Method for testing Bauschinger effect of metal material

Abstract

The invention provides a metal material Bauschinger effect testing method which comprises the following steps: S1) processing a metal material into a standard tensile sample, and carrying out a pre-stretching loading test on the standard tensile sample to obtain pre-stretching strain data and tensile load data; s2) cutting a compressed sample from the central area of the pre-stretched and deformed sample; s3) performing a compression loading test on the compression sample to obtain compression strain data and compression load data; s4) calculating and merging the obtained data to obtain curve data of the pulling-pressing Bauschinger effect of the metal material; 6, the pre-stretching deformation amount is increased, the steps are repeated, and the Bauschinger effect curves of the metal material under different strain conditions.According to the method for testing the Bauschinger effect of the metal material, a pre-stretching-intermediate sampling-compression testing method is provided, and the complete Bauschinger effect curve of the metal material can be simply and efficiently obtained.

Description

Technical Field

[0001] The invention relates to the technical field of material mechanical property testing, and in particular to a method for testing the Schinger effect of a metal material package. Background Art

[0002] Ultra-high-strength steel is prone to springback during the forming process, which affects the precision and quality of parts. Therefore, springback is a difficulty and pain point in the promotion and use of ultra-high-strength steel. High-precision prediction of high-strength steel stamping springback is one of the effective ways to control springback, and the development of advanced material constitutive models (digital models that describe the stress-strain relationship of materials under stress) is the key to accurate prediction and control of springback.

[0003] The Bauschinger effect is an elastic incompleteness phenomenon in which the elastic limit of metal materials increases when loaded in the same direction and decreases when loaded in the opposite direction after they are pre-loaded to produce plastic deformation. It is one of the key factors affecting springback. During the stamping process, the sheet metal flows through the R corner of the die, and the stress state of the inner and outer layers of the sheet metal undergoes a "tension-compression" or "compression-tension" reversal, so the constitutive model must be able to accurately describe the Bauschinger effect curve of the material.

[0004] The industry generally uses cyclic tension-compression tests to test the Bauschinger effect of materials. Dog-bone shaped specimens may buckle when directly compressed after stretching. Traditional tension-compression cyclic loading tests require the design of lateral tooling to prevent the specimen from buckling. However, the specimen will still buckle under large strain compression conditions, and the effect is not ideal.

[0005] Therefore, providing a testing method for the Bauschinger effect of metal sheets is of great significance for the control of ultra-high strength and high rebound. Summary of the invention

[0006] The technical problem solved by the present invention is to provide a method for testing the Bauschinger effect of metal materials. The testing method provided in the present application can simply and efficiently obtain a complete Bauschinger effect curve of the metal material by testing and processing the Bauschinger effect.

[0007] In view of this, the present application provides a method for testing the Schinger effect of a metal material package, comprising the following steps:

[0008] S1) processing the metal material into a standard tensile specimen, and performing a pre-stretching loading test on the standard tensile specimen to obtain pre-stretching strain data and tensile load data;

[0009] S2) cutting a compression specimen from the central area of ​​the pre-stretched deformation specimen obtained in step S1), wherein the compression specimen has a thickness of t, a height of h, a width of w, and h=k*min(w, t), and k is 1.5-1.8;

[0010] S3) performing a compression loading test on the compression specimen, and stopping the test after the compression reaches ≥1 times the pre-stretching deformation, to obtain compression strain data and compression load data;

[0011] S4) obtaining pre-stretching true stress-true strain curve data and compressing true stress-true strain curve data respectively according to the pre-stretching strain data, the tensile load data and the compressing strain data, the compressing load data;

[0012] S5) combining the true stress-true strain curve data of the pre-stretching and the true stress-true strain curve data of the compression to obtain the curve data of the tension-compression Schinger effect of the metal material;

[0013] S6) increasing the pre-stretching deformation, repeating the above steps S1) to S5) to obtain the Bauschinger effect curve of the metal material under different strain conditions.

[0014] Preferably, in step S1), the engineering strain value of the pre-stretching deformation in the pre-stretching loading test is greater than the maximum engineering strain of the yield platform and less than the engineering strain of the necking starting point.

[0015] Preferably, in step S1), during the pre-stretching loading test, the strain of the pre-stretching loading is monitored in real time using a DIC strain measurement system, and the tensile load is monitored in real time using a universal testing machine.

