A method for testing the Schinger effect of metal material packages

Abstract

The present invention provides a method for testing the Bauschinger effect of metal materials, comprising the following steps: S1) processing the metal material into a standard tensile specimen, subjecting the standard tensile specimen to a pre-tension loading test to obtain pre-tension strain data and tensile load data; S2) cutting a compression specimen from the central region of the specimen after pre-tension deformation; S3) subjecting the compression specimen to a compression loading test to obtain compression strain data and compression load data; S4) calculating and combining the obtained data to obtain tension-compression Bauschinger effect curve data for the metal material; S6) increasing the pre-tension deformation and repeating the above steps to obtain Bauschinger effect curves for the metal material under different strain conditions. The present invention provides a method for testing the Bauschinger effect of metal materials, which proposes a "pre-tension-intermediate sampling-compression" test method that can simply and efficiently obtain a complete Bauschinger effect curve for the metal material.

Description

Technical Field

[0001] The present 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. Background Art

[0002] Ultra-high-strength steel is prone to springback during the forming process, which affects part precision and quality. Therefore, springback is a major challenge and pain point in the widespread use of ultra-high-strength steel. High-precision prediction of high-strength steel stamping springback is an effective approach to springback control. Developing advanced material constitutive models (digital models that describe the stress-strain relationship of a material under load) is key to accurately predicting and controlling springback.

[0003] The Bauschinger effect is an elastic incompleteness phenomenon in which, after a metal material is pre-loaded and plastically deformed, its elastic limit increases when loaded in the same direction and decreases when loaded in the opposite direction. 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. Therefore, 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 Schinger 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 this 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 a metal material into a standard tensile specimen, and performing a pre-tension loading test on the standard tensile specimen to obtain pre-tension strain data and tensile load data;

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

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

[0011] S4) obtaining pre-tension true stress-true strain curve data and compression true stress-true strain curve data according to the pre-tension strain data, the tensile load data, and the compressive strain data, the compressive load data;

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

[0013] S6) increasing the pre-stretching deformation, and repeating the above steps S1) to S5) to obtain the Bauschinger effect curves 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 correlated 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 performed 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 the compression device is provided with a DIC strain acquisition system.

[0025] Preferably, the loading and unloading rates of the pre-tensioning 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 Singer 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 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, the strain data and load data are sorted out to obtain true stress-true strain curve data of pre-stretching and compression, respectively, and then the data are combined to obtain curve data of the tension-compression Singer effect of the metal material, and finally, the above steps are repeated to obtain the method for testing the Singer effect of metal materials; the method for testing the Singer 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 pre-stretching deformation, avoiding the additional design of a lateral anti-buckling device, making the compression deformation stable, and completing the stretching and compression processes on an ordinary stretching and compression testing machine. The Bauschinger effect curve of the metal material under large strain conditions before necking occurs is obtained, which can characterize the tension-compression deformation behavior of the material under large strain conditions; at the same time, the tensile loading and compression loading processes of the present application are carried out separately, ensuring the continuity and stability of stress-strain in the two loading processes, avoiding 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 existing plate tension-compression tests; therefore, the test method provided by the present application can simply and efficiently obtain a 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 Schinger effect;

[0028] Figure 2 Schematic diagram of the experimental process of the metal sheet package Schinger effect test of the present invention;

[0029] Figure 3 Schematic diagram of the cutting scheme of the compression specimen (small rectangular specimen) of the present invention;

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

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

[0032] Figure 6 The figure shows the stretching-unloading and compression segmented curves and data processing diagram of the present invention, where point P is the compression starting point, point E is the pre-stretching unloading end point, and point S is the compression starting point;

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

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

[0035] Figure 9 Schematic diagram 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] Figure 10 This 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 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. The test ends when the compression reaches a certain deformation, 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, and obtain Bauschinger effect curves 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 Bauschinger effect curves 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 a metal material into a standard tensile specimen, and performing a pre-tension loading test on the standard tensile specimen to obtain pre-tension strain data and tensile load data;

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

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

[0042] S4) obtaining pre-tension true stress-true strain curve data and compression true stress-true strain curve data according to the pre-tension strain data, the tensile load data, and the compressive strain data, the compressive load data;

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

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

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

[0046] According to the present invention, a pre-stretched sample is first prepared, that is, the 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" standard tensile sample. After the standard tensile sample is prepared, the present application pre-stretches the standard tensile sample into a loading 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 then 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, 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 be 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 the compression specimen from the central area of ​​the pre-stretched deformed specimen, specifically as follows: Figure 2 、 Figure 3 As shown, the compression specimen can be cut from the middle of the pre-stretched deformed specimen, can be cut directly from the middle of the parallel section of the pre-stretched deformed specimen, can be cut from one pre-stretched deformed specimen, or can be cut from multiple compression specimens. The cutting area of ​​the compression specimen is located within a 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 and does not buckle.

