Design method for improving effectiveness of biaxial tensile sample

Abstract

The invention provides a design method for improving effectiveness of a biaxial tensile sample, which comprises the following steps: S1, establishing a finite element model, and performing a simulation test; s2, judging whether the biaxial tensile sample needs to be adjusted or not according to the simulation result of the biaxial tensile test working condition; if the deformation of the biaxial tensile sample mainly occurs in a non-central area, entering S3; s3 comprises the following steps: (1) increasing the lengths of four stretching arms of the biaxial stretching sample and the width of the widest part according to the proportion of 5-20% of the side length of the central region; (2) 1-3 grooves are additionally formed in the four stretching arms respectively; (3) the width of the groove formed in each stretching arm is adjusted to be not larger than 0.2 mm; (4) increasing the length of the groove according to the proportion of 10-50% of the width of the widest part of the stretching arm; and S4, verifying the effectiveness of the biaxial tensile sample after each round of adjustment. The problems that an existing sample design mode is high in machining complexity, the sample is prone to deformation and fracture in a non-central area, and stability is poor in the testing process are solved.

Description

Technical Field

[0001] The invention relates to the technical field of metal sheet material formability analysis, and in particular to a design method for improving the effectiveness of a biaxial tensile test specimen. Background Art

[0002] In the process of formability analysis of metal sheets, biaxial tensile tests are usually performed on the specimens under different loading states to obtain the mechanical property curves of the material under different stress states. At present, there are various shapes and sizes of biaxial tensile specimens in the industry. The shape of the specimen is usually designed to be approximately cross-shaped, including tensile arms in four directions, to meet the equipment requirements of various biaxial tensile testing machines.

[0003] However, although different types of cross-shaped biaxial tensile specimens can complete tensile tests under the action of a biaxial tensile testing machine, the deformation of biaxial tensile specimens of different shapes is not necessarily generated under biaxial loading conditions. If the deformation of the biaxial tensile specimen is mainly concentrated in the non-central area, the specimen will inevitably break in the non-central area. The fracture of the specimen in the non-central area is generally a unidirectional tensile stress state. The test results collected under this stress state are bound to be inconsistent with the actual deformation characteristics of the material and cannot meet the application requirements of engineering practice and scientific research work. In the prior art, some biaxial tensile specimens are thickened in the central area, but due to the reduction in thickness, the thickness of the specimen is reduced. Generally, a milling machine or a grinder is used. This processing method will have a significant impact on the material properties. After milling, the material will undergo work hardening, resulting in a higher yield strength after milling than before processing, and a lower elongation after milling than before milling. The change in material properties will affect the collected test results, and also cause the test results to be inconsistent with the actual performance of the material; some biaxial tensile specimens have holes on the tensile arms or no grooves aligned with the center line of the specimens. Such a structure will affect the force transmission stability of the specimens, resulting in uneven bidirectional force on the biaxial specimens during the test, and will make the specimen processing more complicated, increasing the test cost.

[0004] In summary, in order to prevent deformation of the specimen in non-central areas and ensure that the central area of ​​the specimen is in a biaxial tensile stress state as required by the test, the existing technology will reduce the thickness of the specimen center during specimen design. However, the design of the thickness reduction treatment will affect key performance indicators such as strength and elongation of the test material, resulting in serious distortion of performance test results. In addition, the existing specimen design method also has problems such as complex structure, poor specimen force uniformity and deformation state stability. Therefore, it is very important to develop a design method to improve the effectiveness of biaxial tensile specimens. Summary of the invention

[0005] In view of the problems mentioned above that the design method of the existing specimens will affect the performance of the test materials and cause serious distortion of the performance test results, and the specimens have high processing complexity, poor force uniformity and deformation stability during the test, and cannot meet the requirements of the biaxial tension test, the present invention provides a design method for improving the effectiveness of biaxial tension specimens, which can ensure that the deformation state of the specimens always meets the loading characteristics of the biaxial tension test, overcomes the technical difficulties of performance distortion of the existing specimen test results, poor force uniformity and deformation stability during the test, greatly improves the effectiveness of the biaxial tension specimens and the stability of the test, is particularly suitable for occasions such as research and analysis on the formability of metal sheet materials, and widely meets the application requirements of engineering practice and scientific research work.

