A method, device, equipment and medium for determining load and stress of a cross-shaped biaxial tensile specimen

Abstract

The application discloses a cross-shaped biaxial tensile sample load and stress determination method and device, equipment and medium, applied to the material mechanics performance test technical field, in order to solve the problem that the load and real stress mapping is not accurate, based on the geometric parameters of the cross-shaped biaxial tensile sample, a finite element numerical model is constructed, and the model is parameterized by using the material constitutive parameters in different orientations; the biaxial tensile test process of the model is numerically simulated based on at least one loading ratio, the local stress component of the central region is determined based on the real stress and strain data under uniaxial tensile test; based on the local stress component combined with the corresponding biaxial load and displacement response data, the corresponding biaxial load is determined, and the biaxial load and displacement response data of the cross-shaped biaxial tensile sample are processed to obtain the real stress trajectory data of the central region. The load and real stress mapping accuracy is improved, and reliable data basis is provided for accurate characterization of biaxial yield characteristics.

Description

Technical Field

[0001] This invention relates to the field of material mechanical property testing technology, and in particular to a method, apparatus, equipment and medium for determining the load and stress of a cross-shaped biaxial tensile specimen. Background Technology

[0002] During service, engineering structures (such as pipelines, pressure vessels, marine and ship structures, and energy equipment) are often subjected to the coupled effects of multiple factors, including internal pressure, axial loads, bending, temperature differences, and residual stresses. This can easily lead to significant biaxial or even multiaxial stress states in localized areas. Because the yield behavior, strain path effects, and anisotropic response of materials under multiaxial loading conditions differ significantly from those under uniaxial tension conditions, relying solely on yield strength and hardening curves obtained from uniaxial tension is insufficient to accurately characterize the shape and orientation of the yield surface under complex stress states. This negatively impacts the reliability of safety margin assessments, ultimate bearing capacity analyses, and finite element simulation predictions for engineering structures. Therefore, obtaining yield characteristic parameters of materials under biaxial stress states and establishing biaxial yield data that can be used for constitutive model calibration has become a critical requirement for material characterization and engineering applications.

[0003] Among existing multiaxial performance characterization methods, the cross-shaped biaxial tensile test has become an important scheme for studying the multiaxial yield characteristics of plate and pipe materials because it can apply controllable loads or displacements in two orthogonal directions and achieve different biaxial loading ratios. In engineering, it is often used in conjunction with structural designs such as center thinning and loading arm slotting to obtain deformation information in the central region using strain gauges or digital image correlation (DIC) technology. However, in this test, the geometric non-uniformity of the cross-shaped specimen causes the loading arm and transition area to share the load, resulting in a load diversion effect. This leads to problems such as difficulty in accurately obtaining the true stress and a mismatch between the true stress ratio and displacement ratio in the central region, resulting in a deviation between the measured load-displacement response and the true stress response in the central measurement area of ​​the specimen. Summary of the Invention

[0004] The purpose of this invention is to provide a method, apparatus, electronic device, and computer-readable storage medium for determining the load and stress of a cross-shaped biaxial tensile specimen. During use, these methods can improve the accuracy of the mapping between load and actual stress, providing a reliable data foundation for the accurate characterization of biaxial yield characteristics.

[0005] To address the aforementioned technical problems, the embodiments of the present invention provide the following technical solutions: This invention provides a method for determining the load and stress of a cross-shaped biaxial tensile specimen, comprising: Obtain biaxial load and displacement response data of a cross-shaped biaxial tensile specimen under at least one loading ratio; A finite element numerical model is constructed based on the geometric parameters of the cross-shaped biaxial tensile specimen, and the material constitutive parameters under different orientations are used to assign parameter values ​​to the finite element numerical model. The biaxial tensile test process of the finite element numerical model is numerically simulated based on at least one loading ratio, and the local stress components in the central region during the numerical simulation process are determined based on the actual stress and strain data obtained in the uniaxial tensile test. Based on the local stress components in the central region during the numerical simulation process, and combined with the biaxial load and displacement response data under the loading ratio, the biaxial load corresponding to the local stress components in the central region is determined. Based on the local stress components and corresponding biaxial loads in the central region, the biaxial load and displacement response data are processed to obtain the true stress trajectory data of the central region.

[0006] In one embodiment, before acquiring biaxial load and displacement response data of the cross-shaped biaxial tensile specimen at at least one loading ratio, and before acquiring full-field strain data of the central region of the cross-shaped biaxial tensile specimen, the method further includes: Obtain the actual stress and strain data of the target material under different orientations; Obtain the constitutive parameters of the target material under different orientations; wherein the actual stress and strain data are obtained by performing uniaxial tensile tests on the target material in the corresponding orientations, and the cross-shaped biaxial tensile specimen is a portion cut from the target material.

[0007] In one implementation, the method further includes: Obtain full-field strain data of the central region of the cross-shaped biaxial tensile specimen under at least one loading ratio; Therefore, before performing numerical simulation of the biaxial tensile test process of the finite element numerical model based on at least one loading ratio, the method further includes: The finite element numerical model was verified using full-field strain data from the central region of a cross-shaped biaxial tensile specimen, and the next step was performed after the verification was successful.

[0008] In one embodiment, determining the local stress components in the central region during the numerical simulation process based on the actual stress and strain data obtained from the uniaxial tensile test includes: Obtain the first unit volume equivalent plastic work density at the uniaxial yield state obtained in the uniaxial tensile test; Obtain the second unit volume equivalent plastic work density of the central region during the loading evolution process corresponding to the loading ratio in the numerical simulation process; When the second unit volume equivalent plastic work density reaches the first unit volume equivalent plastic work density, the local stress components of the central region of the numerical model at the current moment are determined.

[0009] In one embodiment, determining the biaxial load corresponding to the local stress components of the central region based on the local stress components in the central region during the numerical simulation process, combined with the biaxial load and displacement response data under the loading ratio, includes: Based on the current moment corresponding to the local stress component, determine the first displacement of the numerical model at the current moment; Based on the biaxial load and displacement response data, determine the biaxial load corresponding to the first displacement.

[0010] In one embodiment, based on the local stress components of the central region and the corresponding biaxial load, the biaxial load and displacement response data are processed to obtain the true stress trajectory data of the central region, including: Based on the local stress components and corresponding biaxial loads in the central region, a mapping relationship between the local stress components and the biaxial loads is established, and the load and stress conversion coefficients corresponding to the corresponding loading ratios under the geometric parameters are obtained. Continuous load data is obtained based on biaxial load and displacement response, and the continuous load data is converted into real stress trajectory data of the central region using the load and stress conversion coefficient.

[0011] In one embodiment, the different orientations include at least the rolling direction of the material, the transverse direction, and the direction at a predetermined angle to the rolling direction.

[0012] In one implementation, the method further includes: Based on the actual stress trajectory, determine the biaxial yield strength or biaxial yield characteristic parameter of the target material at the loading ratio.

[0013] Another aspect of the present invention provides a device for determining the load and stress of a cross-shaped biaxial tensile specimen, comprising: The first acquisition module is used to acquire biaxial load and displacement response data of a cross-shaped biaxial tensile specimen under at least one loading ratio. The construction module is used to construct a finite element numerical model based on the geometric parameters of the cross-shaped biaxial tensile specimen, and to assign parameter values ​​to the finite element numerical model using material constitutive parameters under different orientations. The simulation module is used to perform numerical simulation of the biaxial tensile test process of the finite element numerical model based on at least one loading ratio, and to determine the local stress components in the central region during the numerical simulation process based on the actual stress and strain data obtained in the uniaxial tensile test. The first determining module is used to determine the biaxial load corresponding to the local stress components in the central region based on the local stress components in the central region during the numerical simulation process, combined with the biaxial load and displacement response data under the loading ratio. The processing module is used to process the biaxial load and displacement response data based on the local stress components of the central region and the corresponding biaxial load, so as to obtain the true stress trajectory data of the central region.

