquisition and image analysis runs in the computer 5. The standard specimen 3 is sprayed with speckles before testing for the CCD camera 6 to collect image information. The standard specimen 3 is installed in the tensile fixture 2. The computer 5 controls the tensile testing machine 1 to conduct a tensile test. The force - value sensor 4 obtains stress - value information. The CCD camera 6 identifies and obtains the real - time image information of the standard specimen 3, and obtains the transverse strain value and longitudinal strain value through image recognition.

[0059] Preferably, the size of the speckles corresponds to 3 to 5 pixels in the acquired image of the deformation recognition device.

[0060] Preferably, the CCD camera 6 of the deformation recognition device is specifically a three - dimensional strain measurement system. The standard spline is photographed by at least 2 CCD cameras 6 at different angles. The speckle images on the surface of the standard spline before and after deformation are analyzed by using computer binocular vision theory and material mechanics theory to dynamically track the movement of the speckles on the surface of the standard spline and obtain a three - dimensional displacement field. On this basis, the three - dimensional strain field of the standard spline is calculated.

[0061] Those skilled in the art can understand that the schematic diagram is only an example of the testing device, which does not constitute a limitation on the testing device. It may include more or fewer components than those shown, or combine some components, or different components. For example, the testing device may also include input - output devices, network access devices, buses, etc.

[0062] The Poisson's ratio test device provided by the embodiments of the present invention can calculate the elastic Poisson's ratio, elastoplastic Poisson's ratio, and plastic Poisson's ratio based on the test data through a one-time deformation test, greatly improving the test efficiency and being convenient and efficient to operate.

[0063] As one of the embodiments of the present invention, a method for testing Poisson's ratio is provided. Combining theoretical derivation and actual testing, the calculation method for implementing the Poisson's ratio testing method is as follows:

[0064] (1) The calculation method for the elastic Poisson's ratio value is:

[0065] Let the stress value measured be σ y , the transverse strain be ε y , and the longitudinal strain be ε x ;

[0066] From the stress value σ y and the longitudinal strain ε x data, obtain the engineering stress-strain curve and calculate the elastic modulus value:

[0067] Combine the transverse strain ε y (Y-axis) and the longitudinal strain ε x (X-axis) data to obtain the relationship strain curve;

[0068] The elastic Poisson's ratio value μ e is within the starting linear part of the relationship curve of the transverse strain ε y with respect to the longitudinal strain ε x and is the negative value of the ratio of the tensile deformation amount Δε y of one of the two coordinate axes (transverse) perpendicular to the tensile direction to the deformation amount Δε x in the tensile direction (longitudinal); perform a regression linear fitting on the relationship curve in the starting linear elastic section (the standard ISO527-1:2019 stipulates that the longitudinal strain ε x is in the linear region between 0.3% and the yield strain), and the linear slope is the elastic Poisson's ratio value

[0069] (2) The calculation method for the elastoplastic Poisson's ratio value is:

[0070] Combine the longitudinal strain ε x and the transverse strain ε y relationship curve and calculate the curve slope, which is the elastoplastic Poisson's ratio value μ - longitudinal strain ε x curve;

[0071] The total elastoplastic strain ε is equal to the sum of the elastic strain ε e and the plastic strain ε p , that is, ε = εe + ε p The corresponding elastoplastic Poisson's ratio is μ, the elastic modulus value of the material is E, and the stress σ is a function of the total elastoplastic strain ε, σ = σ(ε); the elastic Poisson's ratio remains μ e to obtain the elastic strain ε e = σ / E; so at this time, the strain in the longitudinal direction (X-axis) of the tensile standard specimen 3 is ε x = ε = ε e + ε p The strains in the width (Y-axis) and thickness (Z-axis) directions should be ε y = ε z = -με;

[0072] Set the initial volume of the test area of the tensile standard specimen 3 of the research object as V0 = length * width * thickness. Due to the effect of elastic deformation during initial tension, the volume changes (the plastic deformation volume remains unchanged). It can be derived from the formula:

[0073]

[0074] Usually, σ / E is much less than 1, and the total elastoplastic strain ε x = ε = ε e + ε p The corresponding elastoplastic Poisson's ratio μ = -ε y / ε x = -ε y / ε. Generally, the true strain ε * = ln(1 + ε), which simplifies to:

[0075]

[0076] Therefore, the transverse strain ε y and the longitudinal true strain ε * show an exponential relationship; according to the test data and formula conversion, a relationship curve of the transverse strain ε y and the longitudinal strain ε x is made. Through the formula of true strain ε * = ln(1 + ε), the longitudinal true strain ε x * is converted, and the transverse strain ε y and the longitudinal true strain ε x * relationship curve is obtained. Based on the exponential relationship, a fitting equation is established, and the derivative of the fitting curve is taken to obtain the curve slope, which is the elastoplastic Poisson's ratio μ - longitudinal true strain ε x * curve, and then the elastoplastic Poisson's ratio μ - longitudinal strain ε x curve can be obtained.

