A fatigue strength assessment method for multicomponent alloys based on slip localization

Abstract

The present application relates to a method for evaluating fatigue strength of a multi-component alloy based on slip localization, comprising: obtaining material parameters of a multi-component alloy used for fatigue testing, and establishing a micro-scale model on a computer based on the material parameters; simulating fatigue loading of the micro-scale model by molecular dynamics simulation; after the simulated fatigue loading enters a steady-state stage, dividing the micro-scale model into a plurality of sub-units of the same size, and calculating the slip irreversibility of each sub-unit based on the shear strain of each atom in each sub-unit, and then calculating the difference in slip irreversibility between each sub-unit; calculating a non-uniform parameter based on the slip irreversibility of each sub-unit and the difference in slip irreversibility; normalizing and de-gridding the non-uniform parameter to obtain a slip localization index; and constructing a fatigue strength evaluation model based on the material parameters and the slip localization index.

Description

Technical Field

[0001] The present application relates to the technical field of fatigue strength assessment of multi-component alloys, and in particular to a fatigue strength assessment method of multi-component alloys based on slip localization. Background Art

[0002] At present, with the widespread application of complex multi-element alloy materials such as high entropy alloys and nickel-based alloys, traditional fatigue performance evaluation methods face greater challenges. The multi-element design of these alloys significantly increases the chemical complexity of the materials. Although it provides more space for composition and structure regulation, it also makes the evaluation of fatigue performance more difficult. At present, the evaluation of the fatigue performance of these multi-element alloys still mainly relies on a large amount of experimental screening, or supplemented by a small amount of theoretical calculations, such as first principles; however, considering the long time and high cost of fatigue testing, the method that relies solely on experimental screening is cumbersome and expensive, and cannot meet the needs of rapid evaluation. At present, there is no method to evaluate the fatigue performance of materials through simulation-assisted experiments. Summary of the invention

[0003] Based on this, it is necessary to provide a multi-element alloy fatigue strength assessment method that can quickly predict the fatigue limit strength of multi-element alloys composed of different elements, specifically a multi-element alloy fatigue strength assessment method based on slip localization, the method comprising:

[0004] S1: obtaining material parameters of a multi-element alloy for fatigue testing, and establishing a micro-scale model on a computer based on the material parameters;

[0005] S2: using molecular dynamics simulation to simulate fatigue loading on the microscale model;

[0006] S3: After the simulated fatigue loading enters the steady-state stage, the micro-scale model is divided into a plurality of sub-units of the same size, and the slip irreversibility of each sub-unit is calculated based on the shear strain of each atom in each sub-unit, and then the difference in slip irreversibility between the sub-units is calculated;

[0007] S4: calculating a non-uniform parameter based on the slip irreversibility of each subunit and the difference in the slip irreversibility; normalizing and de-gridding the non-uniform parameter to obtain a slip localization index;

[0008] S5: Constructing a fatigue strength evaluation model based on the material parameters and the slip localization index.

[0009] Preferably, the material parameters include first ultimate tensile strength, element composition and component ratio.

[0010] Preferably, based on the elemental composition and component ratio, a micro-scale model of the multi-component alloy for fatigue testing is computationally established using Atomsk modeling software.

[0011] Preferably, S2 comprises:

[0012] The micro-scale model is relaxed and subjected to simulated fatigue loading by using LAMMPS software, wherein the simulated fatigue loading is to apply periodic boundary conditions and perform cyclic load loading by using an EAM potential function;

[0013] The relaxed micro-scale model is used as the initial configuration;

[0014] The microscale model in the simulated fatigue loading is used as the target configuration;

[0015] The requirement during the cyclic loading process is to ensure that the strain amplitude of the cyclic loading causes the micro-scale model to produce local slip behavior, and the local slip behavior is manifested as a first difference between the atomic coordinates of the target configuration and the atomic coordinates of the initial configuration;

[0016] The OVITO software is used to visualize and analyze the micro-scale model in the simulated fatigue loading process, extract the stress-strain curve in the cyclic load loading process, and the first difference that appears. The first difference is used to calculate the shear strain of the corresponding atoms.