[0016] Preferably, in step S3), during the compression loading process, the strain of the compression loading is monitored in real time using a DIC strain measurement system, and the compression load is monitored in real time using a universal testing machine.

[0017] Preferably, in step S2), the distance between the upper limit and / or lower limit of the central area and the root of the fillet of the sample after pre-stretching deformation is ≥5 mm.

[0018] Preferably, step S4) is specifically as follows:

[0019] Correlating the pre-stretched strain data and the tensile load data with time to obtain pre-stretched true stress-true strain curve data;

[0020] The compression strain data and compression load data are associated with time to obtain compression true stress-strain curve data.

[0021] Preferably, in step S5), the merging process is specifically as follows:

[0022] The compressed true stress-true strain curve data is offset, and the offset strain is calculated by a linear interpolation method, so that the starting position of the compressed true stress-true strain curve data is connected to the end position of the pre-stretched true stress-true strain curve data.

[0023] Preferably, the pre-stretching loading test is carried out on a pre-stretching-unloading device, and the pre-stretching-unloading device is provided with a DIC strain acquisition system.

[0024] Preferably, the compression loading test is performed on a compression device, and a DIC strain acquisition system is provided on the compression device.

[0025] Preferably, the loading and unloading rates of the pre-stretching loading test are both 1-10 mm / min, and the rate of the compression loading test is 0.5-10 mm / min; and the thickness of the metal material is greater than 3 mm.

[0026] The present application provides a method for testing the Singh effect of metal materials, which first processes the metal material into a standard tensile specimen, then performs a pre-stretching loading test to obtain pre-stretching strain data and tensile load data, then cuts a compression specimen from the central area of ​​the specimen after the pre-stretching deformation, and limits the size of the compression specimen, performs a compression loading test on the compression specimen, and obtains compression strain data and compression load data; then sorts out the strain data and load data to obtain true stress-true strain curve data of pre-stretching and compression, respectively, then combines the data to obtain curve data of the tension-compression Singh effect of the metal material, and finally repeats the above steps to obtain the method for testing the Singh effect of metal materials; the method for testing the Singh effect of metal materials provided by the present application utilizes The pre-stretching-intermediate sampling-compression method cuts the compression specimen from the specimen after the pre-stretching deformation, avoids the additional design of the lateral anti-buckling device, makes the compression deformation stable, and can complete the stretching and compression process on an ordinary stretching and compression testing machine, and obtains the Bauschinger effect curve under the large strain condition before the metal material necks, which can characterize the tension-compression deformation behavior of the material under the large strain condition; at the same time, the tensile loading and compression loading processes of the present application are carried out separately, which ensures the continuity and stability of the stress-strain of the two loading processes, and avoids the problems of sudden changes in external force or constraint conditions, discontinuous and unstable stress and strain caused by the need to change the loading direction in the existing plate tension-compression test; therefore, the test method provided by the present application can simply and efficiently obtain the complete Bauschinger effect curve of the metal material. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a flow chart of the testing and data processing of the metal sheet package Singh effect of the present invention;

[0028] Figure 2 This is a schematic diagram of the experimental process of the metal sheet package Schinger effect test of the present invention;

[0029] Figure 3 It is a schematic diagram of the cutting scheme of the compression specimen (rectangular small specimen) of the present invention;

[0030] Figure 4 It is a schematic diagram of the uniaxial tensile engineering stress-strain curve and the pre-tensile deformation range of the metal material of the present invention;

[0031] Figure 5 It is a schematic diagram of the stretching-unloading and compression segmented curves and the corresponding test process of the present invention;

[0032] Figure 6 The present invention is a stretch-unloading, compression segmented curve and data processing schematic diagram, wherein point P is the compression starting point, point E is the pre-stretch unloading end point, and point S is the compression starting point;

[0033] Figure 7 This is a schematic diagram of a curve after the tensile-unloading-compression test data of the present invention are combined;

[0034] Figure 8 It is a schematic diagram of the Bauschinger effect curve corresponding to the pre-stretching to the preset deformation amount (5% / 7.5% / 10% engineering strain) of the present invention;

[0035] Fig. 9 It is a schematic diagram of the structure of the pre-stretching-unloading device of the present invention, wherein 1 is a testing machine, 2 is a crossbeam, 3-1 is a pre-stretching upper fixture, 4-1 is a pre-stretching specimen, 5-1 is a pre-stretching lower fixture, 6 is a testing machine base, 7 is a movable camera-DIC strain acquisition system, and 8 is a control system;

