Multi-scale calculation method for material failure under laser loading

Abstract

The invention discloses a multi-scale calculation method for material failure under laser loading, and relates to the technical field of laser protection. The method comprises the following steps: firstly, respectively describing temperature changes of free electrons and crystal lattices on the surface of a material through a double-temperature model, simulating a transfer process of laser energy, and calculating thermal diffusion and temperature field evolution of the material under laser irradiation; secondly, simulating atomic-level thermal response, microstructure change, stress field distribution and a fracture process of the material under a laser loading condition by utilizing molecular dynamics; and finally, coupling the double-temperature model and molecular dynamics simulation, and analyzing the failure behavior of the material under laser loading by combining macrothermodynamics and microstructure analysis. According to the method, the influence of laser parameters such as different laser power densities, wavelengths and pulse widths on the material performance can be processed, the failure characteristics of the material can be accurately predicted, and compared with an existing single-scale model, the microstructure change of the material under laser irradiation can be more truly reflected.

Description

Technical Field

[0001] The invention relates to the technical field of laser protection, and in particular to a multi-scale calculation method for material failure under laser loading. Background Art

[0002] With the rapid development and widespread application of laser technology, the response mechanism of laser-irradiated materials and the failure characteristics of materials under laser loading have become key research topics in the field of laser protection. As a high-energy-density energy source, laser can quickly heat the surface and produce complex physical effects when interacting with materials. Especially under ultrafast laser irradiation, the thermal response, phase change, microstructural changes and other phenomena of the material are intertwined, which has a more complex impact on the failure behavior of the material.

[0003] At present, most studies focus on material response and failure mechanisms at two scales: thermal response at the macroscale and structural damage at the microscale. At the macroscale, the research focuses on the temperature distribution, thermal stress and macroscopic deformation or damage caused by the material; while at the microscale, the research focuses more on structural changes and local failures at the atomic or molecular level, such as crack formation and phase change. However, the existing research on the correlation between different scales and its systematic analysis in the material failure process is still insufficient.

[0004] Especially under ultrafast laser irradiation conditions, the impact of the material's microstructure and its dynamic evolution on the material's failure behavior has not been fully studied and understood. Existing theories and calculation methods are often limited to a certain scale and cannot accurately reflect the global process from the material's thermal response to microstructural changes and ultimately failure.

[0005] Therefore, there is an urgent need for a multi-scale and cross-scale computational method to comprehensively describe the thermal response, structural evolution and failure process of materials under laser loading. This method can systematically simulate the response mechanism and failure behavior of materials under laser irradiation from different levels, from the electronic scale, lattice scale to macroscopic material performance, solve the shortcomings of existing technologies in multi-scale analysis, and promote in-depth research on the failure mechanism of materials under laser loading conditions. Summary of the invention

[0006] The purpose of this invention is to propose a multi-scale calculation method for material failure under laser loading, aiming to provide an innovative multi-scale calculation framework for the response and failure mechanism of laser irradiated materials, which can simulate the thermal response, microstructural changes and failure behavior of materials under ultrafast laser irradiation, covering multi-scale analysis from the microscopic atomic scale to the macroscopic material performance.

[0007] To achieve the above purpose, the present invention proposes a multi-scale calculation method for material failure under laser loading, and the specific steps are as follows:

[0008] S1. Introduce a dual-temperature model, establish a coupled heat conduction equation of electron temperature and lattice temperature by describing the temperature changes of electrons and lattices, and calculate the thermal response of electrons and lattices when laser irradiates the material through the dual-temperature model, and obtain the temperature field data of the lattice during laser irradiation;

[0009] S2. Using molecular dynamics simulation technology, based on the temperature field data calculated by the dual-temperature model, simulate the atomic-level thermal response, microstructure change, stress field distribution and fracture process of the material under laser loading conditions;

[0010] S3. The dual-temperature model and molecular dynamics simulation are coupled, and the failure behavior of the material under laser loading is analyzed by combining macroscopic thermodynamics and microstructural analysis.

