Mechanism Of Void Growth And Grain Boundary Fracture Under The High Strain Rate

The mechanical behavior of materials is quite different under high strain rate andquasi-static load. For materials used in modern industry, high strain rate conditions arefrequently applied, such as blasting, armor-piercing weapons, high speed forming and soon. So it is necessary to study the damage and fracture behavior of the materials underhigh pressure and high strain rates. By studying the material behavior under high strainrates, it can be understood that how the void nucleates at grain boundaries, the law thatvoids grow under the external force, and the related mechanism of dislocation motion.And it can explain the reason that materials fracture at grain boundaries under high strainrate. It can predict the mechanical properties of materials under extreme environments.This is of great importance.In this paper, we used molecular dynamics method to simulate the interactionbetween edge dislocation and twin boundary of tungsten, and the interaction betweenscrew dislocation and twin boundary of tungsten. Polycrystalline tungsten under highstrain rate uniaxial tension is also simulated. Simulation results show that when the grainsizes are smaller than9.19nm, the strength of the material increases with the grain sizeand the strain rate. Void nucleates at the grain boundary, then grows along the grainboundary. The connected voids lead to the fracture of material. In this process, thedislocation emission form grain boundaries occurred. When different dislocationsencounter the twin grain boundary, different reaction modes are triggered. The dislocationcan be hindered and absorbed by the grain boundary, penetrate the grain boundary or to bedecomposed into two partial dislocations sliding along the grain boundaries.In this paper, we studied the fracture mechanism of materials at zero temperature andhigh strain rates under uniaxial tension. However the materials under high strain rates usually work in a more complex conditions, such as with spreading stress waves or withrapidly changing temperature in local region, which needs further research andimprovement.