Evaluation method of biaxial tension curve

Abstract

The invention provides a method for evaluating a biaxial tensile curve, comprising: providing a to-be-tested piece and a first sample, wherein the to-be-tested piece and the sample are made of the same material; performing a uniaxial tensile test on the to-be-tested piece to obtain a uniaxial yield strain energy and a uniaxial necking strain energy of the to-be-tested piece; performing a biaxial tensile test on the first sample to obtain a first biaxial tensile curve, and obtaining a first-direction yield strain energy, a first-direction necking strain energy, a second-direction yield strain energy, and a second-direction necking strain energy of the first sample according to the first biaxial tensile curve; performing calculations and comparisons according to the uniaxial yield strain energy, the uniaxial necking strain energy, the first-direction yield strain energy, the first-direction necking strain energy, the second-direction yield strain energy, and the second-direction necking strain energy, and correlating the mechanical properties of the biaxial tensile curve with the strain energy of the material when yielding and necking occur during uniaxial tensile treatment, thereby realizing evaluation of the biaxial tensile curve.

Description

Technical Field

[0001] The invention relates to the technical field of material tensile testing, and in particular to a method for evaluating a biaxial tensile curve. Background Art

[0002] In the field of sheet metal forming simulation, it is usually necessary to conduct biaxial tensile tests to obtain the plastic deformation law of materials under complex loading conditions. The biaxial tensile curve obtained from the test can determine the yield anisotropy of the material after data processing, further improving the prediction accuracy of the forming simulation. The biaxial tensile curve needs to have a certain plastic strain energy during data processing to ensure the accuracy of the yield criterion parameters. Unlike the test curve of uniaxial tension, the biaxial tensile test will output curves in two tensile directions, and the biaxial tensile curves output by the material under different loading ratios are quite different. If the strain energy of the biaxial tensile curve is small under certain loading conditions, the curve will not be able to calibrate the yield parameters of the material after data processing, resulting in test failure. Therefore, it is very important to develop an evaluation method for biaxial tensile curves.

[0003] At present, there is no method to evaluate the biaxial tension curve to determine whether the curve meets the data processing requirements. Since the biaxial tension test will output curves in two tensile directions, the data processing process is relatively complicated. In order to grasp the anisotropic yield characteristics of the material, the test personnel generally directly process the biaxial tension curves of all loading conditions. However, this processing method is time-consuming and labor-intensive, with low work efficiency. In addition, the curves after data processing often cannot calibrate the yield criterion parameters, which cannot meet the needs of scientific research experiments.

[0004] In summary, the present invention discloses a method for evaluating a biaxial tensile curve. Summary of the invention

[0005] According to the above-mentioned technical problem that a biaxial tensile curve cannot be evaluated, a method for evaluating a biaxial tensile curve is provided. The present invention is mainly based on the plastic deformation law of metal materials, and relates the mechanical properties of the biaxial tensile curve to the strain energy of the material when yielding and necking occurs under uniaxial tension. By determining the biaxial tensile yield and necking strain energy under different loading ratios, the strain energy of the biaxial tensile curve is evaluated, and the required strain energy of the biaxial tensile curve can be accurately evaluated and obtained.

[0006] The technical means adopted by the present invention are as follows:

[0007] The present invention provides a method for evaluating a biaxial stretching curve, comprising:

[0008] Providing a to-be-tested object and a sample, wherein the to-be-tested object and the sample are made of the same material, and the sample comprises a first sample;

[0009] Performing a uniaxial tensile test on the test piece to obtain uniaxial tensile mechanical performance parameters of the test piece, and obtaining uniaxial yield strain energy and uniaxial necking strain energy of the test piece according to the uniaxial tensile mechanical performance parameters;

[0010] Performing a biaxial tensile test on the first sample to obtain a first biaxial tensile curve, obtaining biaxial tensile mechanical property parameters of the first sample according to the first biaxial tensile curve, and obtaining first-direction yield strain energy, first-direction necking strain energy, second-direction yield strain energy, and second-direction necking strain energy of the first sample according to the biaxial tensile mechanical property parameters of the first sample, wherein the first direction is a rolling direction of the first sample, and the second direction is perpendicular to the first direction;

