A method for analyzing the mechanical properties of nanomaterials based on molecular dynamics simulation

Abstract

The present invention discloses a method for analyzing the mechanical properties of nanomaterials based on molecular dynamics simulation, comprising the following steps: 1. establishing a pure metal nano-polycrystalline unit cell model; 2. adding solute to the unit cell model and performing structural optimization to obtain a unit cell model with solute equilibrium segregation; 3. performing a simulated deformation test on the unit cell model using molecular dynamics simulation, outputting stress-strain curves and energy evolution curves; 4. performing dislocation analysis on the unit cell model to obtain the evolution of dislocation length / density within the grain and at the grain boundaries with strain; 5. calculating the grain boundary solute concentration using #imgabs0# and analyzing the strength-solute concentration correlation; 6. comprehensively analyzing the deformation mechanism and mechanical properties of the nanocrystalline material and performing alloy design. The present invention distinguishes the evolution of dislocation length / density within the grain and at the grain boundaries during deformation and quantitatively determines the grain boundary solute concentration, providing a method for analyzing material deformation mechanisms and characterizing mechanical properties at the microscale.

Description

Technical Field

[0001] The invention belongs to the technical field of metal materials and molecular simulation, and particularly relates to a method for analyzing the mechanical properties of nanomaterials based on molecular dynamics simulation. Background Art

[0002] Nanocrystalline materials exhibit excellent mechanical properties, including high strength and hardness, due to their structural characteristics, such as small grain size and high grain boundary volume fraction. However, due to the difficulty of deformation and weak atomic bonding in the grain boundary region, nanocrystalline materials are particularly prone to softening behavior and poor plasticity at extremely small grain sizes, which severely limits the processing and application of these materials. Uncovering the deformation mechanisms of nanocrystalline materials at extremely small grain sizes and exploring the strengthening mechanisms of these materials are crucial for the development of ultra-high strength and hardness nanocrystalline materials.

[0003] Studies have found that adding solute elements can effectively improve the strength of nanocrystalline materials. Unfortunately, current experimental methods make it difficult to accurately measure the solute distribution in the intracrystalline and grain boundary regions, and it is difficult to accurately separate the role and contribution of the intracrystalline and grain boundary regions in the deformation process of nanocrystalline materials. Therefore, it is difficult to deeply reveal the softening and strengthening mechanism of nanocrystalline materials by relying solely on experiments. Molecular dynamics simulation is an atomic-scale computer simulation method that can dynamically observe the evolution process of material organization and measure key physical parameters. It has very important applications in materials science research; in particular, molecular dynamics simulation has been widely used in the study of nanocrystalline deformation mechanisms. However, existing studies mainly focus on the influence of grain size / shape on the deformation behavior of nanocrystalline, and lack methods to distinguish grain boundary / intracrystalline deformation mechanisms and their respective contributions to the overall deformation of the material, which makes it difficult to deeply reveal and understand the deformation mechanism of nanocrystalline materials.

[0004] Therefore, it is necessary to provide a method for analyzing the deformation mechanism and mechanical properties of nano-alloys. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for analyzing the mechanical properties of nanomaterials based on molecular dynamics simulation in order to address the deficiencies of the above-mentioned existing technologies. This method establishes a nanocrystalline unit cell model and then performs dislocation analysis to obtain the results of the evolution of dislocation length / density within the crystal and at the grain boundary with strain. Using the formula The grain boundary solute concentration is calculated and the strength-solute concentration relationship is analyzed. The stress-strain curve, the evolution results of dislocation length / density within the grain and at the grain boundary, and the grain boundary solute concentration and strength-solute concentration relationship are integrated to analyze the deformation mechanism and mechanical properties of nanocrystalline materials. This solves the problem of difficulty in distinguishing the contributions of the intracrystalline and grain boundary regions in the nanocrystalline deformation process. The dislocation length / density and solute concentration within the grain and at the grain boundary are distinguished, thereby distinguishing the contributions of the intracrystalline and grain boundary regions to deformation. This helps to understand the deformation mechanism of nanomaterials, thereby achieving mechanical property design by regulating grain size and solute concentration, and designing high-strength nanocrystalline alloys.

