Molecular dynamics-macroscopic multi-scale coupling calculation method

Abstract

The invention discloses a molecular dynamics-macroscopic multi-scale coupling calculation method, which relates to the field of material damage numerical simulation analysis, and comprises the following steps: respectively establishing a microcosmic plate model and a macroscopic plate model; young modulus and Poisson's ratio parameters are calculated through microscale pneumatic simulation in the microcosmic plate model and are transmitted into the macroscopic plate model, a stress value I and a strain value I are obtained through macroscopic pneumatic simulation calculation and are transmitted into the microcosmic plate model, and the stress value I and the strain value I are obtained through microcosmic-macroscopic continuous coupling iteration. And obtaining the mechanical property indexes of the silicon thin plate in each stage from stress starting, crack generation, crack propagation to failure and fracture. The invention provides a molecular dynamics-macroscopic multi-scale coupling calculation method. A new analysis method is provided for researching structural failure and damage in an aerodynamic hot extreme environment through coupling calculation of macroscopic and microscopic scale models.

Description

Technical Field

[0001] The present invention relates to the field of numerical simulation analysis of material damage, and more specifically, to a method of molecular dynamics-macroscopic multi-scale coupling calculation used in the case of numerical prediction and analysis of material damage. Background Art

[0002] Under extreme conditions of high-temperature thermochemistry and non-equilibrium gas flow, huge aerodynamic / thermal loads can easily lead to deformation, softening, melting and other responses of the material structure. This is very different from the failure behavior under normal conditions. It is of practical significance to carry out numerical prediction and analysis of material damage.

[0003] Macro-scale numerical simulation provides a reliable prediction for material structural damage. In the process of strong aerodynamic forces and strict aerodynamic heating, structural deformation has a significant effect on the internal temperature distribution of the material. Simulating physical and mechanical problems requires unified consideration and analysis of the coupled system of heat transfer, deformation and structural stress. To this end, the finite element method (FEA) and GKUA in the field of hypersonic aerodynamics are used to simulate the dynamic thermoelastic coupling response behavior such as internal temperature distribution, structural deformation and thermal damage of the material. Li et al. studied the structural deformation and thermomechanical response caused by reentry aerodynamic and thermal loads. The configuration was subjected to large deformation and stress analysis by applying mechanical and thermal loads. Ji and Li et al. proposed a structural dynamics model for the deformation of aluminum-magnesium alloys under typical loads such as concentrated force, body force and torque. The study showed that aerodynamic forces also have an important influence on the nonlinear mechanical response of the structure, and the effects of thermal and mechanical loads should be considered simultaneously. In addition, GKUA for solving the Boltzmann equation is proposed by combining the direct simulation Monte Carlo (DSMC) method, the Navier-Stokes / DSMC hybrid algorithm, etc. This method can accurately calculate the flow environment such as aerodynamic heat, temperature, and velocity distribution near the typical altitude of the aircraft. However, macroscopic methods are unable to simulate the initiation of atomic defects and the evolution of cracks at the microscopic scale. These microscopic behaviors play a crucial role in providing reliable predictions of structural failure.

[0004] MD simulation methods can understand microstructural thermodynamics, physical properties and macroscopic transport properties at the atomic and molecular scales, and are widely used in physical chemistry, materials science, life sciences and other fields. In the past decade, a large number of studies have been conducted using MD simulations to explore the mechanical behavior of materials and the microscopic mechanisms of structural failure. The generation and evolution of microstructural defects (voids, cracks, dislocations, twins, etc.) depend on temperature, loading mode and material structure.

[0005] Based on the atomic-scale damage mechanism, a large number of dynamic simulations of nanoscale voids and cracks were performed. The dynamic damage behavior of Zr crystals showed that temperature and strain rate play a dominant role in the preference of void nucleation.