[0017] Preferably, the judgment criteria for the simulated fatigue loading to enter the steady state stage are:

[0018] The MATLAB calculation software is used to calculate the area enclosed by the stress-strain curve during each cyclic loading process. The calculation formula is as follows:

[0019] ;

[0020] ;

[0021] in, It represents the area enclosed by the stress-strain curve during the Pth cycle loading process; represents loop integral; represents the stress value during the Pth cycle loading process; represents the strain value during the Pth cycle loading process; a Indicates strain value The minimum value of b Indicates strain value The maximum value of Indicates strain value Corresponding stress values ​​for loading and unloading difference; N Indicates the number of integral segments; Indicates n Strain value ; Indicates n Strain value Corresponding stress values ​​for loading and unloading difference; Indicates n+ 1 strain value ; Indicates n+ 1 strain value Corresponding stress values ​​for loading and unloading difference;

[0022] After calculating the area enclosed by the stress-strain curve during all cyclic loading processes, when the numerical changes in the area enclosed by the stress-strain curve during five consecutive cyclic loading processes are all less than 30%, it is determined that the simulated fatigue loading has entered the steady-state stage.

[0023] Preferably, in S3, in any steady-state stage, the micro-scale model is divided as follows:

[0024] In micro-scale models x , y , z The three sides of the direction are respectively divided into a number of segments of the same length to obtain a number of cubes with the same volume. The cubes are the subunits, and each of the subunits contains a number of atoms.

[0025] Preferably, the process of calculating the shear strain of each atom in each subunit is:

[0026] Step 1: In s In the subunits, based on atoms i and its nearest neighbor atoms j The corresponding first difference, coordinates, calculate the atoms i The displacement gradient is calculated as:

[0027] ;

[0028] in, Represents atoms i The displacement gradient; Represents atoms i The corresponding first difference; Represents atoms i The nearest atom j The corresponding first difference; Represents atoms i The coordinates of Represents atoms i The nearest atomj The coordinates of

[0029] Step 2: Atom-based i The displacement gradient of the atom is calculated i The particle deformation gradient tensor of:

[0030] ;

[0031] in, Represents atoms i The particle deformation gradient tensor of ; I is the identity matrix;

[0032] Step 3: Atom-based i The particle deformation gradient tensor and its transposed matrix are used to calculate the atomic i The Green-Lagrange strain tensor of:

[0033] ;

[0034] Among them, E represents the atom i The Green-Lagrange strain tensor of ; T represents the transpose;

[0035] Step 4: Place the atoms i The Green-Lagrange strain tensor of is expressed in three-dimensional space as:

[0036] ;

[0037] in, Represents atoms i exist x The degree of axial deformation in the direction; Represents atoms i exist y The degree of axial deformation in the direction; Represents atoms i exist z The degree of axial deformation in the direction; Represents atoms i exist xy Shear strain on a plane; Represents atoms i exist xz Shear strain on a plane; Represents atoms i exist yz Shear strain on a plane;

[0038] Step 5: Atom-based i The axial deformation degree in each direction and the shear strain on each plane are calculated. i The shear strain is calculated as:

[0039] ;

[0040] in, Represents atoms i Shear strain;

[0041] Step 6: Repeat steps 1-5 to traverse the s All atoms in the subunit are obtained s The shear strain of all atoms in a subunit;

[0042] Step 7: Repeat steps 1-6, traverse all subunits, and obtain the shear strain of each atom in each subunit;

[0043] The shear strain includes the maximum shear strain during cyclic loading and the residual shear strain after unloading.

[0044] Preferably, the calculation formula of the non-uniform parameter is:

[0045] ;

[0046] ;

[0047] in, express n The heterogeneity parameters of the subunits; n Indicates the number of subunits; Indicated in n In the subunit i The irreversibility of slip of each subunit; N represents the total number of atoms in the microscopic scale model; Indicates j The maximum shear strain of an atom during cyclic loading; Indicates j The residual shear strain of each atom after unloading; Indicates i The number of atoms in a subunit; Indicates i- The number of atoms in 1 subunit.

[0048] Preferably, the normalizing and degridding the non-uniform parameters comprises:

[0049] According to the micro-scale model x , y , z The ratio of the three sides of the direction divides the three-dimensional space into xyz · k ³ blocks, where k=1,2,3,4,…, r ,andr The value of must not result in the number of blocks being larger than the total number of atoms in the microscale model;

[0050] Add weight factors and xyz · k The slip localization index is obtained by normalizing the non-uniformity parameters of the three blocks. The expression of the slip localization index is:

[0051] ;

[0052] in, W represents the slip localization index; r Indicates the upper limit of the level of the three-dimensional space division blocks; Indicates the level of dividing blocks k The weight factor when ; express xyz · k Non-uniformity parameters of ³ blocks; Indicated in xyz · k ³ blocks i The irreversibility of slip of each block; N represents the total number of atoms in the microscopic scale model; Indicates j Maximum shear strain in cyclic loading of atoms; Indicates j The residual shear strain after unloading of atoms.

