Past Event: Oden Institute Seminar

Microstructural Evolution during Plastic Flow

John L. Bassani, Professor, Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania

Abstract

Essentially all solid materials deformed at moderate to large strains undergo changes in microstructure that can significantly affect macroscopic response. Reasonably tractable computational models are lacking, which explains limited success in predicting plastic instabilities and limits to formability. A macroscopic continuum theory is developed for a class of anisotropic elastic-plastic solids in which the orthotropic triad that characterizes material symmetry evolves with deformation. In essence, microstructural evolution arises from non-coaxiality between the plastic rate of stretching and the instantaneous orthotropic triad, which intuitively makes sense. That key result is established rigorously from representation theory for tensor-valued functions. The resulting phenomenological model agrees well with experimental data for metallic polycrystals. A finite element implementation predicts significant effects of microstructural evolution both quasi-static and dynamic strain localization, in particular for necking, shear banding, and buckling. This finding likely explains why analyses that neglect those effects have proven inadequate in many critical applications. This knowledge is proving to be crucial in a DOE grand-challenge to greatly improve automotive efficiency through light-weighting. Simulations of sheet forming and tube crushing show promise in developing new design concepts. Bio John L. Bassani is the Richard H. and S. L. Gabel Professor of Mechanical Engineering at Penn (BS ME Lehigh 1973; Fairchild-Republic Aviation 1973; MS ME Lehigh 1975, PhD Harvard 1978; Assistant Professor MIT, 1979-80; at Penn since 1980 in Mechanical Engineering and Applied Mechanics with a secondary appointment in Materials Science and Engineering). He was Chair of MEAM for 11 years (from 1997-2005 and 2008-2011). He is a member of Penn’s Laboratory for Research on the Structure of Matter and the Institute for Computational Science. He has held visiting professorships UCSB, Harvard, and Brown, was President of the Society of Engineering Science (2008), and has served on several editorial boards. Professor Bassani’s research interests include: interfacial mechanics; nanostructures; adhesion of shells; plastic deformation, material stability; and fracture.