[0006] Jing et al. reported the evolution mechanism of spherical voids in polycrystalline copper under uniaxial tensile loads and proposed a criterion for the existence of a critical void diameter that depends on the grain size. Lubarda et al. pointed out that the vacancy diffusion mechanism can only be used under low strain rate and high temperature conditions. They proposed a dislocation emission mechanism under high strain rate loads. The stress concentration at a certain distance from the crack tip is characterized by void nucleation and final growth. In addition, the structural gradient will also affect the stress distribution near the crack tip and the size of the plastic zone, and the grain size gradient will affect the ability of nanometals to resist crack growth.

[0007] Gao et al. showed through MD simulation that the critical twin boundary spacing and maximum strength for softening in nanotwinned copper depend on the grain size. MD method can estimate the mechanical properties of materials and help understand the fracture mechanism.

[0008] However, the systematic study from macro-scale numerical modeling to MD simulation to reveal the microscopic mechanism of material failure and predict the disintegration of metallic truss structures under extreme aero-thermal environment is a rarely studied concept. Summary of the invention

[0009] An object of the present invention is to solve at least the above problems and / or disadvantages and to provide at least the advantages which will be described hereinafter.

[0010] In order to achieve these purposes and other advantages of the present invention, a method for molecular dynamics-macroscopic multi-scale coupling calculation is provided, comprising:

[0011] S1. Establish microscopic plate model and macroscopic plate model respectively;

[0012] S2. Through micro-scale aerodynamic simulation calculation in the micro-plate model, the failure of the plate under the multi-field coupling of force, heat, chemical and flow, as well as the corresponding Young's modulus I and Poisson's ratio parameter I, are obtained;

[0013] S3, passing the Young's modulus Ⅰ and Poisson's ratio parameter Ⅰ obtained by calculation in S2 into the macro plate model, and obtaining the stress value Ⅰ and strain value Ⅰ of the plate under tension or compression through macro aerodynamic simulation calculation;

[0014] S4, the stress value I and strain value I obtained in S3 are transferred into the micro plate model to perform micro-scale aerodynamic simulation calculation, and Young's modulus II and Poisson's ratio parameter II under the influence of crack propagation are obtained;

[0015] S5, passing the Young's modulus II and Poisson's ratio parameter II calculated by S4 into the macro plate model, and obtaining the stress value II and strain value II in the case of cracks through macro aerodynamic simulation;

[0016] Repeat S4 to S5 to obtain the mechanical performance indicators of the plate at each stage from initial stress, crack generation, crack propagation to failure and fracture under continuous micro-macro coupling iteration.

[0017] Preferably, in S2, the failure condition refers to calculating the chemical ablation condition of the material at different temperatures after obtaining the stress and temperature distribution by calculating the flow field on the plate surface.

[0018] Preferably, in S1, the macro plate model is to simplify the research object into a thin plate I with a size of 0.015m×0.5m in the macro aerodynamic simulation.

[0019] Preferably, in S3, the macroscopic aerodynamic simulation uses GKUA and finite element method to obtain the temperature and pressure distribution of the external flow field as a comparative verification of the atomistic simulation;

[0020] Among them, in the macroscopic simulation, the outside of thin plate I is the re-entry near-continuous transition flow, the inflow Mach number is 8.37, the Knudsen number is 0.01, and the specific heat ratio is 1.4.

[0021] Preferably, in S1, the microscopic plate model is a microscopic aerodynamic simulation in which the research object is simplified to a size of The size of the molecular dynamics simulation system box is

[0022] In the micro-scale aerodynamic simulation, the initial state of the simulation environment is set to a pressure P of 30 atm, a temperature T of 300 K, and a lattice constant of the silicon atomic model is fixed to

[0023] In the micro-scale aerodynamic simulation, the velocity Verlet algorithm is used to perform the integration of the motion equations, and the time step is set to 1 fs. The thin plate II moves in the canonical ensemble at a speed of 1000 m / s along the negative X direction;

[0024] Periodic boundary conditions are applied in the x, y, and z directions of the spatial coordinate system. After the system runs for 6ns, the interaction between atoms is simulated using the Lennard-Jones (LJ) potential function.