[0036] Fig.10 It is a schematic diagram of the structure of the compression device of the present invention, wherein 1 is a testing machine, 2 is a loading unit, 3-2 is a compression upper fixture, 4-2 is a compression specimen, 5-2 is a compression lower fixture, 6 is a testing machine base, 7 is a movable camera-DIC strain acquisition system, and 8 is a control system. DETAILED DESCRIPTION

[0037] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0038] In view of the problem that the conventional tension-compression cyclic loading test of the Bauschinger effect in the prior art requires lateral tooling to prevent the specimen from buckling and the effect is not ideal, the present application provides a method for testing the Bauschinger effect of metal materials, which pre-stretches the standard tensile specimen to a preset deformation amount and then unloads it, then cuts a small rectangular specimen in the middle of the pre-stretched specimen as a compression specimen, and then conducts a compression test on the small rectangular specimen, and ends the test after the compression reaches a certain deformation amount, and finally merges the pre-stretching true stress-true strain curve with the compression true stress-true strain curve to obtain a complete Bauschinger effect curve; repeat the above steps, gradually increase the pre-stretching deformation amount, and obtain the Bauschinger effect curve under different strain conditions; compared with other testing methods for the Bauschinger effect of metal plates, the testing method provided by the present application does not require the additional design of a lateral anti-buckling device, is easy to operate, has stable deformation, and can obtain a Bauschinger effect curve under large strain conditions. Specifically, an embodiment of the present invention discloses a method for testing the Bauschinger effect of metal materials, comprising the following steps:

[0039] S1) processing the metal material into a standard tensile specimen, and performing a pre-stretching loading test on the standard tensile specimen to obtain pre-stretching strain data and tensile load data;

[0040] S2) cutting a compression specimen from the central area of ​​the pre-stretched deformation specimen obtained in step S1), wherein the compression specimen has a thickness of t, a height of h, a width of w, and h=k*min(w, t), and k is 1.5-1.8;

[0041] S3) performing a compression loading test on the compression specimen, and stopping the test after the compression reaches ≥1 times the pre-stretching deformation, to obtain compression strain data and compression load data;

[0042] S4) obtaining pre-stretching true stress-true strain curve data and compressing true stress-true strain curve data respectively according to the pre-stretching strain data, the tensile load data and the compressing strain data, the compressing load data;

[0043] S5) combining the true stress-true strain curve data of the pre-stretching and the true stress-true strain curve data of the compression to obtain the curve data of the tension-compression Schinger effect of the metal material;

[0044] S6) increasing the pre-stretching deformation, repeating the above steps S1) to S5) to obtain the Bauschinger effect curve of the metal material under different strain conditions.

[0045] The schematic diagram of the process of the metal material package Singer effect test method provided in this application is as follows Figure 1As shown, it includes the following steps: (preparation of pre-stretched specimens) - (pre-stretched loading-unloading test) - (intermediate sampling after pre-stretching) - (compression loading test) - (mechanical properties data calculation) - (pre-stretched-compression data merging) - (Bauschinger effect characterization).

[0046] According to the present invention, firstly, a pre-stretched sample is prepared, that is, a metal material is processed into a standard tensile sample. The processing method is a method well known to those skilled in the art, and can be laser cutting or wire cutting. The standard tensile sample is specifically a "dog bone-shaped" standard tensile sample. After the standard tensile sample is prepared, the present application pre-stretches the standard tensile sample to load the sample. The specific process is as follows: Figure 2 As shown, the standard tensile specimen is pre-stretched and loaded, stretched to a preset deformation, and unloaded after pre-stretching to complete the pre-stretching loading test; the loading and unloading rates of the pre-stretching loading test are both 1~10mm / min, and specifically, the loading and unloading rates of the pre-stretching loading test are both 3~8mm / min. The engineering strain value of the preset deformation should satisfy the requirement of being greater than the maximum engineering strain of the yield platform and less than the engineering strain at the starting point of necking. During the pre-stretching loading test to the preset deformation, it is preferred to use a DIC strain measurement system to measure the strain of the pre-stretching loading-unloading process in real time, and use the sensor of the universal testing machine to measure the tensile load in real time to obtain the pre-stretching strain data and tensile load data.

