Design method and test specimen for material fracture performance test under complex stress state

Abstract

The present invention provides a method and specimen for designing a material fracture performance test specimen under a complex stress state. The method comprises: analyzing the main deformed structural components of a target structure under a service limit state, obtaining the stress triaxiality and Lode angle parameter distribution of the main deformed structural components before and after deformation, performing a service stress state analysis of the target structure, and designing the main deformed structural component specimen using a simulation method in combination with the service stress state analysis and the values ​​of the stress triaxiality and Lode angle parameters; performing a fracture performance test simulation of the target structure based on the main deformed structural component specimen and test conditions, obtaining the stress state and strain change of the specimen, and optimizing the specimen size until the optimal main deformed structural component specimen size is obtained. The present invention can design fracture performance test specimens under different stress states and facilitates quasi-static and dynamic testing, thereby being able to specifically reflect the service stress state and fracture performance of the structural component.

Description

Technical Field

[0001] The present invention relates to the technical field of material fracture performance testing, and in particular to a material fracture performance testing specimen design method and specimen under complex stress conditions. Background Art

[0002] During the service life of structural materials, due to the variability of the service environment, the service process is accompanied by the characteristics of a complex stress state. The complex stress state is that the stress state of the material is not a simple pure tension or pure shear, but a composite stress state of three principal stresses.

[0003] Currently, researchers have designed various types of specimens to test the fracture properties of materials under complex stress states. However, based on the evaluation of application results, most of the designed specimens have the following deficiencies:

[0004] The service characteristics of the material are not fully considered, and the designed specimen cannot reflect the stress state of the material when it breaks during service; the shape of the designed specimen is relatively complex, requiring high processing precision and cumbersome processing technology, making it difficult to sample from parts and difficult to promote for use in industry; the designed specimen only meets quasi-static test requirements and is difficult to conduct dynamic testing. Summary of the Invention

[0005] Based on this, it is necessary to provide a design method and specimen for testing the fracture properties of materials under complex stress states in response to the above technical problems.

[0006] A method for designing a specimen for testing material fracture properties under a complex stress state comprises: analyzing a main deformed structural member of a target structure under a service limit state, obtaining stress triaxiality distribution and Lode angle parameter distribution of the main deformed structural member before and after deformation, and performing a service stress state analysis of the target structure based on the stress triaxiality distribution and Lode angle parameter distribution; designing a specimen of the main deformed structural member using a simulation method based on the service stress state analysis of the target structure, in combination with the values ​​of stress triaxiality and Lode angle parameters, and test conditions for material fracture properties; performing a fracture property test simulation of the target structure based on the main deformed structural member specimen and the test conditions, and obtaining the stress state and strain change of the specimen based on the simulation results; and optimizing the specimen size based on the stress state and strain change until the strain of the specimen is concentrated in a measurement area and the values ​​of the stress triaxiality and Lode angle parameters in the measurement area are stable, thereby obtaining the optimal specimen size of the main deformed structural member.

[0007] Furthermore, when the thickness of the main deformable structural member is less than 3 mm, stress triaxiality is used to perform service stress state analysis of the target structure; when the thickness of the main deformable structural member is greater than or equal to 3 mm, stress triaxiality and Lode angle parameters are combined to perform service stress state analysis of the target structure.

[0008] Furthermore, the main deformation structural component specimens include cupped specimens and non-cupped specimens, and the non-cupped specimens are subjected to a fracture performance test using a tensile testing device; the cupped specimens are subjected to a fracture performance test using a cupping device; when the tensile testing device is used for testing, one end of the main deformation structural component specimen is fixed and the other end is loaded, and according to the test conditions, a fracture performance test simulation of the main deformation structural component specimen is performed to analyze the stress state and strain distribution of the main deformation structural component specimen.

[0009] Furthermore, the non-cupping specimens are all set as symmetrical specimens.

[0010] A test specimen for testing the fracture properties of a material under a complex stress state. When the main deformation structural component is a thin plate with a thickness of less than 3 mm, the thin plate main deformation structural component specimen includes a first shear specimen, a first single tension specimen, a first R10 notch specimen, a first R5 notch specimen, and a first cupping specimen; when the main deformation structural component is a thick plate or a cast material with a thickness greater than or equal to 3 mm, the thick plate main deformation structural component specimen includes a thin plate main deformation structural component specimen, a second cupping specimen, a plane strain specimen, and an axisymmetric round bar tensile specimen.