[0025] Preferably, in S2, the micro-scale aerodynamic simulation is performed by loading different external forces and high temperature conditions on the thin plate I to simulate and observe the structural changes of the woven structure under extreme conditions and the evolution of the ablation reaction over time, thereby obtaining the microscopic mechanism of the ablation evolution of the material under the action of the force-heat-chemical-flow coupling field.

[0026] The present invention includes at least the following beneficial effects: Aiming at the degradation and destruction of material structures under extreme aerodynamic thermal environments, the present invention establishes a set of simulation models. Using a simplified thin plate model, the advantages of the multi-scale coupling calculation method are demonstrated through the deformation failure process of the thin plate under extreme conditions of high-temperature thermochemistry and non-equilibrium gas flow. Through this method, the mechanical parameters of the material under different conditions can be accurately obtained, greatly improving the accuracy of the model. The coupling calculation of macro and micro scales provides a new analytical method for studying structural failure and damage under extreme aerodynamic thermal environments.

[0027] Compared with traditional macroscopic or microscopic models, the present invention has the following distinctive effects:

[0028] First, the calculation feature of the present invention lies in the repeated iteration of micro and macro models, rather than the traditional direct application of micro parameters to macro, so as to ensure that the model is more in line with reality and the accuracy will be greatly improved.

[0029] Second, the traditional calculation from micro to macro has the problem of large amount of calculation and long calculation time, while our macro-micro multi-scale coupled iteration has a much shorter calculation time than the traditional method under the same system;

[0030] Third, traditional macroscopic parameters guide microscopic calculations, but there are problems such as insufficient accuracy, impracticality, and inability to explain the mechanism. Our macroscopic and microscopic multi-scale coupling calculations start from the basic atomic potential function and provide parameters to each other, making the calculations more accurate and more realistic.

[0031] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the microscopic model;

[0033] Figure 2 It is a schematic diagram of the macro model;

[0034] Figure 3 This is the flow chart of micro-macro multi-scale coupling calculation;

[0035] Figure 4 It is a schematic diagram of the calculation process of the force-heat-chemical-fluid multi-field coupling model;

[0036] Figure 5 This is the change diagram of Young's modulus of materials at different stages;

[0037] Figure 6 This is the Poisson's ratio variation diagram of materials at different stages;

[0038] Figure 7A schematic diagram showing the comparison of the calculation accuracy between the multi-scale coupling calculation method of the present invention and the traditional microscopic calculation method;

[0039] Figure 8 Schematic diagram for comparing the calculation speeds of the multi-scale coupling calculation method of the present invention and the traditional microscopic calculation method. DETAILED DESCRIPTION

[0040] The present invention is further described in detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0041] The present invention provides a method of molecular dynamics-macroscopic multi-scale coupling calculation, establishes a set of micro-macroscopic simulations, and takes the deformation failure process of a thin plate under extreme conditions of high-temperature thermochemistry and non-equilibrium gas flow as an example to demonstrate the superiority of the multi-scale coupling calculation method. Specifically, the present invention uses a unified gas dynamics algorithm based on the Boltzmann equation at the macro level to calculate and provide the temperature and stress distribution on the flow field surface; at the micro level, the classical molecular dynamics method is applied to construct a physical model of force-heat-chemical-flow multi-field coupling. The focus is on analyzing the changes in Young's modulus and Poisson's ratio during crack initiation. After these microscopic parameters are transmitted to the macroscopic model in real time, the macroscopic model further calculates the stress and strain in the current state, and returns the results to the microscopic model for iterative calculation.

[0042] In the macroscopic aerodynamic simulation, the model is simplified to a plate model with a size of 0.015m×0.5m. The macroscopic mechanical behavior in the hypersonic aerodynamic environment is simulated. The outside of the plate is a transitional flow between continuous flow and rarefied flow, with an inflow Mach number of 8.37, a Knudsen number of 0.01, and a specific heat ratio of γ=1.4. GKUA is used to solve the Boltzmann model equation with rotational non-equilibrium effects, and the plate external flow field of 63×41 grids in the XOZ coordinate system is calculated.

