Method for calculating elastic-plastic constitutive behavior and toughness characteristic of gradient grain size distribution nanostructure metal based on deformation mechanism and microstructure composition

Abstract

The invention discloses a method for calculating elastic-plastic constitutive behaviors and toughness characteristics of gradient grain size distribution nano-structure metal based on a deformation mechanism and microstructure composition, which is based on an elastic-plastic theoretical framework, considers the deformation mechanism and the microstructure composition, realizes numerical calculation through MATLAB (Matrix Laboratory), and obtains the elastic-plastic constitutive behaviors and toughness characteristics of the gradient grain size distribution nano-structure metal. The uniaxial tension / compression elastic-plastic constitutive behavior and the toughness characteristic of the gradient grain size distribution nano-structure metal are simulated and predicted. According to the method, microstructure characteristics such as the grain size in the metal, dislocation density evolution, microcrack generation and evolution and the like are considered, and the uniaxial tension / compression elastic-plastic constitutive behavior and the toughness characteristic of the nano-structure metal material with the grain size in gradient distribution are simulated and predicted. In an experiment for preparing a gradient grain size distribution nano-structure metal material, the method provides a theoretical basis for the tensile / compression performance change of the gradient structure metal, and can provide theoretical guidance for how to improve the toughness performance of the gradient material.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of metal tensile / compressive constitutive behavior and strength-toughness property simulation, and particularly relates to a method for calculating gradient grain size distribution nanostructured metal elastic-plastic constitutive behavior and strength-toughness property based on deformation mechanism and microstructure composition. BACKGROUND

[0002] With the continuous improvement of social productivity, higher requirements for the mechanical properties such as strength-toughness of materials in various industries have been put forward. The development of material science and the progress of industrial production technology enable humans to improve the comprehensive performance of materials by changing the microstructure of materials. In 1981, Professor H. Gleiter of Saar University in Germany first proposed the concept of "nanostructured materials", and successfully prepared a nano-microcrystalline block in 1984, explaining the structural characteristics of nanostructured materials. Due to the grain size effect, nanostructured metal materials usually have very high strength and hardness, but with the significant improvement of strength and hardness, the toughness and work hardening capacity of nanostructured metal materials are reduced, which limits the development and application of nanostructured metal materials.

[0003] The introduction of gradient structure in the microstructure distribution of materials makes the materials improve one or more properties without losing the original performance, which provides a good idea for improving the comprehensive performance of materials. The gradient structure characteristics of gradient nano metal materials make them have excellent mechanical properties, such as: the nanocrystalline of the surface layer makes it have super-high hardness and wear resistance; the combined action mechanism of fine grains and coarse grains makes it have high strength and good toughness; the inhibition effect of the surface ultra-fine grain on the crack makes it have excellent fatigue resistance; the dense passivation film on the surface makes it have strong corrosion resistance. Due to the excellent and diverse performance, gradient nano materials have become a hot research in material science, and a large number of new gradient structure materials have emerged, and at the same time, it is urgent to establish a corresponding theoretical system to describe the comprehensive properties of materials, so as to guide and predict the actual application work. SUMMARY

[0004] The present application aims at the deficiencies of the prior art, and provides a method for calculating gradient grain size distribution nanostructured metal elastic-plastic constitutive behavior and strength-toughness property based on deformation mechanism and microstructure composition.

[0005] The purpose of the present application is achieved by the following technical scheme: a method for calculating gradient grain size distribution nanostructured metal elastic-plastic constitutive behavior and strength-toughness property based on deformation mechanism and microstructure composition, comprising the following steps: (1) Obtain the material parameters and structure information of the metal material through experimental characterization, and determine the elastic modulus, Poisson's ratio, Burgers vector, Taylor parameter, yield strength of coarse grain, grain size gradient distribution law of gradient grain size distribution nanostructured metal, and the true stress-strain curve of uniaxial tension / compression of coarse grain and gradient structure, and set the initial conditions of uniaxial tension / compression, and select the appropriate strain loading rate in the quasi-static tension / compression range; (2) By adjusting the strain gradient parameters of the grain dislocation accumulation zone, the model parameters of the dislocation evolution model, the maximum dislocation number or dislocation slip length coefficient of the back stress model, and the Weber modulus or micro-crack density parameters of the micro-crack failure model, the true stress-strain curves of the four stages of elasticity, yield, strengthening, and failure of the coarse grain and gradient grain size distribution nanostructured metal under uniaxial tension / compression are simulated and fitted respectively; (3) On the basis of the material parameters and model parameters determined in steps (1) and (2), change the grain size distribution law of the material, and predict the uniaxial tension / compression performance of the metal material under different grain size gradient structures.