[0077] (3) The calculation method of the plastic Poisson's ratio is as follows:

[0078] The longitudinal strain data ε x According to the formula, the longitudinal plastic strain ε is converted p , and the longitudinal plastic strain ε p and the transverse strain ε y are combined, and the slope of the curve is calculated, which is the plastic Poisson's ratio μ p - Longitudinal strain ε x curve;

[0079] The total elastic-plastic strain ε is equal to the sum of the longitudinal elastic strain ε e and the longitudinal plastic strain ε p , that is, ε = ε e + ε p , and the strains in the width (transverse Y-axis) and thickness (Z-axis) directions should be ε y = ε z = -(μ e ε e + μ p ε p );

[0080] Set the initial volume of the test area of the tensile standard specimen 3 of the research object as V0 = length * width * thickness, and the plastic Poisson's ratio is obtained according to the formula:

[0081]

[0082] Longitudinal strain ε x = ε = ε e + ε p , the elastic Poisson's ratio μ e corresponding to the longitudinal elastic strain ε e = -ε y / ε e , the plastic Poisson's ratio μ p corresponding to the longitudinal plastic strain ε p = -ε y / ε p , the longitudinal true strain ε * = (ε e * + ε p * ) = ln(1 + ε) = ln(1 + ε e + ε p ), after plastic deformation occurs, the elastic properties μ e and ε e have a negligible effect on the plastic strain and are ignored. Therefore, it is simplified to:

[0083]

[0084] Therefore, the transverse strain ε y and the longitudinal true plastic strain ε p * are in an exponential relationship; according to the test data and formula conversion, the relationship curve of the transverse strain ε y and the longitudinal strain ε x is made. Through the formula ε * = ln(1 + ε), the longitudinal true strain ε x * is calculated. According to ε = ε e + ε p = σ / E + ε p , the relationship curve between the transverse strain ε y and the longitudinal true plastic strain ε p * is obtained. Based on the exponential relationship, a fitting equation is established, the fitting curve is differentiated, and the slope of the curve is obtained, which is the plastic Poisson's ratio μ p and the longitudinal true plastic strain ε p * curve. Based on the conversion relationship between the longitudinal plastic strain ε p and the longitudinal true plastic strain ε p * , the plastic Poisson's ratio μ p -longitudinal plastic strain ε p curve is obtained. Finally, the plastic Poisson's ratio μ p -longitudinal strain ε x curve is obtained.

[0085] See Figures 2 to 16 , which is the specific test data graph and the calculated curve graph of the Poisson's ratio test method provided by one embodiment of the present invention. The calculation steps of the Poisson's ratio test method in this embodiment are specifically described below with reference to the accompanying drawings.

[0086] See Figure 2 and Figure 3 . The material to be tested is formed into a standard specimen 3 by injection molding or machining, and adjusted for a specified time in a standard environment;

[0087] The standard specimen 3 is pre-treated: speckle preparation, and a speckle pattern with randomly changing gray levels is formed on the surface of the standard specimen 3 for the CCD camera 6 and the image analysis system using digital image correlation (DIC) technology to identify and obtain image information.

[0088] The standard specimen 3 is installed on the tensile fixture 2 of the tensile testing machine 1, and the parameters of the standard specimen 3, such as spacing, test rate, acquisition frequency, etc., are set;

[0089] Adjust the CCD camera 6 and the light source to obtain a clear image of the standard specimen 3 on the tensile testing machine 1, and adjust the camera exposure frequency to be the same as that of the tensile testing machine 1;

[0090] Start the tensile test program of the tensile testing machine 1 and the CCD camera 6 to monitor the image information simultaneously;

[0091] After the test, stop the image acquisition of the CCD camera 6, and export the stress value data of the tensile testing machine 1 and the image data of the CCD camera 6;

[0092] Import the image data into the computer 5 and calibrate it through the image analysis system, establish a virtual extensometer, calculate and combine to draw the transverse strain ε y (Y-axis) and the longitudinal strain ε x (X-axis) relationship curve.