[0043] In the micro-scale aerodynamic simulation, the size of the atomic plate model is The size of the molecular dynamics simulation system box is The system is filled with 1000 atoms. The initial state of the simulation environment is set to pressure P = 30atm and temperature T = 300K. The lattice constant of the silicon atom model is fixed to The velocity Verlet algorithm with a time step of 1fs is used for the integration of the equation of motion. The plate moves in the canonical ensemble (NVT) at a speed of 1000m / s along the negative X direction. Periodic boundary conditions are applied in all three directions (the boundary conditions are periodic boundary conditions, which means that the physical system is periodic in space, that is, the boundaries of the system in the three directions of xyz are interconnected. When a particle leaves one end of the system, it re-enters the system from the other end in the same state). The system runs for 6ns, and the interaction between atoms is accurately simulated using the Lennard-Jones (LJ) potential function. By loading the model with different external effects and high temperature conditions, the structural changes of the braided structure under extreme conditions and the evolution of the ablation reaction over time are simulated and observed, and the microscopic mechanism of the ablation evolution of the material under the action of the force-heat-chemical-fluid coupling field is obtained.

[0044] Taking the deformation failure process of thin plates under extreme conditions of high-temperature thermochemistry and non-equilibrium gas flow as an example, the superiority of the multi-scale coupling calculation method is demonstrated. In the macro aspect, the gas dynamics theory unified algorithm of the Boltzmann model equation is used to provide the surface temperature and stress distribution of the flow field, and the classical molecular dynamics method is used in the micro aspect. The focus is on calculating the changes in the Young's modulus and Poisson's ratio of the material during the crack initiation process, and these parameters are transmitted to the macro model in real time. After receiving the parameters, the macro model calculates the stress and strain in the current state, and then returns to the micro for iteration. In this way, the mechanical parameters of the material under various conditions can be obtained, and the accuracy of the model will be greatly improved. The coupling calculation of macro and micro scale models provides a new analysis method for studying structural failure and damage under extreme aerodynamic thermal environments.

[0045] Example:

[0046] like Figure 1-Figure 2 As shown in the figure, the microscopic and macroscopic silicon thin plate models are established respectively. Taking the beam model as an example, Figure 3 As shown, a method for molecular dynamics-macroscopic multi-scale coupling calculation includes the following steps:

[0047] Step 1: Construct a physical model of microscopic force-heat-chemical-flow multi-field coupling and establish a process such as Figure 4 As shown, the plate is first moved in the negative X direction at a speed of 1000m / s in the canonical ensemble (NVT). After running for 6ns, the surface flow field distribution of the plate under high-speed motion conditions is obtained. Then the temperature distribution and stress distribution under the flow field are extracted. Through theoretical calculations of temperature, stress and chemical reaction kinetics, the chemical ablation at the corresponding temperature is obtained. In this multi-field coupling model, the focus is on calculating the changes in the material's Young's modulus and Poisson's ratio during crack initiation, and these parameters are passed to the macro model in real time. Figure 4As shown in the figure, taking the beam model as an example, the stress and temperature distribution are obtained by calculating the flow field on the surface, and then the chemical ablation of the material at different temperatures is calculated. Compared with the traditional molecular dynamics model, this method can better describe the material failure under extreme conditions of high-temperature thermochemistry and non-equilibrium gas flow by studying the microstructural evolution of defects and the changes in physical parameters under different load modes.

[0048] Step 2: Use the Young's modulus and Poisson's ratio obtained from the previous microscopic calculation to calculate the stress and strain of the material under tension or compression, and then transfer the stress and strain back to the microscopic model.

[0049] Step 3: Apply the new stress and strain parameters in the microscopic model, study the expansion of cracks inside the material under this step, obtain new Young's modulus and Poisson's ratio parameters affected by crack expansion, and then return the parameters to the macroscopic model.