[0048] According to the present invention, the compression specimen is then subjected to a compression loading test, e.g. Figure 2During the compression loading process, compression is stopped after reaching ≥1 times the pre-stretched deformation. Specifically, compression is stopped when the deformation reaches 2-3 times the pre-stretched deformation or the specimen fractures. The compression loading test rate is 0.5-10 mm / min, specifically 0.5-3 mm / min. During the compression process, the strain during the compression loading process is preferably measured in real time using a DIC strain measurement system, and the compressive load is measured in real time using a sensor on a universal testing machine to obtain compression strain and compression load data.

[0049] After obtaining the pre-tension strain and tensile load data, and the compression strain and compressive load values, the pre-tension and compression data are then correlated based on their time relationship to obtain the engineering stress-engineering strain curves for the pre-tension and compression processes, respectively. The Bauschinger effect focuses on the true stress-true strain curve. Therefore, according to the conversion formulas for engineering stress and strain to true stress and strain: true stress = engineering stress * (1 + engineering strain), true strain = ln (1 + engineering strain), the engineering stress-engineering strain curves are converted to true stress-true strain curves.

[0050] According to the present invention, the pre-stretching true stress-true strain curve data and the compression true stress-true strain curve data are then merged to obtain the tension-compression Singer effect curve data 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 Singer 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 necking starting point, repeat the above steps multiple times, and finally obtain a complete Bauschinger effect curve under different strain conditions of the metal material.

[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 this application is preferably greater than 3 mm.

[0053] The pre-stretching loading test in the method for testing the Singer effect of a metal material package provided in this 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 Figure 9 As shown, Figure 9In the figure, 1 is a testing machine, 2 is a loading unit, 3-1 is a pre-stretching upper clamp, 4-1 is a pre-stretching specimen, 5-1 is a pre-stretching lower clamp, 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 clamp is connected to the loading unit, the pre-stretching lower clamp is connected to the testing machine base, the two ends of the pre-stretching specimen are clamped by the pre-stretching upper clamp and the pre-stretching lower clamp respectively, and the loading unit realizes the loading and unloading of the standard tensile specimen by driving the pre-stretching upper clamp; 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 real time during the deformation process and transmits it to the control system, 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 acquisition, data analysis and data output processes in the above-mentioned pre-stretching device.

[0054] The compression device is specifically as follows Figure 10 As shown, Figure 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 achieve compression loading, the control system is connected to the DIC strain acquisition system and the loading unit respectively, to achieve 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 this application implements 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 tension-compression process stable through the pre-stretching-intermediate sampling-compression test method. It does not require the design of an additional 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. In addition, the tension-compression loading process is carried out separately, ensuring the continuity and stability of the stress-strain of the two loading processes, avoiding 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 existing material tension-compression tests. 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 stable Bauschinger effect curves under different deformation amounts have been 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 with reference to the examples. The protection scope of the present invention is not limited by the following examples.

[0057] Example 1

[0058] Combine Figures 1 to 7 The Singer effect test method for sheet metal is carried out in the following steps:

[0059] S1) Specimen preparation: Laser cutting or wire cutting is used to process 750L (tensile strength exceeds 750 MPa) metal sheets into "dog bone" standard tensile specimens. The two ends of the specimen serve as clamping areas, and the middle parallel section serves as the deformation test area.

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

[0061] S3) Sampling after pre-stretching: Cut a small rectangular specimen (i.e., a compression specimen) from the pre-stretched standard specimen using laser cutting or wire cutting. The compression specimen has a thickness of t, a height of h, and a width of w. The dimensions of the compression specimen must satisfy h = k * min (w, t), where k is in the range of 1.5 to 1.8. In this embodiment, the compression specimen has a thickness of 5 mm and a width of 6 mm. The specimen height is then set in the range of 7.5 to 9 mm, specifically 8 mm.