[0006] Further, the step (1) specifically includes the following sub-steps: (1.1) Obtain the material parameters and structure information of the metal to be tested through experimental characterization, and determine the elastic modulus, Poisson's ratio, yield strength of coarse grain, grain size of coarse grain, uniaxial tension / compression stress engineering strain curve of coarse grain, uniaxial tension / compression engineering stress-strain curve of gradient structure, and grain size gradient distribution law of gradient grain size distribution nanostructured metal of the metal to be tested; the engineering stress-strain curve includes four stages of elasticity, yield, strengthening, and failure; (1.2) Convert the uniaxial tension / compression stress engineering strain curve of coarse grain into the true stress-strain curve of uniaxial tension / compression of coarse grain according to the mechanical basic formula, and convert the uniaxial tension / compression engineering stress-strain curve of gradient structure into the true stress-strain curve of uniaxial tension / compression of gradient structure; then calculate the shear modulus and bulk modulus of the material of the metal to be tested according to the elastic modulus and Poisson's ratio; subsequently, perform continuous function curve fitting on the grain size gradient distribution law of the gradient grain size distribution nanostructured metal, and obtain the grain size gradient distribution law used in the simulation of the true stress-strain curve of the uniaxial tension / compression of the gradient structure; (1.3) Set the initial conditions of the material of the metal to be tested, the initial elastic-plastic stress and strain of the material of the metal to be tested are set to 0, the normalized initial dislocation density is 1, the strain loading of the material of the metal to be tested is within the quasi-static loading range, the strain step is 10 -5 , and the strain rate is 10 -3 / s.