[0047] The present application then cuts a compression specimen from the central area of ​​the pre-stretched deformed specimen, as follows: Figure 2 , Figure 3 As shown, the compression specimen can be intercepted in the middle of the pre-stretched deformed specimen, can be intercepted directly in the middle of the parallel section of the pre-stretched deformed specimen, can be intercepted from one pre-stretched deformed specimen, or can be intercepted from multiple compression specimens. The interception area of ​​the compression specimen is located within the range of ≥5mm from the root of the transition fillet of the parallel section of the pre-stretched deformed specimen to ensure the uniformity of the overall pre-deformation of the compression specimen. The thickness of the compression specimen is t, the height is h, and the width is w, and h=k*min(w, t), k is 1.5~1.8, specifically, k is 1.5, 1.6, 1.7 or 1.8; the size of the compression specimen is limited as above to ensure that the compression specimen is stably deformed during the compression process without buckling.

[0048] According to the present invention, the compression specimen is then subjected to a compression loading test, such as Figure 2In the compression loading process, the compression is stopped after the deformation is ≥1 times the pre-stretching deformation, specifically, the compression is stopped when the deformation is 2-3 times the pre-stretching deformation or the sample breaks; the rate of the compression loading test is 0.5-10 mm / min, specifically, the rate of the compression loading test is 0.5-3 mm / min. In the compression process, it is preferred to use a DIC strain measurement system to measure the strain of the compression loading process in real time, and use a sensor of a universal testing machine to measure the compression load in real time to obtain the compression strain data and compression load data.

[0049] After obtaining the above-mentioned pre-stretching strain data and tensile load data, compression strain data and compression load values, the above-mentioned pre-stretching related data and compression related data are associated according to the time relationship, that is, the engineering stress-engineering strain curves of the pre-stretching and compression processes are obtained respectively. The Bauschinger effect focuses on the true stress-true strain curve. Therefore, according to the conversion formula of engineering stress-strain and true stress-strain: true stress = engineering stress*(1+engineering strain), true strain = ln(1+engineering strain), the above-mentioned engineering stress-engineering strain curve is converted to obtain the true stress-true strain curve.

[0050] According to the present invention, the true stress-true strain curve data of pre-stretching and the true stress-true strain curve data of compression are then combined to obtain the curve data of the tension-compression Singh effect of the metal sheet; in the present application, since the pre-stretching process and the compression process are experimented separately, the true stress-true strain curve data all start from the origin, the curve is not continuous, the compression curve is offset to the right, and the offset strain is calculated by a linear interpolation method. Finally, the starting position of the compression curve is connected to the end position of the pre-stretching unloading curve to obtain complete and continuous tension-compression Singh effect curve data.

[0051] The above process completes a set of pre-stretching deformation-compression Bauschinger effect curves. In order to obtain a complete Bauschinger effect curve, it is necessary to continue to gradually increase the pre-stretching deformation between the maximum engineering strain of the yield platform and the engineering strain at the beginning of necking, repeat the above steps many times, and finally obtain a complete Bauschinger effect curve of the metal material under different strain conditions.

[0052] In order to make the Bauschinger effect curve have higher accuracy, the thickness of the metal material in the Bauschinger effect test method provided in the present application is preferably greater than 3 mm.

[0053] The pre-stretching loading test in the method for testing the Schinger effect of a metal material package provided in the present application is carried out on a pre-stretching device, and the compression test is carried out on a compression device; the pre-stretching device is specifically as follows Fig. 9 As shown, Fig. 9In the figure, 1 is a testing machine, 2 is a loading unit, 3-1 is a pre-stretching upper fixture, 4-1 is a pre-stretching specimen, 5-1 is a pre-stretching lower fixture, 6 is a testing machine base, 7 is a movable camera-DIC strain acquisition system, and 8 is a control system; wherein the pre-stretching upper fixture is connected to the loading unit, the pre-stretching lower fixture is connected to the testing machine base, the two ends of the pre-stretching specimen are clamped by the pre-stretching upper fixture and the pre-stretching lower fixture respectively, and the loading unit realizes the loading and unloading of the standard tensile specimen by driving the pre-stretching upper fixture; the control system is respectively connected to the loading unit and the DIC strain acquisition system to realize the speed control and displacement control of the loading unit, the loading unit controls the load information of the pre-stretching specimen in the pre-stretching loading test and transmits it to the control system, the DIC strain acquisition system measures the surface strain of the pre-stretching specimen in the deformation process in real time and transmits it to the control system, and the control system analyzes the load and strain to obtain the stress-strain relationship of the pre-stretching specimen in the pre-stretching loading-unloading process. The pre-stretching loading test described in the present application realizes the pre-stretching loading-unloading, data collection, data analysis and data output processes in the above-mentioned pre-stretching device.