[0093] See Figure 4 , combine the stress value σ y and the longitudinal strain ε x data, obtain the engineering stress-strain curve, and calculate the elastic modulus value:

[0094] See Figure 5 , the elastic Poisson's ratio μ e : Within the initial linear part of the relationship curve between the transverse strain ε y and the longitudinal strain ε x , the negative value of the ratio of the tensile deformation Δε y in one of the two coordinate axes (transverse) perpendicular to the tensile direction to the tensile deformation Δε x in the tensile direction (longitudinal). For the initial linear elastic segment (specified in standard ISO527-1:2019 to be in the linear region between the longitudinal strain ε x from 0.3% to the yield strain of 4.3%), perform a regression linear fitting on the relationship curve, and take the linear regression fitting from 0.7% to 2.3% to obtain the elastic Poisson's ratio:

[0095] See Figure 6 , the elastoplastic Poisson's ratio μ: Combine the longitudinal strain ε x (X-axis) and the transverse strain ε y (Y-axis) relationship curve.

[0096] See Figure 7 , directly calculate the slope of the above curve. Since there are many data points (more than 2,800 data), the curve appears smooth as a whole, but there are fluctuations locally, which are caused by the test accuracy and system errors. The obtained elastoplastic Poisson's ratio μ and the longitudinal strain ε xThe relationship curve has large data fluctuations and strong interference. The overall trend is to increase first, then decrease and gradually stabilize, but the target result cannot be obtained.

[0097] See Figure 8 and Figure 9 , by reducing the data volume method, the longitudinal strain ε x (X-axis) and the transverse strain ε y (Y-axis) relationship curve is relatively smooth as a whole. Therefore, the data volume can be reduced, the fluctuation interference can be reduced, and the obtained elastic-plastic Poisson's ratio μ and the longitudinal strain ε x relationship curve. Reducing the data volume can significantly improve the data volatility, and the curve trend is more obvious. When the longitudinal strain ε x is large, the longitudinal strain ε x (X-axis) and the transverse strain ε y (Y-axis) relationship curve shows a linear trend, and the elastic-plastic Poisson's ratio can be represented by the linear regression fitting coefficient; when the longitudinal strain ε x is in the initial elastic stage, it is represented by the elastic Poisson's ratio. However, this method of reducing data points cannot effectively retain and reflect the information at the turning point of the curve because the data point interval becomes larger, and the slope is the average value of the secant slopes of adjacent data points, which cannot accurately reflect the elastic-plastic Poisson's ratio of the material at the curve turning point.

[0098] See Figure 10 and Figure 11 , according to the formula, the longitudinal true strain ε * =ln(1 + ε). When the longitudinal strain ε x is less than 30%, it can be approximately regarded that the longitudinal true strain ε * and the longitudinal strain ε x are linearly related, then the transverse strain ε y and the longitudinal strain ε x are also exponentially related. Perform exponential fitting on the relationship curve where the longitudinal strain ε x is within 30% to obtain a fitting curve, take the derivative of the fitting curve to obtain the elastic-plastic Poisson's ratio curve, and merge it with the linear trend above 30% to obtain the elastic-plastic Poisson's ratio - longitudinal strain ε x curve, and the curve is smooth and stable.

[0099] See Figure 12 , the plastic Poisson's ratio μ p : According to the formula ε = ε e +ε p =σ / E + ε p convert the plastic strain ε p , merge the longitudinal plastic strain ε p (X-axis) and the transverse strain ε y(Y-axis) relationship curve; directly calculate the curve slope. Since there are many data points (more than 2,800 data), the curve appears smooth as a whole, but there are fluctuations locally, which are affected by the test accuracy and system error, and the obtained plastic Poisson's ratio μ p - Longitudinal plastic strain ε p Relationship curve graph, with large data fluctuations and strong interference. The overall trend is to increase first, then decrease and gradually stabilize, but the target result cannot be obtained.

[0100] See Figure 13 and Figure 14 , longitudinal plastic strain ε p (X-axis) and transverse strain ε y (Y-axis) relationship curve is relatively smooth as a whole. Therefore, the amount of data can be reduced, the fluctuation interference can be reduced, and the obtained plastic Poisson's ratio μ p and longitudinal plastic strain ε p relationship curve graph. Reducing the amount of data can significantly improve the data volatility, and the curve trend is more obvious. When the longitudinal plastic strain ε p is relatively large, the longitudinal plastic strain ε p (X-axis) and transverse strain ε y (Y-axis) relationship curve shows a linear trend, and the plastic Poisson's ratio can be represented by the linear regression fitting coefficient. However, this method of reducing data points cannot effectively retain and reflect the information at the turning points of the curve, because the interval between data points becomes larger, and the slope is the average value of the secant slopes of adjacent data points, which cannot accurately reflect the plastic Poisson's ratio of the material at the curve turning point.