[0007] Further, the step (2) specifically comprises the following sub-steps: (2.1) Taylor dislocation model calculates the corresponding flow stress through the dislocation density in the grain and the dislocation density of the grain boundary dislocation accumulation zone simulated by the dislocation evolution model; the dislocation density of the grain boundary dislocation accumulation zone is related to the grain size of the coarse grain, the thickness of the grain boundary dislocation accumulation zone, the strain gradient parameter of the grain dislocation accumulation zone, the geometric parameter and the size of the burgers vector; the thickness of the grain boundary dislocation accumulation zone, the geometric parameter and the size of the burgers vector are model constants; by adjusting the grain strain gradient parameter and the dynamic sensitivity coefficient in the viscoplastic model, the trend of the elastic and yield stages in the simulated uniaxial tensile / compression real stress-strain curve of the coarse grain is consistent with the trend of the elastic and yield stages in the experimental characterization uniaxial tensile / compression real stress-strain curve of the coarse grain, respectively; (2.2) Adjust the maximum dislocation number or dislocation slip length coefficient in the back stress model parameter, so that the trend of the strengthening stage in the simulated uniaxial tensile / compression real stress-strain curve of the coarse grain is consistent with the trend of the strengthening stage in the experimental characterization uniaxial tensile / compression real stress-strain curve of the coarse grain; (2.3) Adjust the Weber modulus or microcrack density in the microcrack failure model parameter, so that the trend of the failure stage in the simulated uniaxial tensile / compression real stress-strain curve of the coarse grain is consistent with the trend of the failure stage in the experimental characterization uniaxial tensile / compression real stress-strain curve of the coarse grain; (2.4) Calculate the parameters in the dislocation evolution model through the yield strength of the coarse grain of the material of the metal to be tested and the grain size of the coarse grain obtained by experimental characterization and the shear modulus of the metal to be tested; after adjusting the parameters of the four stages of the uniaxial tensile / compression stress-strain curve of the coarse grain in steps (2.1)-(2.3), modify the uniaxial tensile / compression stress engineering strain curve obtained by experimental characterization in a small range, so that the simulated uniaxial tensile / compression real stress-strain curve of the coarse grain is consistent with the experimental characterization uniaxial tensile / compression real stress-strain curve of the coarse grain; (2.5) According to the shape of the metal to be tested, divide the layers, and determine the grain size of each layer according to the grain size gradient distribution law fitted in step (1.2); the process of simulating the uniaxial tensile / compression real stress-strain curve of the gradient structure is compared with the process of simulating the uniaxial tensile / compression real stress-strain curve of the coarse grain, the material parameters including the elastic modulus, the Poisson's ratio, the burgers vector, the Taylor parameter and the yield strength of the coarse grain are the same, but the grain size is different, but the maximum dislocation number or dislocation slip length coefficient is different; By adjusting the grain strain gradient parameter and the dynamic sensitive coefficient in the viscoplastic model, the trend of the elastic and yield stages in the simulated real stress-strain curves of the gradient structure under uniaxial tension / compression is consistent with the trend of the elastic and yield stages in the experimental real stress-strain curves of the gradient structure under uniaxial tension / compression, respectively. (2.6) Adjusting the maximum dislocation number or dislocation slip length coefficient in the back stress model parameter, so that the trend of the strengthening stage in the simulated real stress-strain curves of the gradient structure under uniaxial tension / compression is consistent with the trend of the strengthening stage in the experimental real stress-strain curves of the gradient structure under uniaxial tension / compression. (2.7) Adjusting the Weber modulus or microcrack density in the microcrack failure model parameter, so that the trend of the failure stage in the simulated real stress-strain curves of the gradient structure under uniaxial tension / compression is consistent with the trend of the failure stage in the experimental real stress-strain curves of the gradient structure under uniaxial tension / compression. (2.8) After adjusting the parameters of the four stages of elasticity, yield, strengthening, and failure of the uniaxial tension / compression stress-strain curves of the gradient structure in steps (2.5)-(2.7), the uniaxial tension / compression stress engineering strain curves of the gradient structure obtained by experimental characterization are modified in a small range, so that the simulated real stress-strain curves of the gradient structure under uniaxial tension / compression are consistent with the experimental real stress-strain curves of the gradient structure under uniaxial tension / compression. (2.9) Repeat steps (2.1)-(2.8) so that the simulated real stress-strain curves of the coarse grain and gradient structure under uniaxial tension / compression are consistent with the experimental real stress-strain curves of the coarse grain and gradient structure under uniaxial tension / compression, respectively, to determine the final all model parameters.

[0008] Further, the step (3) specifically includes the following sub-steps: (3.1) On the basis of keeping all the material parameters determined in step (1) and all the model parameters determined in step (2.9), change the grain size distribution law of the metal material, and predict the uniaxial tension / compression performance of the metal material under different grain size gradient structures; (3.2) On the basis of keeping all the material parameters determined in step (1) and all the model parameters determined in step (2.9), change the grain size in the uniaxial tension / compression simulation program of the coarse grain, and predict the grain size uniform distribution grain size on the tensile / compression elastic-plastic constitutive behavior and toughness characteristics of the material.

[0009] The beneficial effects of the present invention are that it can simulate, predict and analyze the tensile / compressive constitutive behavior and toughness characteristics of metal materials based on microstructures, which is of great significance for the analysis and guidance of experimental results. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 Flowchart of a method for calculating the elastic-plastic constitutive behavior and strength-toughness properties of nanostructured metals with gradient grain size distribution based on deformation mechanism and microstructural composition. DETAILED DESCRIPTION

[0011] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to illustrate the present invention, rather than to represent all embodiments. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0012] This model (which ultimately yields a stress-strain curve) is based on an elastic-plastic constitutive relationship. The elastic component utilizes linear elasticity theory, while the plastic component utilizes J2 theory. The reference plastic strain rate in the J2 theory utilizes a power-law viscoplastic model. The flow stress in the viscoplastic model is calculated using the Taylor model. The dislocation density in the Taylor model is derived by adding the intra-grain dislocation density calculated using the KM model to the dislocation density calculated at the grain boundary dislocation accumulation. The Taylor model also considers the influence of back stress when calculating flow stress, introducing a back stress model. Ultimately, failure is controlled using a microcrack failure model.