[0014] Another aspect of the present invention provides an electronic device, comprising: Memory, used to store computer programs; A processor is used to execute the computer program to implement the steps of the method for determining the load and stress of a cross-shaped biaxial tensile specimen as described above.

[0015] In another aspect, the present invention provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps of the method for determining the load and stress of a cross-shaped biaxial tensile specimen as described above.

[0016] As can be seen from the above technical solutions, the embodiments of the present invention have the following advantages: This invention provides a method for determining the load and stress of a cross-shaped biaxial tensile specimen, comprising: acquiring biaxial load and displacement response data of the cross-shaped biaxial tensile specimen under at least one loading ratio; constructing a finite element numerical model based on the geometric parameters of the cross-shaped biaxial tensile specimen, and assigning parameter values ​​to the finite element numerical model using material constitutive parameters under different orientations; performing numerical simulation of the biaxial tensile test process of the finite element numerical model based on at least one loading ratio, and determining the local stress components in the central region during the numerical simulation process based on the actual stress and strain data obtained in the uniaxial tensile test; determining the biaxial load corresponding to the local stress components in the central region based on the local stress components in the central region during the numerical simulation process, combined with the biaxial load and displacement response data under the loading ratio; and processing the biaxial load and displacement response data based on the local stress components in the central region and the corresponding biaxial load to obtain the actual stress trajectory data of the central region.

[0017] Therefore, this application obtains biaxial load and displacement response data of a cross-shaped biaxial tensile specimen and constructs a finite element numerical model based on the specimen's geometric parameters. Simultaneously, it assigns values ​​to the model using material constitutive parameters calibrated from uniaxial tensile tests with different orientations. This quantitatively reproduces the load diversion effect of the loading arm and transition zone in the numerical simulation. Furthermore, by combining numerical simulation with actual stress and strain data, the local stress components in the central region are obtained, effectively eliminating the load diversion effect caused by the geometric non-uniformity of the cross-shaped biaxial tensile specimen. This solves the problem in the prior art where the actual stress in the center is difficult to obtain accurately due to the load being shared by the loading arm and transition zone. This application further determines the biaxial load corresponding to the local stress components in the center based on the biaxial load and displacement response data under the loading ratio, so that the actual stress and displacement in the central region match. Then, based on the local stress components and the corresponding biaxial load, the experimentally measured continuous load data is converted into the actual stress trajectory in the central region, improving the accuracy of the load-to-actual stress mapping and providing a reliable data basis for the accurate characterization of biaxial yield characteristics under any loading ratio.

[0018] Furthermore, the present invention also provides a corresponding implementation device, electronic device, and computer-readable storage medium for determining the load and stress of a cross-shaped biaxial tensile specimen, which further makes the method more practical. The device, electronic device, and computer-readable storage medium have corresponding advantages. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the prior art and embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A schematic flowchart illustrating a method for determining the load and stress of a cross-shaped biaxial tensile specimen provided in an embodiment of the present invention; Figure 2 A flowchart illustrating another method for determining the load and stress of a cross-shaped biaxial tensile specimen provided in an embodiment of the present invention; Figure 3 A geometrical schematic diagram of a centrally thinned cross-shaped specimen provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of a finite element model of a cross-shaped specimen provided in an embodiment of the present invention; Figure 5 A stress-strain relationship diagram before and after geometric correction is provided for an embodiment of the present invention; Figure 6A material yield trajectory comparison diagram with marked biaxial measurement points provided in an embodiment of the present invention; Figure 7 A schematic diagram of a device for determining the load and stress of a cross-shaped biaxial tensile specimen provided in an embodiment of the present invention; Figure 8 This is a schematic diagram of the structure of an electronic device provided in an embodiment of the present invention; Figure 9 This is a schematic diagram of the structure of a computer storage medium provided in an embodiment of the present invention. Detailed Implementation

[0021] This invention provides a method, apparatus, electronic device, and computer-readable storage medium for determining the load and stress of a cross-shaped biaxial tensile specimen. During use, it can improve the accuracy of the mapping between load and actual stress, and provide a reliable data basis for the accurate characterization of biaxial yield characteristics.

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] It should be noted that, due to the differences in yield behavior, strain path effects, and anisotropic response of materials under multiaxial loading compared to uniaxial tensile conditions, relying solely on yield strength and hardening curves obtained under uniaxial tension is insufficient to accurately characterize the yield surface shape and orientation correlation of materials under complex stress states. This can affect the reliability of structural safety margin assessment, ultimate bearing capacity analysis, and finite element simulation predictions. Therefore, obtaining yield characteristic parameters of materials under biaxial stress states and establishing biaxial yield data that can be used for constitutive model calibration has become a key requirement for material characterization and engineering applications.

[0024] Multiaxial performance characterization methods in related technologies include sheet bulging tests, pipe internal pressure expansion tests, and biaxial tensile tests on flat cruciform specimens. Among these, the cruciform biaxial tensile specimen has become an important experimental scheme for studying the multiaxial yield characteristics of sheet / pipe materials because it can apply controllable loads or displacements in two orthogonal directions and achieve different biaxial loading ratios within a certain range. To promote biaxial plastic deformation in the central region, engineering often employs structural designs such as central thinning and slotted loading arms, and uses strain gauges or digital image correlation (DIC) technology to obtain deformation information in the central region.

[0025] However, in a cross-shaped biaxial tensile test, the load-displacement response measured by the testing machine is usually not equivalent to the true stress response in the central measurement area of ​​the specimen. This is mainly because the cross-shaped specimen exhibits geometric inhomogeneity (differences in thickness / width between the central thinned area and the loading arm, rounded transitions, slotted structures, etc.). The loading arm and transition area share some of the load and alter the stress state of the central region, creating a significant load diversion effect. This effect leads to the following problems: 1) Directly converting the test load into nominal stress using the nominal cross-sectional area makes it difficult to reflect the true stress components in the central measurement area; 2) Under displacement ratio control conditions, the true stress ratio in the central region is not necessarily equal to the displacement ratio. The experimental state often does not meet the strict assumption of equibiaxial stress, resulting in the inapplicability or large error of the yield strength definition or equivalent treatment based on the premise of equibiaxial stress; 3) Even if the strain distribution of the entire central region is obtained through DIC, the strain information itself cannot directly give the stress components and yield stress point. It is necessary to combine the material constitutive relation and mechanical constraint conditions to invert the true stress state; 4) For anisotropic materials, the stress reconstruction in the central region is also closely related to the yield strength, r-value and hardening law related to the material orientation. If there is a lack of a stable and reusable load-stress mapping construction method, it will lead to strong uncertainty in the identification of biaxial yield points and parameter calibration.

[0026] Solutions to this problem include: arranging strain gauges in the central region and using simplified stress assumptions for estimation; correcting the nominal stress using empirical or analytical correction factors; or indirectly obtaining the central stress state by matching the load-displacement curve / strain field through finite element inversion. While these methods can improve the error of the nominal stress to some extent, they still generally have the following shortcomings: First, analytical or empirical correction often depends on specific specimen size and loading method, limiting its versatility; second, the inversion process relying solely on load-displacement curve fitting is easily affected by boundary conditions, friction, mesh, and initial material parameters, resulting in insufficient repeatability and robustness; third, it is difficult to achieve consistent calibration of the yield point under various biaxial loading ratios, easily introducing subjectivity in yield point selection; and fourth, it is difficult to simultaneously ensure a strict correspondence between experimentally measurable quantities (load, displacement, DIC strain field) and the true local stress state at the center, thus affecting the calibration accuracy and efficiency of biaxial yield characteristic parameters.

[0027] Therefore, there is an urgent need for a method that can establish a mapping relationship between the nominal load of the biaxial test and the local true stress in the central measurement area for cross-shaped biaxial tensile specimens, taking into account the effects of geometric non-uniformity and load shunting. This method would enable the stable determination of the biaxial yield strength and yield characteristics of the material under different biaxial loading ratios, and provide reliable input for the identification of parameters of anisotropic constitutive models and numerical simulation of engineering structures.

