MSE Colloquium: Chris Weinberger, Building Physically-­Based Single Crystal and Polycrystal Models for Low-­Temperature Deformation in BCC Metals

Abstract

Despite the technological importance of body-centered cubic (BCC) metals, models of their plastic deformation are less common than those of face-centered cubic (FCC) metals, due in part to the complexity of slip in BCC crystals. In order to study the effect of microstructure on low-temperature plasticity in BCC metals, we have developed a single crystal plasticity model based on the atomistic results of Groger et al. for molybdenum and tungsten. The complexity of BCC crystal plasticity is due largely to non-Schmid stresses that govern the flow behavior. At the atomic scale, these non-Schmid stresses are caused by asymmetries in the dislocation core structure, which allow the motion of screw dislocations to be assisted by shear stresses that do not lie on the slip plane. This leads to both a non-associative flow law and the well-known tension/compression asymmetry in the yield surface.

In order to study the effects of microstructure on plasticity, we implemented the BCC crystal plasticity model in a polycrystal plasticity finite element formulation. Using this model, we can not only reproduce continuum response; but also resolve individual grains’ responses via stress, strain, and crystallographic rotation. The non-Schmid effects create tension/compression asymmetry that causes substantial differences in response at the grain scale.

Bio

Christopher R. Weinberger is a Senior R&D S&E staff at Sandia National Laboratories whose research interests include using theory and simulations to model the mechanical properties of materials at the macro-, micro- and nano-scale using a variety of simulation methodologies including molecular dynamics, discrete dislocation dynamics and crystal plasticity models.  Dr. Weinberger received his B.S. in Mechanical Engineering from Cal Poly San Luis Obispo in 2001. After graduation, he took a job at Lockheed Martin Space Systems Company in Sunnyvale, CA.  He earned his M.S. in Mechanical Engineering from Stanford in 2005 while working full time at Lockheed.  He then pursued his Ph.D. full time at Stanford, working in the area of plasticity in confined volumes and received his degree in 2009.  Dr. Weinberger received the Harry S. Truman Fellowship from Sandia National Laboratories, 2009-2012, and became a staff member at Sandia in September 2012.