[0101] See Figure 15 and Figure 16 , according to the formula, the longitudinal true strain ε * =ln(1 + ε). When the longitudinal plastic strain ε p is less than 30%, it can be approximately regarded that the longitudinal true plastic strain ε p * and longitudinal plastic strain ε p show a linear relationship, then the transverse strain ε y and longitudinal plastic strain ε p also show an exponential relationship. Perform exponential fitting on the relationship curve where the longitudinal plastic strain ε p is within 30%, obtain the fitting curve, take the derivative of the fitting curve, and merge it with the linear trend above 30% to obtain the plastic Poisson's ratio - longitudinal plastic strain ε p curve, and the curve is smooth and stable.

[0102] The present invention also discloses a test device for Poisson's ratio, including: a deformation test module, a first calculation module, a second calculation module, and a Poisson's ratio calculation module.

[0103] The deformation test module is used to perform a deformation test on a sample to be measured, and measure a plurality of stress data of the sample to be measured that change with the test time during the deformation test; wherein, the plurality of stress data include stress values, transverse strain values, and longitudinal strain values.

[0104] The first calculation module is used to calculate the longitudinal strain value - stress value curve of the sample to be measured according to the plurality of stress data, calculate the elastic modulus value, and calculate the longitudinal plastic strain value based on the plurality of stress data and the elastic modulus value.

[0105] The second calculation module is used to obtain the transverse strain value - longitudinal strain value relationship curve by combining the transverse strain value and the longitudinal strain value, perform regression linear fitting on its initial linear elastic segment, and the resulting linear slope is the elastic Poisson's ratio.

[0106] The Poisson's ratio calculation module is used to obtain the Poisson's ratio measurement result of the sample to be measured according to the elastic Poisson's ratio and the longitudinal plastic strain value.

[0107] The Poisson's ratio calculation module includes an elastic-plastic Poisson's ratio calculation unit and a plastic Poisson's ratio calculation unit.

[0108] The elastic-plastic Poisson's ratio calculation unit is used to calculate the elastic Poisson's ratio and the elastic modulus value based on the plurality of stress data, and further calculate the longitudinal true strain; obtain the transverse strain value - longitudinal true strain value relationship curve, establish a first fitting equation for it based on the exponential relationship, and take the derivative of the fitting curve of the first fitting equation to obtain the curve slope, thereby obtaining the elastic-plastic Poisson's ratio - longitudinal strain value curve.

[0109] The plastic Poisson's ratio calculation unit is used to calculate the longitudinal plastic strain value from the longitudinal strain value, obtain the longitudinal plastic strain value - transverse strain value relationship curve, calculate its curve slope, that is, obtain the plastic Poisson's ratio - longitudinal strain value curve; calculate the longitudinal true strain value based on the elastic Poisson's ratio, obtain the relationship curve of the transverse strain value - longitudinal true plastic strain value, establish a second fitting equation for it based on the exponential relationship, take the derivative of the fitting curve of the second fitting equation to obtain the curve slope, which is the plastic Poisson's ratio - longitudinal true plastic strain value curve; and then calculate the plastic Poisson's ratio - longitudinal plastic strain value curve.

[0110] The present invention also discloses a terminal device, which includes a processor and a storage device. The storage device is used to store one or more programs. When the one or more programs are executed by the processor, the processor implements the above-mentioned method for testing Poisson's ratio. The so-called processor may be a Central Processing Unit (CPU), or may also be other general-purpose processors, Digital Signal Processors (DSPs), Application-Specific Integrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor, or the processor may also be any conventional processor, etc. The so-called processor is the control center of the test device, and connects various parts of the entire test device through various interfaces and lines.

[0111] The storage device can be used to store computer programs and / or modules. The processor realizes various functions of the terminal device by running or executing the computer programs and / or modules stored in the storage device, and by calling the data stored in the storage device. The storage device mainly includes a program storage area and a data storage area. Among them, the program storage area can store an operating system, application programs required for at least one function, etc.; the data storage area can store data created according to the use of the terminal device, etc. In addition, the storage device may include high-speed random access memory, and may also include non-volatile memory, such as a hard disk, a memory, a plug-in hard disk, a Smart Media Card (SMC), a Secure Digital (SD) card, a Flash Card, at least one magnetic disk storage device, a flash memory device, or other volatile solid-state storage devices.