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

[0007] A design method for improving the effectiveness of a biaxial tensile specimen, wherein the biaxial tensile specimen is a cross-shaped specimen including four tensile arms, and a square central area is divided at the center of the cross-shaped specimen where the four tensile arms intersect; the design method specifically comprises the following steps:

[0008] S1. Establish a finite element model according to the shape and size of the biaxial tensile specimen, and perform a simulation test according to the biaxial tensile test conditions;

[0009] S2. Determine whether the biaxial tensile specimen needs to be adjusted based on the simulation results of the biaxial tensile test conditions:

[0010] If the deformation of the biaxial tensile specimen mainly occurs in the central area, it means that the biaxial tensile specimen is valid and can meet the test requirements;

[0011] If the deformation of the biaxial tensile specimen mainly occurs in the non-central area, it means that the biaxial tensile specimen cannot meet the test requirements and enters S3;

[0012] S3. Adjust the shape and size of the finite element model of the biaxial tensile specimen:

[0013] (1) Increase the length of the four stretching arms and the width at the widest point of the biaxial tensile test specimen by 5 to 20% of the length of the side of the center area; ensure that the length of the stretching arm is not less than 150% of the length of the side of the center area, and the width of the widest point of the stretching arm is not less than the length of the side of the center area;

[0014] (2) 1 to 3 grooves are added to each of the four tensile arms, and the number of grooves on each tensile arm is the same and an odd number, and the groove located in the middle of the tensile arm is coaxial with the center line of the biaxial tensile specimen, and the other grooves are symmetrically arranged on both sides of the groove located in the middle of the tensile arm;

[0015] (3) The width of the grooves on each stretching arm is adjusted to not exceed 0.5 mm; the width of the grooves on each stretching arm is the same;

[0016] (4) increasing the length of the groove by 10 to 50% of the width of the widest part of the stretching arm; the length of the groove on each stretching arm is the same;

[0017] S4. Verify the validity of the biaxial tensile specimen after each round of adjustment:

[0018] Repeat S1 and S2 for the biaxial tension specimen adjusted by S3. If it is judged by S2 that the biaxial tension specimen cannot meet the test requirements, repeat S3 for the next round of adjustment. Repeat the above process until the biaxial tension specimen is judged by S2 to be valid and can meet the test requirements.

[0019] Furthermore, in S2, the region where the deformation of the biaxial tension specimen mainly occurs is determined by using the finite element analysis cloud diagram.

[0020] Furthermore, in (2), the grooves are opened along the length direction of the stretching arm, and the spacing between adjacent grooves is equal.

[0021] Furthermore, in (2), ensure that the number of grooves on each stretching arm is not less than 3.

[0022] Furthermore, in (2), if the number of existing grooves on the stretching arm is an odd number, 2 grooves are added; if the number of existing grooves on the stretching arm is 0, 3 grooves are added; if the number of existing grooves on the stretching arm is an even number other than 0, 1 groove is added.

[0023] Furthermore, in (3), if there is already a groove on the tensile arm, the width of the groove is reduced by 10 to 25% of the width of the existing groove in (3).

[0024] Furthermore, in (3), if the width of the existing groove on the stretching arm exceeds 0.2 mm, the width of the existing groove is gradually adjusted by reducing the width of the existing groove by 10 to 25% each time until the width of the existing groove does not exceed 0.2 mm.

[0025] Furthermore, in (4), if the number of existing grooves on the stretching arm is 0, the length of the additional groove is controlled to be 10 to 50% of the width of the widest part of the stretching arm.

[0026] Further, in (4), ensure that the groove length does not exceed 90% of the length of the stretching arm.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] The design method for improving the effectiveness of a biaxial tensile test specimen provided by the present invention does not make structural changes to the central area of ​​the specimen, thereby ensuring that the material properties of the specimen are not affected. The present invention uses a finite element method to determine the loading history of the specimen under complex deformation, and progressively adjusts the shape and size of the specimen. The progressive adjustment method adopted by the present invention can cause the final deformation of the specimen to occur in the central area, and can simplify the processing of the specimen as much as possible while ensuring the use requirements of the specimen, thereby reducing the preparation cost of the specimen; at the same time, it can ensure that the deformation state of the final specimen always meets the loading characteristics of the biaxial tensile test, thereby improving the force uniformity, effectiveness and test stability of the biaxial tensile specimen, overcoming the technical difficulties of performance distortion of existing specimen test results, poor force uniformity and deformation stability during the test, and reducing unnecessary specimen production costs.