[0011] Furthermore, the first single-pull specimen is designed according to the method of GB / T228.1-2010, and the first cup-convex specimen and the second cup-convex specimen are designed according to the method of GB / T15825.8-2008.

[0012] Furthermore, the stress triaxiality of the first shear specimen is 0, the stress triaxiality of the first single tension specimen is 0.333, the stress triaxiality of the first R10 notch specimen is 0.48, the stress triaxiality of the first R5 notch specimen is 0.577, and the stress triaxiality of the first cupping specimen is 0.666.

[0013] Furthermore, the Lode angle parameter of the second cup-convex specimen is -1, the Lode angle parameter of the plane strain specimen is 0, and the Lode angle parameter of the axisymmetric round rod tensile specimen is 1.

[0014] Furthermore, the second cup-convex specimen includes a 70 mm wide cup-convex specimen and a 90 mm wide cup-convex specimen; the plane strain specimen includes an R1.5 plane strain specimen, an R3 plane strain specimen and an R6 plane strain specimen; the axisymmetric round bar tensile specimen includes a second round bar tensile specimen, an open R5 round bar tensile specimen, an open R7.5 round bar tensile specimen and an open R10 round bar tensile specimen.

[0015] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0016] 1. The present invention can fully consider the service characteristics of the material and design different complex stress state fracture performance test specimens for thin plates, thick plates and casting materials. The specimens have a simple shape and are convenient for dynamic testing, thereby being able to specifically reflect the service fracture stress state of the structural parts.

[0017] 2. The present invention simplifies the structure of the fracture performance test specimen under complex stress state, facilitates sampling on raw materials and parts, is suitable for promotion, and the specimen can be subjected to dynamic testing while meeting the requirements of static testing. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic flow chart of a method for designing a specimen for testing fracture properties of a material under a complex stress state in one embodiment;

[0019] Figure 2 This is a rendering of the stress state of the front longitudinal beam of a vehicle after a frontal collision in one embodiment;

[0020] Figure 3 This is a diagram showing the stress state of the A-pillar of a car after a 25% offset collision in one embodiment;

[0021] Figure 4 This is a rendering of the stress state of the B-pillar of a car after a side collision in one embodiment;

[0022] Figure 5 for Figure 2 Stress triaxiality interval distribution diagram of the front longitudinal beam at the initial and final stages of deformation;

[0023] Figure 6 for Figure 3 The stress triaxiality interval distribution diagram of the A-pillar at the initial and final stages of deformation;

[0024] Figure 7 for Figure 4 Stress triaxiality interval distribution diagram of the B-pillar at the initial and final stages of deformation;

[0025] Figure 8 This is a diagram showing the stress state of an aluminum alloy wheel in a frontal collision according to an embodiment;

[0026] Figure 9 The specimen types corresponding to different stress triaxiality and Lode angle parameters in one embodiment;

[0027] Figure 10 is a schematic structural diagram of a first shear specimen in one embodiment;

[0028] Figure 11 Schematic diagram of the structure of a first single-pull specimen in one embodiment;

[0029] Figure 12 Schematic diagram of the structure of the first R10 notch specimen in one embodiment;

[0030] Figure 13 Schematic diagram of the structure of the first R5 notch specimen in one embodiment;

[0031] Figure 14 Schematic diagram of the structure of a first cup-convex specimen in one embodiment;

[0032] Figure 15 Schematic diagram of the structure of a 70mm wide cupping specimen in one embodiment;

[0033] Figure 16 Schematic diagram of the structure of a 90mm wide cup convex specimen in one embodiment;

[0034] Figure 17 Schematic diagram of the structure of an R1.5 plane strain specimen in one embodiment;

[0035] Figure 18 Schematic diagram of the structure of an R3 plane strain specimen in one embodiment;

[0036] Figure 19 Schematic diagram of the structure of an R6 plane strain specimen in one embodiment;

[0037] Figure 20 Schematic diagram of the structure of a second round bar tensile specimen in one embodiment;

[0038] Figure 21 Schematic diagram of the structure of an open R5 round bar tensile specimen in one embodiment;

[0039] Figure 22 Schematic diagram of the structure of an open R7.5 round bar tensile specimen in one embodiment;

