Multi Scale Modelling Of High Strain Rate Deformation And Spall Fracture In Poly Crystalline Metals

Abstract

Shock-induced dynamic response of materials has been studied over decades by high velocity impact experiments, theoretical and computational methods. In these studies, mostly macroscopic and microscopic physics were examined. Molecular Dynamics (MD) methods are useful to understand the underlying physics in the dynamic response of materials at atomic scales. The emergence of MD methods along with the growing power of computing, facilitates the modeling and simulation of shock propagation in materials at atomistic spatial and temporal scales. Associated dynamic responses of materials due to high strain rates are being studied using MD simulations. Generally, a material fails under compressive as well as tensile stresses. Tensile pressure can be created by a flyer-target impact system in which the one-dimensional strain shock state is generated. Upon impact, the compressive shock wave is generated and it propagates into the flyer and the target in opposite directions. These waves reach the respective free surface of the flyer-target system and they reflect as the tensile/rarefaction wave. These oppositely travelling tensile waves meet and create high tensile pressure. When the magnitude of the tensile pressure exceeds a critical value namely spall strength , the materials fail. Such a process is called spallation . The spall strength is a material dependant parameter. Over the years experiments at the macroscopic levels have generated spallation data. Details of these phenomena can be obtained from MD simulations. Shock and spall data are available for conventional materials from experiments. Suit able and the most accurate diagnostic facilities are critical in evaluating the dynamic Andhra University, Visakhapatnam xv material properties. Setting up the experiments and deploying accurate diagnostic meth ods are very sophisticated. Modeling and simulations are relatively easier to set up for repeated studies. For the materials of interest and new alloys, MD methods can be used to understand the underlying physics