[0029] Based on the above reasons, the present invention can be widely promoted in the field of formability analysis of metal sheet materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] 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.

[0031] Figure 1 This is the initial state of the biaxially stretched specimen in Example 1 of the present invention.

[0032] Figure 2 This is a schematic diagram of the simulation test results of the biaxial tensile specimen in Example 1 of the present invention according to the biaxial tensile test conditions.

[0033] Figure 3 This is a schematic diagram of the simulation test results of the biaxial tensile specimen in Example 1 of the present invention after the shape and size are adjusted according to the biaxial tensile test conditions.

[0034] Figure 4 This is the initial state of the biaxially stretched specimen in Example 2 of the present invention.

[0035] Figure 5 This is a schematic diagram of the simulation test results of the biaxial tension specimen in Example 2 of the present invention after the shape and size are adjusted according to the biaxial tension test conditions. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions 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. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] like Figure 1-3 As shown, the present invention provides a design method for improving the effectiveness of a biaxial tensile specimen, wherein the biaxial tensile specimen is a cross-shaped specimen including four tensile arms, and a square central area is divided at the center of the cross-shaped specimen where the four tensile arms intersect;

[0038] The design method specifically comprises the following steps:

[0039] S1. Establish a finite element model according to the shape and size of the biaxial tensile specimen, and perform a simulation test according to the biaxial tensile test conditions;

[0040] S2. Determine whether the biaxial tensile specimen needs to be adjusted based on the simulation results of the biaxial tensile test conditions:

[0041] If the deformation of the biaxial tensile specimen mainly occurs in the central area, it means that the biaxial tensile specimen is valid and can meet the test requirements;

[0042] If the deformation of the biaxial tensile specimen mainly occurs in the non-central area, it means that the biaxial tensile specimen cannot meet the test requirements and enters S3;

[0043] S3. Adjust the shape and size of the finite element model of the biaxial tensile specimen:

[0044] (1) The length and the width of the widest part of the four stretching arms of the biaxial tensile specimen are increased by 5 to 20% of the length of the side of the central area; the length of the stretching arm is ensured to be not less than 150% of the length of the side of the central area, and the width of the widest part of the stretching arm is not less than the length of the side of the central area; such a specimen size can prevent the insufficient force transmission space between the stretching arm and the central area of ​​the specimen due to the too small size of the stretching arm, thereby causing the deformation of the specimen to be less likely to occur in the central area, and if the length of the stretching arm is too short, the area of ​​the specimen clamping area (the clamping area is the entire stretching arm minus the groove area) will be too small, and the specimen will easily slip during the test; however, the size of the stretching arm should not be too large, as an excessively large size will easily cause waste of test sheet material, and the specific size can be determined by the method of the present invention after each round of adjustment and verification;

[0045] (2) 1 to 3 grooves are added to each of the four tensile arms, and the number of grooves on each tensile arm is the same and an odd number, and the groove located in the middle of the tensile arm is coaxial with the center line of the biaxial tensile specimen, and the other grooves are symmetrically arranged on both sides of the groove located in the middle of the tensile arm; since in the biaxial tensile test, it is necessary to collect the change process of two pairs of gauge lengths based on the center line of the specimen, so that the center line of one groove on the tensile arm can be aligned with the center line of the specimen, and the other grooves are symmetrically arranged on both sides, which can ensure the orthogonality of the strain state of the two pairs of gauge lengths, and avoid the occurrence of shear force during the test due to the deviation of the groove position, which affects the test results;

[0046] (3) The width of the grooves on each stretching arm is adjusted to not exceed 0.5 mm; the width of the grooves on each stretching arm is the same; if the groove width does not exceed 0.5 mm, the effect of the grooves on the specimen stiffness can be reduced. If the grooves are too wide, stress concentration is likely to occur at the grooves of the stretching arm during the test, resulting in the specimen deformation not being easy to occur at the center of the specimen;

[0047] (4) The length of the groove is increased by 10 to 50% of the width of the widest part of the stretching arm. Increasing the length of the groove can improve the force transmission stability during the stretching process of the sample, thereby ensuring that the deformation of the sample is more likely to occur in the central area; the length of the groove on each stretching arm is the same;

[0048] S4. Verify the validity of the biaxial tensile specimen after each round of adjustment:

[0049] Repeat S1 and S2 for the biaxial tension specimen adjusted by S3. If it is judged by S2 that the biaxial tension specimen cannot meet the test requirements, repeat S3 for the next round of adjustment. Repeat the above process until the biaxial tension specimen is judged by S2 to be valid and can meet the test requirements.