[0040] Figure 23 Schematic diagram of the structure of an open R10 round rod tensile specimen in one embodiment. DETAILED DESCRIPTION

[0041] Before describing the specific embodiments of the present invention, the research and development background of the present invention is described as follows:

[0042] The present invention is mainly developed based on the actual material fracture performance test process. During the service process of structural materials, due to the variability of the service environment, their service process is accompanied by the characteristics of complex stress states. The so-called complex stress state means that the stress state of the material is not simply pure tension or pure shear, but a composite stress state of three principal stresses. The complex stress state of the material is often characterized by stress triaxiality η and Lode angle parameter ξ, and their values ​​are between -1 and 1. When the stress triaxiality value is negative, it indicates compression, and when it is positive, it indicates tension. The calculation formula is as follows:

[0043]

[0044]

[0045] Where σ1, σ2, and σ3 are the first, second, and third principal stresses, respectively; I1 is the first stress invariant; J2 and J3 are the second and third strain deviator invariants, respectively. Under plane stress, where only two-dimensional principal stresses exist and the third principal stress is zero, the stress triaxiality η and the Lode angle parameter ξ can be converted to each other as shown in the following formula:

[0046]

[0047] For plate structural parts with a thickness of less than 3 mm, plane stress shell elements are often used for calculation in simulation. This belongs to a plane stress state, and its stress state only needs to be characterized by η. For thicker plates, castings and other structural parts, solid elements are often used for calculation in simulation. This belongs to a three-dimensional stress state, and its stress state needs to be characterized by both η and ξ.

[0048] To predict the fracture behavior of structural materials during service, it is necessary to develop high-precision fracture models that consider stress state characteristics, such as Johnson-Cook, Gissmo, MMC, and DIEM. Complex stress state fracture performance testing is the foundation for developing high-precision fracture models and provides the data support. Complex stress state fracture performance test specimens are a prerequisite for experimental testing.

[0049] The design of specimens for testing fracture properties under complex stress states is quite difficult. The designed specimens must meet several requirements: (1) The specimens can reflect the complex stress state characteristics of the material; (2) The specimens must be easy to sample and test, that is, they can be processed using conventional tensile specimens such as wire cutting, and can be tested on conventional equipment such as tensile testing machines; (3) During the test, the strain of the specimen must be concentrated in the measurement area; (4) During the test, the η and ξ in the measurement area change little, that is, they are relatively stable; (5) During the test, the crack initiation position must be in the measurement area.

[0050] In order to make the present invention more clearly understood, the present invention will be further described in detail below through specific embodiments in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0051] like Figure 1 As shown, a method for designing a specimen for testing the fracture properties of a material under a complex stress state is provided, comprising the following steps:

[0052] Step S1: Analyze the main deformed structural components of the target structure under the service limit state, obtain the stress triaxiality distribution and Lode angle parameter distribution of the main deformed structural components before and after deformation, and perform service stress state analysis of the target structure based on the stress triaxiality distribution and Lode angle parameter distribution.

[0053] Among them, when the thickness of the main deformed structural parts is less than 3mm, stress triaxiality is used to analyze the stress state of the structural material; when the thickness of the main deformed structural parts is greater than or equal to 3mm, the service stress state of the material structure is analyzed in combination with stress triaxiality and Lode angle parameters.

[0054] In one embodiment, taking an automobile safety structural component with a thickness of less than 3mm as an example, the extreme service conditions are frontal collision, 25% offset collision and side collision. In the frontal collision condition, the front longitudinal beam is the main deforming structural component; in the 25% offset collision, the A-pillar is the main deforming structural component; in the side collision, the B-pillar is the main deforming structural component. The stress state of each structural component under extreme service conditions is as follows: Figures 2 to 4 The front longitudinal beam, A-pillar and B-pillar are all plates with a thickness of less than 3 mm, so the stress state only needs to be characterized by stress triaxiality, as shown in Figures 5 to 7 As shown in Figure 2, the stress triaxiality range distribution of the front longitudinal beam, A-pillar and B-pillar before and after deformation is shown.