[0006] To solve the above technical problems, the present invention adopts a technical solution: a method for analyzing the mechanical properties of nanomaterials based on molecular dynamics simulation, characterized in that the method comprises the following steps:

[0007] Step 1: Establish a pure metal nano-polycrystalline unit cell model;

[0008] Step 2: Add solute to the unit cell model established in step 1 and perform structural optimization using the Monte Carlo-molecular dynamics method to obtain a unit cell model of solute equilibrium segregation;

[0009] Step 3: Using molecular dynamics simulation method to simulate deformation test on the unit cell model obtained in step 2, and output stress-strain curve and energy evolution curve;

[0010] Step 4: Separate the microstructure of the unit cell model after the simulated deformation test in step 3 into the intragranular and grain boundary regions, and then perform dislocation analysis using OVITO software to obtain the results of the evolution of dislocation length / density within the grain and at the grain boundary with strain;

[0011] Step 5: Based on the data obtained from the dislocation analysis using OVITO software in step 4, use the formula Calculate and obtain the grain boundary solute concentration and analyze the strength-solute concentration relationship, where x gb represents the grain boundary solute concentration, V represents the unit cell volume, C0 represents the total solute concentration, A gb represents the grain boundary area, δ represents the grain boundary thickness, and κ represents the ratio of the atomic density within the grain and at the grain boundary;

[0012] Step 6. Integrate the stress-strain curve obtained in step 3, the intragranular and grain boundary dislocation length / density evolution results obtained in step 4, and the grain boundary solute concentration and strength-solute concentration correlation obtained in step 5 to analyze the deformation mechanism and mechanical properties of the nanocrystalline material and perform alloy design.

[0013] The present invention uses ATOMSK software to construct a nano-polycrystalline unit cell. The unit cell constructed in step 1 is used as the initial structure file and imported into the LAMMPS software for structural optimization. Subsequently, different concentrations of solute are added using the Monte Carlo-Molecular Dynamics simulation (MC-MD) method. After the program runs a certain number of steps, it is ensured that the solute concentration reaches the set value and the segregation has reached an equilibrium state (the system energy reaches a stable value), thereby obtaining a unit cell model of solute equilibrium segregation. The unit cell model of solute equilibrium segregation constructed in step 2 is used as the input file and imported into the LAMMPS software for tensile deformation, with the deformation rate set to approximately 1×10 7 ~1×10 9 s -1 , set the maximum strain to 20%, record the key physical parameters during deformation, obtain the stress-strain curve and the energy evolution of the system during deformation, the grain boundary solute concentration depends on factors such as the total solute concentration, grain size and grain shape; according to the formula Calculate and determine the grain boundary solute concentration under a certain total solute concentration and grain size; use VESTA software to analyze the overall dislocation length / density of the sample and establish the evolution relationship between the total dislocation length / density and the simulation time; use VESTA software to delete "other" type atoms and retain intracrystalline atoms, then analyze the intracrystalline dislocation length / density and establish the evolution relationship between the intracrystalline dislocation length / density and the simulation time; subtract the intracrystalline dislocation length from the total dislocation length to obtain the evolution relationship between the grain boundary dislocation length / density and the simulation time; the dislocation length / density begins to increase significantly, corresponding to the destruction of the structure and the yield of the material. Combined with the stress-strain curve obtained in step three, the evolution results of the intracrystalline and grain boundary dislocation length / density obtained in step four, and the grain boundary solute concentration and strength-solute concentration correlation obtained in step five, the deformation mechanism and mechanical properties of the nanocrystalline material are analyzed;

[0014] The formula in the present invention Applicable to polycrystalline materials with arbitrary grain shapes.