[0053] Preferably, S5 includes:

[0054] Taking an average of the slip localization index in all steady-state stages to obtain an average slip localization value of the multi-element alloy for fatigue testing;

[0055] The first ultimate tensile strength is associated with the fatigue strength based on the average slip localization value, and is corrected by parameters to construct the fatigue strength evaluation model. The expression of the fatigue strength evaluation model is:

[0056] ;

[0057] in, Indicates fatigue strength; represents the first ultimate tensile strength; represents the average slip localization value; A Represents the first parameter; B Represents the second parameter; C Represents the third parameter;

[0058] The multi-element alloy used for fatigue test is simulated three times, and the values ​​of the first parameter, the second parameter and the third parameter are calibrated based on the average slip localization value and the first ultimate tensile strength in the three simulation calculations;

[0059] The target multi-component alloy similar to the multi-component alloy used for fatigue test is subjected to simulation calculation and tensile test to obtain the target average slip localization value and the second ultimate tensile strength, which are then substituted into the fatigue strength evaluation model after calibration parameter values ​​to obtain the fatigue strength evaluation value of the target multi-component alloy.

[0060] Beneficial effects: This method is based on micro-scale simulation and slip localization index to evaluate fatigue strength, and can effectively and quickly evaluate the fatigue performance of complex multi-component alloys. This method is not only highly universal in theory, but also supported by physical mechanisms. It can evaluate the fatigue performance of materials without a large number of experimental screenings, effectively reducing the workload and cost of multi-component alloy fatigue testing. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0062] Figure 1 This is a flow chart of a method for evaluating fatigue strength of a multi-component alloy based on slip localization in an embodiment of the present application.

[0063] Figure 2 is the slip localization index in the embodiment of the present application W Schematic diagram of the strain field evolution of the microscale model corresponding to the numerical values.

[0064] Figure 3 It is a comparison chart of the evaluation results and the test results in the examples of this application. DETAILED DESCRIPTION

[0065] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present application, so the present application is not limited by the specific embodiments disclosed below.

[0066] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of this application, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0067] Fatigue failure is one of the most common failure forms in mechanical structures. In engineering applications, fracture damage caused directly or indirectly by fatigue accounts for 50% to 90% of all mechanical damage. The fatigue life of a material is usually divided into fatigue crack initiation life and fatigue crack propagation life, of which fatigue crack initiation life usually occupies the main part of the fatigue life. The initiation of fatigue cracks is a cumulative manifestation of local damage. In alloys, fatigue damage is often caused by the irreversibility of cyclic slip, resulting in local differences in the microstructure of reverse slip and forward slip. With the increase in the number of cycles, the permanent organizational and topological changes caused by the accumulation of partially irreversible microstrains gradually accumulate, leading to the localization of slip deformation, thereby forming microcracks, and ultimately leading to fatigue failure of the material. Therefore, measuring the degree of slip localization of the material and evaluating the fatigue performance from a microscopic scale are of great significance for accurately predicting the fatigue life of the material.

[0068] With the rapid development of computational simulation methods, especially the application of molecular dynamics (MD) simulation in materials science, a new approach has been provided for in-depth understanding of the deformation mechanism of materials and evaluation of their mechanical properties. A large number of studies have shown that microscopic simulation plays an important role in revealing the deformation mechanism of multi-element alloys and predicting their mechanical properties. Therefore, using microscale simulation methods combined with experimental data to construct a rapid evaluation model based on fatigue damage mechanism can effectively reduce a large amount of experimental screening work and greatly reduce related costs, which has important technical and application value.

[0069] This embodiment proposes a slip localization index based on the classical slip irreversibility theory, and based on the index, the fatigue performance of the multi-element alloy is quickly evaluated by simulation.

[0070] like Figure 1 As shown, this embodiment provides a method for evaluating fatigue strength of multi-element alloys based on slip localization, the method comprising:

[0071] S1: Obtain material parameters of a multi-element alloy for fatigue testing, and establish a micro-scale model on a computer based on the material parameters.

[0072] In this embodiment, the material parameters include a first ultimate tensile strength, element composition, and component ratio, wherein the first ultimate tensile strength is measured by performing a tensile test on a multi-element alloy used for a fatigue test.

[0073] Furthermore, based on the elemental composition and component ratio, a micro-scale model of the multi-component alloy for fatigue testing is computationally established using Atomsk modeling software.

[0074] S2: Molecular dynamics simulation is used to simulate fatigue loading on the micro-scale model.