[0011] In the biaxial tensile test of the first sample, if the first sample is stretched in equal proportions along the first direction and the second direction, the average yield strain energy is calculated according to the yield strain energy in the first direction and the yield strain energy in the second direction, and the average necking strain energy is calculated according to the necking strain energy in the first direction and the necking strain energy in the second direction;

[0012] Determining whether the average yield strain energy is greater than the unidirectional yield strain energy, and the average necking strain energy is greater than 10%×the unidirectional necking strain energy;

[0013] If the average yield strain energy is greater than the unidirectional yield strain energy, and the average necking strain energy is greater than 10%×the unidirectional necking strain energy, the first biaxial stretching curve meets the strain energy requirement for data processing.

[0014] Further, the sample also includes a second sample that is the same as the first sample;

[0015] If the average yield strain energy is greater than the unidirectional yield strain energy and the average necking strain energy is greater than 10%×the unidirectional necking strain energy, the total yield strain energy is calculated according to the first-direction yield strain energy and the second-direction yield strain energy, and the total necking strain energy is calculated according to the first-direction necking strain energy and the second-direction necking strain energy, and it is determined whether the total yield strain energy is greater than the unidirectional yield strain energy and the difference between the total necking strain energy and 20%×the unidirectional necking strain energy is less than or equal to 20%×the unidirectional necking strain energy.

[0016] If the total yield strain energy is greater than the unidirectional yield strain energy, and the difference between the total necking strain energy and 20%×the unidirectional necking strain energy is less than or equal to 20%×the unidirectional necking strain energy, the thickness of the deformation area of ​​the second sample is reduced by 25% to obtain a first processed sample;

[0017] A biaxial tensile test is performed on the first treated sample to obtain a first treated biaxial tensile curve, and the first treated biaxial tensile curve meets the strain energy requirement of data processing.

[0018] Further, if the total yield strain energy is not greater than the unidirectional yield strain energy, and the difference between the total necking strain energy and 20%×the unidirectional necking strain energy is less than or equal to 20%×the unidirectional necking strain energy, the thickness of the deformation area of ​​the second sample is reduced by 50% to obtain a second processed sample;

[0019] A biaxial tensile test is performed on the second treated sample to obtain a second treated biaxial tensile curve, and the second treated biaxial tensile curve meets the strain energy requirement of data processing.

[0020] Further, if the first sample is not stretched in equal proportions along the first direction and the second direction, a total yield strain energy is calculated according to the yield strain energy in the first direction and the yield strain energy in the second direction, and a total necking strain energy is calculated according to the necking strain energy in the first direction and the necking strain energy in the second direction, and it is determined whether the total yield strain energy is greater than the unidirectional yield strain energy, and the total necking strain energy is greater than 20%×the unidirectional necking strain energy;

[0021] If the total yield strain energy is greater than the unidirectional yield strain energy, and the total necking strain energy is greater than 20%×the unidirectional necking strain energy, the first biaxial stretching curve meets the strain energy requirement for data processing.

[0022] Further, the sample also includes a third sample that is the same as the first sample;

[0023] If the total yield strain energy is greater than the unidirectional yield strain energy and the total necking strain energy is greater than 20%×the unidirectional necking strain energy, it is determined whether the total yield strain energy is greater than the unidirectional yield strain energy and the difference between the total necking strain energy and 20%×the unidirectional necking strain energy is less than or equal to 20%×the unidirectional necking strain energy;

[0024] If the total yield strain energy is greater than the unidirectional yield strain energy, and the difference between the total necking strain energy and 20%×the unidirectional necking strain energy is less than or equal to 20%×the unidirectional necking strain energy, the thickness of the deformation region of the third sample is reduced by 25% to obtain a third processed sample;

[0025] A biaxial tensile test is performed on the third treated sample to obtain a third treated biaxial tensile curve, and the third treated biaxial tensile curve meets the strain energy requirement of data processing.