[0028] The following section will provide a detailed explanation and introduction to this technical solution. Please refer to [link / reference]. Figure 1 , Figure 1 This is a flowchart illustrating a method for determining the load and stress of a cross-shaped biaxial tensile specimen according to an embodiment of the present invention. The method includes the following steps S110 to S150.

[0029] S110: Obtain biaxial load and displacement response data of a cross-shaped biaxial tensile specimen at at least one loading ratio.

[0030] It should be noted that in this embodiment, a cross-shaped biaxial tensile specimen can be cut from the target material, and the specimen is geometrically designed according to a preset standard (e.g., ISO 16842). The specimen includes a central thinning region and load transfer grooves or unloading grooves on the four loading arms to reduce the constraint of the loading arms and promote uniform biaxial plastic deformation in the central region. The specimen is mounted on a biaxial tensile testing machine, and displacement control loading is set for any one of the preset loading ratios, for example, a displacement control loading with a loading ratio of 1:1 is set, and a corresponding loading rate (e.g., 0.02 mm / s) is set. The real-time load and displacement data of the loading arms are recorded simultaneously to obtain biaxial load and displacement response data corresponding to each loading ratio.

[0031] The loading ratio can include two forms: displacement control or load control. For example, the loading ratio can be any ratio in the range of 1:1 to 1:4.

[0032] S120: A finite element numerical model is constructed based on the geometric parameters of a cross-shaped biaxial tensile specimen, and the material constitutive parameters under different orientations are used to assign parameter values ​​to the finite element numerical model.

[0033] It is understood that, in the embodiments of this application, a finite element numerical model with completely consistent dimensions can be established based on the geometric parameters of the above-mentioned cross-shaped biaxial tensile specimen, and the model can be assigned values ​​using material constitutive parameters obtained from uniaxial tensile tests with different orientations. The material constitutive parameters may include, but are not limited to, elastic modulus, Poisson's ratio, hardening parameters determined by the actual stress-plastic strain curve, and anisotropic parameters used to describe the anisotropic yield criterion.

[0034] S130: Numerical simulation of the biaxial tensile test process of the finite element numerical model based on at least one loading ratio, and determination of the local stress components in the central region during the numerical simulation process based on the real stress and strain data obtained in the uniaxial tensile test.

[0035] It should be noted that, in this embodiment, after obtaining the constructed finite element numerical model, boundary conditions consistent with those in the experiment can be applied to the finite element numerical model for each of at least one loading ratio. Numerical simulations of biaxial tensile tests are then performed on the finite element numerical model to quantitatively reproduce the load diversion effect of the loading arm and transition zone. During the numerical simulation, the model's loading rate, boundary constraints, and loading ratio are strictly consistent with the physical experiment to ensure the comparability of the simulation results with the experimental results. In this embodiment, the local stress components in the central region of the finite element numerical model during the numerical simulation can be determined based on the true stress and strain data obtained from the uniaxial tensile test. This central region is the central thinning region. In practical applications, the unit volume equivalent plastic work density of the uniaxial yield state extracted from the uniaxial tensile test can be used as a reference index to accurately determine the local stress components in the central region during the numerical simulation.

[0036] S140: Based on the local stress components in the central region during the numerical simulation process, and combined with the biaxial load and displacement response data under the loading ratio, determine the biaxial load corresponding to the local stress components in the central region.

[0037] It should be noted that, in the embodiments of this application, after determining the local stress components in the central region during the numerical simulation process, it is necessary to further determine the biaxial load and displacement response data of the cross-shaped biaxial tensile specimen under the same loading ratio, and then find the biaxial load corresponding to the local stress components from the biaxial load and displacement response data, so as to establish the correspondence between the numerical simulation and the physical experiment.

[0038] S150: Based on the local stress components of the central region and the corresponding biaxial load, the biaxial load and displacement response data are processed to obtain the true stress trajectory data of the central region.

[0039] It is understood that, in the embodiments of this application, after obtaining the local stress components and corresponding biaxial loads of the central region, a mapping relationship between the local stress components and corresponding biaxial loads of the central region can be further established. Then, based on the mapping relationship, the entire biaxial load and displacement response data of the cross-shaped biaxial tensile specimen obtained under the same loading ratio are converted from load to stress, thereby obtaining the true stress trajectory of the central region during the entire loading process.

[0040] Therefore, this method effectively eliminates the load diversion effect caused by the geometric non-uniformity of the cruciform specimen, solves the problem in the prior art that the true stress in the center is difficult to obtain accurately due to the load sharing by the loading arm and transition area, and improves the accuracy of obtaining the true stress in the center region. At the same time, since this mapping relationship is based on the synchronous establishment of displacement rather than relying on the assumption of equal biaxial stress, it avoids the misjudgment of yield strength introduced by the mismatch between the true stress ratio in the center region and the applied displacement ratio, thus providing a reliable data basis for the accurate characterization of biaxial yield characteristics under arbitrary loading ratios.

[0041] Based on the above embodiments, the embodiments of this application will further explain and optimize the technical solution. Please refer to... Figure 2 The flowchart shows another method for determining the load and stress of a cross-shaped biaxial tensile specimen, which includes the following steps S210 to 280.

[0042] In one embodiment, before acquiring biaxial load and displacement response data of the cross-shaped biaxial tensile specimen at at least one loading ratio, and before acquiring full-field strain data of the central region of the cross-shaped biaxial tensile specimen, the method further includes: S210: Obtain the true stress and strain data of the target material under different orientations; obtain the material constitutive parameters of the target material under different orientations; wherein, the true stress and strain data are obtained by performing uniaxial tensile tests on the target material in the corresponding orientations, and the cross-shaped biaxial tensile specimen is a portion cut from the target material.

[0043] It should be noted that, in this embodiment, uniaxial tensile tests can be performed on the target material with different orientations, and the changes in the true stress and strain of the target material during the uniaxial tensile tests can be recorded to obtain the true stress and strain data of the target material under the corresponding orientation. Specifically, the true stress and strain data can be a true stress and strain curve; specifically, the true stress and strain data corresponding to each orientation can be obtained. Furthermore, the constitutive parameters of the target material under different orientations are determined. These constitutive parameters may include the elastic modulus, Poisson's ratio, hardening parameters determined by the true stress-plastic strain relationship, and parameters describing the anisotropic yielding behavior (i.e., anisotropic yield characteristic parameters). The uniaxial tensile tests on the target material with different orientations include at least the rolling direction, the transverse direction, and the direction at a preset angle (e.g., 45°) to the rolling direction. Additionally, in this application, the yield stress state determined by the 0.2% plasticity offset method in the uniaxial tensile test can be taken as the uniaxial yield state.

[0044] For example, an X52 pipe steel with an initial wall thickness of 11 mm can be selected. A portion of this pipe steel can be chosen as the target material, and standard uniaxial tensile specimens (i.e., the target material in this application) can be cut along the circumferential direction (CD, defined as the 0° reference direction), axial direction (AD, 90° direction), and diagonal direction (DD, 45° direction). In practical applications, to eliminate the influence of the wall thickness gradient, the specimens are all taken from the central layer of the pipe wall and thinned to 1 mm. Specifically, a uniaxial tensile test can be performed on the target material according to the ISO 6892 standard. Digital image correlation (DIC) technology can be used to obtain the full-field strain distribution information of the specimen in the gauge length region during the uniaxial tensile test. This full-field strain distribution information includes axial strain and transverse strain. Specifically, based on the load recorded by the testing machine and the strain data measured by DIC, the corresponding engineering stress-strain curves for each orientation can be calculated and further converted into true stress-strain curves (i.e., obtaining true stress and strain data). For example, the true stress-strain curve in the circumferential direction (CD direction) can also be selected as the benchmark for subsequent analysis. Then, based on the obtained actual stress and strain data under different orientations, the constitutive parameters of the target material under different orientations are determined. Among them, the elastic modulus can be 210 GPa and the Poisson's ratio can be 0.3.