[0054] The compression device is specifically as follows Fig.10 As shown, Fig.10 In the figure, 1 is a testing machine, 2 is a loading unit, 3-2 is a compression upper fixture, 4-1 is a compression specimen, 5-2 is a compression lower fixture, 6 is a testing machine base, 7 is a movable camera-DIC strain acquisition system, and 8 is a control system; wherein the compression upper fixture is connected to the loading unit, the compression lower fixture is connected to the testing machine base, the two ends of the compression specimen are clamped by the compression upper fixture and the compression lower fixture respectively, the loading unit drives the compression upper fixture to realize compression loading, the control system is respectively connected to the DIC strain acquisition system and the loading unit to realize speed control and displacement control of the loading unit, the loading unit controls the load information of the compression specimen during the compression loading process and transmits it to the control system, the DIC strain acquisition system measures the surface strain of the compression specimen during the deformation process in real time and transmits it to the control system, the control system analyzes the load and strain to obtain the stress-strain relationship of the compression specimen during the compression loading process. The compression test described in the present application realizes the compression loading, data acquisition, data analysis and data output processes in the above-mentioned compression device.

[0055] The Bauschinger effect test method for metal materials provided in the present application makes the deformation of the stretching-compression process stable through the pre-stretching-intermediate sampling-compression test method, does not require the additional design of a lateral anti-buckling device, is easy to operate, and the test of the present invention can be completed on an ordinary tensile testing machine; at the same time, the Bauschinger effect curve under large strain conditions before the material necks can be obtained, which can characterize the tension-compression deformation behavior of the material under large strain conditions; and the stretching-compression loading process is carried out separately, which ensures the continuity and stability of the stress-strain of the two loading processes, and avoids the problems of sudden changes in external forces or constraints, discontinuous and unstable stress and strain caused by the need to change the loading direction in the existing material tension-compression test. The Bauschinger effect test method for metal materials provided in the present application has been applied to the Bauschinger effect test of hot-rolled beam steel thick plates, and the Bauschinger effect curves under different deformation amounts have been stably obtained.

[0056] In order to further understand the present invention, the method for testing the Schinger effect of a metal material package provided by the present invention is described in detail below in conjunction with embodiments, and the protection scope of the present invention is not limited by the following embodiments.

[0057] Example 1

[0058] Combination Figure 1 to Figure 7 The testing method for the Balsinger effect of metal sheets is carried out in the following steps:

[0059] S1) Sample preparation: Use laser cutting or wire cutting to process 750L (tensile strength exceeds 750MPa) metal sheets into "dog bone-shaped" standard tensile specimens. The two ends of the specimen are clamping areas, and the middle parallel section is the deformation test area;

[0060] S2) Pre-stretching loading-unloading: The standard tensile specimen is pre-stretched and loaded, and the engineering strain value of the pre-stretching deformation satisfies the requirement of being greater than the maximum engineering strain of the yield platform and less than the engineering strain at the beginning of necking. Figure 4 In this embodiment, the maximum engineering strain of the yield platform of the metal material is about 4%, and the engineering strain at the necking start point is about 13%, so the pre-stretching preset deformation range is 4% to 13%; in the process of pre-stretching to the preset deformation, the strain of the pre-stretching loading-unloading process is measured in real time by using the DIC strain measurement system, and the tensile load is measured in real time by using the sensor of the universal testing machine;

[0061] S3) Sampling in the middle after pre-stretching: a small rectangular sample (i.e., a compression sample) is cut from the standard sample after pre-stretching deformation by laser cutting or wire cutting. The compression sample has a thickness of t, a height of h, and a width of w. The size of the compression sample must satisfy h=k*min(w,t), and the value range of k is 1.5-1.8. In this embodiment, the thickness of the compression sample is 5 mm, and the width is 6 mm. The sample height setting range is 7.5-9 mm, specifically 8 mm.