[0026] Further, if the total yield strain energy is not greater than the unidirectional yield strain energy, and the difference between the total necking strain energy and 20%×the unidirectional necking strain energy is less than or equal to 20%×the unidirectional necking strain energy, the thickness of the deformation area of ​​the third sample is reduced by 50% to obtain a fourth processed sample;

[0027] A biaxial tensile test is performed on the fourth treated sample to obtain a fourth treated biaxial tensile curve, and the fourth treated biaxial tensile curve meets the strain energy requirement of data processing. Further, the number of the samples is at least 5, and biaxial tensile tests are performed on at least 5 samples respectively, and the stretching ratio of each biaxial tensile test is different.

[0028] Furthermore, the unidirectional tensile mechanical performance parameters include unidirectional yield strength, unidirectional yield elongation, unidirectional tensile strength and unidirectional maximum force elongation;

[0029] The one-way yield strain energy = the one-way yield strength × the one-way yield elongation;

[0030] The unidirectional necking strain energy=the unidirectional tensile strength×the unidirectional maximum force elongation.

[0031] Furthermore, the biaxial tensile mechanical performance parameters include yield strength in the first direction, yield elongation in the first direction, tensile strength in the first direction, elongation at maximum force in the first direction, yield strength in the second direction, yield elongation in the second direction, tensile strength in the second direction, and elongation at maximum force in the second direction;

[0032] The first direction yield strain energy=the first direction yield strength×the first direction yield elongation;

[0033] The necking strain energy in the first direction = the tensile strength in the first direction × the maximum elongation in the first direction;

[0034] The yield strain energy in the second direction = the yield strength in the second direction × the yield elongation in the second direction;

[0035] The necking strain energy in the second direction=the tensile strength in the second direction×the maximum elongation in the second direction.

[0036] Compared with the prior art, the present invention has the following advantages:

[0037] The evaluation method of the biaxial tensile curve provided by the present invention overcomes the shortcomings of the existing method of directly processing all the data of a large number of test curves, which is time-consuming and labor-intensive, and has low work efficiency. It can accurately evaluate and obtain the required strain energy of the biaxial tensile curve, effectively improve work efficiency, and meet the actual application requirements of engineering such as yield criterion parameter calibration. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0039] Figure 1 A flow chart of the method for evaluating the biaxial stretching curve provided by the present invention.

[0040] Figure 2 It is a biaxially stretched thinned specimen.

[0041] In the figure: 1. Tensile arm; 2. Deformation area. DETAILED DESCRIPTION

[0042] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0043] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0044] Reference Figure 1 and Figure 2 , Figure 1 A flow chart of the evaluation method of the biaxial stretching curve provided by the present invention, Figure 2 A specific embodiment of the method for evaluating a biaxial stretch curve provided by the present invention is described for a biaxially stretched thinned specimen, comprising:

[0045] Providing a test piece and a sample, the test piece and the sample are made of the same material, and the sample includes a first sample;

[0046] Perform a uniaxial tensile test on the test piece to obtain uniaxial tensile mechanical performance parameters of the test piece, and obtain uniaxial yield strain energy and uniaxial necking strain energy of the test piece according to the uniaxial tensile mechanical performance parameters;

[0047] Specifically, the unidirectional tensile mechanical performance parameters include unidirectional yield strength, unidirectional yield elongation, unidirectional tensile strength and unidirectional maximum force elongation; unidirectional yield strain energy = unidirectional yield strength × unidirectional yield elongation; unidirectional necking strain energy = unidirectional tensile strength × unidirectional maximum force elongation.

[0048] Performing a biaxial tensile test on the first sample to obtain a first biaxial tensile curve, obtaining biaxial tensile mechanical property parameters of the first sample according to the first biaxial tensile curve, and obtaining first-direction yield strain energy, first-direction necking strain energy, second-direction yield strain energy, and second-direction necking strain energy of the first sample according to the biaxial tensile mechanical property parameters of the first sample, wherein the first direction is a rolling direction of the first sample, and the second direction is perpendicular to the first direction;

[0049] Specifically, the biaxial tensile mechanical performance parameters include yield strength in the first direction, yield elongation in the first direction, tensile strength in the first direction, elongation at maximum force in the first direction, yield strength in the second direction, yield elongation in the second direction, tensile strength in the second direction, and elongation at maximum force in the second direction;

[0050] Yield strain energy in the first direction = yield strength in the first direction × yield elongation in the first direction;

[0051] Neck strain energy in the first direction = tensile strength in the first direction × maximum elongation in the first direction;

[0052] Yield strain energy in the second direction = yield strength in the second direction × yield elongation in the second direction;

[0053] Neck strain energy in the second direction = tensile strength in the second direction × maximum elongation in the second direction.