[0045] S220: Obtain biaxial load and displacement response data of a cross-shaped biaxial tensile specimen under at least one loading ratio, wherein the biaxial load and displacement response are obtained by performing a biaxial tensile test on the cross-shaped biaxial tensile specimen under the corresponding loading ratio.

[0046] In other words, in this embodiment of the application, a cross-shaped biaxial tensile specimen can be cut from the target material (e.g., X52 pipe steel). The cross-shaped biaxial tensile specimen can be geometrically designed with reference to the ISO 16842 standard. It can include a central thinning region and load transfer grooves or load reduction grooves set on the four loading arms to reduce the constraint of the loading arms and promote uniform biaxial plastic deformation in the central region. Furthermore, all four loading arms can be provided with a slotted structure, which can be used to reduce the stiffness of the loading arms and weaken the load diversion effect, thereby improving the uniformity of biaxial deformation in the central thinning region.

[0047] The specimen is mounted on a biaxial tensile testing machine. For example, a displacement-controlled loading with a loading ratio of 1:1 and a loading rate of 0.02 mm / s can be set. Real-time load and displacement data of the loading arm are recorded simultaneously to obtain biaxial load and displacement response data corresponding to each loading ratio. Furthermore, when multiple loading ratios (such as 2:1, 1:2, 1:4, etc.) are required, the above process is repeated to obtain biaxial load-displacement response data for each loading ratio.

[0048] In this embodiment, a cross-shaped biaxial tensile test is used to obtain the load-displacement response of the material under biaxial stress, providing original experimental data for establishing the load-stress mapping relationship.

[0049] S230: Obtain full-field strain data of the central region of a cross-shaped biaxial tensile specimen under at least one loading ratio.

[0050] It should be noted that, in this embodiment of the application, while performing a biaxial tensile test on the cruciform biaxial tensile specimen, digital image correlation (DIC) technology can be used to simultaneously acquire full-field strain data of the central thinning region (i.e., the central region) of the cruciform biaxial tensile specimen. Specifically, the DIC system can calculate the full-field strain distribution of the central region of the cruciform biaxial tensile specimen at different loading moments in real time during the biaxial tensile test, including axial strain, transverse strain, and shear strain. This full-field strain data records the complete strain evolution process of the central region from elastic deformation to plastic yielding. Due to the anisotropic strength of the material, the measured circumferential load is significantly higher than the axial load, and correspondingly, the strain field in the central region also exhibits anisotropic distribution characteristics.

[0051] The full-field strain data obtained by DIC in this embodiment can be used to verify the accuracy of the subsequent finite element numerical model, and can also be used to help locate the uniform deformation region in the center, so as to ensure that the selected representative element can truly reflect the average stress state of the central region.

[0052] S240: A finite element numerical model is constructed based on the geometric parameters of a cross-shaped biaxial tensile specimen, and the material constitutive parameters under different orientations are used to assign parameter values ​​to the finite element numerical model.

[0053] It is understood that, in this embodiment of the application, a finite element numerical model with completely consistent dimensions can be established using finite element software based on the geometric parameters of the aforementioned cross-shaped biaxial tensile specimen. This finite element numerical model can be defined using the Hill48 anisotropic yield criterion. The model element type is a solid element, and the size of the central observation area element (i.e., the central region) is no larger than a preset size (e.g., 0.5 × 0.5 mm) to ensure the accuracy of stress gradient capture. When establishing the finite element numerical model, a 1 / 4 or 1 / 8 simplified model can be set according to the symmetry condition, and the loading conditions are completely synchronized with the biaxial tensile test. Then, the model is assigned values ​​using material constitutive parameters obtained from uniaxial tensile tests with different orientations, including the elastic modulus (e.g., 210 GPa), Poisson's ratio (e.g., 0.3), hardening parameters determined by the actual stress-plastic strain curve (e.g., Swift, Voce model coefficients), and anisotropic yield characteristic parameters (e.g., R) used to describe the anisotropic yield criterion. 11 , R 22 , R 12 wait).

[0054] In this application, the geometric parameters of the cross-shaped biaxial tensile specimen may include, but are not limited to, the diameter of the central thinning zone, the minimum thickness, the length and width of the loading arm, the location and size of the slot, and the radius of the transition fillet. The anisotropic yield characteristic parameters include the initial yield stress under different orientations, the anisotropic plastic strain ratio (r value), and the hardening criterion parameters.

[0055] In this embodiment of the application, by constructing a finite element numerical model that is completely consistent with the geometry of the real specimen and assigning anisotropic constitutive parameters calibrated by uniaxial tests, the model can quantitatively reproduce the load shunting effect of the loading arm and transition zone on the load, laying the foundation for the subsequent accurate extraction of local stress components.

[0056] It should also be noted that in practical applications, the anisotropic plastic strain ratio r can be calculated from the axial and transverse plastic strains within the gauge length region during the uniform plastic deformation stage of the material. The strain field within the gauge length region corresponding to this uniform plastic deformation stage is approximately uniformly distributed. The gauge length region is the area determined during the uniaxial tensile test of the target material. The specific calculation expression for the anisotropic plastic strain ratio r is as follows: ,in, ε l Indicates axial strain, ε w Indicates lateral strain, ε t This indicates strain in the thickness direction.

[0057] In addition, the hardening criterion parameters in this application embodiment can be determined in the following way: Specifically, the hardening criterion can be selected from one or more of the following models: power-law hardening model, Swift hardening model, Voce hardening model, or Multi-Voce hardening model. The hardening criterion parameters are obtained by fitting the true plastic strain determined by DIC with the true stress determined by uniaxial testing. The true plastic strain can be obtained based on axial strain and elastic strain. The specific expressions for each model are as follows: The expression for the power-law hardening model is: ; The expression for the Swift hardened model is: ; The expression for the Voce hardening model is as follows: ; The expression for the Multi-Voce hardening model is: .

[0058] in, Indicates flow stress, Represents equivalent plastic strain. C 1. C 2. C 3. C 4 and C 5 represents the undetermined coefficient in the hardening criterion.

[0059] In this embodiment, the actual plastic strain determined by DIC and the actual stress determined by uniaxial test can be fitted to obtain the specific values ​​of each undetermined coefficient in each hardening criterion model, thereby obtaining the hardening criterion parameters.

[0060] It should also be noted that the actual stress-plastic strain curves in this embodiment are fitted according to the hardening criterion and extrapolated to a preset upper limit of plastic strain to meet the needs of numerical simulation, wherein the preset upper limit of plastic strain is 0.8. Furthermore, the anisotropic yield characteristic parameters used for the Hill anisotropic yield criterion in this embodiment include R... 11 R 22 R 33 R 12 R 13 and R 23 These anisotropic yield characteristic parameters can be determined by calibrating the yield stress and r value for different orientations.

[0061] S250: The full-field strain data of the central region of the cross-shaped biaxial tensile specimen is used to verify the finite element numerical model. After the verification is passed, the biaxial tensile test process of the finite element numerical model is numerically simulated based on at least one loading ratio. Based on the real stress and strain data obtained in the uniaxial tensile test, the local stress components of the central region in the numerical simulation process are determined.

[0062] It should be noted that, in this embodiment of the application, after establishing and assigning values ​​to the finite element numerical model, the full-field strain data of the central region obtained in step S230 above can be used to verify the finite element model. Specifically, the same boundary conditions as those in the biaxial tensile test of the cross-shaped biaxial tensile specimen can be applied to the finite element model for trial calculation. The strain field of the central region obtained by simulation can be compared with the full-field strain data measured by DIC. When the degree of agreement between the two reaches a preset threshold (e.g., the average strain error is less than 5%, or the strain distribution trend is consistent), it can be determined that the finite element numerical model has passed verification. If the verification fails, the model parameters (such as boundary conditions, friction coefficient, or mesh density) are adjusted until the verification is passed, and a verified finite element numerical model is obtained.

