Numerical Simulation Of High Speed Crack Under Impact Loading

The study of high speed crack in brittle materials under dynamic tensile stress has important scientific significance and application value.The characteristics about propagation and bifurcation of high speed crack based on the experimental and numerical simulation has gained important understanding,but until now,the interpretation of high speed crack within the mesoscopic and microscopic mechanism under shock wave loading is still controversial and uncertain.In this paper,the crack propagation mechanism in brittle materials under impact loading is studied by means of numerical simulation,which can help to understand the impact damage evolution of ceramics,solid explosives and other brittle materials.This paper adopts the lattice-spring model which can show the mechanical properties of brittle materials accurately,the spring stiffness coefficient is calculated through the quantitative parameter mapping method proposed by Gusev,using the energy criterion based on the Griffith energy balance model as the principle of fracture.The accuracy of model when dealing with dynamic crack propagation is verified by the stress concentration of a square plate with an elliptical hole and stress field distribution on crack tips under the dynamic tensile stress.The simulation results show that even if the tensile stress has exceeded the bearing capacity of the material under quasi-static condition,the crack will not be extended immediately.Along with the continuous action of the tensile stress,the stress intensity factors on crack tips increases gradually,and then crack initiate and propagate after the critical value is reached.There existed an "incubation time" before the initiation of crack,and the"incubation time" required for initiation was gradually decreased with the increasing of tensile stress.When the crack initiate,the crack velocity will jump to the order of subsonic speed suddenly,the stable crack speed is up to 0.6 times more than the Rayleigh wave speed,and it also increase with the increasing of the tensile ’stress.The comparison shows that the crack velocity is related to the evolution of maximum tensile stress on crack tips significantly.The.stress concentration region on crack tips changed significantly before and after crack initiation,the stress concentration region of high speed crack exists a sweep angle which is decided by crack velocity.The simulation results show that when the maximum tensile stress on crack tips reaches the critical value,high speed crack evolved into two branching crack with obvious symmetry,coincident with the direction of maximum tensile stress,which explained the crack bifurcation mechanism from mesoscopic.