[0062] The compression specimen can be cut from the middle of the pre-tensioned specimen or directly from the middle of the parallel section of the pre-tensioned specimen. One or more compression specimens can be cut from one pre-tensioned specimen, so that 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 a range of ≥5mm from the root of the transition fillet of the parallel section of the pre-tensioned specimen; specifically, Figure 3 As shown;

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

[0064] S5) Calculation of mechanical properties data: The load data and strain data of the pre-stretching and compression processes are correlated 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 to 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 prepares for the subsequent pre-tension-compression data merging;

[0065] S6) Pre-tension-compression data merging: Since the pre-tension 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-tension 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-tension unloading end segment E and the compression starting segment S respectively, and the TREND function is used to calculate the true strain value after the compression starting point P is offset to the right according to the true stress value. By offsetting point P to the right, the starting position of the compression curve is connected with the end position of the pre-tension unloading curve to obtain the complete and continuous tension-compression package Singer 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 is set to 5%, 7.5% and 10% for pre-stretching. 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] Combine Figure 9 and Figure 10 The main structure of the device used in the test method for the Singer effect of metal sheets and its loading method are described as follows:

[0069] The pre-tensioning-unloading device and the compression device of the metal sheet package Singer effect test device are respectively as follows Figure 9 、 Figure 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 specimen 4-1 was cleaned with detergent and anhydrous ethanol to remove surface oil and prevent the paint from separating from the specimen during the stretching process. After cleaning, the middle section of the specimen was sprayed with paint. First, a layer of white primer was evenly sprayed on the surface of the specimen, and then matte black paint was evenly sprayed on the primer to form a mixed black and white speckle pattern for DIC deformation measurement.

[0071] During the pre-stretching loading-unloading process, the pre-stretching upper fixture 3-1 is connected to the loading unit 2, and the pre-stretching lower fixture 5-1 is connected to the testing machine base 6. The two ends of the pre-stretching specimen 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 both set to 3 mm / min. The control system 8 is connected to the DIC strain acquisition system 7 and the loading unit 2 respectively to realize speed control and displacement control of the loading unit 2. The loading unit 2 collects the load information of the specimen 4-1 during 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 specimen 4-1 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 specimen 4-1 during the pre-stretching loading-unloading process.

[0072] Compression specimen 4-2 was cleaned with detergent and anhydrous ethanol to remove surface oil and prevent the paint from separating from the specimen during the tensile process. After cleaning, the deformation measurement surface of the specimen was sprayed with paint. First, a layer of white primer was evenly sprayed on the specimen surface, and then matte black paint was evenly sprayed on the primer to form a mixed black and white speckle pattern for DIC deformation measurement.

[0073] During the compression loading process, the upper compression fixture 3-2 is connected to the loading unit 2, and the lower compression fixture 5-2 is connected to the base of the testing machine 6. The two ends of the compression specimen 4-2 are clamped by the upper compression fixture 3-2 and the lower compression 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 0.5 mm / min; the control system 8 is connected to the DIC strain acquisition system 7 and the loading unit 2 respectively to realize speed control and displacement control of the loading unit 2. The loading unit 2 collects the load information of the specimen 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 specimen 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 specimen 4-2 during the compression loading process.

[0074] The above embodiments are only intended to help understand the method and core concept of the present invention. It should be noted that, without departing from the principles of the present invention, a number of improvements and modifications may be made to the present invention by those skilled in the art, and such 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 is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily 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 is not limited to the embodiments shown herein but is intended to conform 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 a metal material into a standard tensile specimen, and performing a pre-tension loading test on the standard tensile specimen to obtain pre-tension strain data and tensile load data; S2) cutting a compression specimen from the central region of the pre-stretched deformed specimen obtained in step S1), wherein the compression specimen has a thickness of t, a height of h, and a width of w, and h = k*min(w, t), where k is 1.5-1.8; and the distance between the upper limit and / or lower limit of the central region and the root of the fillet of the pre-stretched deformed specimen is ≥ 5 mm; S3) performing a compression loading test on the compression specimen, stopping after the compression reaches ≥1 times the pre-stretching deformation, and obtaining compression strain data and compression load data; S4) obtaining pre-tension true stress-true strain curve data and compression true stress-true strain curve data according to the pre-tension strain data, the tensile load data, and the compressive strain data, the compressive load data; S5) combining the pre-stretched true stress-true strain curve data and the compressed true stress-true strain curve data to obtain curve data of the tension-compression Schinger effect of the metal material; S6) increasing the pre-stretching deformation, and repeating the above steps S1) to S5) to obtain the Bauschinger effect curves of the metal material under different strain conditions.

2. The testing method according to claim 1, wherein: 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, wherein: In step S1), during the pre-tension loading test, the strain of the pre-tension 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, wherein: 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, wherein: 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 correlated with time to obtain compression true stress-strain curve data.

6. The testing method according to claim 1, wherein: 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.

7. The testing method according to claim 1, wherein: The pre-stretching loading test is carried out on a pre-stretching-unloading device, which is equipped with a DIC strain acquisition system.

8. The testing method according to claim 1, wherein: The compression loading test is performed on a compression device, which is equipped with a DIC strain acquisition system.

9. The testing method according to claim 1, wherein: The loading and unloading rates of the pre-tension 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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