[0063] Specifically, after verification, the same loading ratio (e.g., 1:1 displacement-controlled loading) as the biaxial tensile test of the cruciform biaxial tensile specimen was applied to the finite element numerical model, and the displacement boundary conditions consistent with the experiment were applied to conduct a numerical simulation of the biaxial tensile test process. Based on this, the local stress components in the central region during the numerical simulation were determined using the actual stress and strain data obtained from the uniaxial tensile test.

[0064] In one embodiment, the process of determining the local stress components in the central region during the numerical simulation based on the actual stress and strain data obtained from the uniaxial tensile test in S250 above may include: Obtain the first unit volume equivalent plastic work density at the uniaxial yield state obtained in the uniaxial tensile test; In the numerical simulation, the second unit volume equivalent plastic work density of the central region during the loading evolution process corresponding to the loading ratio is obtained. When the equivalent plastic work density per unit volume of the second unit volume reaches the equivalent plastic work density per unit volume of the first unit volume, the local stress components of the central region of the numerical model at the current moment are determined.

[0065] It should be noted that, in this embodiment, the first unit volume equivalent plastic work density at the uniaxial yield state can be extracted from the uniaxial tensile test. The first uniaxial yield state is the stress state corresponding to the yield determined by the 0.2% plasticity offset method in the uniaxial tensile test. In this embodiment, the unit volume equivalent plastic work density corresponding to this stress state is used as the first unit volume equivalent plastic work density, and this first unit volume equivalent plastic work density is used as a reference index.

[0066] For example, the CD direction can be selected as the energy benchmark, and the cumulative plastic work density in the CD direction at the 0.2% plastic offset (yield point) can be extracted as a reference index. σ ref Using the formula for calculating the plastic work density per unit volume, the plastic work density per unit volume (i.e., the reference index) w at this point is calculated. p ref The formula for calculating the plastic work density per unit volume is: ,in, This represents the true axial stress in a uniaxial tensile test along the CD direction. This represents the corresponding plastic strain. ε p 0.2% This indicates the plastic strain corresponding to the yield point determined using the 0.2% plastic offset method.

[0067] In the biaxial tensile test of a cruciform biaxial tensile specimen, the equivalent plastic work density per unit volume in the central region of the specimen is taken from a representative element located at the mid-thickness surface of the central thinning zone. That is, during the numerical simulation, the evolution data of the second equivalent plastic work density per unit volume of the representative element at the mid-thickness surface of the central thinning zone as a function of loading can be extracted. Specifically, the second equivalent plastic work density per unit volume can be obtained by combining the calculation formula of the second equivalent plastic work density with the cumulative calculation of the plastic work density from the stress tensor components and plastic strain increments of the central element during loading. This yields the plastic work density evolution curve of the geometric central element (i.e., the central region) of the central thinning zone. The calculation formula for the second equivalent plastic work density per unit volume is as follows: ,in, w p This represents the equivalent plastic work density per unit volume; Represents the components of the stress tensor; Represents the increment of the plastic strain tensor components; i and j These are tensor component subscripts used to indicate coordinate direction numbers when using a three-dimensional coordinate system. i ,j =1,2,3, corresponding to each coordinate direction. This relational expression defaults to handling repeated indices. i , j Summation is performed according to the tensor summation rules.

[0068] The second unit volume equivalent plastic work density is compared with the first unit volume equivalent plastic work density (reference index). When the second unit volume equivalent plastic work density first reaches or exceeds the first unit volume equivalent plastic work density, this moment is taken as the current moment. This current moment is also the yield benchmark moment, and the local stress components of the central thinning zone calculated by the finite element numerical model at this time are extracted.

[0069] It should be noted that, in this embodiment, the first unit volume equivalent plastic work density is used as a unified benchmark, which realizes the physical alignment of uniaxial yield and yield state under biaxial loading, and provides an objective and repeatable yield point identification scheme, which significantly improves the accuracy of biaxial yield stress determination.

[0070] S260: Based on the local stress components in the central region during the numerical simulation process, combined with the biaxial load and displacement response data under the loading ratio, determine the biaxial load corresponding to the local stress components in the central region.

[0071] It should be noted that, in this embodiment of the application, after determining the yield benchmark time and the local stress component of the central region corresponding to the yield benchmark time, the biaxial load corresponding to the local stress component can be further found from the test data (i.e., biaxial load and displacement response data) obtained from biaxial tensile tests under the same loading ratio. Specifically, the biaxial load corresponding to the local stress component can be determined based on displacement synchronization.

[0072] In one embodiment, the process of determining the biaxial load corresponding to the local stress components of the central region based on the local stress components in the central region during the numerical simulation process, combined with the biaxial load and displacement response data under the loading ratio, in step S260 above may include: Based on the current moment corresponding to the local stress component, determine the first displacement of the numerical model at the current moment; Based on the biaxial load and displacement response data, determine the biaxial load corresponding to the first displacement.

[0073] In other words, based on the yield benchmark time determined above (i.e., the current time), the model simulation displacement corresponding to the yield benchmark time can be read from the numerical simulation results, and this model simulation displacement can be recorded as the first displacement. D simThe simulated displacement in this model can be the applied displacement at the end of the loading arm, maintaining consistency with the displacement data recorded by the testing machine in physical experiments. Then, the biaxial load-displacement response data recorded through the physical biaxial tensile test includes the measured displacement by the testing machine at each moment during the entire loading process and the biaxial load value (e.g., circumferential load) under that displacement. P CD exp and axial load P AD exp In this biaxial load-displacement response data, the first displacement value is matched. D sim Displacement points with equal values ​​or within a certain allowable error range (e.g., relative displacement error not exceeding 1%) are identified, and the corresponding biaxial load value (e.g., circumferential load) at that displacement point is determined on the biaxial load-displacement curve obtained from the experiment. P CD exp and axial load P AD exp The biaxial load value is determined as the biaxial load quantity (i.e., the test load) corresponding to the local stress components in the central region. In other words, the biaxial load quantity is the macroscopic load value in two orthogonal directions recorded by the testing machine in the physical test when the cruciform specimen deforms to the same deformation level as the yield benchmark time in the numerical simulation.

[0074] In this embodiment, displacement synchronization is used as an objective and precisely measurable physical bridge to stably establish a one-to-one correspondence between the local stress components output by numerical simulation and the macroscopic load measured by physical experiments. This correspondence ensures that the subsequent calibration of the load-stress mapping coefficients is performed under the same material physical state (same deformation level), thereby eliminating calibration errors introduced by loading history or asynchronous deformation.

[0075] S270: Based on the local stress components of the central region and the corresponding biaxial load, the biaxial load and displacement response data are processed to obtain the true stress trajectory data of the central region.

[0076] It should be noted that after obtaining the local stress components of the central region and the corresponding biaxial load in the embodiments of this application, a mapping relationship between the two can be established, and the biaxial load data of the entire process can be converted using the mapping relationship to obtain the true stress trajectory of the central region throughout the entire loading process.

[0077] In one embodiment, the process in S270 above, which processes the biaxial load and displacement response data based on the local stress components of the central region and the corresponding biaxial load, to obtain the true stress trajectory data of the central region, may include: Based on the local stress components and corresponding biaxial loads in the central region, a mapping relationship between the local stress components and the biaxial loads is established, and the load and stress conversion coefficients corresponding to the corresponding loading ratios under the geometric parameters are obtained. Continuous load data is obtained based on biaxial load and displacement response, and load and stress conversion coefficients are used to convert the continuous load data into real stress trajectory data of the central region.