[0015] The above-mentioned method for analyzing the mechanical properties of nanomaterials based on molecular dynamics simulation is characterized in that the polycrystalline unit cell model in step 1 is constructed using ATOMSK software, the polycrystalline unit cell model is an equiaxed crystal structure, a columnar crystal structure, or a layered structure, and the grain size of the polycrystalline unit cell model is 5nm to 30nm. In the present invention, ATOMSK software is used to construct a polycrystalline unit cell model, a variety of crystal structures are constructed, and it is suitable for analyzing a variety of polycrystalline materials.

[0016] The above-mentioned method for analyzing the mechanical properties of nanomaterials based on molecular dynamics simulation is characterized in that the process of adding solute in step 2 is to gradually add solute by Monte Carlo-molecular dynamics simulation, so that the solute concentration gradually increases from zero to grain boundary saturation, or initially replaces the solute of a set value, and then energy optimization is performed by Monte Carlo-molecular dynamics simulation method, so that the solute gradually segregates to the grain boundaries to achieve equilibrium distribution. The present invention facilitates subsequent analysis and ultimately analyzes the deformation mechanism and mechanical properties of nanocrystalline materials by adding solute to gradually segregate to the grain boundaries to achieve equilibrium distribution. The specific value for achieving grain boundary saturation in the present invention depends on the grain size and system.

[0017] The aforementioned method for analyzing the mechanical properties of nanomaterials based on molecular dynamics simulation is characterized in that the simulated deformation test in step 3 is uniaxial tension, uniaxial compression, uniaxial shear, multiaxial tension, multiaxial compression, or multiaxial shear. The present invention is applicable to a variety of simulated deformation tests, and ultimately analyzes the deformation mechanism and mechanical properties of the nanocrystalline material based on the simulated deformation tests.

[0018] The above-mentioned method for analyzing the mechanical properties of nanomaterials based on molecular dynamics simulation is characterized in that the process of dislocation analysis in step 4 is:

[0019] Step 101: using the nearest neighbor coordination number analysis in OVITO software to identify atoms in the intracrystalline and grain boundary regions, obtaining the total area of ​​the grain boundaries and the total volume of the unit cell, and based on this, obtaining the total volume of the grain boundary region and the total volume of the intracrystalline region;

[0020] Step 102: Perform dislocation analysis on the entire unit cell using a dislocation analysis algorithm to obtain a total dislocation length, and then use OVITO software to obtain a total unit cell volume and a total dislocation density of the unit cell;

[0021] Step 103: Identify atoms in the intracrystalline and grain boundary regions based on the nearest neighbor coordination number analysis in the OVITO software, delete the atoms in the grain boundary region and retain the atoms in the intracrystalline region, perform dislocation analysis in the intracrystalline region using a dislocation analysis algorithm to obtain the dislocation length of the intracrystalline region, and then obtain the dislocation density in the intracrystalline region by combining the total volume of the intracrystalline region obtained in step 101;

[0022] Step 104: Subtract the dislocation length in the intragranular region obtained in step 103 from the total dislocation length obtained in step 102 to obtain the dislocation length in the grain boundary region. Then, combined with the volume of the grain boundary region obtained in step 101, the evolution results of the dislocation length / density in the intragranular region and the grain boundary region with strain are obtained.

[0023] The above-mentioned method for analyzing the mechanical properties of nanomaterials based on molecular dynamics simulation is characterized in that V and A in step 5 gb , δ, and κ were obtained using OVITO software.

