题目：An Integrated Computational & Experimental Framework to Quantify the Competing Failure Mechanisms in Polycrystalline Metals
报告人：李妍 博士 （美国加州州立大学长滩分校）
The fracture toughness of ductile materials depends on the combined effect of plastic dissipation in the constituents and energy spent on creating new crack surfaces. The design of polycrystalline metals with improved fracture toughness requires in-depth understanding of two levels of competing mechanisms: the competition between plastic deformation and crack formation as well as the competition between transgranular and intergranular fracture. Currently, no systematic approach exists to analyze the effects of the two competitions. The fundamental challenges lie in the difficulty in separating the two forms of energy dissipation and inadequate knowledge about the correlation between fracture mechanisms and material fracture toughness. In this paper, a multiscale framework based on the Cohesive Finite Element Method (CFEM) is developed to quantify the two levels of competitions and to predict the fracture toughness of ductile materials by calculating the J-integral at the macroscale. The fracture surface energy for the crack paths associated with different types of failure mechanisms is evaluated through explicit simulation of crack propagation at the microstructure level. The calculations carried out here concern the AZ31 Mg alloy, but the overall approach applies to other materials as well. Results indicate that a proper balance between transgranular and intergranular failure can lead to optimized fracture toughness. Microstructures with refined grain sizes and balanced grain boundary bonding strength can best promote the manifestation of favorable failure mechanisms, and as a result, enhance fracture toughness.
Dr. Yan Li joined the Department of Mechanical and Aerospace Engineering at California State University, Long Beach as an Assistant Professor in Fall 2014. She received her PhD degree in Mechanical Engineering from Georgia Institute of Technology in 2014. Dr. Li's primary research interests are in the area of mechanics of advanced materials, involving multiscale/multiphysics modelling, integrated computational/experimental approaches for next generation material design, and application of material science and solid mechanics in advanced manufacturing. Dr. Li has worked on research projects supported by the U.S. Army Research Laboratory, Sandia National Laboratories, NSF CCMD (Center for Computational Materials Design) and collaborated with industry partners including Boeing, Gulfstream and GE.