[0078] Specifically, a mapping relationship between local stress components and biaxial loads can be established based on the local stress components in the central region at the yield benchmark time and the corresponding biaxial loads, and the load-stress conversion coefficient under the current specimen geometry and corresponding loading ratio can be calibrated. In one implementation, this mapping relationship can be expressed as a linear proportional relationship; specifically, the aforementioned determined local stress components are obtained. σ sim and the corresponding biaxial load P exp Then, the cross-sectional area of ​​the central measuring region of the cross-shaped biaxial tensile specimen can be combined. A (Where, the length is calculated from the ends of the side grooves at both ends of the loading arm, and the thickness is calculated based on the minimum thickness of the central thinning zone.) The load-stress conversion factor is calibrated using the conversion factor relationship. k The conversion coefficient relationship is as follows: ,in, P exp The biaxial load obtained from the experiment, σ sim For the corresponding local stress components in the numerical simulation, A This indicates the cross-sectional area of ​​the central measurement zone.

[0079] It should also be noted that in practical applications, the nominal stress in the central region can be obtained by first determining the cross-sectional area A of the central region of the biaxial tensile specimen, combined with the biaxial load corresponding to the local stress components in the central region. This nominal stress = P exp / A, from which we can know that the conversion factor k is the ratio of the nominal stress to the local stress component in the central region.

[0080] In this embodiment, continuous load data can be further obtained from the biaxial load and displacement response obtained in the biaxial tensile test of the cross-shaped biaxial tensile specimen. This continuous load data is the nominal load. The continuous load data can be converted into the true stress trajectory data of the central region by combining the conversion coefficient obtained above, thereby realizing the conversion of the test nominal load into the true local stress in the center.

[0081] In addition, the biaxial yield characteristic parameters are expressed as the stress components at the yield benchmark ( It can be characterized and can be further used to construct an equivalent biaxial yield strength index. Used for characterizing, comparing, or plotting yield trajectories of biaxial yield properties.

[0082] Anisotropic yield property parameters R 11 , R 22 , R 33 , R 12 , R 13 and R 23 For thin sheet materials, under the assumption of plane stress, let R 11 =1, R 22 and R 33 The yield strength is determined by the ratio of transverse yield stress to rolling direction yield stress, and by the yield strength in the thickness direction and related ratios, respectively; or, by the plastic strain ratio in each orientation. r 0、 r 45 and r 90 Conversion: , , , , and by , , and Further conversion into isotropic yield characteristic parameters , r 0 indicates the plastic strain ratio when the orientation is circumferential (0°). r 45 This represents the plastic strain ratio at an orientation of 45°. r 90 The above represents the plastic strain ratio when the orientation is axial (90°). , , and The coefficient of the Hill48 yield function under plane stress conditions can be further converted into the corresponding anisotropic yield parameter by combining the yield stress ratio and thickness direction assumptions.

[0083] S280: Determine the biaxial yield strength or biaxial yield characteristic parameters of the target material under the loading ratio based on the actual stress trajectory.

[0084] It should be noted that, in this embodiment, after obtaining the true stress trajectory of the central region, the biaxial yield strength or biaxial yield characteristic parameters of the target material under the corresponding loading ratio are further determined based on the true stress trajectory. Specifically, the stress point on the true stress trajectory corresponding to the yield benchmark time can be determined based on the true stress trajectory, and the combination of each stress component at the stress point can be obtained as the biaxial yield strength under the corresponding loading ratio (e.g., 1:1).

[0085] When conducting biaxial tensile tests with at least two different loading ratios (e.g., 1:1, 2:1, 1:2, 1:4, etc.), the stress components at the yield benchmark time obtained under each loading ratio are plotted in stress space, and these discrete yield points are fitted or interpolated to obtain the complete biaxial yield trajectory (or yield surface) of the target material. This biaxial yield trajectory can be directly used to characterize the anisotropic yielding behavior of the material. Furthermore, the obtained biaxial yield strength or biaxial yield characteristic parameters can be used as input parameters for numerical simulation of engineering structures.

[0086] The following example illustrates this technical solution: For example, in this embodiment of the application, an X52 pipe steel with an initial wall thickness of 11 mm is used as the experimental object so as to construct a load-actual stress mapping relationship through the method provided in this application, so as to accurately identify its yield characteristics under multiaxial stress state.

[0087] First, standard tensile specimens are taken along the pipe's circumferential (CD, defined as the 0° reference direction), axial (AD, 90° direction), and diagonal (DD, 45° direction) directions. To eliminate the influence of wall thickness gradients, all specimens are taken from the central layer of the pipe wall and thinned to 1 mm. Specifically, uniaxial tensile tests can be performed according to ISO 6892 standard, and the full-field strain of the gauge length region or gauge length segment of the specimen is obtained using digital image correlation (DIC) technology. Then, based on the definition of anisotropy, the steady-state plastic strain ratios under the three characteristic orientations are determined. r 0 = 0.87 r 45 =0.87, r 90=0.96. The CD direction can be selected as the energy benchmark, and the cumulative plastic work density in the CD direction at the 0.2% plastic offset (yield point) can be extracted as a reference index. σ ref Using the formula for calculating the plastic work density per unit volume, the plastic work density per unit volume (i.e., the reference index) w at this point is calculated. p ref The formula for calculating the plastic work density per unit volume is: .

[0088] Calculations show that the first unit volume plastic work density corresponding to this embodiment is 0.6817 mJ / mm3.

[0089] Secondly, a cross-shaped sample can be cut from the aforementioned pipe steel (such as...). Figure 3 As shown in the image, the specimen has a double-sided arc-shaped thinning zone with a diameter of 8 mm at its center, and a minimum thickness of 1 mm at the center. The loading arm of the specimen has a laser-cut unloading groove to eliminate lateral stiffness constraints. Specifically, a displacement-controlled biaxial tensile test with a loading ratio of 1:1 can be selected. That is, the specimen can be mounted on a biaxial tensile testing machine, and a displacement-controlled loading with a loading ratio of 1:1 and a loading rate of 0.02 mm / s can be set. During the tensile test, the real-time load P of the loading arm is recorded synchronously. exp The displacement data was used, and the full-field strain evolution of the central region of the cruciform specimen was acquired using DIC. Due to strength anisotropy, the measured circumferential load was significantly higher than the axial load.

[0090] Then, finite element software can be used to establish and... Figure 3 Cross-shaped specimens with identical dimensions 1 / finite element numerical model (e.g.) Figure 4 As shown in the figure, the Hill48 yield criterion is defined. Wherein, the Hill parameters... R 11 ~ R 23 The calibration method is as follows: Let R 11 =1, based on the plastic strain ratio R 11 =1, according to r Value conversion relationship determined F =0.4857, G =0.5362, H =0.4638, N =1.404. The anisotropy parameters are derived based on equation (8). R 22 =1.4379, R 12 =0.6938,R 33 = R 23 = R 13 =1.

[0091] The finite element numerical model was simulated by applying the same displacement boundary conditions as the biaxial tensile test described above. The evolution curve of the plastic work density of the geometric center element of the thinned region in the numerical model was extracted. The moment when the value of the curve equals the plastic work density of the first unit volume (i.e., the yield benchmark moment) was searched, and the local true stress component calculated by the numerical model at that moment was recorded. σ 11 sim =341MPa and σ 22 sim =389MPa.

[0092] Determine the numerical model simulation displacement corresponding to the yield benchmark time. D sim In the biaxial load and displacement response data obtained in the biaxial tensile test, the nominal load of the test machine under the same deformation level was found by synchronous displacement. P CD exp and P AD exp Based on this, the geometric correction factors (i.e., the conversion factors mentioned above) are calculated for both directions. k This coefficient characterizes the load shunting effect at the arm of the cross-shaped specimen, where: , ,in, A min The measured minimum cross-sectional area of ​​the central thinning zone. k CD and k AD The load correction effects caused by the load shunting effect at the arm of the cruciform specimen in the two orthogonal loading directions are characterized respectively. Specifically, the obtained correction coefficients... k CD =0.37 and k AD =0.44, this coefficient effectively transforms the macroscopic load, including the arm resistance, into the actual material stress in the central region. For details, please refer to... Figure 5 The stress-strain relationship diagrams before and after geometric correction are shown.