[0050] Step 4, apply the parameters again in the macro model to obtain new stress-strain parameters in the presence of cracks. Through continuous coupling iteration of micro-macro, the mechanical properties of the material from the beginning of stress, crack generation, crack propagation to failure and fracture can be studied. The present invention first obtains a more accurate Young's modulus and Poisson's ratio of the material through microscopic calculations of multi-physical field coupling, and then applies the parameters to the macro model to obtain the stress, strain and damage of the material. These parameters under the damage condition guide the macro model to iteratively update the parameters, and then the parameters are further introduced into the micro model to study the material properties under the next damage state. Compared with traditional macro or micro models, this model is more practical and the accuracy will be greatly improved. The coupled calculation of macro and micro scale models provides a new analysis method for studying structural failure and damage under extreme aerodynamic thermal environments.

[0051] The calculation parameters of the microscopic and macroscopic models are obtained by calculation, and they are mutually provided and verified to ensure the accuracy of the model. The microscopic model uses the classical molecular dynamics method to construct a material failure model of force-heat-chemical-flow multi-field coupling. The temperature and stress distribution are obtained through flow field calculation, and then the chemical ablation at the corresponding temperature is calculated. The focus is on calculating the changes in the Young's modulus and Poisson's ratio of the material during crack initiation, and these parameters are transmitted to the macroscopic model in real time. After receiving the parameters, the macroscopic model calculates the stress and strain in the current state, and then returns to the microscopic model for iteration. The macroscopic aspect adopts the unified algorithm of gas dynamics theory of the Boltzmann model equation to provide the surface temperature and stress distribution of the flow field. After that, the temperature, load and other parameters obtained by the macroscopic method are re-entered into the microscopic study, and the mechanical properties and plastic transformation mechanism of the silicon thin plate are proposed. Including the Young's modulus and Poisson's ratio parameters under different crack conditions, these parameters re-guide the macroscopic model to iteratively update the parameters, so that the mechanical parameters of the material under various conditions can be obtained, and the accuracy of the model will be greatly improved. The process of alternating macro and micro calculations not only ensures the accuracy of the calculations, but also overcomes the huge amount of calculations required from traditional micro to macro calculations, thereby improving calculation efficiency.

[0052] Figure 5 and Figure 6 In the process of microscopic calculation of 4 picoseconds, we took the Young's modulus ( Figure 5 ) and Poisson's ratio ( Figure 6 ) three data points each. It can be seen that at different stages of crack propagation, the Young's modulus and Poisson's ratio of the material show a downward trend. Therefore, according to the traditional macroscopic calculation method, specifying unchanged Young's modulus and Poisson's ratio parameters cannot conform to reality very well. Therefore, the macroscopic calculation parameters of the present invention are taken from the results of microscopic calculations, and the new force and strain are obtained by macroscopic calculations to correct the force and strain parameters of the microscopic model, and then the microscopic model is used to perform the next step of calculation. By iterating the calculations in sequence, the state of the material from deformation to failure can be more accurately described. We compared the calculation accuracy of traditional microscopic calculations and multi-scale coupling calculations. Figure 7 It can be seen that with the increase of the computing system (number of atoms), the accuracy of traditional microscopic computing methods tends to decrease, while the accuracy of multi-scale coupling calculations decreases slowly and is higher than traditional microscopic calculations in all aspects.

[0053] In order to more intuitively illustrate the effect of the present invention, by comparing the calculation speeds of traditional microscopic calculations and multi-scale coupled calculations, the inverse of the maximum calculation time is set to 1, and the speed difference can be intuitively seen. Figure 8 It can be seen that with the increase in the number of atoms in the system, the calculation speed of the traditional microscopic method shows a downward trend, while the speed of the multi-scale coupling calculation method has not changed much, and is almost three times faster than the traditional microscopic calculation method of 600,000 atoms.

[0054] In summary, the difference between the calculation method of the present invention and traditional macro and micro applications is that: 1. Traditional calculations from micro to macro have the problems of large amount of calculation and long calculation time, while our macro-micro multi-scale coupled iteration has a calculation time much shorter than the traditional method under the same system; 2. Traditional macro parameters guide micro calculations, which have the problems of insufficient accuracy, unrealistic and inexplicable mechanism, while our macro-micro multi-scale coupled calculations start from the basic atomic potential function and provide parameters to each other, so the calculation is more accurate and more practical.

