Microstructure Simulation And Fracture Toughness Prediction Of Whisker Toughening Ceramic Tools

Whisker toughening ceramic tools are widely used in high-speed cutting and the cutting of difficult-to-machine material due to their high hardness,excellent wear resistance and good chemical stability.To predict the fracture toughness of whisker toughening ceramic tools and guide the design of material system by simulation,the research and development cost can be reduced and the development cycle can be shortened.At present,there are many researches on the microstructure simulation technology of traditional ceramic tool materials,but there are few researches on the microstructure simulation and mechanical properties prediction of whisker toughening ceramic tools.Therefore,the present research purpose is to predict the fracture toughness of whisker toughening ceramic tools,simulate and study the microstructure damage,and study the influence of whisker distribution pose,size,morphology and toughening mechanism on the fracture toughness,so as to provide guidance for the research and development of ceramic tool materials.In this dissertation,a prediction model based on whisker toughening mechanism and a prediction model based on fracture energy are established.The effectiveness of the prediction models is verified by experiments,and a software system for microstructure simulation and fracture toughness prediction is developed.The two-dimensional and three-dimensional microstructure simulation models of whisker toughening ceramic tools are established.The microstructure simulation results provided the original parameters for the fracture toughness prediction of whisker toughening ceramic tools.The anti-agglomeration algorithms for two-dimensional whiskers with the elliptical section shape and three-dimensional whiskers are proposed.The experimental results show that the simulation results of two-dimensional and three-dimensional microstructure cracking and damage morphology are in good agreement with the fracture morphology of the prepared ceramic tool materials.The tensile damage simulation of the microstructure of ceramic tools is realized.The microstructure simulation results show that the simulated crack propagates from the initial defect,and its transgranular fracture and intergranular fracture behavior is consistent with the experimental results.The fracture morphology of the prepared Al2O3-matrix ceramic tool toughened by SiC whisker is analyzed,which verifies the correctness of microstructure simulation results.A representative volume element(RVE)containing three whiskers is established,and the elastic modulus is obtained.The elastic stiffness tensor and eigenstrain of whisker toughening ceramic tool are studied.The effects of the distribution angle of a single whisker on the stress and strain of ceramic tool material is analyzed,and the superposition effect of stress and strain of the interaction of two or three whiskers,and their effects on the elastic stiffness tensor of RVE are analyzed.The influence of the angle between the whisker and the stretching direction on the stress and strain of a single whisker is discussed.The simulation results show that the stress and strain of the whisker are symmetrically distributed at 90°.The spacing between the center points of two whisker axes leads to the attenuation of stress superposition.The stress and strain of the defect-free whisker toughening ceramic tool containing three whiskers are studied.The influence factor and attenuation function of the stress superposition of the whisker toughening ceramic tool under the interaction of three whiskers are obtained.Then the elastic stiffness tensor and elastic modulus of the ceramic tool containing three whiskers are obtained.The experimental result shows that the error between the theoretical value and the experimental value of the elastic modulus is small.The fracture toughness prediction models of whisker toughening ceramic tools based on fracture energy and whisker toughening mechanism are established.The fracture toughness values of whisker toughening ceramic tools based on mechanical energy,fracture energy and cohesion element method are predicted.The results show that the prediction results based on fracture energy method are closer to the experimental results.The weights of the fracture morphology of whisker pull-out,bridging and crack deflection on the contribution value of fracture toughness are studied.The influence of the angle between the crack propagation direction and the whisker axis on the whisker deflection,potential energy and elastic strain energy is revealed.Based on the mechanical energy method and considering the shear stress work,the corrected total energy formula of whiskers is established.The concept of the effective ratio of crack propagation area of a single whisker is proposed,and the influence of the angle between the crack propagation direction and the whisker axis on the effective ratio of crack propagation area is revealed.The contribution values and their weights of whisker pull-out,whisker bridging and crack deflection to fracture toughness are determined.A software system for microstructure simulation and fracture toughness prediction of whisker toughening ceramic tools is developed.