[0050] Furthermore, in S2, the region where the deformation of the biaxial tension specimen mainly occurs is determined by using the finite element analysis cloud diagram.

[0051] Furthermore, in (2), the grooves are opened along the length direction of the stretching arm, and the spacing between adjacent grooves is equal.

[0052] Furthermore, in (2), ensure that the number of grooves on each stretching arm is not less than 3.

[0053] Furthermore, in (2), if the number of existing grooves on the stretching arm is an odd number, 2 grooves are added; if the number of existing grooves on the stretching arm is 0, 3 grooves are added; if the number of existing grooves on the stretching arm is an even number other than 0, 1 groove is added.

[0054] Furthermore, in (3), if there is already a groove on the tensile arm, the width of the groove is reduced by 10 to 25% of the width of the existing groove in (3).

[0055] Furthermore, in (3), if the width of the existing groove on the stretching arm exceeds 0.5 mm, the width of the existing groove is gradually adjusted by reducing the width of the existing groove by 10 to 25% each time until the width of the existing groove does not exceed 0.5 mm.

[0056] Preferably, in (3), the width of the grooves on each stretching arm is adjusted to not exceed 0.2 mm, so that the effect achieved is better and stress concentration is more likely to occur in the grooves; if the width of the existing grooves on the stretching arms exceeds 0.2 mm, the width of the existing grooves is gradually adjusted by reducing the width of the existing grooves by 10 to 25% each time until the width of the existing grooves does not exceed 0.2 mm.

[0057] Furthermore, in (4), if the number of existing grooves on the stretching arm is 0, the length of the additional groove is controlled to be 10 to 50% of the width of the widest part of the stretching arm; if the number of existing grooves on the stretching arm is not 0, the length of the groove is increased at a ratio of 10 to 50% of the width of the widest part of the stretching arm.

[0058] Further, in (4), ensure that the groove length does not exceed 90% of the length of the stretching arm.

[0059] The design method for improving the effectiveness of a biaxial tensile specimen provided by the present invention does not require a thickness reduction treatment in the central area, and can ensure the true material properties of the specimen. The present invention is based on the biaxial tensile deformation mechanism of the material, associates the loading characteristics of a biaxial tensile testing machine with the bidirectional deformation characteristics of a part, and uses a finite element method to determine the loading history of the specimen under complex deformation, and progressively adjusts the shape and size of the specimen. The progressive adjustment method adopted by the present invention can make the final specimen deformation occur in the central area, and simplify the specimen processing process as much as possible under the premise of ensuring the specimen use requirements, thereby reducing the processing difficulty and the specimen preparation cost; at the same time, the present invention can overcome the technical difficulties of performance distortion of existing specimen test results, poor force uniformity and deformation stability during the test, can greatly improve the force uniformity, effectiveness and test stability of the biaxial tensile specimen, and can ensure that the specimen always maintains a biaxial loading state, widely meeting the actual needs of the project.

[0060] Example 1

[0061] The design method for improving the effectiveness of a biaxial tensile specimen according to the present invention is described below in conjunction with a specific embodiment, and specifically comprises the following steps:

[0062] S1, such as Figure 1As shown, a finite element model is established according to the shape and size of the biaxial tensile specimen, and a simulation test is carried out according to the biaxial tensile test conditions;

[0063] S2. The simulation results of the biaxial tensile test conditions are as follows Figure 2 As shown, it can be seen that the deformation of the initial biaxial tensile specimen in this embodiment mainly occurs in the non-central area, such as Figure 2 As shown by the dotted line in , it is necessary to enter S3 to adjust the shape and size of the finite element model of the biaxial tension specimen;

[0064] S3. Adjust the shape and size of the finite element model of the biaxial tensile specimen:

[0065] (1) Increase the length of the four stretching arms and the width at the widest point of the biaxial tensile test specimen by 5 to 20% of the length of the central area, so that the length of the stretching arm = 2 × the length of the central area, and the width of the widest point of the stretching arm = the length of the central area;