[0093] In addition, the calibrated correction coefficients can be used. k CD and kAD The load sequence throughout the experiment is converted in real time into the actual stress components of the central thinning region. The specific conversion can be performed using the following formula: , ,in, σ 11 (t) and σ 22 (t) represents time respectively. t The true stress components were obtained by converting the two orthogonal loading directions in the thinned region at the center of the specimen. Indicates time t Biaxial tensile test measured load, A min This represents the measured minimum cross-sectional area of ​​the central thinning zone. and It represents the actual strain along the loading direction in the central thinning region, and is used to correct the cross-sectional area based on the approximate invariance of volume.

[0094] Specifically, the corrected biaxial yield point ( σ 11 , σ 22 By combining the yield strength in each uniaxial direction with the least squares method to decouple and solve for the anisotropy coefficient of the Hill 48 yield criterion, and calculating the equivalent biaxial yield stress according to the Mises equivalent stress criterion based on the biaxial yield point, the equivalent biaxial yield stress is used as an auxiliary characterization index for the biaxial yield strength. The resulting yield surface trajectory can accurately pass through the measured biaxial asymmetric stress point, thus achieving robust prediction of the failure limit of pipeline steel under complex loads such as internal pressure.

[0095] This invention also provides a corresponding apparatus for determining the load and stress of a cross-shaped biaxial tensile specimen, further enhancing the practicality of the method. The apparatus can be described from both a functional module perspective and a hardware perspective. The apparatus for determining the load and stress of a cross-shaped biaxial tensile specimen provided by this invention is described below. This apparatus is used to implement the method for determining the load and stress of a cross-shaped biaxial tensile specimen provided by this invention. In this embodiment, the apparatus for determining the load and stress of a cross-shaped biaxial tensile specimen may include or be divided into one or more program modules. These program modules are stored in a storage medium and executed by one or more processors to complete the method for determining the load and stress of a cross-shaped biaxial tensile specimen disclosed in the above embodiments. The following description will specifically introduce the functions of each program module in this embodiment. The apparatus for determining the load and stress of a cross-shaped biaxial tensile specimen described below corresponds to the method for determining the load and stress of a cross-shaped biaxial tensile specimen described above.

[0096] From the perspective of functional modules, see Figure 7 , Figure 7 This invention provides a structural diagram of a device for determining the load and stress of a cross-shaped biaxial tensile specimen. The device may include: The first acquisition module 11 is used to acquire biaxial load and displacement response data of a cross-shaped biaxial tensile specimen under at least one loading ratio. Module 12 is used to construct a finite element numerical model based on the geometric parameters of the cross-shaped biaxial tensile specimen, and to assign parameter values ​​to the finite element numerical model using material constitutive parameters under different orientations. The simulation module 13 is used to perform numerical simulation of the biaxial tensile test process of the finite element numerical model based on at least one loading ratio, and to determine the local stress components in the central region during the numerical simulation process based on the real stress and strain data obtained in the uniaxial tensile test. The first determining module 14 is used to determine the biaxial load corresponding to the local stress components in the central region based on the local stress components in the central region during the numerical simulation process, combined with the biaxial load and displacement response data under the loading ratio. The processing module 15 is used to process the biaxial load and displacement response data based on the local stress components of the central region and the corresponding biaxial load, so as to obtain the true stress trajectory data of the central region.

[0097] In one embodiment, the device may further include: The second acquisition module is used to acquire the actual stress and strain data of the target material under different orientations. The third acquisition module is used to acquire the material constitutive parameters of the target material under different orientations; among them, the real stress and strain data are obtained by conducting uniaxial tensile tests on the target material in the corresponding orientations, and the cross-shaped biaxial tensile specimen is a part cut from the target material.

[0098] In one embodiment, the device further includes: The fourth acquisition module is used to acquire full-field strain data of the central region of a cross-shaped biaxial tensile specimen under at least one loading ratio; The verification module is used to verify the finite element numerical model using full-field strain data of the central region of the cross-shaped biaxial tensile specimen, and triggers the simulation module after the verification is successful.

[0099] In one implementation, the simulation module includes: The first acquisition unit is used to acquire the first unit volume equivalent plastic work density at the uniaxial yield state obtained in the uniaxial tensile test. The second acquisition unit is used to acquire the second unit volume equivalent plastic work density of the central region during the loading evolution process corresponding to the loading ratio in the numerical simulation process. The first determining element is used to determine the local stress components of the central region of the numerical model at the current moment when the equivalent plastic work density per unit volume of the second unit volume reaches the equivalent plastic work density per unit volume of the first unit volume.

[0100] In one implementation, the first determining module includes: The second determining unit is used to determine the first displacement of the numerical model at the current moment based on the current moment corresponding to the local stress component; The third determining unit is used to determine the biaxial load amount corresponding to the first displacement amount based on the biaxial load and displacement response data.

[0101] In one implementation, the processing module includes: The first establishment unit is used to establish the mapping relationship between the local stress components and the corresponding biaxial load based on the local stress components of the central region and the corresponding biaxial load, and to obtain the load and stress conversion coefficients corresponding to the corresponding loading ratio under the geometric parameters. The conversion unit is used to obtain continuous load data based on biaxial load and displacement response, and to convert the continuous load data into real stress trajectory data of the central region using load and stress conversion coefficients.

[0102] In one embodiment, different orientations include at least the rolling direction of the material, the transverse direction, and the direction at a predetermined angle to the rolling direction.

[0103] In one embodiment, the device further includes: The second determining module is used to determine the biaxial yield strength or biaxial yield characteristic parameters of the target material under the loading ratio based on the actual stress trajectory.

[0104] It should be noted that the load and stress determination device for the cross-shaped biaxial tensile specimen provided in this application embodiment has the same beneficial effects as the load and stress determination method for the cross-shaped biaxial tensile specimen provided in the above embodiments. For a detailed description of the load and stress determination method for the cross-shaped biaxial tensile specimen involved in this application embodiment, please refer to the above embodiments. This application embodiment will not be repeated here.

[0105] The device for determining the load and stress of the cross-shaped biaxial tensile specimen mentioned above is described from the perspective of functional modules. Furthermore, the present invention also provides an electronic device, which is described from the perspective of hardware. Figure 8 A structural diagram of an electronic device provided in an embodiment of this application, such as... Figure 8 As shown, the electronic device includes: a memory 20 for storing computer programs; The processor 21 is used to execute a computer program to implement the steps of the method for determining the load and stress of a cross-shaped biaxial tensile specimen as described in the above embodiment.

[0106] The electronic devices provided in this embodiment may include, but are not limited to, smartphones, tablets, laptops, or desktop computers.

[0107] The processor 21 may include one or more processing cores, such as a quad-core processor or an octa-core processor. The processor 21 may be implemented using at least one hardware form selected from DSP (Digital Signal Processing), FPGA (Field-Programmable Gate Array), and PLA (Programmable Logic Array). The processor 21 may also include a main processor and a coprocessor. The main processor, also known as a CPU (Central Processing Unit), is used to process data in the wake-up state; the coprocessor is a low-power processor used to process data in the standby state. In some embodiments, the processor 21 may integrate a GPU (Graphics Processing Unit), which is responsible for rendering and drawing the content to be displayed on the screen. In some embodiments, the processor 21 may also include an AI (Artificial Intelligence) processor, which is used to handle computational operations related to machine learning.

[0108] The memory 20 may include one or more computer-readable storage media, which may be non-transitory. The memory 20 may also include high-speed random access memory and non-volatile memory, such as one or more disk storage devices or flash memory devices. In some embodiments, the memory 20 may be an internal storage unit of an electronic device, such as a server hard drive. In other embodiments, the memory 20 may be an external storage device of an electronic device, such as a plug-in hard drive on a server, a Smart Media Card (SMC), a Secure Digital (SD) card, a Flash Card, etc. Furthermore, the memory 20 may include both internal and external storage units of the electronic device. The memory 20 can be used not only to store application software and various types of data installed in the electronic device, such as the code of a program executing a method for determining the load and stress of a cross-shaped biaxial tensile specimen, but also to temporarily store data that has been output or will be output. In this embodiment, the memory 20 is used to store at least the following computer program 201, which, after being loaded and executed by the processor 21, is capable of implementing the relevant steps of the method for determining the load and stress of a cross-shaped biaxial tensile specimen disclosed in any of the foregoing embodiments. In addition, the resources stored in the memory 20 may also include an operating system 202 and data 203, and the storage method may be temporary or permanent storage. The operating system 202 may include Windows, Unix, Linux, etc. The data 203 may include, but is not limited to, data corresponding to the load and stress determination results of the cross-shaped biaxial tensile specimen.