[0062] The compression specimen can be cut from the middle of the pre-stretched specimen, or directly from the middle of the parallel section of the pre-stretched specimen. One or more compression specimens can be cut from one pre-stretched specimen, and sufficient specimens can be prepared for the subsequent compression test. In this embodiment, two compression specimens are cut, and the cutting area of ​​the compression specimen is located within the range of ≥5mm from the root of the transition fillet of the parallel section of the pre-stretched specimen; specifically, Figure 3 As shown;

[0063] S4) Compression loading: The compression test is performed on the compression specimen obtained above, and the compression is stopped when the compression is 2 times the pre-stretching deformation. The test is ended, and the strain of the compression loading process is measured in real time using the DIC strain measurement system, and the compression load is measured in real time using the sensor of the universal testing machine;

[0064] S5) Calculation of mechanical properties data: The load data and strain data of the pre-stretching and compression processes are associated with each other according to the time relationship to obtain the engineering stress-engineering strain curves of the pre-stretching and compression processes respectively; then, according to the conversion formula of engineering stress-strain and true stress-strain: true stress = engineering stress*(1+engineering strain), true strain = ln(1+engineering strain), the true stress-true strain curve data is converted, such as Figure 5 As shown, it is prepared for the subsequent pre-tension-compression data merging;

[0065] S6) Pre-stretching-compression data merging: Since the pre-stretching and compression processes are carried out separately, their true stress-true strain curve data all start from the origin, and the curve is not continuous (the pre-stretching unloading end segment E and the compression starting segment S are not connected). The compression curve needs to be offset to the right, and the offset strain is calculated by linear interpolation method: 20 data points are selected in the pre-stretching unloading end segment E and the compression starting segment S respectively, and the TREND function is used to calculate the true strain value of point P after the true stress value of the compression starting point P is offset to the right. By offsetting point P to the right, the starting position of the compression curve is connected with the end position of the pre-stretching unloading curve to obtain the complete and continuous tension-compression package Singh effect curve data, as shown in Figure 6 , Figure 7 As shown;

[0066] S7) Characterization of Bauschinger effect: Repeat the above steps and gradually increase the pre-stretching deformation. Figure 4 The uniaxial tensile curve of the example material, the pre-stretching preset deformation is set to 5%, 7.5% and 10%, and the Bauschinger effect curves under different strain conditions are obtained through pre-stretching and compression tests, such as Figure 8 shown.

[0067] Example 2

[0068] Combination Fig. 9 and Fig.10 The main structure of the device used in the test method for the Balsinger effect of metal sheets and its loading method are described as follows:

[0069] The pre-stretching-unloading device and the compression device of the metal sheet package Singh effect test device are respectively as follows Fig. 9 , Fig.10 As shown, it includes 1 testing machine, 2 loading unit, 3-1 pre-stretching upper fixture, 3-2 compression upper fixture, 4-1 pre-stretching specimen, 4-2 compression specimen, 5-1 pre-stretching lower fixture, 5-2 compression lower fixture, 6 testing machine base, 7 movable camera-DIC strain acquisition system, 8 control system;

[0070] The pre-stretched sample 4-1 is cleaned with detergent and anhydrous ethanol to remove the oil on the surface and prevent the paint from separating from the sample during the stretching process. After cleaning, the middle section of the sample is sprayed with paint. First, a layer of white primer is evenly sprayed on the surface of the sample, and then matte black paint is evenly sprayed on the primer to form a black and white mixed speckle for DIC deformation measurement.

[0071] In the pre-stretching loading-unloading process, the pre-stretching upper fixture 3-1 is connected to the loading unit 2, the pre-stretching lower fixture 5-1 is connected to the testing machine base 6, and the two ends of the pre-stretching sample 4-1 are clamped by the pre-stretching upper fixture 3-1 and the pre-stretching lower fixture 5-1 respectively. The loading unit 2 drives the upper fixture 3-1 to realize pre-stretching loading and unloading, and the loading and unloading rates are set to 3mm / min; the control system 8 is connected to the DIC strain acquisition system 7 and the loading unit 2 respectively to realize the speed control and displacement control of the loading unit 2. The loading unit 2 collects the load information of the sample 4-1 in the pre-stretching loading-unloading process and transmits it to the control system 8. The DIC strain acquisition system 7 measures the surface strain of the sample 4-1 in the deformation process in real time and transmits it to the control system 8. The control system 8 analyzes the load and strain to obtain the stress-strain relationship of the sample 4-1 in the pre-stretching loading-unloading process;