[0024] The above-mentioned method for analyzing the mechanical properties of nanomaterials based on molecular dynamics simulation is characterized in that the process of analyzing the deformation mechanism of nanocrystalline materials in step 6 is as follows: analyzing the stress-strain curve obtained in step 3, clarifying the elastic deformation stage, the plastic deformation stage and the position where the material begins to yield, then comparing the positions where the dislocation length / density in the crystal and the grain boundary begins to increase significantly, and analyzing the dominant mechanism of deformation of the nano-polycrystalline material; combining the stress-strain curve and the evolution of the grain boundary solute concentration, analyzing the relationship between the yield position of the material, the yield strength and the grain boundary solute saturation state. In the present invention, if the corresponding dislocation length / density in the crystal increases significantly when the material yields, the deformation is dominated by the crystal; if the corresponding dislocation length / density in the grain boundary increases significantly when the material yields, the deformation is dominated by the grain boundary; combining the stress-strain curve and the evolution of the grain boundary solute concentration, analyzing the relationship between the yield position of the material, the yield strength and the grain boundary solute saturation state, when the total solute concentration is given, the grain boundary solute concentration is related to the grain size, so the relationship between the yield strength and the grain boundary solute concentration and the grain size can be established for alloy design.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] 1. The present invention establishes a nano-polycrystalline unit cell model and then performs dislocation analysis to obtain the evolution of dislocation length / density within the crystal and at the grain boundary with strain. Using the formula By calculating the grain boundary solute concentration and analyzing the strength-solute concentration relationship, the deformation mechanism and mechanical properties of nanocrystalline materials are analyzed by integrating stress-strain curves, the evolution of dislocation lengths and densities within and at grain boundaries, and the relationship between solute concentration and strength-solute concentration. This solves the problem of difficulty distinguishing the contributions of the intracrystalline and grain boundary regions during nanocrystalline deformation. Distinguishing dislocation lengths / densities and solute concentrations within and at grain boundaries, and thus distinguishing the contributions of the intracrystalline and grain boundary regions to deformation, helps understand the deformation mechanism of nanomaterials, thereby enabling mechanical property design by manipulating grain size and solute concentration, and designing high-strength nanocrystalline alloys.

[0027] 2. The present invention combines stress-strain curves with analysis of dislocation initiation and proliferation positions within grains and at grain boundaries, and finds that the solute concentration at grain boundaries affects grain boundary energy, thereby affecting grain boundary structural stability and material mechanical properties: at large sizes, grain boundaries are unsaturated, and material strength is determined by the evolution of dislocations within the grains; at small sizes, grain boundaries are saturated, and material strength is determined by the evolution of dislocations at grain boundaries. Based on this, the softening and strengthening mechanism of nanocrystals is revealed, and combined with the analysis of grain boundary solute concentration and material yield stress, the correlation between mechanical properties-grain size / solute concentration is established, guiding the design of high-strength nanocrystalline alloys.

[0028] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The figure is a flow chart of the method for analyzing the mechanical properties of nanomaterials based on molecular dynamics simulation of the present invention.

[0030] Figure 2 Schematic diagram of the nano-polycrystalline unit cell model constructed in Example 1 of the present invention.

[0031] Figure 3 This is the evolution of yield stress with grain size in Example 1 of the present invention.

[0032] Figure 4 The evolution of dislocation length in the unit cell as a whole, within the crystal and in the grain boundary region with strain in Example 1 of the present invention is shown.

[0033] Figure 5 The evolution of grain boundary solute concentration with grain size in Example 1 of the present invention. DETAILED DESCRIPTION

[0034] Figure 1 This is a flow chart of the method for analyzing the mechanical properties of nanomaterials based on molecular dynamics simulation of the present invention. Figure 1 It can be seen that the present invention first establishes a pure metal nano-polycrystalline unit cell model, then adds solute based on Monte Carlo-molecular dynamics and obtains the equilibrium segregation structure, and then analyzes the evolution of dislocation length with strain, i.e., the total dislocation length, intracrystalline dislocation length, and grain boundary dislocation length, and obtains the stress-strain curve and energy evolution curve, i.e., the change of temperature, strain rate and grain size, and obtains the grain boundary solute concentration and its correlation with strength, i.e., grain boundary solute concentration calculation, grain boundary saturation segregation, and strength-solute concentration correlation. Through the above analysis, the contribution of intracrystalline and grain boundary to deformation is distinguished, which helps to understand the deformation mechanism of nanomaterials, thereby realizing mechanical property design by regulating grain size and solute concentration, and designing high-strength nanocrystalline alloys.