[0054] In the biaxial tensile test of the first sample, if the first sample is stretched in equal proportions along the first direction and the second direction, the average yield strain energy is calculated according to the yield strain energy in the first direction and the yield strain energy in the second direction, and the average necking strain energy is calculated according to the necking strain energy in the first direction and the necking strain energy in the second direction;

[0055] Determine whether the average yield strain energy is greater than the unidirectional yield strain energy, and the average necking strain energy is greater than 10% × unidirectional necking strain energy;

[0056] If the average yield strain energy is greater than the unidirectional yield strain energy, and the average necking strain energy is greater than 10%×the unidirectional necking strain energy, the first biaxial tension curve meets the strain energy requirements for data processing.

[0057] The test specimen further includes a second test specimen that is identical to the first test specimen;

[0058] If the average yield strain energy is greater than the unidirectional yield strain energy and the average necking strain energy is greater than 10%×unidirectional necking strain energy, the total yield strain energy is calculated according to the yield strain energy in the first direction and the yield strain energy in the second direction, and the total necking strain energy is calculated according to the necking strain energy in the first direction and the necking strain energy in the second direction, and it is determined whether the total yield strain energy is greater than the unidirectional yield strain energy and the difference between the total necking strain energy and 20%×unidirectional necking strain energy is less than or equal to 20%×unidirectional necking strain energy;

[0059] It can be understood that the total yield strain energy=yield strain energy in the first direction+yield strain energy in the second direction, and the total necking strain energy=necking strain energy in the first direction+necking strain energy in the second direction.

[0060] If the total yield strain energy is greater than the unidirectional yield strain energy, and the difference between the total necking strain energy and 20%×unidirectional necking strain energy is less than or equal to 20%×unidirectional necking strain energy, the thickness of the deformation region 2 of the second specimen is reduced by 25% to obtain a first processed specimen; specifically, the specimen is a plate having a cross-shaped orthographic projection, including a deformation region 2 and four tensile arms 1 connected to the deformation region 2.

[0061] A biaxial tensile test is performed on the first treated sample to obtain a first treated biaxial tensile curve, and the first treated biaxial tensile curve meets the strain energy requirement of data processing.

[0062] If the total yield strain energy is not greater than the unidirectional yield strain energy, and the difference between the total necking strain energy and 20%×unidirectional necking strain energy is less than or equal to 20%×unidirectional necking strain energy, the thickness of the deformation region 2 of the second sample is reduced by 50% to obtain a second processed sample;

[0063] A biaxial tensile test is performed on the second treated sample to obtain a second treated biaxial tensile curve, and the second treated biaxial tensile curve meets the strain energy requirement of data processing.

[0064] If the first sample is not stretched in equal proportions along the first direction and the second direction, the total yield strain energy is calculated according to the yield strain energy in the first direction and the yield strain energy in the second direction, and the total necking strain energy is calculated according to the necking strain energy in the first direction and the necking strain energy in the second direction, to determine whether the total yield strain energy is greater than the unidirectional yield strain energy and the total necking strain energy is greater than 20%×the unidirectional necking strain energy;

[0065] If the total yield strain energy is greater than the unidirectional yield strain energy, and the total necking strain energy is greater than 20%×the unidirectional necking strain energy, the first biaxial tension curve meets the strain energy requirements for data processing.

[0066] The sample also includes a third sample that is the same as the first sample; if the total yield strain energy is greater than the unidirectional yield strain energy and the total necking strain energy is greater than 20%×the unidirectional necking strain energy, it is determined whether the total yield strain energy is greater than the unidirectional yield strain energy and the difference between the total necking strain energy and 20%×the unidirectional necking strain energy is less than or equal to 20%×the unidirectional necking strain energy;

[0067] If the total yield strain energy is greater than the unidirectional yield strain energy, and the difference between the total necking strain energy and 20%×unidirectional necking strain energy is less than or equal to 20%×unidirectional necking strain energy, the thickness of the deformation region 2 of the third sample is reduced by 25% to obtain a third processed sample.