[0066] (2) Grooves are added to the four stretching arms respectively. In this embodiment, the number of existing grooves on the stretching arm is 0, so three grooves are added in the first round of adjustment, and two grooves are added in each subsequent adjustment, and the number of grooves on each stretching arm is ensured to be the same, the grooves are opened along the length direction of the stretching arm, the spacing between adjacent grooves is equal, and the groove located in the middle of the stretching arm is coaxial with the center line of the biaxial tensile specimen, and the other grooves are symmetrically arranged on both sides of the groove located in the middle of the stretching arm;

[0067] (3) Adjust the width of the grooves on each stretching arm to ensure that the width of the grooves does not exceed 0.2 mm to reduce the effect of the grooves on the stiffness of the specimen; the width of the grooves on each stretching arm is the same;

[0068] (4) The groove length is set equal to the width of the widest part of the stretching arm to ensure the stability of the force transmission of the sample; the length of the groove on each stretching arm is the same;

[0069] S4. Verify the validity of the biaxial tensile specimen after each round of adjustment:

[0070] Repeat S1 and S2 for the biaxial tensile specimen adjusted by S3. If it is determined by S2 that the biaxial tensile specimen cannot meet the test requirements, repeat S3 for the next round of adjustment. Repeat the above process until the biaxial tensile specimen is determined by S2 to be valid and can meet the test requirements.

[0071] In this embodiment, the effective biaxial tensile specimen finally obtained has 7 grooves on the tensile arm, the groove width is 0.1 mm, and the groove length is equal to the width of the tensile arm. After the simulation test according to the biaxial tensile test conditions, the deformation mainly occurs in the central area, such as Figure 3As shown, it means that the sample can meet the test requirements.

[0072] Example 2

[0073] The design method for improving the effectiveness of a biaxial tensile specimen according to the present invention is described below in conjunction with a specific embodiment, and specifically comprises the following steps:

[0074] S1, such as Figure 4 As shown, a finite element model is established according to the shape and size of the biaxial tensile specimen, and a simulation test is carried out according to the biaxial tensile test conditions;

[0075] S2. The deformation of the initial biaxial tensile specimen in this embodiment mainly occurs in the non-central area, so it is necessary to enter S3 to adjust the shape and size of the finite element model of the biaxial tensile specimen;

[0076] S3. Adjust the shape and size of the finite element model of the biaxial tensile specimen:

[0077] (1) Increase the length of the four stretching arms and the width at the widest point of the biaxial tensile specimen by 10% of the length of the center area, so that the length of the stretching arm = 2.5 × the length of the center area, and the width of the widest point of the stretching arm = the length of the center area;

[0078] (2) Grooves are added to the four stretching arms respectively. In this embodiment, the number of existing grooves on the stretching arm is 2, such as Figure 4 As shown, one groove is added in the first round of adjustment, and two grooves are added in each subsequent adjustment, and the number of grooves on each stretching arm is ensured to be the same, the grooves are opened along the length direction of the stretching arm, the spacing between adjacent grooves is equal, and the groove located in the middle of the stretching arm is coaxial with the center line of the biaxial tensile specimen, and the other grooves are symmetrically arranged on both sides of the groove located in the middle of the stretching arm;

[0079] (3) adjusting the width of the grooves on each stretching arm. In this embodiment, the existing groove width is 1.5 mm. The existing groove width is gradually adjusted by reducing the existing groove width by 25% each time until the existing groove width does not exceed 0.2 mm, so as to reduce the influence of the grooves on the stiffness of the sample. The width of the grooves on each stretching arm is the same.

[0080] (4) Increase the length of the groove by 50% of the width of the widest part of the stretching arm to ensure the stability of the force transmission of the sample; the length of the groove on each stretching arm is the same;

[0081] S4. Verify the validity of the biaxial tensile specimen after each round of adjustment:

[0082] Repeat S1 and S2 for the biaxial tensile specimen adjusted by S3. If it is determined by S2 that the biaxial tensile specimen cannot meet the test requirements, repeat S3 for the next round of adjustment. Repeat the above process until the biaxial tensile specimen is determined by S2 to be valid and can meet the test requirements.