[0035] Example 1

[0036] This embodiment includes the following steps:

[0037] Step 1: Use ATOMSK software to construct a pure copper nano-polycrystalline unit cell model, where the unit cell size is 40×40×3.65nm 3 and 80×80×3.65nm 3 , the grain size is 5nm to 18nm, the Z axis of the unit cell is along the

[001] direction, and the X and Y axes are randomly positioned; the polycrystalline unit cell model is an equiaxed crystal structure;

[0038] Step 2: Using LAMMPS software to perform structural optimization on the pure copper nanopolycrystalline unit cell model, the energy optimization algorithm used in the structural optimization is the conjugate gradient method, and the potential energy file is the embedded atomic potential proposed by Williams in 2006. For each grain size, the Monte Carlo-molecular dynamics method is used to add 0.008 to 0.05 silver solute to optimize the unit cell model established in step 1. The program is run for no less than 200,000 steps to allow the solute to gradually segregate toward the grain boundaries to achieve equilibrium distribution until energy convergence, thereby obtaining a unit cell model with equilibrium solute segregation, i.e., a copper-silver nanoalloy with equilibrium segregation.

[0039] Step 3: Using LAMMPS software and molecular dynamics simulation method, the copper-silver nanoalloy with equilibrium segregation obtained in step 2 was heated and kept warm. The temperature was set to 300K, the ensemble was NPT, and the total time was 20ps. Then, tensile deformation was performed and the deformation rate was set to about 5×10 8 s -1 , the maximum strain is 20%, the ensemble is set to NPT, and the stress-strain curve and energy evolution curve are output; the tensile deformation is uniaxial tension;

[0040] Step 4: Separate the grain boundary and intragranular regions of the microstructure of the unit cell model after the simulated deformation test in step 3, and then perform dislocation analysis using OVITO software to obtain the results of the evolution of dislocation length / density within the grain and at the grain boundary with strain; the process of the dislocation analysis is as follows:

[0041] Step 101: using the nearest neighbor coordination number analysis in OVITO software to identify atoms in the intracrystalline and grain boundary regions, obtaining the total area of ​​the grain boundaries and the total volume of the unit cell, and based on this, obtaining the total volume of the grain boundary region and the total volume of the intracrystalline region;

[0042] Step 102: Perform dislocation analysis on the entire unit cell using a dislocation analysis algorithm to obtain a total dislocation length, and then use OVITO software to obtain a total unit cell volume and a total dislocation length / density of the unit cell;

[0043] Step 103: Identify atoms in the intracrystalline and grain boundary regions according to the nearest neighbor coordination number analysis in the OVITO software, delete atoms in the grain boundary region and retain atoms in the intracrystalline region, perform dislocation analysis in the intracrystalline region using a dislocation analysis algorithm to obtain the dislocation length in the intracrystalline region, and then obtain the dislocation length / density in the intracrystalline region by combining the total volume of the intracrystalline region obtained in step 101;

[0044] Step 104: Subtract the dislocation length in the intragranular region obtained in step 103 from the total dislocation length obtained in step 102 to obtain the dislocation length in the grain boundary region. Then, combined with the volume of the grain boundary region obtained in step 101, the strain evolution results of the dislocation length / density in the intragranular region and the grain boundary region are obtained.

[0045] Step 5: Based on the data obtained from the dislocation analysis using OVITO software in step 4, use the formula Calculate and obtain the grain boundary solute concentration and analyze the strength-solute concentration relationship. The C0 represents the total solute concentration. Other parameters such as V, A gb , δ, and κ can be obtained through OVITO software;

[0046] Step 6. Combining the stress-strain curve obtained in step 3, the evolution results of the intracrystalline and grain boundary dislocation length / density obtained in step 4, and the grain boundary solute concentration and strength-solute concentration obtained in step 5, analyze the deformation mechanism and mechanical properties of the nanocrystalline material and perform alloy design; the process of analyzing the deformation mechanism of the nanocrystalline material is as follows: analyzing the stress-strain curve obtained in step 3, clarifying the elastic deformation stage, the plastic deformation stage, and the position where the material begins to yield, and then comparing the positions where the intracrystalline and grain boundary dislocation length / density begin to increase significantly, analyzing the dominant mechanism of deformation of the nano-polycrystalline material, and combining the stress-strain curve and the evolution of grain boundary solute concentration to analyze the relationship between the material yield position, yield strength and grain boundary solute saturation state.