[0068] A biaxial tensile test is performed on the third treated sample to obtain a third treated biaxial tensile curve, and the third treated biaxial tensile curve meets the strain energy requirement of data processing.

[0069] If the total yield strain energy is not greater than the unidirectional yield strain energy, and the difference between the total necking strain energy and 20%×unidirectional necking strain energy is less than or equal to 20%×unidirectional necking strain energy, the thickness of the deformation region 2 of the third sample is reduced by 50% to obtain a fourth processed sample;

[0070] A biaxial tensile test is performed on the fourth treated sample to obtain a fourth treated biaxial tensile curve, and the fourth treated biaxial tensile curve meets the strain energy requirement of data processing.

[0071] It can be understood that by evaluating the biaxial tensile curve, it can be known whether the biaxial tensile curve data after processing meets the actual engineering application requirements such as yield criterion parameter calibration, and effectively avoid the situation where the biaxial tensile data after processing cannot meet the needs of scientific research experiments.

[0072] In some optional embodiments, the number of samples is at least 5, and biaxial stretching tests are performed on at least 5 samples respectively, with the stretching ratio of each biaxial stretching test being different.

[0073] In some optional embodiments, a test piece and at least 5 identical specimens are provided. The test piece and the specimen are made of the same material, both of which are DP980 steel. The test piece is subjected to a uniaxial tensile test, and the uniaxial yield strength of the test piece is 662MPa, the uniaxial yield elongation is 0.00187, the uniaxial tensile strength is 1011MPa, and the uniaxial maximum force elongation is 0.107. The uniaxial yield strain energy of the test piece can be calculated to be 1.24, and the uniaxial necking strain energy is 108.18. Biaxial tensile tests are performed on the 5 specimens respectively, and the stretching ratios of the 5 biaxial tensile tests along the first direction and the second direction are 3:1, 3:2, 3:3, 2:3, and 1:3, respectively, and the biaxial tensile mechanical property parameters of the 5 groups of specimens are obtained, as shown in Table 1.

[0074] Table 1. Biaxial tensile mechanical properties of DP980 steel

[0075]

[0076] According to the biaxial tensile mechanical property parameters of the five groups of samples, the biaxial tensile strain energies of the five groups of samples were obtained accordingly. Each group of biaxial tensile strain energy includes: yield strain energy in the first direction, necking strain energy in the first direction, yield strain energy in the second direction, and necking strain energy in the second direction, as shown in Table 2.

[0077] Table 2. Biaxial tensile strain energy of DP980 steel

[0078]

[0079] When the sample is stretched in equal proportions along the first direction and the second direction, referring to the stretching ratio of 3:3, the average yield strain energy of the sample is 1.94 and the average necking strain energy is 18.65, which satisfies the conditions that the average yield strain energy is greater than the unidirectional yield strain energy, and the average necking strain energy is greater than 10% × unidirectional necking strain energy, that is, under the condition of a stretching ratio of 3:3, the biaxial tensile curve of the sample meets the strain energy requirements for data processing.

[0080] The unidirectional yield strain energy is 1.24, and the 20%×unidirectional necking strain energy is 21.63. When the sample is not stretched in equal proportions along the first direction and the second direction, it is determined whether the total yield strain energy is greater than 1.24 and the total necking strain energy is greater than 21.63.

[0081] When the stretching ratio is 3:1, the total yield strain energy is 2.38, the total necking strain energy is 29.18, and the biaxial stretching curve meets the strain energy requirements of data processing; when the stretching ratio is 3:2, the total yield strain energy is 2.88, the total necking strain energy is 19.17, and the biaxial stretching curve does not meet the strain energy requirements of data processing; when the stretching ratio is 2:3, the total yield strain energy is 2.77, the total necking strain energy is 18.26, and the biaxial stretching curve does not meet the strain energy requirements of data processing; when the stretching ratio is 1:3, the total yield strain energy is 2.28, the total necking strain energy is 25.55, and the biaxial stretching curve meets the strain energy requirements of data processing.