[0109] In some embodiments, the electronic device may further include a display screen 22, an input / output interface 23, a communication interface 24, a power supply 25, and a communication bus 26. The display screen 22 and input / output interface 23, such as a keyboard, are user interfaces; optional user interfaces may also include standard wired interfaces, wireless interfaces, etc. Optionally, in some embodiments, the display may be an LED display, a liquid crystal display, a touch-sensitive liquid crystal display, or an OLED (Organic Light-Emitting Diode) touchscreen, etc. The display may also be appropriately referred to as a screen or display unit, used to display information processed in the electronic device and to display a visual user interface. The communication interface 24 may optionally include a wired interface and / or a wireless interface, such as a Wi-Fi interface, a Bluetooth interface, etc., typically used to establish communication connections between the electronic device and other electronic devices. The communication bus 26 may be a peripheral component interconnect (PCI) bus or an extended industry standard architecture (EISA) bus, etc. This bus can be divided into an address bus, a data bus, a control bus, etc. For ease of representation, Figure 8 The bus is represented by a single thick line, but this does not mean that there is only one bus or one type of bus.

[0110] Those skilled in the art will understand that Figure 8 The structures shown do not constitute a limitation on electronic devices and may include more or fewer components than those shown.

[0111] It is understood that if the method for determining the load and stress of the cross-shaped biaxial tensile specimen in the above embodiments is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and executes all or part of the steps of the methods in the various embodiments of this application. The aforementioned storage medium includes: USB flash drive, mobile hard disk, read-only memory (ROM), random access memory (RAM), electrically erasable programmable ROM, register, hard disk, removable disk, CD-ROM, magnetic disk, or optical disk, and other media capable of storing program code.

[0112] Based on this, such as Figure 9As shown, this embodiment of the invention also provides a computer-readable storage medium 30, on which a computer program 31 is stored. When the computer program 31 is executed by a processor, it implements the steps of the method for determining the load and stress of the cross-shaped biaxial tensile specimen as described above.

[0113] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to in the method section.

[0114] It should also be noted that, in this specification, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0115] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for determining load and stress of a cross-shaped biaxially-stretched specimen, characterized by, include: Obtain biaxial load and displacement response data of a cross-shaped biaxial tensile specimen under at least one loading ratio; A finite element numerical model is constructed based on the geometric parameters of the cross-shaped biaxial tensile specimen, and the material constitutive parameters under different orientations are used to assign parameter values ​​to the finite element numerical model. The biaxial tensile test process of the finite element numerical model is numerically simulated based on at least one loading ratio, and the local stress components in the central region during the numerical simulation process are determined based on the actual stress and strain data obtained in the uniaxial tensile test. Based on the local stress components in the central region during the numerical simulation process, and combined with the biaxial load and displacement response data under the loading ratio, the biaxial load corresponding to the local stress components in the central region is determined. Based on the local stress components and corresponding biaxial loads in the central region, the biaxial load and displacement response data are processed to obtain the true stress trajectory data of the central region.

2. The method of claim 1, wherein Before acquiring the biaxial load and displacement response data of the cross-shaped biaxial tensile specimen under at least one loading ratio, and before acquiring the full-field strain data of the central region of the cross-shaped biaxial tensile specimen, the method further includes: Obtain the actual stress and strain data of the target material under different orientations; Obtain the constitutive parameters of the target material under different orientations; wherein the actual stress and strain data are obtained by performing uniaxial tensile tests on the target material in the corresponding orientations, and the cross-shaped biaxial tensile specimen is a portion cut from the target material.

3. The method for determining the load and stress of a cross-shaped biaxial tensile specimen according to claim 2, characterized in that, Also includes: Obtain full-field strain data of the central region of the cross-shaped biaxial tensile specimen under at least one loading ratio; Therefore, before performing numerical simulation of the biaxial tensile test process of the finite element numerical model based on at least one loading ratio, the method further includes: The finite element numerical model was verified using full-field strain data from the central region of a cross-shaped biaxial tensile specimen, and the next step was performed after the verification was successful.

4. The method for determining the load and stress of a cross-shaped biaxial tensile specimen according to claim 2, characterized in that, The determination of local stress components in the central region during the numerical simulation process, based on the actual stress and strain data obtained from uniaxial tensile tests, includes: Obtain the first unit volume equivalent plastic work density at the uniaxial yield state obtained in the uniaxial tensile test; Obtain the second unit volume equivalent plastic work density of the central region during the loading evolution process corresponding to the loading ratio in the numerical simulation process; When the second unit volume equivalent plastic work density reaches the first unit volume equivalent plastic work density, the local stress components of the central region of the numerical model at the current moment are determined.

5. The method for determining the load and stress of a cross-shaped biaxial tensile specimen according to claim 4, characterized in that, The determination of the biaxial load corresponding to the local stress components in the central region based on the local stress components in the central region during the numerical simulation process, combined with the biaxial load and displacement response data under the loading ratio, includes: Based on the current moment corresponding to the local stress component, determine the first displacement of the numerical model at the current moment; Based on the biaxial load and displacement response data, determine the biaxial load corresponding to the first displacement.

6. The method for determining the load and stress of a cross-shaped biaxial tensile specimen according to claim 5, characterized in that, Based on the local stress components and corresponding biaxial loads in the central region, the biaxial load and displacement response data are processed to obtain the true stress trajectory data of the central region, including: Based on the local stress components and corresponding biaxial loads in the central region, a mapping relationship between the local stress components and the biaxial loads is established, and the load and stress conversion coefficients corresponding to the corresponding loading ratios under the geometric parameters are obtained. Continuous load data is obtained based on biaxial load and displacement response, and the continuous load data is converted into real stress trajectory data of the central region using the load and stress conversion coefficient.

7. The method for determining the load and stress of a cross-shaped biaxial tensile specimen according to any one of claims 1 to 6, characterized in that, Also includes: Based on the actual stress trajectory, determine the biaxial yield strength or biaxial yield characteristic parameter of the target material at the loading ratio.

8. A device for determining the load and stress of a cross-shaped biaxial tensile specimen, characterized in that, include: The first acquisition module is used to acquire biaxial load and displacement response data of a cross-shaped biaxial tensile specimen under at least one loading ratio. The construction module is used to construct a finite element numerical model based on the geometric parameters of the cross-shaped biaxial tensile specimen, and to assign parameter values ​​to the finite element numerical model using material constitutive parameters under different orientations. The simulation module is used to perform numerical simulation of the biaxial tensile test process of the finite element numerical model based on at least one loading ratio, and to determine the local stress components in the central region during the numerical simulation process based on the actual stress and strain data obtained in the uniaxial tensile test. The first determining module is used to determine the biaxial load corresponding to the local stress components in the central region based on the local stress components in the central region during the numerical simulation process, combined with the biaxial load and displacement response data under the loading ratio. The processing module is used to process the biaxial load and displacement response data based on the local stress components of the central region and the corresponding biaxial load, so as to obtain the true stress trajectory data of the central region.

9. An electronic device, characterized in that, include: Memory, used to store computer programs; A processor, configured to execute the computer program to implement the steps of the method for determining the load and stress of a cross-shaped biaxial tensile specimen as described in any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, implements the steps of the method for determining the load and stress of a cross-shaped biaxial tensile specimen as described in any one of claims 1 to 7.

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