[0055] Depend on Figures 2 to 4 It can be seen that under various extreme working conditions, as the structural parts deform, the stress triaxiality values ​​in different areas of the structural parts are different, and the stress triaxiality values ​​are between -0.67 and 0.67, indicating that the structural parts are subjected to both compression and tension. Figures 5 to 7 It can be seen that under various extreme conditions, from the initial to the final stages of deformation, the stress triaxiality of the structural component clusters towards the high stress triaxiality range, 0.3 to 0.67. This clustering increases with increasing deformation. When the structural component undergoes bending deformation, the stress triaxiality values ​​before fracture often converge around 0.577.

[0056] In another embodiment, taking a cast aluminum alloy wheel as an example, in a frontal collision condition, its stress state is as follows: Figure 8As shown in the figure, it can be seen that with the deformation of the wheel, the stress triaxiality and Lode angle parameter values ​​in different areas are different, all between -1 and 1.

[0057] Step S2: Based on the service stress state analysis of the target structure, combined with the values ​​of stress triaxiality and Lode angle parameters, and the test conditions of material fracture performance, a simulation method is used to design the main deformation structure component specimens.

[0058] like Figure 9 As shown in the figure, for thin plates less than 3 mm thick, the design of specimens for the primary deformation components of the thin plate is based on the service stress triaxiality analysis of the structural component. Since compressive fracture failure is not considered for metal plates, the designed specimen stress triaxiality value should be greater than or equal to 0. Therefore, the primary deformation components of the thin plate can include pure shear specimens, notched specimens with stress triaxiality values ​​between 0.333 and 0.577, and cupped specimens with a stress triaxiality value of 0.666.

[0059] According to the definition of stress triaxiality, when the stress triaxiality is 0, it indicates a pure shear stress state; when the stress triaxiality is 0.333, it indicates a single tensile stress state; and when the stress triaxiality is 0.666, it indicates a double tensile stress state.

[0060] For castings and thick plates with a thickness greater than or equal to 3mm, specimens with Lode parameters of -1, 0, and 1 corresponding to different stress triaxialities, as well as flat plate specimens, are designed. Based on the values ​​of stress triaxiality and the Lode angle parameter, combined with the service stress state distribution of the structural component, specimens for the main deformation structures of the thick plate are designed. Therefore, specimens for the main deformation structures of the thick plate can include cupping specimens with a Lode angle parameter of -1, plane strain specimens with a Lode angle parameter of 0, axisymmetric round bar tensile specimens with a Lode angle parameter of 1, and flat plate specimens identical to those for the main deformation structures of the thin plate.

[0061] Single-tension specimens can be designed with reference to GB / T228.1-2010 (Metallic Materials - Tensile Testing - Part 1: Room-Temperature Test Methods), while cupping specimens can be designed directly with reference to GB / T15825.8-2008 (Sheet Metal Formability and Test Methods - Part 8: Guide for Determination of Forming Limit Diagrams (FLD)). Shear, notched, plane strain, and axisymmetric round bar tensile specimens require simulation to determine their final dimensions, with initial geometric dimensions obtained through CAD drawing.

[0062] Step S3: Based on the main deformed structural component specimens and test conditions, a fracture performance test simulation of the target structure is performed, and the stress state and strain change of the specimens are obtained according to the simulation results.

[0063] Specifically, the main deformed structural component specimens include cupped specimens and non-cupped specimens. Cupping equipment and cupping test conditions are used to perform fracture tests on the cupped specimens. When simulating the fracture performance test, the stress state and strain changes of the cupped specimens are analyzed. Conventional tensile testing equipment and corresponding test conditions are used to perform fracture tests on non-cupped specimens. When simulating the fracture performance test, the stress state and strain changes of the non-cupped specimens are analyzed.

[0064] When using conventional tensile testing equipment for testing, one end of the non-cupping specimen is fixed and the other end is loaded. Referring to the test conditions of the quasi-static unidirectional tensile test, the fracture performance test simulation of the non-cupping specimen is carried out to analyze the stress state and strain distribution of the non-cupping specimen.

[0065] To facilitate testing, the designed non-cupping specimens need to be able to be tested on conventional tensile testing equipment. Therefore, non-cupping specimens are set as symmetrical specimens. Cupping specimens are tested using cupping equipment and do not need to be symmetrical specimens.

[0066] Step S4: Optimize the sample size according to the stress state and strain change until the strain of the sample is concentrated in the measurement area and the values ​​of the stress triaxiality and Lode angle parameters in the measurement area are stable, thereby obtaining the optimal sample size of the main deformed structural component.