[0013] Example 1 like Figure 1 As shown, the present invention provides a method for calculating the elastic-plastic constitutive behavior and toughness properties of gradient grain size distribution nanostructured metals based on deformation mechanism and microstructure composition, comprising the following steps: (1) Obtain the parameters and structural information of metal materials through experimental characterization, clarify the elastic modulus, Poisson's ratio, Burgers vector, Taylor parameter, yield strength of coarse grains, gradient grain size distribution of nanostructured metals, and the true stress-strain curves of uniaxial tension / compression of coarse grains and gradient structures, set the initial conditions of uniaxial tension / compression, and select the appropriate strain loading rate within the quasi-static tension / compression range.

[0014] The step (1) specifically includes the following sub-steps: (1.1) Obtain the material parameters and structure information of the metal to be tested through experimental characterization, and determine the elastic modulus, Poisson's ratio, yield strength of coarse grains, grain size of coarse grains, uniaxial tensile / compressive stress engineering strain curve of coarse grains, uniaxial tensile / compressive engineering stress strain curve of gradient structure, and grain size gradient distribution law of gradient grain size distribution nanostructured metal of the material of the metal to be tested; the engineering stress strain curve includes four stages of elasticity, yield, strengthening and failure; (1.2) Convert the uniaxial tensile / compressive stress engineering strain curve of coarse grains into the uniaxial tensile / compressive true stress strain curve of coarse grains according to the mechanical basic formula, and convert the uniaxial tensile / compressive engineering stress strain curve of gradient structure into the uniaxial tensile / compressive true stress strain curve of gradient structure; then calculate the shear modulus and bulk modulus of the material of the metal to be tested according to the elastic modulus and Poisson's ratio; then continuously function curve fitting is performed on the grain size gradient distribution law of the gradient grain size distribution nanostructured metal, and the grain size gradient distribution law used for simulating the uniaxial tensile / compressive true stress strain curve of the gradient structure is obtained by fitting; (1.3) Set the initial conditions of the material of the metal to be tested, the initial elastic-plastic stress and strain of the material of the metal to be tested are set to 0, the initial dislocation density is normalized to 1, the strain loading of the material of the metal to be tested is in the quasi-static loading range, the strain step is 10 -5 , and the strain rate is 10 -3 / s.

[0015] (2) By adjusting the strain gradient parameters of the grain dislocation accumulation zone, the model parameters of the dislocation evolution model, the maximum number of dislocations or the dislocation slip length coefficient of the back stress model, and the Weber modulus or microcrack density parameters of the microcrack failure model, the uniaxial tensile / compressive true stress strain curves of coarse grains and gradient grain size distribution nanostructured metal in the four stages of elasticity, yield, strengthening and failure are simulated and fitted respectively.