[0112] Among them, if the modules / units integrated in the test device for Poisson's ratio are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on such an understanding, to implement all or part of the processes in the above-described embodiment methods of the present invention, it can also be completed by instructing relevant hardware through a computer program. The computer program can be stored in at least one computer-readable storage medium. When the computer program is executed by a processor, the steps of the above-described various method embodiments can be implemented. Among them, the computer program includes computer program code, and the computer program code can be in the form of source code, object code, executable file, or some intermediate form, etc. The computer-readable medium can include: any entity or device capable of carrying the computer program code, recording medium, USB flash drive, mobile hard disk, magnetic disk, optical disc, computer memory, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), electrical carrier signal, telecommunication signal, and software distribution medium, etc.

[0113] It should be noted that the above-described embodiments of the device and apparatus are merely illustrative. The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. In addition, in the drawings of the apparatus embodiment provided by the present invention, the connection relationship between the modules indicates that they have a communication connection, which can be specifically implemented as one or more communication buses or signal lines. Those of ordinary skill in the art can understand and implement it without creative efforts.

[0114] The above is the preferred implementation manner of the present invention. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements are also regarded as the protection scope of the present invention.

Claims

1. A method for testing Poisson's ratio, characterized in that Including: Performing a deformation test on the sample to be measured, and measuring a plurality of stress data of the sample to be measured changing with the test time during the deformation test; wherein, the plurality of stress data includes a stress value, a transverse strain value, and a longitudinal strain value; According to the plurality of stress data, calculating to obtain a longitudinal strain value-stress value curve of the sample to be measured, calculating an elastic modulus value, and calculating a longitudinal plastic strain value based on the plurality of stress data and the elastic modulus value; By the method of reducing data volume, smoothing the transverse strain value-longitudinal strain value curve, and obtaining an elastic Poisson's ratio according to the transverse strain value-longitudinal strain value curve; According to the elastic Poisson's ratio and the longitudinal plastic strain value, obtaining the Poisson's ratio measurement result of the sample to be measured; When obtaining the Poisson's ratio measurement result of the sample to be measured, it further includes: When obtaining an elastic-plastic Poisson's ratio-longitudinal strain value curve, performing exponential fitting on the relationship curve with a longitudinal strain value within 30%, obtaining a fitting curve, taking the derivative of the fitting curve, obtaining an elastic-plastic Poisson's ratio curve, and merging it with the linear trend above 30% to obtain an elastic-plastic Poisson's ratio-longitudinal strain value curve; When obtaining a plastic Poisson's ratio-longitudinal plastic strain value curve, performing exponential fitting on the relationship curve with a longitudinal plastic strain value within 30%, obtaining a fitting curve, taking the derivative of the fitting curve, and merging it with the linear trend above 30% to obtain a plastic Poisson's ratio-longitudinal plastic strain value curve; The method for obtaining the Poisson's ratio measurement result of the sample to be measured according to the elastic Poisson's ratio and the longitudinal plastic strain value is: Based on the plurality of stress data, calculating an elastic Poisson's ratio and an elastic modulus value, and further calculating a longitudinal true strain; Obtaining a transverse strain value-longitudinal true strain value relationship curve, establishing a first fitting equation for it based on an exponential relationship, taking the derivative of the fitting curve of the first fitting equation, and obtaining a curve slope, which is the elastic-plastic Poisson's ratio-longitudinal strain value curve; Through the longitudinal strain value and the calculated longitudinal plastic strain value, obtaining a longitudinal plastic strain value-transverse strain value relationship curve, calculating its curve slope, and obtaining a plastic Poisson's ratio-longitudinal strain value curve; Calculating a longitudinal true strain value based on the elastic Poisson's ratio, obtaining a relationship curve between the transverse strain value and the longitudinal true plastic strain value, establishing a second fitting equation for it based on an exponential relationship, taking the derivative of the fitting curve of the second fitting equation, and obtaining a curve slope, which is the plastic Poisson's ratio-longitudinal true plastic strain value curve; Furthermore, calculating to obtain a plastic Poisson's ratio-longitudinal plastic strain value curve.