[0011] Preferably, in S2, the simulation steps based on the molecular dynamics simulation technology are as follows:

[0012] S21. Calculate the thermal response, atomic motion trajectory and local temperature distribution of materials under laser irradiation through molecular dynamics simulation;

[0013] S22. Calculate the stress field, dislocation slip and crystal defects inside the material, and simulate the yield, plastic deformation and fracture behavior of the material during laser loading;

[0014] S23. Analyze the microstructural changes and crack propagation process of the material under different laser power density and laser wavelength conditions.

[0015] Preferably, in S3, when performing the multi-scale coupling calculation, failure behavior prediction is performed by combining the temperature field data in the dual-temperature model calculation results with the stress field and atomic displacement information in the molecular dynamics simulation results.

[0016] Preferably, in S3, the coupling between the two-temperature model and the molecular dynamics simulation is achieved through electron-lattice heat conduction and energy transfer, wherein the electron-phonon coupling term combines the energy transfer of the electronic system and the lattice system.

[0017] Preferably, in S3, the failure behaviors include phase change, delamination and pores.

[0018] Preferably, the multi-scale calculation method is applicable to different types of materials and different laser loading conditions; wherein the materials include metal materials, ceramic materials and semiconductor materials.

[0019] Preferably, the multi-scale calculation method is implemented by computer simulation, using LAMMPS open source software for molecular dynamics simulation, combining the finite difference method to solve the two-temperature equation, and performing post-processing analysis of the simulation results through visualization software.

[0020] Preferably, the multi-scale calculation method can flexibly adjust laser parameters related to different laser power densities, pulse widths, and wavelengths, and accurately predict the failure characteristics of materials under different laser loading conditions.

[0021] Therefore, the present invention proposes a multi-scale calculation method for material failure under laser loading, and its beneficial effects are as follows:

[0022] (1) The present invention provides a multi-scale calculation method for material failure under laser loading, which can comprehensively analyze the failure behavior of materials from the microscopic atomic scale to the macroscopic material failure behavior, and provides a more accurate material failure prediction method, especially under high-power laser irradiation, which can accurately simulate the microscopic failure process of materials.

[0023] (2) The present invention provides a multi-scale calculation method for material failure under laser loading, which can handle the influence of various laser loading conditions (such as different power densities, laser wavelengths, etc.) on material properties.

[0024] (3) The multi-scale calculation method of material failure under laser loading provided by the present invention provides a new theoretical basis and calculation tool for the study of the interaction between high-energy laser and materials, and has broad engineering application prospects.

[0025] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is an overall flow chart of a multi-scale calculation method for material failure under laser loading of the present invention;

[0027] Figure 2 Schematic diagram of a GaN molecular dynamics model constructed by a multi-scale calculation method of material failure under laser loading in the present invention; wherein a is a top view of the GaN molecular dynamics model, and b is a left view of the GaN molecular dynamics model;

[0028] Figure 3 It is a schematic diagram of the coupling of a dual-temperature model and a molecular dynamics model of a multi-scale calculation method for material failure under laser loading of the present invention. DETAILED DESCRIPTION

[0029] In order to make the technical solutions, advantages and purposes of the present invention clearer, the technical solutions of the embodiments of the present invention are clearly and completely described below. The described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the protection scope of this application.

[0030] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0031] like Figure 1 As shown, the present invention provides a multi-scale calculation method for material failure under laser loading, and the specific calculation steps are as follows:

[0032] 1. Introduction of dual-temperature model

[0033] The interaction between laser and material usually causes the temperature of the material to change within a very short time scale, and the temperature rise process of electrons and lattices often exhibits different time scales. The traditional heat conduction model cannot effectively describe the phenomenon of separation of electron and lattice temperature, and therefore cannot accurately predict the thermal response of the material under laser irradiation. The dual-temperature model can solve this problem by treating electrons and lattices as two systems with different temperatures, and using different temperature rise rates to describe their energy transfer processes respectively.

