Study On Crack Propagation Path In Brittle Materials With Defects

In brittle failure,the crack propagation path has a very important effect on the safety of the component.However,in the component with defects,the interaction between crack tip and defect is very complex,which makes it difficult to determine the crack propagation path based on crack tip stress field.In this paper,based on the phase field fracture method,the effect of square hole on the stress intensity factor of crack tip is studied for two typical brittle fractures,the failure of brittle materials and the quasi-cleavage failure of ferritic steel.Firstly,the relationship between the critical stress intensity factor and the critical strain energy density factor and the direction of crack propagation in the process of crack propagation is given for the I-II type composite fracture problem,which provides a theoretical basis for the study of crack deflection with defects.Secondly,the tensile test of plexiglass specimen is carried out.The effect of the position of the square hole on the crack propagation path and the load-displacement curve of the tensile specimen containing a crack is studied.The results show that the crack will kink toward the hole when the distance between the square hole and the crack is closer,and the closer distance between the hole and the crack,the greater the propagation range of the crack toward the hole.Thirdly,based on the phase field fracture method,the crack propagation path is simulated for the plexiglass models containing only cracks and those containing both cracks and square holes.The results are consistent with the experimental results.The results show that the mesh density has little effect on the crack propagation direction,while the crack width has great effect.Finally,the crack deflection of plexiglass and A508? steel model with crack and square hole under tensile condition is studied.Based on the relationship between the crack propagation direction and the critical stress intensity factor,an equivalent stress intensity factor expression based on the shape function is proposed to represent the effect of the square hole on the stress field at the crack tip.The results show that the size of the shape function is determined by the distance between the crack tip and the hole center and the cracking Angle.The effect of the square hole on the shape function of the type ? stress intensity factor at the crack tip is obviously stronger than that of the type I stress intensity factor.On the basis of a large number of model calculated data,the distribution diagrams of the opposite hole positions of two kinds of shape functions are given.In this paper,based on the phase field fracture method,the effect of the square hole position on the stress intensity factor at the crack tip of the model with crack and square hole in the case of brittle failure is inversion based on the energy release rate criterion of ?-? composite fracture.The results obtained can provide reference value for engineering application.