2. The testing method of Poisson's ratio according to claim 1, characterized in that, The method for performing a deformation test on the sample to be measured includes: Installing the sample to be measured on a test device and inputting test parameters into the test device; wherein, the test device is used to deform the sample to be measured and record the real-time stress value; Simultaneously starting the test device and the deformation recognition device to perform a deformation test on the sample to be measured; wherein, the deformation recognition device is used to measure the transverse strain and the longitudinal strain of the sample to be measured in real time.

3. The method for testing Poisson's ratio according to claim 2, wherein Before installing the sample to be measured on the test device, it further includes: Make the sample to be measured into a standard specimen; Set speckles with randomly varying gray levels on the surface of the standard specimen for the deformation recognition device to obtain the transverse strain value and longitudinal strain value data of the standard specimen through image recognition.

4. The testing method of Poisson's ratio according to claim 1, characterized in that, The method for obtaining the elastic Poisson's ratio according to the transverse strain value - longitudinal strain value curve is: Combine the transverse strain value and the longitudinal strain value to obtain a transverse strain value - longitudinal strain value relationship curve, perform regression linear fitting on its initial linear elastic segment, and the resulting linear slope is the elastic Poisson's ratio.

5. A test device for Poisson's ratio, characterized in that, It includes: A deformation test module, a first calculation module, a second calculation module, and a Poisson's ratio calculation module; The deformation test module is used to perform deformation tests on the sample to be measured and measure multiple strain force data of the sample to be measured that change with the test time during the deformation test; The first calculation module is used to calculate the elastic modulus value and the longitudinal plastic strain value of the sample to be measured according to the multiple strain force data; The second calculation module is used to smooth the transverse strain value - longitudinal strain value curve by the data reduction method and obtain the elastic Poisson's ratio according to the transverse strain value - longitudinal strain value curve; The Poisson's ratio calculation module is used to obtain the Poisson's ratio measurement result of the sample to be measured according to the elastic Poisson's ratio and the longitudinal plastic strain value; When obtaining the Poisson's ratio measurement result of the sample to be measured, it also includes: When obtaining the elastic - plastic Poisson's ratio - longitudinal strain value curve, perform exponential fitting on the relationship curve with a longitudinal strain value within 30%, obtain the fitting curve, take the derivative of the fitting curve, obtain the elastic - plastic Poisson's ratio curve, and merge it with the linear trend above 30% to obtain the elastic - plastic Poisson's ratio - longitudinal strain value curve; When obtaining the plastic Poisson's ratio - longitudinal plastic strain value curve, perform exponential fitting on the relationship curve with a longitudinal plastic strain value within 30%, obtain the fitting curve, take the derivative of the fitting curve, and merge it with the linear trend above 30% to obtain the plastic Poisson's ratio - longitudinal plastic strain value curve; The method for obtaining the Poisson's ratio measurement result of the sample to be measured according to the elastic Poisson's ratio and the longitudinal plastic strain value is: Based on the multiple strain force data, calculate the elastic Poisson's ratio and the elastic modulus value, and further calculate the longitudinal true strain; Obtain the transverse strain value - longitudinal true strain value relationship curve, establish a first fitting equation for it based on the exponential relationship, and take the derivative of the fitting curve of the first fitting equation to obtain the curve slope, which is the elastic - plastic Poisson's ratio - longitudinal strain value curve; Through the longitudinal strain value and the calculated longitudinal plastic strain value, obtain the longitudinal plastic strain value - transverse strain value relationship curve, calculate its curve slope, and obtain the plastic Poisson's ratio - longitudinal strain value curve; Based on the elastic Poisson's ratio, calculate the longitudinal true strain value, obtain the relationship curve between the transverse strain value and the longitudinal true plastic strain value, establish a second fitting equation for it based on the exponential relationship, take the derivative of the fitting curve of the second fitting equation to obtain the curve slope, which is the plastic Poisson's ratio - longitudinal true plastic strain value curve; Furthermore, calculate the plastic Poisson's ratio - longitudinal plastic strain value curve.

6. A terminal device, characterized in that, It includes: A processor and a storage device, the storage device being configured to store one or more programs; When the one or more programs are executed by the processor, the processor implements the method for testing the Poisson's ratio according to any one of claims 1 to 4.

7. A computer-readable storage medium, characterized in that, The computer-readable storage medium includes a stored computer program, wherein when the computer program runs, it controls the device where the computer-readable storage medium is located to execute the method for testing the Poisson's ratio according to any one of claims 1 to 4.

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