[0067] According to the stress state and strain change of each specimen, the specimen size is continuously optimized. When the strain of the specimen is concentrated in the measurement area, and the values ​​of the stress triaxiality and Lode angle parameters in the measurement area change little and tend to be stable, the optimal specimen size is obtained.

[0068] In this embodiment, by analyzing the main deformed structural members of the target structure under the service limit state, the stress triaxiality distribution and Lode angle parameter distribution of the main deformed structural members before and after deformation are obtained. Based on the stress triaxiality distribution and Lode angle parameter distribution, the service stress state analysis of the target structure is performed. Based on the service stress state analysis of the target structure, the main deformed structural member specimens are designed using a simulation method in combination with the values ​​of the stress triaxiality and Lode angle parameters, and the test conditions of the material fracture performance. Based on the main deformed structural member specimens and the test conditions, a fracture performance test simulation of the target structure is performed. Based on the simulation results, the stress state and strain change of the specimen are obtained to optimize the specimen size until the strain of the specimen is concentrated in the measurement area and the values ​​of the stress triaxiality and Lode angle parameters in the measurement area are stable, that is, the optimal main deformed structural member specimen size is obtained. This fully considers the service characteristics of the material and designs different complex stress state fracture performance test specimens for thin plates, thick plates, and cast materials. The specimens have a simple shape and are convenient for dynamic testing, thereby being able to specifically reflect the service stress state and fracture performance of the structural member.

[0069] In one embodiment, Figures 10 to 23 As shown, according to the above method, several material fracture performance test specimens under complex stress states were obtained. When the main deforming structural member is a thin plate with a thickness of less than 3mm, the thin plate main deforming structural member specimens include a first shear specimen, a first single tension specimen, a first R10 notch specimen, a first R5 notch specimen, and a first cupping specimen; when the main deforming structural member is a thick plate or cast material with a thickness greater than or equal to 3mm, the thick plate main deforming structural member specimens include a thin plate main deforming structural member specimen, a second cupping specimen, a plane strain specimen, and an axisymmetric round bar tensile specimen. Of course, the specimens claimed for protection in this application are not limited to the above specimens, but all specimens that can be obtained by the above method.

[0070] Specifically, since thin plate materials do not need to consider compressive fracture failure and are in a plane stress state, the service stress state of the structural component only needs to be characterized by stress triaxiality. Based on this, the service stress state of the thin plate can be determined by designing the stress triaxiality of the first shear specimen, the first single-tension specimen, the first R10 notch specimen, the first R5 notch specimen, and the first cupping specimen.

[0071] The stress state of cast materials and thick plates greater than or equal to 3mm is three-dimensional, requiring a combination of stress triaxiality and Lode angle parameters to characterize the structural component's service stress state. Therefore, stress triaxiality can be determined by designing a specimen identical to the primary deformation specimen for the thin plate. Simultaneously, a second cupping specimen, a plane strain specimen, and an axisymmetric round bar tensile specimen can be designed to determine the structural component's Lode angle parameters, thereby fully reflecting the structural component's service stress state.

[0072] Among them, the stress triaxiality of the first shear specimen is 0, the stress triaxiality of the first single tension specimen is 0.333, the stress triaxiality of the first R10 notch specimen is 0.48, the stress triaxiality of the first R5 notch specimen is 0.57, and the stress triaxiality of the first cupping specimen is 0.666.

[0073] Among them, the Lode angle parameter of the second cup-convex specimen is -1, the Lode angle parameter of the plane strain specimen is 0, and the angle parameter of the axisymmetric round bar tensile specimen is 1.

[0074] Among them, the second cup-convex specimen includes a 70mm wide cup-convex specimen and a 90mm wide cup-convex specimen; the plane strain specimens include R1.5 plane strain specimens, R3 plane strain specimens and R6 plane strain specimens; the axisymmetric round bar tensile specimens include the second round bar tensile specimen, the open R5 round bar tensile specimen, the open R7.5 round bar tensile specimen and the open R10 round bar tensile specimen.

[0075] In this embodiment, the above-mentioned specimens can be used to conduct complex stress state fracture performance tests on thin plates, thick plates or structural parts of casting materials, and can reflect the service stress state and fracture performance of the material.

[0076] The above contents are further detailed descriptions of the present invention in conjunction with specific embodiments, and the specific implementation of the present invention cannot be considered to be limited to these descriptions. For those skilled in the art of the present invention, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all of these should be considered to fall within the scope of protection of the present invention.