[0075] Specifically, the step includes:

[0076] The micro-scale model is relaxed and subjected to simulated fatigue loading by using LAMMPS software, wherein the simulated fatigue loading is to apply periodic boundary conditions and perform cyclic load loading by using an EAM potential function;

[0077] The relaxed micro-scale model is used as the initial configuration;

[0078] The microscale model in the simulated fatigue loading is used as the target configuration;

[0079] Periodic boundary conditions are applied during cyclic loading to eliminate boundary effects;

[0080] The requirement during the cyclic loading process is to ensure that the strain amplitude of the cyclic loading causes the micro-scale model to produce local slip behavior, and the local slip behavior is manifested as a first difference between the atomic coordinates of the target configuration and the atomic coordinates of the initial configuration;

[0081] The OVITO software is used to visualize and analyze the micro-scale model in the simulated fatigue loading process, extract the stress-strain curve in the cyclic load loading process, and the first difference that appears. The first difference is used to calculate the shear strain of the corresponding atoms.

[0082] S3: After the simulated fatigue loading enters the steady-state stage, the micro-scale model is divided into a plurality of sub-units of the same size, and the slip irreversibility of each sub-unit is calculated based on the shear strain of each atom in each sub-unit, and then the difference in slip irreversibility between the sub-units is calculated.

[0083] Specifically, the judgment criteria for simulated fatigue loading entering the steady-state stage are:

[0084] The MATLAB calculation software is used to calculate the area enclosed by the stress-strain curve during each cyclic loading process. The calculation formula is as follows:

[0085] ;

[0086] That is, the stress value during the P-th cycle loading process Corresponding strain value The integral of is used to represent the area enclosed by the stress-strain curve during the cyclic loading process, and the calculation process can be approximated by trapezoidal integral, and the calculation formula is:

[0087] ;

[0088] in, It represents the area enclosed by the stress-strain curve during the Pth cycle loading process; represents loop integral; represents the stress value during the Pth cycle loading process; represents the strain value during the Pth cycle loading process; a Indicates strain value The minimum value of b Indicates strain value The maximum value of Indicates strain value Corresponding stress values ​​for loading and unloading difference; N represents the number of integration segments; the integration step is ( b - a ) / N ; Indicates n Strain value ; Indicates n Strain value Corresponding stress values ​​for loading and unloading difference; Indicates n+ 1 strain value ; Indicates n+ 1 strain value Corresponding stress values ​​for loading and unloading difference;

[0089] After calculating the area enclosed by the stress-strain curve during all cyclic loading processes, when the numerical changes in the area enclosed by the stress-strain curve during five consecutive cyclic loading processes are all less than 30%, it is determined that the simulated fatigue loading has entered the steady-state stage.

[0090] Furthermore, in any steady-state stage, the micro-scale model is divided as follows:

[0091] In micro-scale models x , y , z The three sides of the direction are respectively divided into a number of segments of the same length to obtain a number of cubes with the same volume. The cubes are the subunits, and each of the subunits contains a number of atoms.

[0092] Furthermore, the process of calculating the shear strain of each atom in each subunit is:

[0093] Step 1: In s In the subunits, based on atoms i and its nearest neighbor atoms j The corresponding first difference, coordinates, calculate the atoms i The displacement gradient is calculated as:

[0094] ;

[0095] in, Represents atoms i The displacement gradient; Represents atoms i The corresponding first difference; Represents atoms i The nearest atom j The corresponding first difference; Represents atoms i The coordinates of Represents atoms i The nearest atom j The coordinates of

[0096] In this embodiment, the criteria for determining the nearest neighbor atom are:

[0097] Define a cutoff radius ,generally , c is the lattice constant. When the distance between two atoms is less than the cutoff radius, the two atoms are each other's nearest neighbor atoms.

[0098] Step 2: Atom-based i The displacement gradient of the atom is calculated i The particle deformation gradient tensor of:

[0099] ;

[0100] in, Represents atoms i The particle deformation gradient tensor of ; I is the identity matrix;

[0101] Step 3: Atom-based i The particle deformation gradient tensor and its transposed matrix are used to calculate the atomic i The Green-Lagrange strain tensor of:

[0102] ;

[0103] Among them, E represents the atomi The Green-Lagrange strain tensor of ; T represents the transpose;

[0104] Step 4: Place the atoms i The Green-Lagrange strain tensor of is expressed in three-dimensional space as:

[0105] ;

[0106] in, Represents atoms i exist x The degree of axial deformation in the direction (normal strain); Represents atoms i exist y The degree of axial deformation in the direction; Represents atoms i exist z The degree of axial deformation in the direction (normal strain); Represents atoms i exist xy Shear strain on a plane; Represents atoms i exist xz Shear strain on a plane (normal strain); Represents atoms i exist yz Shear strain on a plane;

[0107] Step 5: Atom-based i The axial deformation degree in each direction and the shear strain on each plane are calculated. i The shear strain is calculated as:

[0108] ;

[0109] in, Represents atoms i Shear strain;

[0110] Step 6: Repeat steps 1-5 to traverse the s All atoms in the subunit are obtained s The shear strain of all atoms in a subunit;

[0111] Step 7: Repeat steps 1-6, traverse all subunits, and obtain the shear strain of each atom in each subunit;

[0112] The shear strain includes the maximum shear strain during cyclic loading and the residual shear strain after unloading.