[0055] The above solution is only an illustration of a preferred embodiment, but is not limited thereto. When implementing the present invention, appropriate replacement and / or modification can be performed according to user needs.

[0056] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and the embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily realized. Therefore, without departing from the general concept defined by the claims and equivalent scope, the present invention is not limited to the specific details and the illustrations shown and described here.

Claims

1. A method for molecular dynamics-macroscopic multi-scale coupling calculation, characterized in that: include: S1. Establish microscopic plate model and macroscopic plate model respectively; S2. Through micro-scale aerodynamic simulation calculation in the micro-plate model, the failure of the plate under the multi-field coupling of force, heat, chemical and flow, as well as the corresponding Young's modulus I and Poisson's ratio parameter I, are obtained; S3, passing the Young's modulus Ⅰ and Poisson's ratio parameter Ⅰ obtained by calculation in S2 into the macro plate model, and obtaining the stress value Ⅰ and strain value Ⅰ of the plate under tension or compression through macro aerodynamic simulation calculation; S4, the stress value I and strain value I obtained in S3 are transferred into the micro plate model to perform micro-scale aerodynamic simulation calculation, and Young's modulus II and Poisson's ratio parameter II under the influence of crack propagation are obtained; S5, passing the Young's modulus II and Poisson's ratio parameter II calculated by S4 into the macro plate model, and obtaining the stress value II and strain value II in the case of cracks through macro aerodynamic simulation; Repeat S4 to S5 to obtain the mechanical performance indicators of the plate at each stage from initial stress, crack generation, crack propagation to failure and fracture under continuous micro-macro coupling iteration.

2. The method of molecular dynamics-macroscopic multi-scale coupling calculation according to claim 1, characterized in that: In S2, the failure condition refers to calculating the chemical ablation of the material at different temperatures after obtaining the stress and temperature distribution by calculating the flow field on the plate surface.

3. The method of molecular dynamics-macroscopic multi-scale coupling calculation according to claim 1, characterized in that: In S1, the macro plate model is used to simplify the research object into a thin plate I with a size of 0.015 m × 0.5 m in the macro aerodynamic simulation.

4. The method of molecular dynamics-macroscopic multi-scale coupling calculation as claimed in claim 3, characterized in that: In S3, the macroscopic aerodynamic simulation uses GKUA and finite element method to obtain the temperature and pressure distribution of the external flow field as a comparative verification of the atomistic simulation; Among them, in the macroscopic simulation, the outside of thin plate I is the re-entry near-continuous transition flow, the inflow Mach number is 8.37, the Knudsen number is 0.01, and the specific heat ratio is 1.

4.

5. The method of molecular dynamics-macroscopic multi-scale coupling calculation according to claim 1, characterized in that: In S1, the microscopic plate model is used to simplify the research object to a size of The size of the molecular dynamics simulation system box is In the micro-scale aerodynamic simulation, the initial state of the simulation environment is set to a pressure P of 30 atm, a temperature T of 300 K, and a lattice constant of the silicon atomic model is fixed to In the micro-scale aerodynamic simulation, the velocity Verlet algorithm is used to perform the integration of the motion equations, and the time step is set to 1 fs. The thin plate II moves in the canonical ensemble at a speed of 1000 m / s along the negative X direction; Periodic boundary conditions are applied in the x, y, and z directions of the spatial coordinate system. After the system runs for 6ns, the interaction between atoms is simulated using the Lennard-Jones (LJ) potential function.

6. The method of molecular dynamics-macroscopic multi-scale coupling calculation as claimed in claim 5, characterized in that: In S2, the micro-scale aerodynamic simulation is carried out by loading different external forces and high temperature conditions on the thin plate I to simulate and observe the structural changes of the woven structure under extreme conditions and the evolution of the ablation reaction over time, thereby obtaining the microscopic mechanism of the ablation evolution of the material under the action of the force-heat-chemical-flow coupling field.

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