[0034] In the present invention, the core idea of ​​the dual-temperature model is to regard electrons and lattices as two systems with different temperatures, and use different temperature rise rates to describe their respective energy transfer processes. Specifically, the laser energy is first absorbed and heated by free electrons on the surface of the material, and the electron temperature rises sharply. The electron temperature is transferred to the lattice through electron-lattice scattering, causing the lattice temperature to gradually rise, that is, the laser energy absorbed by electrons in the form of photons and the electron-phonon interaction heat the atomic lattice. This process can be described by coupling the following two heat conduction equations:

[0035] Electronic heat equation:

[0036]

[0037] Among them, C e is the heat capacity of electrons, k e is the thermal conductivity of electrons, T e is the electron temperature, T l is the lattice temperature, G is the electron-lattice coupling coefficient, and Q is the laser heating source term.

[0038] Lattice heat equation:

[0039]

[0040] Among them, C l is the heat capacity of the lattice.

[0041] Q(x,y,z,t): Laser heating source term, which is expressed as:

[0042] Q(x,y,z,t)=S(x,y,z).T(t);

[0043] Among them, S(x,y,z) represents the spatial distribution and T(t) represents the temporal distribution.

[0044] Distribution space S(x,y,z):

[0045]

[0046] Where R is the surface reflectivity, δ is the absorption depth of the material, and δ b Plasma shielding length, F is the laser flux; w0 is the laser spot radius; x0, y0 are the coordinates of the laser spot center.

[0047] Time distribution T(t):

[0048]

[0049] Among them, t p is the laser half-peak pulse width, t is the time.

[0050] Through the above coupling equations, the energy transfer and temperature evolution during laser irradiation can be accurately simulated. The different temperature change processes of electrons and lattices provide initial conditions for subsequent molecular dynamics simulations and ensure accurate calculation of the thermal response of materials under laser action.

[0051] 2. Molecular dynamics simulation

[0052] Under laser loading, the microstructure of the material, especially the changes at the atomic level, directly affects its failure behavior. Molecular dynamics simulation (MD) technology can accurately describe the microscopic deformation and fracture process of materials under high temperature and laser irradiation by modeling the interaction forces between atoms. The present invention uses MD simulation to analyze the atomic movement on the surface and inside of the material under laser irradiation, including microscopic phenomena such as bond fracture between atoms and dislocation slip.

[0053] In the method of the present invention, MD simulation mainly plays a role in the following aspects:

[0054] (1) Thermal response at the atomic scale: MD simulation is used to calculate the motion trajectory of each atom in the material under laser irradiation, and the local temperature distribution and thermal wave propagation process of the material are obtained, which further provides microscopic support for the macroscopic thermal behavior of the material.

[0055] (2) Stress and fracture analysis: MD simulation can directly analyze the stress distribution inside the material and simulate the yield, plastic deformation and fracture behavior of the material during laser loading. By studying the destruction mechanism of atomic bonds inside the material under different laser power densities, it can provide a basis for predicting material failure.

[0056] (3) Multi-scale material failure: One of the key innovations of this invention is to develop a multi-scale failure calculation method by combining micro-scale MD simulation with macro-scale thermodynamic model. By modeling the micro-deformation process of the material, the failure characteristics of the material such as fracture, peeling, and pores can be obtained, and this information can be connected with the macro-material mechanical properties to predict the failure behavior under laser loading.

[0057] 3. Two-temperature model coupled with molecular dynamics

[0058] The multi-scale calculation method of the present invention establishes a multi-scale analysis framework from atomic scale to macroscopic material performance by coupling the dual-temperature model with molecular dynamics simulation. The specific steps are as follows:

[0059] (1) Preliminary thermal response simulation: The dual-temperature model is used to simulate the temperature field on the surface and inside of the material under laser irradiation, and the thermal response data under different laser power density, laser duration and other conditions are obtained.

[0060] (2) Molecular dynamics simulation: The temperature field data provided by the dual-temperature model provides the initial conditions for molecular dynamics simulation and simulates the atomic-level thermal response, microstructural changes, and stress field distribution of the material.

[0061] (3) Failure behavior analysis: Based on MD simulation, the failure mechanism of the material under different laser loading conditions is analyzed, and the influence of factors such as laser power density and irradiation time on the microstructural damage, crack propagation and overall failure of the material is explored.