[0016] The step (2) specifically comprises the following sub-steps: (2.1) Taylor dislocation model calculates the corresponding flow stress by simulating the dislocation density in the grain and the dislocation density of the grain boundary dislocation accumulation zone through the dislocation evolution model; the dislocation density of the grain boundary dislocation accumulation zone is related to the grain size of the coarse grain, the thickness of the grain boundary dislocation accumulation zone, the strain gradient parameter of the grain dislocation accumulation zone, the geometric parameter and the size of the burgers vector; the thickness of the grain boundary dislocation accumulation zone, the geometric parameter and the size of the burgers vector are model constants; by adjusting the grain strain gradient parameter and the dynamic sensitivity coefficient in the viscoplastic model, the trend of the elastic and yield stages in the simulated uniaxial tensile / compression real stress-strain curve of the coarse grain is consistent with the trend of the elastic and yield stages in the experimental characterization uniaxial tensile / compression real stress-strain curve of the coarse grain, respectively; (2.2) Adjust the maximum dislocation number or dislocation slip length coefficient in the back stress model parameter, so that the trend of the strengthening stage in the simulated uniaxial tensile / compression real stress-strain curve of the coarse grain is consistent with the trend of the strengthening stage in the experimental characterization uniaxial tensile / compression real stress-strain curve of the coarse grain; (2.3) Adjust the Weber modulus or microcrack density in the microcrack failure model parameter, so that the trend of the failure stage in the simulated uniaxial tensile / compression real stress-strain curve of the coarse grain is consistent with the trend of the failure stage in the experimental characterization uniaxial tensile / compression real stress-strain curve of the coarse grain; (2.4) Calculate the parameters in the dislocation evolution model through the yield strength of the coarse grain of the material of the metal to be tested and the grain size of the coarse grain obtained by experimental characterization and the shear modulus of the metal to be tested; after adjusting the parameters of the four stages of the uniaxial tensile / compression stress-strain curve of the coarse grain in steps (2.1)-(2.3), the uniaxial tensile / compression stress engineering strain curve obtained by experimental characterization is modified in a small range, so that the simulated uniaxial tensile / compression real stress-strain curve of the coarse grain is consistent with the experimental characterization uniaxial tensile / compression real stress-strain curve of the coarse grain; (2.5) According to the shape of the metal to be tested, the number of layers is divided, and the grain size of each layer is determined according to the grain size gradient distribution law obtained in step (1.2); compared with the process of simulating the uniaxial tensile / compression real stress-strain curve of the coarse grain, the material parameters including the elastic modulus, the Poisson's ratio, the burgers vector, the Taylor parameter and the yield strength of the coarse grain are the same, but the grain size is different, and the maximum dislocation number or dislocation slip length coefficient is different; By adjusting the grain strain gradient parameter and the dynamic sensitive coefficient in the viscoplastic model, the trend of the elastic and yield stages in the simulated real stress-strain curves of the gradient structure under uniaxial tension / compression is consistent with the trend of the elastic and yield stages in the experimental real stress-strain curves of the gradient structure under uniaxial tension / compression, respectively. (2.6) Adjusting the maximum dislocation number or dislocation slip length coefficient in the back stress model parameter, so that the trend of the strengthening stage in the simulated real stress-strain curves of the gradient structure under uniaxial tension / compression is consistent with the trend of the strengthening stage in the experimental real stress-strain curves of the gradient structure under uniaxial tension / compression; (2.7) Adjusting the Weber modulus or microcrack density in the microcrack failure model parameter, so that the trend of the failure stage in the simulated real stress-strain curves of the gradient structure under uniaxial tension / compression is consistent with the trend of the failure stage in the experimental real stress-strain curves of the gradient structure under uniaxial tension / compression; (2.8) After adjusting the parameters of the four stages of elasticity, yield, strengthening, and failure of the uniaxial tension / compression stress-strain curves of the gradient structure in steps (2.5)-(2.7), a small range modification is made to the experimental characterization of the uniaxial tension / compression stress engineering strain curve of the gradient structure, so that the simulated real stress-strain curves of the gradient structure under uniaxial tension / compression are consistent with the experimental real stress-strain curves of the gradient structure under uniaxial tension / compression; (2.9) Repeat steps (2.1)-(2.8) so that the simulated real stress-strain curves of the coarse grain and gradient structure under uniaxial tension / compression are consistent with the experimental real stress-strain curves of the coarse grain and gradient structure under uniaxial tension / compression, respectively, to determine the final all model parameters.

[0017] (3) On the basis of the material parameters and model parameters determined in steps (1) and (2), change the grain size distribution law of the material to predict the uniaxial tension / compression performance of the metal material under different grain size gradient structures.

[0018] The step (3) specifically includes the following sub-steps: (3.1) On the basis of all the material parameters determined in step (1) and all the model parameters determined in step (2.9), change the grain size distribution law of the metal material to predict the uniaxial tension / compression performance of the metal material under different grain size gradient structures; (3.2) Based on keeping all the material parameters determined in step (1) and all the model parameters determined in step (2.9), in the coarse-grained uniaxial tension / compression simulation program, the grain size is changed, and the grain size uniform distribution is predicted to predict the grain size of the material tensile / compressive elastic-plastic constitutive behavior and the strength and toughness characteristics.

[0019] The above description is merely preferred embodiments of the present application, and is not used to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of protection of the present application.