[0113] S4: calculating a non-uniform parameter based on the slip irreversibility of each subunit and the difference in the slip irreversibility; normalizing and de-gridding the non-uniform parameter to obtain a slip localization index.

[0114] Specifically, the calculation formula of the non-uniform parameter is:

[0115] ;

[0116] ;

[0117] in, express n The heterogeneity parameters of the subunits; n Indicates the number of subunits; Indicated in n In the subunit i The irreversibility of slip of each subunit; N represents the total number of atoms in the microscopic scale model; Indicates j The maximum shear strain of an atom during cyclic loading; Indicates j The residual shear strain of each atom after unloading; Indicates i The number of atoms in a subunit; Indicates i- The number of atoms in 1 subunit.

[0118] Furthermore, the normalizing and degridding the non-uniform parameters includes:

[0119] According to the micro-scale model x , y , z The ratio of the three sides of the direction divides the three-dimensional space into xyz · k ³ blocks, where k=1,2,3,4,…, r ,and r The value of must not make the number of blocks larger than the total number of atoms in the microscopic model; this indicates that the degree of division into blocks is graded, with each level k Corresponds to a state of number of divided blocks. For example: if the three-sided ratio of the microscopic 3D model x : y : z =2:3:4, k=1, then the number of divided blocks is 2×3×4×1=24, at this time a weight factor is defined for this division state α k = α 1= α Similarly, when k=2, the number of divided blocks is 2×3×4×2=48, and the weight factor defined in this state is α k = α 2 This layer-by-layer partitioning method is used until the value of k is large enough to make the number of partitioned blocks close to the number of atoms in the model. After that, all the partitioned block states are weighted by the weight factor, and the weight factor of the state with more partitioned blocks is made smaller (to reduce the statistical distortion caused by the small number of atomic samples in the block), so that the proposed slip localization index is independent of the number of partitioned blocks.

[0120] Add weight factors and xyz · k The slip localization index is obtained by normalizing the non-uniformity parameters of the three blocks. W The numerical corresponding micro-scale model strain field evolution process, such as Figure 2 The expression of slip localization index is:

[0121] ;

[0122] in, W represents the slip localization index; r Indicates the upper limit of the level of the three-dimensional space division blocks; Indicates the level of dividing blocks k The weight factor when a <1); express xyz · k Non-uniformity parameters of ³ blocks; Indicated in xyz · k ³ blocks i The irreversibility of slip of each block; N represents the total number of atoms in the microscopic scale model; Indicates j Maximum shear strain in cyclic loading of atoms; Indicates j The residual shear strain after unloading of atoms.

[0123] After degridding and normalization, the calculation results of non-uniform parameters no longer depend on the number of sub-units of grid division, thus achieving the universality and accuracy of non-uniform parameters.

[0124] In this embodiment, the weight factor The value of is determined by making the slip localization index W The theoretical maximum value of is 1, and the calculation formula is:

[0125] ;

[0126] When confirmed r and micro-scale models x , y , z The ratio of the three sides of the direction xyz When the weight factor The real number solution can be obtained by computing software such as MATLAB. Through the weight factor, the value of the slip localization index is within the range of [0,1], and the value is independent of the number of divided blocks.

[0127] S5: Constructing a fatigue strength evaluation model based on the material parameters and the slip localization index.

[0128] Specifically, the step includes:

[0129] Taking an average of the slip localization index in all steady-state stages to obtain an average slip localization value of the multi-element alloy for fatigue testing;

[0130] The first ultimate tensile strength is associated with the fatigue strength based on the average slip localization value, and is corrected by parameters to construct the fatigue strength evaluation model. The expression of the fatigue strength evaluation model is:

[0131] ;

[0132] in, Indicates fatigue strength; represents the first ultimate tensile strength; represents the average slip localization value; A Represents the first parameter; B Represents the second parameter; C Represents the third parameter;

[0133] In this embodiment, the slip localization index W The cyclic slip irreversibility index proposed by Mughrabi.H is referred to, and the non-uniformity of slip is considered on this basis; the fatigue strength evaluation model is based on the origin of fatigue strength of metal materials proposed by JC Tinville, which indicates that the slip degree of the material can be used as a connection indicator of its fatigue strength and tensile strength in a cyclic loading; in short, the more obvious the slip characteristics of the material (such as the higher the irreversibility or localization of the slip), the worse the fatigue performance of the material (fatigue strength / tensile strength can be used as a measurement indicator). Based on this relationship, the initial fatigue strength evaluation model is constructed, which is expressed as:

[0134] ;

[0135] The model shows that fatigue strength and first limit tensile strength are related through the average slip localization value. According to the above theory, the value of the third parameter is generally negative, that is, the higher the average slip localization value, the worse the fatigue performance of the material. In practical applications, fatigue strength and first limit tensile strength may not present a standard inverse proportional function relationship. Therefore, the first parameter and the second parameter are added for correction to adapt to more possible situations. The corrected fatigue strength assessment model is expressed as:

[0136] ;

[0137] In order to satisfy the above theory, the first parameter A Generally positive, the second parameter B Generally a smaller value, the third parameter C is a negative value, so the fatigue performance of the material shows an inverse relationship with the average slip localization value. A simple transformation of the modified fatigue strength evaluation model can obtain the final fatigue strength evaluation model.

[0138] Further, the multi-element alloy used for fatigue test is simulated and calculated three times, and the values ​​of the first parameter, the second parameter and the third parameter are calibrated based on the average slip localization value and the first ultimate tensile strength in the three simulation calculations;

[0139] The target multi-component alloy similar to the multi-component alloy used for fatigue test (such as AlCoCrFeNi high entropy alloy) is subjected to simulation calculation and tensile test to obtain the target average slip localization value and the second ultimate tensile strength, which are then substituted into the fatigue strength assessment model after calibration parameter values ​​to obtain the fatigue strength assessment value of the target multi-component alloy.

[0140] As long as the mechanical constitutive model (EAM potential function) of the micro-scale model remains unchanged, the results obtained from this simulation are of certain reference value. If the potential function is changed, the simulation calculation and experimental calibration must be repeated.

[0141] This embodiment takes AlCoCrFeNi high entropy alloy as an example, and uses AlCoCrFeNi high entropy alloys with different Al / Ni molar ratios (e.g. Al 0.1 CoCrFeNi、Al 0.3 CoCrFeNi、Al 0.7 CoCrFeNi and AlCoCrFeNi 2.1 The simulation results are compared with the existing test results to verify the accuracy of the method provided in this implementation.

[0142] The elemental composition and component ratio of the AlCoCrFeNi high entropy alloy with different Al / Ni molar ratios used in this embodiment are shown in Table 1;

[0143] Table 1 is the chemical composition of AlCoCrFeNi high entropy alloy;

[0144] ;

[0145] According to the elemental composition and component ratio of AlCoCrFeNi high entropy alloys with different Al / Ni molar ratios shown in Table 1, microscale high entropy alloy models were established. These models contain 288,000 atoms, and the models xyz The three side dimensions are 30 c ×30 c ×80 c ( c is the lattice constant), so it can be substituted into the weight factor calculation formula and the weight factor is calculated to be 0.0231. Molecular dynamics simulations of these models were performed using LAMMPS software, using the embedded atom method (EAM) potential function, applying periodic boundary conditions and loading cyclic strain, with a loading strain rate of 1×10 9 s -1 , the loading amplitude is 7.5%. The simulation environment adopts an isothermal and isobaric system, the temperature is controlled at 300K, the simulation time step is 1fs, the Verlet method is used to integrate the motion equation, and the load application direction is z In the simulation, the local shear strain distribution is calculated by the atomic-scale strain tensor (ASM), and the OVITO software is used to visualize and record the relevant data. Python is used to extract the data and the slip localization index calculation formula is used to realize the real-time calculation of the slip localization index.

[0146] The slip localization index of the material in all steady-state stages of the cycle is calculated and the average is calculated. The obtained data are shown in Table 2;

[0147] Table 2 is a table of average slip localization values ​​of AlCoCrFeNi high entropy alloy under cyclic loading;

[0148] ;

[0149] Substitute the data in Table 2 into the fatigue strength evaluation model, and calibrate the values ​​of the first parameter, the second parameter, and the third parameter using data from some fatigue tests. The results are: A=0.307, B=0.008, C=-0.244. Then, the fatigue strength of the material is evaluated based on its ultimate tensile strength. The evaluation results are shown in Table 3. The comparison between the simulation results and the experimental results is shown in Table 3. Figure 3 shown.

[0150] Table 3 is a comparison table of fatigue strength simulation results and test results of AlCoCrFeNi high entropy alloy based on average slip localization value evaluation;

[0151] ;

[0152] From Table 3, Figure 3 It can be seen that the deviation between the fatigue strength evaluated by the method provided in this embodiment and the test result is only within 10%, which shows that the fatigue strength evaluation model provided in this embodiment has effective guiding significance for the fatigue strength evaluation of AlCoCrFeNi high entropy alloy.

