My coworkers (Dan Gianola, Yixiang Gan, and Kevin Hemker) and I have published research results in the December 18th, 2009 issue of Science.  In this work, we perform tension tests on specially designed thin film samples to studying the influence of different stress and strain states on mechanically-induced grain growth in nanocrystalline aluminum.  Our results indicate that shear stresses drive grain boundaries to move in a manner consistent with recent molecular dynamics simulations and theoretical predictions of coupled grain boundary migration.

Our paper can be found at:

http://dx.doi.org/10.1126/science.1178226

As stated by Richard Vinci and Oliver Kraft in the announcement of 2008 Gordon Research Conference on Thin Film and Small-Scale Mechanical Behavior, there is a compelling need to understand the critical roles of different deformation mechanisms in structures with small characteristic dimensions, like nanocrystals and thin films. We have recently studied deformation behaviors in nanostructured materials and thin films with deformation mechanisms including grain-boundary diffusion, grain-boundary sliding, and grain-interior plasticity. Some interesting mechanical phenomena associated with heterogeneous grain-boundary properties are found and summarized here.