[0082] In this embodiment, taking the thickness of the sample as 2 mm as an example, under the conditions of stretching ratios of 3:2 and 2:3, the total yield strain energy is greater than the unidirectional yield strain energy, and the difference between the total necking (necking) strain energy and 20%×unidirectional necking strain energy is less than or equal to 20%×unidirectional necking strain energy. Therefore, the thickness of the deformation area 2 of the new sample is reduced by 25%, and the thickness of the thinned sample is 1.5 mm. Under the conditions of stretching ratios of 3:2 and 2:3, the thinned sample is subjected to a biaxial tensile test to obtain a new biaxial tensile curve, and new biaxial tensile performance parameters are obtained according to the new biaxial tensile curve, as shown in Table 3.

[0083] Table 3. Biaxial tensile mechanical properties of DP980 steel specimens after 25% center thinning

[0084]

[0085] According to the new biaxial tensile performance parameters, the new biaxial tensile strain energy under the conditions of stretching ratios of 3:2 and 2:3 is calculated, as shown in Table 4.

[0086] Table 4 Biaxial tensile strain energy of DP980 steel specimen after 25% center thinning

[0087]

[0088] Calculation shows that under the condition of a stretching ratio of 3:2, the new total yield strain energy is 3.2979, which is greater than 1.24; the total necking strain energy is 24.927, which is greater than 21.63, and the new biaxial stretching curve meets the strain energy requirements of data processing; under the condition of a stretching ratio of 2:3, the new total yield strain energy is 3.294, which is greater than 1.24; the total necking strain energy is 23.846, which is greater than 21.63, and the new biaxial stretching curve meets the strain energy requirements of data processing.

[0089] In the above embodiments of the present invention, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for evaluating a biaxial tensile curve, characterized in that: include: Providing a to-be-tested object and a sample, wherein the to-be-tested object and the sample are made of the same material, and the sample comprises a first sample; Performing a uniaxial tensile test on the test piece to obtain uniaxial tensile mechanical performance parameters of the test piece, and obtaining uniaxial yield strain energy and uniaxial necking strain energy of the test piece according to the uniaxial tensile mechanical performance parameters; Performing a biaxial tensile test on the first sample to obtain a first biaxial tensile curve, obtaining biaxial tensile mechanical property parameters of the first sample according to the first biaxial tensile curve, and obtaining first-direction yield strain energy, first-direction necking strain energy, second-direction yield strain energy, and second-direction necking strain energy of the first sample according to the biaxial tensile mechanical property parameters of the first sample, wherein the first direction is a rolling direction of the first sample, and the second direction is perpendicular to the first direction; In the biaxial tensile test of the first sample, if the first sample is stretched in equal proportions along the first direction and the second direction, the average yield strain energy is calculated according to the yield strain energy in the first direction and the yield strain energy in the second direction, and the average necking strain energy is calculated according to the necking strain energy in the first direction and the necking strain energy in the second direction; Determining whether the average yield strain energy is greater than the unidirectional yield strain energy, and the average necking strain energy is greater than 10%×the unidirectional necking strain energy; If the average yield strain energy is greater than the unidirectional yield strain energy, and the average necking strain energy is greater than 10%×the unidirectional necking strain energy, the first biaxial stretching curve meets the strain energy requirements for data processing; The sample also includes a second sample that is identical to the first sample; If the average yield strain energy is greater than the unidirectional yield strain energy and the average necking strain energy is greater than 10%×the unidirectional necking strain energy, the total yield strain energy is calculated according to the first-direction yield strain energy and the second-direction yield strain energy, and the total necking strain energy is calculated according to the first-direction necking strain energy and the second-direction necking strain energy, and it is determined whether the total yield strain energy is greater than the unidirectional yield strain energy and the difference between the total necking strain energy and 20%×the unidirectional necking strain energy is less than or equal to 20%×the unidirectional necking strain energy. If the total yield strain energy is greater than the unidirectional yield strain energy, and the difference between the total necking strain energy and 20%×the unidirectional necking strain energy is less than or equal to 20%×the unidirectional necking strain energy, the thickness of the deformation area of ​​the second sample is reduced by 25% to obtain a first processed sample; Performing a biaxial tensile test on the first treated sample to obtain a first treated biaxial tensile curve, wherein the first treated biaxial tensile curve meets the strain energy requirement of data processing; If the total yield strain energy is not greater than the unidirectional yield strain energy, and the difference between the total necking strain energy and 20%×the unidirectional necking strain energy is less than or equal to 20%×the unidirectional necking strain energy, the thickness of the deformation region of the second sample is reduced by 50% to obtain a second processed sample; A biaxial tensile test is performed on the second treated sample to obtain a second treated biaxial tensile curve, and the second treated biaxial tensile curve meets the strain energy requirement of data processing.

