Seminar Schedule – Spring 2018
Tuesday, May 8, 2018
Time: 3:30pm – 5:00pm
Place: WRW 102
On Migrating Twins and Growing Voids in Crystalline Plasticity
Shailendra P. Joshi, University of Houston
It is recognized that ductile failure is a multi-scale phenomenon. In metals, crystallographic deformation mechanisms interact with micromechanical length-scales defined by the size and distribution of microscopic defects to trigger damage through void nucleation and growth. Coarser length-scales appear with inter-void interactions that coalesce to form mesoscopic damage zones. Finally, interaction of damage zones with the component scale causes macroscopic failure. Coupling between these scales is often complicated by the anisotropic nature of plasticity involving slip and twinning. We discuss two examples pertaining to the micromechanics of anisotropic ductile damage evolution by void growth and coalescence with an emphasis on the role of twins.
First, we present the deformation stability and failure of face-centered cubic (FCC) nanotwinned materials whose grain-scale anisotropy is brought about by size-effects associated with fine-scale growth twins. Using a length-scale dependent FCC crystal plasticity finite element framework, we investigate the role of twin boundary mediated microstructural evolution in the damage due to nano-void evolution. The interaction between the rates of twin boundary migration and void growth is discussed from the vantage point of macroscopic deformation stability.
The second example focuses on the crystal plasticity of void growth in hexagonal close packed (HCP) materials. The remarkable crystallographic plastic anisotropy, tension-compression asymmetry and strong texture effects in such low symmetry materials (e.g. magnesium) are often referred to as origins of damage intolerance. While post-mortem experimental evidences indicate ductile processes at play, the role of anisotropic slip and twinning on the rates and states of damage accumulation remains elusive. We probe the emergent interactions between intra-granular void evolution with slip and twinning.
Shailendra Joshi is Bill D. Cook Assistant Professor in the Department of Mechanical Engineering at University of Houston (UH). Prior to joining UH, he was an associate professor at the National University of Singapore (2008-2018). During 2005-2008, he was a post-doctoral fellow in the Department of Mechanical Engineering at Johns Hopkins University. He earned his PhD in Civil Engineering from Indian Institute of Technology Bombay in 2002. After a short stint as a visiting scientist at the University of Stuttgart (2002), he worked as a research engineer at GE-India Technology Center in Bangalore, India (2003-2005). His research interest is in understanding, modeling and controlling material responses through the mechanics of defects and failure processes at multiple length-scales and time-scales.
For further information, please contact Dr. Justin Wilkerson at wilkerson@utexas.edu or (512) 471-4371.