[0083] In this embodiment, the effective biaxial tensile specimen finally obtained has 9 grooves on the tensile arm, the groove width is 0.15 mm, and the groove length is equal to twice the size of the widest part of the tensile arm. After the simulation test according to the biaxial tensile test conditions, the deformation mainly occurs in the central area, such as Figure 5 As shown, it means that the sample can meet the test requirements.

[0084] 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 by 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 design method for improving the effectiveness of a biaxial tensile specimen, wherein the biaxial tensile specimen is a cross-shaped specimen including four tensile arms, and a square central area is divided at the center of the cross-shaped specimen where the four tensile arms intersect; characterized in that: The design method specifically comprises the following steps: S1. Establish a finite element model according to the shape and size of the biaxial tensile specimen, and perform a simulation test according to the biaxial tensile test conditions; S2. Determine whether the biaxial tensile specimen needs to be adjusted based on the simulation results of the biaxial tensile test conditions: If the deformation of the biaxial tensile specimen mainly occurs in the central area, it means that the biaxial tensile specimen is valid and can meet the test requirements; If the deformation of the biaxial tensile specimen mainly occurs in the non-central area, it means that the biaxial tensile specimen cannot meet the test requirements and enters S3; S3. Adjust the shape and size of the finite element model of the biaxial tensile specimen: (1) Increase the length of the four stretching arms and the width at the widest point of the biaxial tensile test specimen by 5 to 20% of the length of the side of the center area; ensure that the length of the stretching arm is not less than 150% of the length of the side of the center area, and the width of the widest point of the stretching arm is not less than the length of the side of the center area; (2) 1 to 3 grooves are added to each of the four tensile arms, and the number of grooves on each tensile arm is the same and an odd number, and the groove located in the middle of the tensile arm is coaxial with the center line of the biaxial tensile specimen, and the other grooves are symmetrically arranged on both sides of the groove located in the middle of the tensile arm; (3) The width of the grooves on each stretching arm is adjusted to not exceed 0.5 mm; the width of the grooves on each stretching arm is the same; (4) increasing the length of the groove by 10 to 50% of the width of the widest part of the stretching arm; the length of the groove on each stretching arm is the same; S4. Verify the validity of the biaxial tensile specimen after each round of adjustment: Repeat S1 and S2 for the biaxial tension specimen adjusted by S3. If it is judged by S2 that the biaxial tension specimen cannot meet the test requirements, repeat S3 for the next round of adjustment. Repeat the above process until the biaxial tension specimen is judged by S2 to be valid and can meet the test requirements.

2. The design method for improving the effectiveness of a biaxial tensile specimen according to claim 1, characterized in that: In S2, the area where the deformation of the biaxial tension specimen mainly occurs is determined by the finite element analysis cloud map.

3. The design method for improving the effectiveness of a biaxial tensile specimen according to claim 1, characterized in that: In (2), the grooves are opened along the length direction of the stretching arm, and the spacing between adjacent grooves is equal.

4. The design method for improving the effectiveness of a biaxial tensile specimen according to claim 1, characterized in that: In S3-2, ensure that the number of grooves on each stretching arm is not less than 3.

5. The design method for improving the effectiveness of a biaxial tensile specimen according to claim 1, characterized in that: In (2), if the number of existing grooves on the stretching arm is an odd number, two more grooves are added; If the number of existing grooves on the stretching arm is 0, then 3 grooves are added; if the number of existing grooves on the stretching arm is an even number other than 0, then 1 groove is added.

6. The design method for improving the effectiveness of a biaxial tensile specimen according to claim 1, characterized in that: In (3), if there is already a groove on the tensile arm, the groove width is reduced by 10 to 25% of the existing groove width in (3).

7. The design method for improving the effectiveness of a biaxial tensile specimen according to claim 1, characterized in that: In (3), if the width of the existing groove on the stretching arm exceeds 0.5 mm, the width of the existing groove is gradually adjusted by reducing the width of the existing groove by 10 to 25% each time until the width of the existing groove does not exceed 0.5 mm.

8. The design method for improving the effectiveness of a biaxial tensile specimen according to claim 1, characterized in that: In (4), if the number of existing grooves on the stretching arm is 0, the length of the additional groove is controlled to be 10-50% of the width of the widest part of the stretching arm.

9. The design method for improving the effectiveness of a biaxial tensile specimen according to claim 1, characterized in that: In (4), ensure that the groove length does not exceed 90% of the length of the tension arm.

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