2. The method for evaluating a biaxial tensile curve according to claim 1, characterized in that: If the first sample is not stretched in equal proportions along the first direction and the second direction, a total yield strain energy is calculated according to the yield strain energy in the first direction and the yield strain energy in the second direction, and a total necking strain energy is calculated according to the necking strain energy in the first direction and the necking strain energy in the second direction, and it is determined whether the total yield strain energy is greater than the unidirectional yield strain energy and the total necking strain energy is greater than 20%×the unidirectional necking strain energy; If the total yield strain energy is greater than the unidirectional yield strain energy, and the total necking strain energy is greater than 20%×the unidirectional necking strain energy, the first biaxial stretching curve meets the strain energy requirement for data processing.

3. The method for evaluating a biaxial tension curve according to claim 2, characterized in that: The sample also includes a third sample that is identical to the first sample; If the total yield strain energy is greater than the unidirectional yield strain energy and the total necking strain energy is greater than 20%×the unidirectional necking strain energy, it is determined whether the total yield strain energy is greater than the unidirectional yield strain energy and the difference between the total necking strain energy and 20%×the unidirectional necking strain energy is less than or equal to 20%×the unidirectional necking strain energy; If the total yield strain energy is greater than the unidirectional yield strain energy, and the difference between the total necking strain energy and 20%×the unidirectional necking strain energy is less than or equal to 20%×the unidirectional necking strain energy, the thickness of the deformation region of the third sample is reduced by 25% to obtain a third processed sample; A biaxial tensile test is performed on the third treated sample to obtain a third treated biaxial tensile curve, and the third treated biaxial tensile curve meets the strain energy requirement of data processing.

4. The method for evaluating a biaxial stretch curve according to claim 3, characterized in that: If the total yield strain energy is not greater than the unidirectional yield strain energy, and the difference between the total necking strain energy and 20%×the unidirectional necking strain energy is less than or equal to 20%×the unidirectional necking strain energy, the thickness of the deformation region of the third sample is reduced by 50% to obtain a fourth processed sample; A biaxial tensile test is performed on the fourth treated sample to obtain a fourth treated biaxial tensile curve, and the fourth treated biaxial tensile curve meets the strain energy requirement of data processing.

5. The method for evaluating a biaxial tension curve according to claim 1, characterized in that: The number of the samples is at least 5, and biaxial stretching tests are performed on at least 5 samples respectively, with the stretching ratio of each biaxial stretching test being different.

6. The method for evaluating a biaxial tensile curve according to claim 1, characterized in that: The unidirectional tensile mechanical performance parameters include unidirectional yield strength, unidirectional yield elongation, unidirectional tensile strength and unidirectional maximum force elongation; The one-way yield strain energy = the one-way yield strength × the one-way yield elongation; The unidirectional necking strain energy=the unidirectional tensile strength×the unidirectional maximum force elongation.

7. The method for evaluating a biaxial tension curve according to claim 1, characterized in that: The biaxial tensile mechanical performance parameters include yield strength in the first direction, yield elongation in the first direction, tensile strength in the first direction, elongation at maximum force in the first direction, yield strength in the second direction, yield elongation in the second direction, tensile strength in the second direction, and elongation at maximum force in the second direction; The first direction yield strain energy=the first direction yield strength×the first direction yield elongation; The necking strain energy in the first direction = the tensile strength in the first direction × the maximum elongation in the first direction; The yield strain energy in the second direction = the yield strength in the second direction × the yield elongation in the second direction; The necking strain energy in the second direction=the tensile strength in the second direction×the maximum elongation in the second direction.

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