Discrete Dislocation Dynamics Simulation And Crack Evolution Of Diamond Crystal

In the microfabrication,the failure mechanism of the tool material at the micro-nano scale has undergone a fundamental change compared to the macro state as the tool size continues to shrink,and grasping the failure behavior at the micro-nano scale is to achieve its design.The movement of crystal internal defects and dislocations on the micrometer scale has an important influence on the mechanical behavior of the material.Therefore,it is of great significance to master the dislocation of the diamond crystal inside the extreme evolution of the diamond micro tool design and application.Taking dislocations as the basic unit of calculation,taking into account the nature of crystal plastic deformation,it can effectively explain the special mechanical behavior of small-scale crystals.The coupled simulation framework of Discrete Dislocation Dynamics(DDD)and Finite Element Method(FEM)is an important tool for revealing the mechanical properties of crystals at micro and nano scales and for efficient simulation.Based on DDD theory and the contact algorithm of ABAQUS,this dissertation uses MATLAB and Python to establish a 2.5D DDD-FEM simulation program for diamond crystals.The program can perform dislocation motion calculations such as dislocation proliferation,dislocation blocking,forest dislocations,and annihilation products.This program can automatically perform pre-processing,establish a model and couple it with ABAQUS to calculate the boundary load conditions,change the initial conditions of each simulation,perform iterative coupling simulation calculations,and perform post-processing after the calculation is completed.Using the self-developed 2.5D DDD-FEM simulation program,the simulation of the dislocation evolution of diamond crystals under nanoindentation and scribing loading was simulated,and the nanoindentation and diamond under scribing load were analyzed.The relationship between internal dislocation behavior and stress distribution in single crystals.The variation of crystal dislocation distribution and its effect on stress distribution under nanoindentation were simulated and analyzed for different size and preset different crack crystal models.The influence of preset cracks on the micro-delineation simulation results was studied.A polycrystalline stochastic partition model of CVD diamond film was established.The dislocation evolution rule and mechanical properties of diamond film under nanoindentation and scratch loading were studied.The characteristics of dislocation distribution and the influence on stress distribution were analyzed.The diamond film models with different grain sizes were established and the effects of dislocations and stress distribution on the diamond film model were simulated.Finally,using the existing experimental conditions,the nanoindentation and scribing experiments of single crystal diamond and CVD diamond film were studied respectively.The force,displacement and depth data in the experiment were analyzed,and the simulation results were compared and analyzed.In the experiment,the surface morphology of nanoindentation and scratching was actually observed and measured,and the gap between the experimental data and the data was analyzed.