[0062] (4) Multiscale coupling: The microscopic failure data of MD simulation is combined with the macroscopic material mechanics model. Based on the principles of thermodynamics and mechanics, macroscopic failure analysis of the material is carried out, ultimately achieving an accurate prediction of the overall failure behavior of the material under laser loading.

[0063] The purpose of this invention is to provide a multi-scale calculation method for material failure under laser loading based on a dual-temperature model and molecular dynamics simulation, which accurately describes the thermal response of laser-irradiated materials, the energy exchange between electrons and lattices, and the microstructural changes and failure mechanisms caused by them. This method can simulate the temperature evolution, thermal stress, crystal defects and crack formation of materials at the nanoscale, reveal the influence of different laser parameters on material failure, and provide theoretical support for laser processing and laser protection.

[0064] Example 1

[0065] 1. Selection of simulation materials

[0066] The present invention takes metal materials (such as aluminum alloy, titanium alloy, etc.) as research objects. These materials have obvious thermal response and structural changes under high-power laser irradiation.

[0067] 2. Establishment of dual-temperature model

[0068] The two-temperature equation is used to describe the temperature changes of the material's electrons and lattice respectively. The electron temperature increases through the interaction between the photoelectrons and the lattice caused by laser irradiation, while the lattice temperature is affected by thermal conductivity. The equation of this model can be realized by solving the partial differential equation by the finite difference method.

[0069] 3. Molecular dynamics simulation

[0070] In molecular dynamics simulation, by applying external laser irradiation, the atomic-level response inside the material is simulated, including processes such as energy transfer, thermal expansion, material deformation and crack propagation. The results of molecular dynamics provide an intuitive representation of the microscopic mechanism of material failure.

[0071] like Figure 2 As shown in the figure, the established dynamic model of ultrashort pulse laser ablation of GaN is established; the present invention uses the open source software LAMMPS to simulate the structural evolution process of ultrafast laser ablation materials. Since the absorption depth of laser energy in the material is much smaller than the diameter of the laser beam, the laser ablation process is simplified to a one-dimensional heat conduction problem along the laser irradiation direction. On this basis, the MD simulation area is divided into multiple sub-strips in the radial direction, and the spatial distribution of laser energy in the micro-strip area is approximately uniform. In order to save computing resources and time, the one-dimensional TTM-MD model is selected to simulate the center of the laser beam.

[0072] MD simulation includes equilibrium phase and non-equilibrium phase. Before laser irradiation, the whole system needs to be processed for energy balance to eliminate the unreasonable structure of the model. The initial system undergoes a tens of picoseconds of equilibrium relaxation process at 300K, and then undergoes a non-equilibrium process of ultrashort pulse laser irradiation. The image post-processing software OVITO is used to visualize and analyze the motion trajectory files obtained by MD simulation.

[0073] 4. Two-temperature model coupled with molecular dynamics calculation

[0074] The macroscopic temperature field provided by the dual-temperature model is combined with the microscopic stress field, atomic displacement and other data in the molecular dynamics simulation results, and multi-scale calculations of the material are performed on this basis. Under different laser power densities, the response of the material at both the macroscopic and microscopic scales will be taken into account, so that the location, type and time of the failure point can be predicted.

[0075] Due to the lack of electronic models in classical molecular dynamics, the change of electron temperature cannot be directly simulated. In LAMMPS, the "Fix_ttm" command is based on a hybrid atomic continuum model of TTM and MD coupling, in which a finite element mesh is used to describe the electron temperature and the electron-phonon coupling is added to the normal MD motion equations by adding additional terms.

[0076] However, for the simulation of laser ablation, these instructions lack the description of electron excitation, electron migration and electron number density distribution. Therefore, the present invention solves TTM and MD separately, and uses the energy transferred from the electron subsystem to the lattice system to connect the two models. When the electron temperature and lattice temperature of the whole system reach equilibrium, the energy transferred from the electron in the laser absorption layer to the lattice obtained by the two-temperature equation is regarded as the input energy load of the lattice in molecular dynamics. Figure 3 The figure is a schematic diagram of the coupling between the two-temperature model and the molecular dynamics model. The specific process is as follows: First, the two-temperature model is used to calculate the laser energy in the free electrons when the laser irradiates the material, and the energy transfer rate between the electron-electron system and the lattice system is calculated from the electron-phonon coupling term. Secondly, the atoms in the effective absorption layer in the molecular dynamics model are layered, and the energy obtained by the two-temperature equation is the heat source load of the material lattice. Finally, in the non-equilibrium stage of the MD simulation, the energy is introduced into the effective absorption layer through the thermal instruction "Fix_Heat", realizing the simulation of the electron-lattice relaxation heating process when the ultrashort pulse laser acts on the material.