[0047] Figure 2 This is a schematic diagram of the nano-polycrystalline unit cell model constructed in this embodiment, from Figure 2 It can be seen from the figure that the nano-polycrystalline unit cell model constructed in this embodiment has a grain size of 5.2 nm.

[0048] Figure 3 The evolution of yield stress with grain size in this example is shown in Figure 2. Figure 3 As can be seen from the figure, in this embodiment, a simple analysis of the stress-strain curve is performed to obtain the yield strength. The yield strength of the material first increases and then decreases with the decrease of the grain size. The grain boundary segregation increases the yield stress of the material while reducing the grain size of the sample where softening occurs (the grain size decreases from 12.3 nm to below 10.3 nm).

[0049] Figure 4 The evolution of dislocation length in the unit cell, intracrystalline and grain boundary regions with strain in this embodiment is shown in Figure 2. Figure 4 It can be seen that by comparing the correspondence between the evolution of intracrystalline dislocation length, grain boundary dislocation length and overall dislocation length and the stress-strain curve, the contribution of intracrystalline and grain boundary regions to the deformation process of nanocrystalline can be revealed. The yield position of nanocrystalline and the position where the grain boundary dislocation length increases significantly are highly coincident, but not coincident with the position where the intracrystalline dislocation length increases significantly, indicating that grain boundary slip dominates the deformation process of nanocrystalline materials.

[0050] Figure 5 The evolution of grain boundary solute concentration with grain size in this example is shown in Figure 2. Figure 5It can be seen that the intrinsic relationship between the material deformation process and the grain boundary solute concentration can be analyzed. At small grain size (<10.3nm), grain boundary segregation reaches saturation, and grain boundary atomic slip dominates material deformation; at large grain size (>10.3nm), grain boundary segregation does not reach saturation, and intracrystalline dislocation movement dominates material deformation. At the same time, combined with Figure 2 The mechanical properties analysis showed that the grain boundary segregation increased the yield stress of nanocrystals and reduced the softening size of nanocrystals (from D c Reduce to D s ), the grain size range of nanocrystals with maximum yield stress is about 7.3nm~10.3nm, and the corresponding optimal grain boundary solute concentration is the saturation value of 0.23 (the overall solute concentration can be calculated according to the formula calculated).

[0051] The above analysis in this embodiment shows that the deformation mechanism depends on the grain size, that is, at a small grain size (<10.3 nm), grain boundary segregation reaches saturation, and atomic slip at the grain boundaries dominates material deformation; at a large grain size (>10.3 nm), grain boundary segregation has not reached saturation, and intragranular dislocation motion dominates material deformation. When the strength is highest, the corresponding grain boundary just reaches saturation (the grain boundary solute concentration is about 0.23), thereby realizing alloy design.

