Numerical Study On Brittle Fracture Behavior Of Thin Plate Based On Phase Field Model

The fracture problem of brittle thin plates widely exists in engineering practice.This type of fracture happens suddenly and has no obvious omen before the fracture,which seriously threatens the safe operation of engineering structures and engineering equipment.The in-depth study of brittle fracture of thin plate is of great significance to explain the mechanical mechanism of complex fracture phenomena such as crack initiation,propagation and bifurcation and optimize structural design,so as to prevent fracture accidents.The traditional brittle fracture analysis is based on Griffith’s fracture theory.In numerical calculation,it is necessary to deal with the step displacement at the crack and the singularity of the crack tip,which makes the numerical simulation of complex cracks very difficult,and the classical fracture theory can not directly simulate the initiation and bifurcation of cracks.Fracture phase field model is another way to study fracture problems.In this method,the material state is expressed by introducing the order parameter,the crack tip problem is transformed into the continuous distribution of the phase field function,the direct tracking of the crack discontinuity is avoided.To study the brittle fracture of thin plate,two fracture phase field models are established to simulate the crack propagation of thin plate under different loading conditions,and compared with the existing experimental results.The specific contents are as follows:1.The fracture phase field model of isotropic plate fracture problem is established,and the numerical calculation is carried out by using the commercial software Comsol Multiphysics(Comsol for short).The crack propagation process of thin plate with initial crack under tension,shear and tension shear coupling loads is studied,and the effects of various parameters on crack propagation are calculated.2.The fracture two-phase field model of fiber reinforced composite plate is established.Due to the convergence problem of Comsol for two-phase field model,this study uses Meshfree method programming for numerical calculation.Firstly,the reliability of the model is verified by comparing with the existing experiments,then different variable stiffness composite thin plates are obtained by changing the fiber path,and the crack propagation process under tensile and shear loads is calculated.It is found that the crack propagation path is always parallel to the fiber path.Changing the fiber path can prolong the transition region of variable stiffness composites from crack propagation to complete fracture,so as to delay the crack propagation and provide criterion for its application in engineering.