[0153] The multi-component alloy fatigue strength assessment method provided in this embodiment is based on micro-scale simulation and slip localization index to perform fatigue strength assessment, and can effectively and quickly assess the fatigue performance of complex multi-component alloys. This method is not only theoretically highly universal, but also supported by physical mechanisms, and can assess the fatigue performance of materials without a large number of experimental screenings, effectively reducing the workload and cost of multi-component alloy fatigue tests. Compared with traditional experimental screening, the present invention can give an assessment value of material fatigue strength in a short time, greatly accelerating the process of material research and development, and has important application value, especially in the field of material anti-fatigue research and development.

[0154] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0155] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent application shall be subject to the attached claims.

Claims

1. A method for evaluating fatigue strength of multi-element alloys based on slip localization, characterized in that: include: S1: obtaining material parameters of a multi-element alloy for fatigue testing, and establishing a micro-scale model on a computer based on the material parameters; S2: using molecular dynamics simulation to simulate fatigue loading on the microscale model; S3: After the simulated fatigue loading enters the steady-state stage, the micro-scale model is divided into a plurality of sub-units of the same size, and the slip irreversibility of each sub-unit is calculated based on the shear strain of each atom in each sub-unit, and then the difference in slip irreversibility between the sub-units is calculated; S4: calculating a non-uniform parameter based on the slip irreversibility of each subunit and the difference in the slip irreversibility; normalizing and de-gridding the non-uniform parameter to obtain a slip localization index; S5: Constructing a fatigue strength evaluation model based on the material parameters and the slip localization index.

2. The method for evaluating fatigue strength of multi-component alloys based on slip localization according to claim 1, characterized in that: The material parameters include first ultimate tensile strength, element composition and component ratio.

3. The method for evaluating fatigue strength of multi-component alloys based on slip localization according to claim 2, characterized in that: Based on the elemental composition and component ratio, a micro-scale model of the multi-component alloy for fatigue testing was computationally established using Atomsk modeling software.

4. The method for evaluating fatigue strength of multi-component alloys based on slip localization according to claim 2, characterized in that S2 include: The micro-scale model is relaxed and subjected to simulated fatigue loading by using LAMMPS software, wherein the simulated fatigue loading is to apply periodic boundary conditions and perform cyclic load loading by using an EAM potential function; The relaxed micro-scale model is used as the initial configuration; The microscale model in the simulated fatigue loading is used as the target configuration; The requirement during the cyclic loading process is to ensure that the strain amplitude of the cyclic loading causes the micro-scale model to produce local slip behavior, and the local slip behavior is manifested as a first difference between the atomic coordinates of the target configuration and the atomic coordinates of the initial configuration; The OVITO software is used to visualize and analyze the micro-scale model during the simulated fatigue loading process, extract the stress-strain curve during the cyclic load loading process, and extract the first difference that appears. The first difference is used to calculate the shear strain of the corresponding atoms.

5. The method for evaluating fatigue strength of multi-component alloys based on slip localization according to claim 4, characterized in that: The judgment criteria for entering the steady-state stage of simulated fatigue loading are: The MATLAB calculation software is used to calculate the area enclosed by the stress-strain curve during each cyclic loading process. The calculation formula is as follows: ； ； in, It represents the area enclosed by the stress-strain curve during the Pth cycle loading process; represents loop integral; represents the stress value during the Pth cycle loading process; represents the strain value during the Pth cycle loading process; a Indicates strain value The minimum value of b Indicates strain value The maximum value of Indicates strain value Corresponding stress values ​​for loading and unloading difference; N Indicates the number of integral segments; Indicates n Strain value ; Indicates n Strain value Corresponding stress values ​​for loading and unloading difference; Indicates n+ 1 strain value ; Indicates n+ 1 strain value Corresponding stress values ​​for loading and unloading difference; After calculating the area enclosed by the stress-strain curve during all cyclic loading processes, when the numerical changes in the area enclosed by the stress-strain curve during five consecutive cyclic loading processes are all less than 30%, it is determined that the simulated fatigue loading has entered the steady-state stage.

6. The method for evaluating fatigue strength of multi-component alloys based on slip localization according to claim 4, characterized in that: In S3, in any steady-state stage, the micro-scale model is divided as follows: In micro-scale models x , y , z The three sides of the direction are respectively divided into a number of segments of the same length to obtain a number of cubes with the same volume. The cubes are the subunits, and each of the subunits contains a number of atoms.