[0052] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent variation made to the above embodiment based on the essence of the invention technology shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for analyzing the mechanical properties of nanomaterials based on molecular dynamics simulation, characterized in that: The method comprises the following steps: Step 1: Establish a pure metal nano-polycrystalline unit cell model; Step 2: Add solute to the unit cell model established in step 1 and perform structural optimization using the Monte Carlo-molecular dynamics method to obtain a unit cell model of solute equilibrium segregation; Step 3: Using molecular dynamics simulation method to simulate deformation test on the unit cell model obtained in step 2, and output stress-strain curve and energy evolution curve; Step 4: Separate the microstructure of the unit cell model after the simulated deformation test in step 3 into the intragranular and grain boundary regions, and then perform dislocation analysis using OVITO software to obtain the results of the evolution of dislocation length / density within the grain and at the grain boundary with strain; Step 5: Based on the data obtained from the dislocation analysis using OVITO software in step 4, use the formula Calculate the grain boundary solute concentration and analyze the strength-solute concentration relationship, where x gb represents the grain boundary solute concentration, V represents the unit cell volume, C0 represents the total solute concentration, A gb represents the grain boundary area, δ represents the grain boundary thickness, and κ represents the ratio of the atomic density within the grain and at the grain boundary; Step 6. Combining the stress-strain curve obtained in step 3, the evolution results of the dislocation length / density within the grain and at the grain boundary obtained in step 4, and the grain boundary solute concentration and strength-solute concentration correlation obtained in step 5, the deformation mechanism and mechanical properties of the nanocrystalline material are analyzed, and alloy design is performed. The process of analyzing the deformation mechanism of the nanocrystalline material is as follows: analyzing the stress-strain curve obtained in step 3, clarifying the elastic deformation stage, the plastic deformation stage, and the position where the material begins to yield, and then comparing the positions where the dislocation length / density within the grain and at the grain boundary begins to increase significantly, analyzing the dominant mechanism of deformation of the nano-polycrystalline material, and combining the stress-strain curve and the evolution of the grain boundary solute concentration to analyze the relationship between the yield position of the material, the yield strength, and the grain boundary solute saturation state.

2. The method for analyzing the mechanical properties of nanomaterials based on molecular dynamics simulation according to claim 1, characterized in that: The polycrystalline unit cell model in step 1 is constructed using ATOMSK software. The polycrystalline unit cell model is an equiaxed crystal structure, a columnar crystal structure or a layered structure. The grain size of the polycrystalline unit cell model is 5 nm to 30 nm.

3. The method for analyzing the mechanical properties of nanomaterials based on molecular dynamics simulation according to claim 1, characterized in that: The process of adding solute in step 2 is to gradually add solute by Monte Carlo-molecular dynamics simulation, so that the solute concentration gradually increases from zero to grain boundary saturation, or initially replaces the set value of solute, and then optimize the energy by Monte Carlo-molecular dynamics simulation method, so that the solute gradually segregates to the grain boundary to achieve equilibrium distribution.

4. The method for analyzing the mechanical properties of nanomaterials based on molecular dynamics simulation according to claim 1, characterized in that: The simulated deformation test in step 3 is uniaxial tension, uniaxial compression, uniaxial shear, multiaxial tension, multiaxial compression or multiaxial shear.

5. The method for analyzing the mechanical properties of nanomaterials based on molecular dynamics simulation according to claim 1, characterized in that: The process of dislocation analysis described in step 4 is: Step 101: using the nearest neighbor coordination number analysis in OVITO software to identify atoms in the intracrystalline and grain boundary regions, obtaining the total area of ​​the grain boundaries and the total volume of the unit cell, and based on this, obtaining the total volume of the grain boundary region and the total volume of the intracrystalline region; Step 102: Perform dislocation analysis on the entire unit cell using a dislocation analysis algorithm to obtain a total dislocation length, and then use OVITO software to obtain a total unit cell volume and a total dislocation density of the unit cell; Step 103: Identify atoms in the intracrystalline and grain boundary regions based on the nearest neighbor coordination number analysis in the OVITO software, delete the atoms in the grain boundary region and retain the atoms in the intracrystalline region, perform dislocation analysis in the intracrystalline region using a dislocation analysis algorithm to obtain the dislocation length of the intracrystalline region, and then obtain the dislocation density in the intracrystalline region by combining the total volume of the intracrystalline region obtained in step 101; Step 104: Subtract the dislocation length in the intragranular region obtained in step 103 from the total dislocation length obtained in step 102 to obtain the dislocation length in the grain boundary region. Then, combined with the volume of the grain boundary region obtained in step 101, the evolution results of the dislocation length / density in the intragranular region and the grain boundary region with strain are obtained.

6. The method for analyzing the mechanical properties of nanomaterials based on molecular dynamics simulation according to claim 1, characterized in that: V and A in step 5 gb , δ, and κ were obtained using OVITO software.

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