Claims

1. A method for calculating the elastic-plastic constitutive behavior and toughness properties of nanostructured metals with gradient grain size distribution based on deformation mechanism and microstructural composition, characterized in that: The following steps are involved: (1) Obtain the parameters and structural information of metal materials through experimental characterization, clarify the elastic modulus, Poisson's ratio, Burgers vector, Taylor parameter, yield strength of coarse grains, gradient grain size distribution, grain size gradient distribution law of nanostructured metals, and the true stress-strain curves of uniaxial tension / compression of coarse grains and gradient structures, set the initial conditions of uniaxial tension / compression, and select the appropriate strain loading rate within the quasi-static tension / compression range; (2) By adjusting the strain gradient parameters of the grain dislocation accumulation zone, the model parameters of the dislocation evolution model, the maximum number of dislocations or the dislocation slip length coefficient of the back stress model, and the Weber modulus or the microcrack density parameter of the microcrack failure model, the true stress-strain curves of the elastic, yield, strengthening, and failure stages of uniaxial tension / compression of coarse-grained and gradient grain size distribution nanostructured metals are simulated and fitted respectively; (3) Based on the material parameters and model parameters determined in steps (1) and (2), the grain size distribution of the material is changed to predict the uniaxial tensile / compressive properties of the metal material under different grain size gradient structures.

2. The method for calculating the elastic-plastic constitutive behavior and toughness properties of nanostructured metals with gradient grain size distribution based on deformation mechanism and microstructure composition according to claim 1, characterized in that: The step (1) specifically includes the following sub-steps: (1.1) Obtain material parameters and structural information of the metal to be tested through experimental characterization, and clarify the elastic modulus, Poisson's ratio, yield strength of coarse grains, grain size of coarse grains, uniaxial tensile / compressive stress-strain curve of coarse grains, uniaxial tensile / compressive engineering stress-strain curve of gradient structures, and gradient grain size distribution and grain size gradient distribution of nanostructured metals. The engineering stress-strain curve includes four stages: elasticity, yield, strengthening, and failure. (1.2) Convert the coarse-grained uniaxial tensile / compressive stress-engineering strain curve into a coarse-grained uniaxial tensile / compressive true stress-strain curve according to the basic mechanical formula, and convert the gradient structure's uniaxial tensile / compressive engineering stress-strain curve into a gradient structure's uniaxial tensile / compressive true stress-strain curve; then calculate the shear modulus and bulk modulus of the metal to be tested based on the elastic modulus and Poisson's ratio; Then, the grain size gradient distribution law of the gradient grain size distribution nanostructured metal is fitted with a continuous function curve to obtain the grain size gradient distribution law used in simulating the real stress-strain curve of the uniaxial tension / compression of the gradient structure; (1.3) Set the initial conditions of the metal material to be tested. The initial elastic-plastic stress and strain of the metal material to be tested are set to 0, the initial dislocation density is normalized to 1, the strain loading of the metal material to be tested is within the quasi-static loading range, and the strain step size is 10 -5 , the strain rate is 10 -3 / s.