[0077] 5. Analysis of simulation results

[0078] The effectiveness of this method was verified through a series of simulations, and the simulation results showed that the present invention can accurately predict the failure characteristics of materials under different laser parameters.

[0079] Therefore, the present invention provides a multi-scale calculation method for material failure under laser loading, which can systematically and accurately analyze the thermal response and failure process of materials under laser loading. Compared with the traditional single-scale model, the present invention can more realistically simulate the influence of laser irradiation on the microstructure of the material, and can realize a unified calculation framework at the macro and micro scales, thereby improving the calculation accuracy and efficiency. At the same time, the method is applicable to a variety of materials and laser loading conditions, and has broad engineering application prospects.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A multi-scale calculation method for material failure under laser loading, characterized in that: The following steps are involved: S1. Introduce a dual-temperature model, establish a coupled heat conduction equation of electron temperature and lattice temperature by describing the temperature changes of electrons and lattices, and calculate the thermal response of electrons and lattices when laser irradiates the material through the dual-temperature model, and obtain the temperature field data of the lattice during laser irradiation; S2. Using molecular dynamics simulation technology, based on the temperature field data calculated by the dual-temperature model, simulate the atomic-level thermal response, microstructure change, stress field distribution and fracture process of the material under laser loading conditions; S3. The dual-temperature model and molecular dynamics simulation are coupled, and the failure behavior of the material under laser loading is analyzed by combining macroscopic thermodynamics and microstructural analysis.

2. The multi-scale calculation method for material failure under laser loading according to claim 1, characterized in that: In S2, the simulation steps based on the molecular dynamics simulation technology are as follows: S21. Calculate the thermal response, atomic motion trajectory and local temperature distribution of materials under laser irradiation through molecular dynamics simulation; S22. Calculate the stress field, dislocation slip and crystal defects inside the material, and simulate the yield, plastic deformation and fracture behavior of the material during laser loading; S23. Analyze the microstructural changes and crack propagation process of the material under different laser power density and laser wavelength conditions.

3. The multi-scale calculation method for material failure under laser loading according to claim 1, characterized in that: In S3, when performing the multi-scale coupling calculation, failure behavior prediction is performed by combining the temperature field data in the dual-temperature model calculation results with the stress field and atomic displacement information in the molecular dynamics simulation results.

4. The multi-scale calculation method for material failure under laser loading according to claim 1, characterized in that: In S3, the coupling between the two-temperature model and molecular dynamics simulation is achieved through electron-lattice heat conduction and energy transfer, among which the electron-phonon coupling term combines the energy transfer of the electronic system and the lattice system.

5. The multi-scale calculation method for material failure under laser loading according to claim 1, characterized in that: In S3, the failure behaviors include phase change, delamination and pores.

6. The multi-scale calculation method for material failure under laser loading according to claim 1, characterized in that: The multi-scale calculation method is applicable to different types of materials and different laser loading conditions; wherein the materials include metal materials, ceramic materials and semiconductor materials.

7. The multi-scale calculation method for material failure under laser loading according to claim 1, characterized in that: The multi-scale calculation method is implemented by computer simulation, using LAMMPS open source software for molecular dynamics simulation, combining the finite difference method to solve the two-temperature equation, and performing post-processing analysis of the simulation results through visualization software.

8. The multi-scale calculation method for material failure under laser loading according to claim 1, characterized in that: The multi-scale calculation method can flexibly adjust laser parameters related to different laser power densities, pulse widths, and wavelengths, and accurately predict the failure characteristics of materials under different laser loading conditions.

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