Claims

1. A method for designing a specimen for testing material fracture properties under complex stress states, characterized in that: The following steps are involved: Analyze the main deformed structural components of the target structure under the service limit state, obtain the stress triaxiality distribution and Lode angle parameter distribution of the main deformed structural components before and after deformation, and perform service stress state analysis of the target structure based on the stress triaxiality distribution and Lode angle parameter distribution; Based on the service stress state analysis of the target structure, combined with the values ​​of stress triaxiality and Lode angle parameters, and the test conditions of material fracture performance, the simulation method is used to design the main deformation structure specimens; Conduct a fracture performance test simulation of the target structure based on the main deformed structural component specimens and test conditions, and obtain the stress state and strain change of the specimens based on the simulation results; The sample size is optimized according to the stress state and strain change until the strain of the sample is concentrated in the measurement area and the values ​​of the stress triaxiality and Lode angle parameters in the measurement area are stable, thereby obtaining the optimal sample size of the main deformed structural component.

2. The method for designing a specimen for testing material fracture properties under complex stress states according to claim 1, characterized in that: When the thickness of the main deformable structural member is less than 3 mm, stress triaxiality is used to perform service stress state analysis of the target structure; when the thickness of the main deformable structural member is greater than or equal to 3 mm, stress triaxiality and Lode angle parameters are combined to perform service stress state analysis of the target structure.

3. The method for designing a specimen for testing material fracture properties under complex stress states according to claim 2, characterized in that: The main deformed structural member specimens include cupped specimens and non-cupped specimens, and the non-cupped specimens are subjected to a fracture performance test using a tensile testing device; the cupped specimens are subjected to a fracture performance test using a cupping device; When using tensile testing equipment for testing, one end of the main deformed structural component specimen is fixed and the other end is loaded. According to the test conditions, the fracture performance test simulation of the main deformed structural component specimen is carried out to analyze the stress state and strain distribution of the main deformed structural component specimen.

4. The method for designing a specimen for testing material fracture properties under complex stress states according to claim 3, characterized in that: The non-cupping specimens are all set as symmetrical specimens.

5. A test specimen for testing material fracture properties under complex stress conditions, characterized in that: The method for designing test specimens for material fracture properties under complex stress states as described in any one of claims 1 to 4 is used to design the test specimens, including: when the main deformation structural member is a thin plate with a thickness of less than 3 mm, the thin plate main deformation structural member specimens include a first shear specimen, a first single tension specimen, a first R10 notch specimen, a first R5 notch specimen and a first cupping specimen; when the main deformation structural member is a thick plate or cast material with a thickness greater than or equal to 3 mm, the thick plate main deformation structural member specimens include a thin plate main deformation structural member specimen, a second cupping specimen, a plane strain specimen and an axisymmetric round bar tensile specimen.

6. The material fracture performance test specimen under complex stress state according to claim 5, characterized in that: The first single-pull specimen is designed according to the method of GB / T228.1-2010, and the first cup-convex specimen and the second cup-convex specimen are designed according to the method of GB / T15825.8-2008.

7. The material fracture performance test specimen under complex stress state according to claim 5, characterized in that: The stress triaxiality of the first shear specimen is 0, the stress triaxiality of the first single tension specimen is 0.333, the stress triaxiality of the first R10 notch specimen is 0.48, the stress triaxiality of the first R5 notch specimen is 0.577, and the stress triaxiality of the first cupping specimen is 0.

666.

8. The test specimen for testing material fracture properties under complex stress state according to claim 5, characterized in that: The Lode angle parameter of the second cup-convex specimen is -1, the Lode angle parameter of the plane strain specimen is 0, and the Lode angle parameter of the axisymmetric round bar tensile specimen is 1.

9. The test specimen for testing material fracture properties under complex stress state according to claim 5, characterized in that: The second cup-convex specimen includes a 70mm wide cup-convex specimen and a 90mm wide cup-convex specimen; the plane strain specimen includes an R1.5 plane strain specimen, an R3 plane strain specimen and an R6 plane strain specimen; the axisymmetric round bar tensile specimen includes a second round bar tensile specimen, an open R5 round bar tensile specimen, an open R7.5 round bar tensile specimen and an open R10 round bar tensile specimen.

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