[0072] The compression sample 4-2 is cleaned with detergent and anhydrous ethanol to remove the oil on the surface and prevent the paint from separating from the sample during the stretching process; after cleaning, the deformation measurement surface of the sample is sprayed with paint. First, a layer of white primer is evenly sprayed on the surface of the sample, and then matte black paint is evenly sprayed on the primer to form a black and white mixed speckle for DIC deformation measurement;

[0073] During the compression loading process, the compression upper fixture 3-2 is connected to the loading unit 2, the compression lower fixture 5-2 is connected to the testing machine base 6, and the two ends of the compression sample 4-2 are clamped by the compression upper fixture 3-2 and the compression lower fixture 5-2 respectively. The loading unit 2 drives the upper fixture 3-2 to realize compression loading, and the loading rate is set to 0.5mm / min; the control system 8 is connected to the DIC strain acquisition system 7 and the loading unit 2 respectively to realize the speed control and displacement control of the loading unit 2. The loading unit 2 collects the load information of the sample 4-2 during the compression loading process and transmits it to the control system 8. The DIC strain acquisition system 7 measures the surface strain of the sample 4-2 during the deformation process in real time and transmits it to the control system 8. The control system 8 analyzes the load and strain to obtain the stress-strain relationship of the sample 4-2 during the compression loading process.

[0074] The above embodiments are only used to help understand the method and core idea of ​​the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0075] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for testing the Schinger effect of a metal material package, comprising the following steps: S1) processing the metal material into a standard tensile specimen, and performing a pre-stretching loading test on the standard tensile specimen to obtain pre-stretching strain data and tensile load data; S2) cutting a compression specimen from the central area of ​​the pre-stretched deformation specimen obtained in step S1), wherein the compression specimen has a thickness of t, a height of h, a width of w, and h=k*min(w, t), and k is 1.5-1.8; S3) performing a compression loading test on the compression specimen, and stopping the test after the compression reaches ≥1 times the pre-stretching deformation, to obtain compression strain data and compression load data; S4) obtaining pre-stretching true stress-true strain curve data and compressing true stress-true strain curve data respectively according to the pre-stretching strain data, the tensile load data and the compressing strain data, the compressing load data; S5) combining the true stress-true strain curve data of the pre-stretching and the true stress-true strain curve data of the compression to obtain the curve data of the tension-compression Schinger effect of the metal material; S6) increasing the pre-stretching deformation, repeating the above steps S1) to S5) to obtain the Bauschinger effect curve of the metal material under different strain conditions.

2. The testing method according to claim 1, characterized in that: In step S1), the engineering strain value of the pre-stretching deformation in the pre-stretching loading test is greater than the maximum engineering strain of the yield platform and less than the engineering strain of the necking starting point.

3. The testing method according to claim 1, characterized in that: In step S1), during the pre-stretching loading test, the strain of the pre-stretching loading is monitored in real time using a DIC strain measurement system, and the tensile load is monitored in real time using a universal testing machine.

4. The testing method according to claim 1, characterized in that: In step S3), during the compression loading process, the strain of the compression loading is monitored in real time using a DIC strain measurement system, and the compression load is monitored in real time using a universal testing machine.

5. The testing method according to claim 1, characterized in that: In step S2), the distance between the upper limit and / or the lower limit of the central area and the root of the fillet of the sample after pre-stretching deformation is ≥5 mm.

6. The testing method according to claim 1, characterized in that: Step S4) is specifically as follows: Correlating the pre-stretched strain data and the tensile load data with time to obtain pre-stretched true stress-true strain curve data; The compression strain data and compression load data are associated with time to obtain compression true stress-strain curve data.

7. The testing method according to claim 1, characterized in that: In step S5), the merging process is specifically as follows: The compressed true stress-true strain curve data is offset, and the offset strain is calculated by a linear interpolation method, so that the starting position of the compressed true stress-true strain curve data is connected to the end position of the pre-stretched true stress-true strain curve data.

8. The testing method according to claim 1, characterized in that: The pre-stretching loading test is carried out on a pre-stretching-unloading device, and a DIC strain acquisition system is provided on the pre-stretching-unloading device.

9. The testing method according to claim 1, characterized in that: The compression loading test is carried out on a compression device, and a DIC strain acquisition system is provided on the compression device.

10. The testing method according to claim 1, characterized in that: The loading and unloading rates of the pre-stretching loading test are both 1-10 mm / min, and the rate of the compression loading test is 0.5-10 mm / min; the thickness of the metal material is greater than 3 mm.

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