Professor Thomas R. Bieler
Department of Chemical Engineering and Materials Science, Michigan State University, USA.
The phenomenon of slip transfer through grain boundaries has been simulated with atomistic simulations in a small fraction of grain boundary misorientation space. Such simulations are constrained by periodic boundary conditions, where the imposed stress tensor is necessarily simple. At the mesoscale, the local boundary conditions operating on a volume of material containing a grain boundary vary with strain, which coupled with lattice rotations arising from slip, lead to complex evolving boundary conditions that are not conducive to simulation in an atomistic (or dislocation density based) simulation. A highly simplified geometrical approach applied at the mesoscale can be implemented into crystal plasticity finite element simulations, but this lacks the atomistic detail. Whether the atomistic detail is needed or not is an open question. To address this question, experiments and correlated mesoscale simulations under way will be described in pure aluminum (using oligocrystal foil samples examined with SEM/EBSD) and pure titanium (bending experiment examined with differential aperture x-ray microscopy), and a titanium alloy polycrystal (examined with SEM/EBSD).
Professor Thomas R. Bieler earned a B.A. in Applied Mechanics at University of California at San Diego in 1978 and a M.S. in Ceramic Engineering at University of Washington (Seattle) in 1980. He worked at Sandia National Laboratory in Livermore for five years on high rate deformation. He completed his Ph.D. in Materials Science (with a minor in continuum mechanics) at University of California at Davis in 1989 and has been at Michigan State University thereafter. His research focuses on characterization of mesoscale deformation mechanisms and plasticity modeling in titanium-based alloys, tin in the context of lead-free solder joints, and high purity niobium used in superconducting particle accelerator cavities. With colleagues, he has published over 320 papers, with more than 6600 citations and an h-index (ISI) of 43. He is active in ABET Engineering Accreditation, and he is an organizer or co-organizer of many recent symposia involving heterogeneous deformation related to grain or phase boundaries, and a fellow of TMS.