7. The method for evaluating fatigue strength of multi-component alloys based on slip localization according to claim 6, characterized in that: The process of calculating the shear strain of each atom in each subunit is: Step 1: In s In the subunits, based on atoms i and its nearest neighbor atoms j The corresponding first difference, coordinates, calculate the atoms i The displacement gradient is calculated as: ； in, Represents atoms i The displacement gradient; Represents atoms i The corresponding first difference; Represents atoms i The nearest atom j The corresponding first difference; Represents atoms i The coordinates of Represents atoms i The nearest atom j The coordinates of Step 2: Atom-based i The displacement gradient of the atom is calculated i The particle deformation gradient tensor of: ； in, Represents atoms i The particle deformation gradient tensor of ; I is the identity matrix; Step 3: Atom-based i The particle deformation gradient tensor and its transposed matrix are used to calculate the atomic i The Green-Lagrange strain tensor of: ； Among them, E represents the atom i The Green-Lagrange strain tensor of ; T represents the transpose; Step 4: Place the atoms i The Green-Lagrange strain tensor of is expressed in three-dimensional space as: ； in, Represents atoms i exist x The degree of axial deformation in the direction; Represents atoms i exist y The degree of axial deformation in the direction; Represents atoms i exist z The degree of axial deformation in the direction; Represents atoms i exist xy Shear strain on a plane; Represents atoms i exist xz Shear strain on a plane; Represents atoms i exist yz Shear strain on a plane; Step 5: Atom-based i The axial deformation degree in each direction and the shear strain on each plane are calculated. i The shear strain is calculated as: ； in, Represents atoms i Shear strain; Step 6: Repeat steps 1-5 to traverse the s All atoms in the subunit are obtained s The shear strain of all atoms in a subunit; Step 7: Repeat steps 1-6, traverse all subunits, and obtain the shear strain of each atom in each subunit; The shear strain includes the maximum shear strain during cyclic loading and the residual shear strain after unloading.

8. The method for evaluating fatigue strength of multi-component alloys based on slip localization according to claim 7, characterized in that: The calculation formula of the non-uniform parameter is: ； ； in, express n The heterogeneity parameters of the subunits; n Indicates the number of subunits; Indicated in n In the subunit i The irreversibility of slip of each subunit; N represents the total number of atoms in the microscopic scale model; Indicates j The maximum shear strain of an atom during cyclic loading; Indicates j The residual shear strain of each atom after unloading; Indicates i The number of atoms in a subunit; Indicates i- The number of atoms in 1 subunit.

9. The method for evaluating fatigue strength of multi-component alloys based on slip localization according to claim 8, characterized in that: The normalizing and degridding the non-uniform parameters comprises: According to the micro-scale model x , y , z The ratio of the three sides of the direction divides the three-dimensional space into xyz · k ³ blocks, where k=1,2,3,4,…, r ,and r The value of must not result in the number of blocks being larger than the total number of atoms in the microscale model; Add weight factors and xyz · k The slip localization index is obtained by normalizing the non-uniformity parameters of the three blocks. The expression of the slip localization index is: ； in, W represents the slip localization index; r Indicates the upper limit of the level of the three-dimensional space division blocks; Indicates the level of dividing blocks k The weight factor when ; express xyz · k Non-uniformity parameters of ³ blocks; Indicated in xyz · k ³ blocks i The irreversibility of slip of each block; N represents the total number of atoms in the microscopic scale model; Indicates j Maximum shear strain in cyclic loading of atoms; Indicates j The residual shear strain after unloading of atoms.

10. The method for evaluating fatigue strength of multi-element alloys based on slip localization according to claim 9, characterized in that S5 include: Taking an average of the slip localization index in all steady-state stages to obtain an average slip localization value of the multi-element alloy for fatigue testing; The first ultimate tensile strength is associated with the fatigue strength based on the average slip localization value, and is corrected by parameters to construct the fatigue strength evaluation model. The expression of the fatigue strength evaluation model is: ； in, Indicates fatigue strength; represents the first ultimate tensile strength; represents the average slip localization value; A Represents the first parameter; B Represents the second parameter; C Represents the third parameter; The multi-element alloy used for fatigue test is simulated three times, and the values ​​of the first parameter, the second parameter and the third parameter are calibrated based on the average slip localization value and the first ultimate tensile strength in the three simulation calculations; The target multi-component alloy similar to the multi-component alloy used for fatigue test is subjected to simulation calculation and tensile test to obtain the target average slip localization value and the second ultimate tensile strength, which are then substituted into the fatigue strength evaluation model after calibration parameter values ​​to obtain the fatigue strength evaluation value of the target multi-component alloy.

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