3. According to the method for calculating the elastic-plastic constitutive behavior and toughness properties of gradient grain size distribution nanostructured metals based on deformation mechanism and microstructure composition according to claim 2, said step (2) specifically comprises the following sub-steps: (2.1) The Taylor dislocation model calculates the corresponding flow stress by using the dislocation density within the grains and the dislocation density in the grain boundary dislocation accumulation zone simulated by the dislocation evolution model; the dislocation density in the grain boundary dislocation accumulation zone is related to the grain size of the coarse grain, the thickness of the grain boundary dislocation accumulation zone, the strain gradient parameter, geometric parameters, and the size of the Burgers vector of the grain boundary dislocation accumulation zone; the thickness, geometric parameters, and the size of the Burgers vector of the grain boundary dislocation accumulation zone are model constants; by adjusting the grain strain gradient parameter and the dynamic sensitivity coefficient in the viscoplastic model, the trends of the elastic and yield stages in the simulated true stress-strain curve of the coarse grain under uniaxial tension / compression are made consistent with the trends of the elastic and yield stages in the true stress-strain curve of the coarse grain under uniaxial tension / compression obtained by experimental characterization; (2.2) Adjusting the maximum number of dislocations or the dislocation slip length coefficient in the back stress model parameters so that the trend of the strengthening stage in the simulated true stress-strain curve of coarse grains under uniaxial tension / compression is consistent with the trend of the strengthening stage in the experimentally characterized true stress-strain curve of coarse grains under uniaxial tension / compression; (2.3) Adjusting the Weber modulus or microcrack density in the microcrack failure model parameters so that the trend of the failure stage in the simulated true stress-strain curve of coarse grains under uniaxial tension / compression is consistent with the trend of the failure stage in the experimentally characterized true stress-strain curve of coarse grains under uniaxial tension / compression; (2.4) Calculating the calculable parameters in the dislocation evolution model based on the yield strength and grain size of the coarse crystals of the metal material to be tested obtained through experimental characterization and the shear modulus of the metal material to be tested; after completing the parameter adjustments of the elastic, yield, strengthening, and failure stages of the uniaxial tension / compression stress-strain curve of the coarse crystals in steps (2.1) to (2.3), making small modifications to the uniaxial tension / compression stress engineering strain curve of the coarse crystals obtained through experimental characterization so that the simulated true stress-strain curve of the coarse crystals is consistent with the true stress-strain curve of the coarse crystals obtained through experimental characterization; (2.5) Divide the number of layers according to the shape of the metal to be tested, and determine the grain size of each layer according to the grain size gradient distribution law obtained by fitting in step (1.2); The process of simulating the true stress-strain curve of uniaxial tension / compression of the gradient structure is compared with the process of simulating the true stress-strain curve of uniaxial tension / compression of the coarse grain. The material parameters including elastic modulus, Poisson's ratio, Burgers vector, Taylor parameter, and yield strength of the coarse grain are the same, but the grain size is different, but the maximum number of dislocations or the dislocation slip length coefficient is different; By adjusting the grain strain gradient parameters and the dynamic sensitivity coefficient in the viscoplastic model, the trends of the elastic and yield stages in the simulated true stress-strain curves of the gradient structure under uniaxial tension / compression are made consistent with the trends of the elastic and yield stages in the true stress-strain curves of the gradient structure under uniaxial tension / compression obtained by experimental characterization. (2.6) Adjusting the maximum number of dislocations or the dislocation slip length coefficient in the back stress model parameters so that the trend of the strengthening stage in the simulated true stress-strain curve of the gradient structure under uniaxial tension / compression is consistent with the trend of the strengthening stage in the experimentally characterized true stress-strain curve of the gradient structure under uniaxial tension / compression; (2.7) Adjusting the Weber modulus or microcrack density in the microcrack failure model parameters so that the trend of the failure stage in the simulated true stress-strain curve of the gradient structure under uniaxial tension / compression is consistent with the trend of the failure stage in the experimentally characterized true stress-strain curve of the gradient structure under uniaxial tension / compression; (2.8) After completing the parameter adjustments for the four stages of elasticity, yielding, strengthening, and failure of the uniaxial tension / compression stress-strain curve of the gradient structure in steps (2.5) to (2.7), the uniaxial tension / compression stress-engineering strain curve of the gradient structure obtained by experimental characterization is slightly modified to ensure that the simulated true uniaxial tension / compression stress-strain curve of the gradient structure is consistent with the true uniaxial tension / compression stress-strain curve of the gradient structure obtained by experimental characterization; (2.9) Repeat steps (2.1) to (2.8) to ensure that the simulated true stress-strain curves of the coarse-grained and gradient structures under uniaxial tension / compression match the experimentally characterized true stress-strain curves of the coarse-grained and gradient structures under uniaxial tension / compression, respectively, and determine all the final model parameters.

4. According to the method of calculating the elastic-plastic constitutive behavior and toughness characteristics of gradient grain size distribution nanostructured metals based on deformation mechanism and microstructure composition according to claim 3, the step (3) specifically comprises the following sub-steps: (3.1) While maintaining all the material parameters determined in step (1) and all the model parameters determined in step (2.9), change the grain size distribution of the metal material and predict the uniaxial tensile / compressive properties of the metal material under different grain size gradient structures; (3.2) Maintaining all the material parameters determined in step (1) and all the model parameters determined in step (2.9), in the coarse-grained uniaxial tension / compression simulation program, change the grain size and predict the effect of grain size on the tensile / compressive elastoplastic constitutive behavior and toughness properties of the material when the grain size is uniformly distributed.

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