Numerical Analysis Of Three Point Bending Model For Piezoelectric Semiconductor

With the development of technology and the impact to the environment,the automotive industry is moving towards electrification,intelligence and lightweight.The new generation semiconductors such as Ga N and ZnO are increasingly used to replace traditional semiconductors to the power driven parts of new energy vehicles because of its wide band gap,high breakdown electric field and high mobility.Furthermore,because of the piezoelectric properties of these semiconductor s,they can be made into various sensors and actuators for automotive electronic control systems.However,the researchs on the coupling performance of piezoelectric semiconductor are relatively rare,and the reliability of its use is also lack of theoretical guidance.Three point bending test is a basic method to study the strength and fracture properties of materials.In order to correspond with the related test,the piezoelectric semiconductor GaN is used in the three point bending test.Combining the knowledge of semiconductor and piezoelectric materials,the strength and fracture problems of piezoelectric semiconductor are numerically simulated using the commercial software COMSOL Multiphysics.The main contributions of the thesis are as follows:1.Based on the strict governing equations,constitutive equations and boundary conditions of piezoelectric semiconductor,the variation of stress,electric displacement and current density with applied load under different polarization are calculated by numerical simulation.Compared with the corresponding results of nonlinear constitutive equations,the effect of linearization is analyzed.For two different MS contacts,Ohmic contact and Schottky contact,the influence of different boundary conditions on the results is analyzed.2.Based on the linear basic equations,the variation of stress,electric displacement and current intensity factors with applied load under different polarization is studied.The expression for three intensity factors under two different polarization conditions are obtained by the least squares fitting.The difference between the results of the linear and nonlinear equations is illustrated;The J integral is used to analyze the nonlinear fracture problem.The local J integral,J_l of piezoelectric semiconductor is given,and the variation trend of J_l with external loading is studied.