Monday, November 2 2009

For over 50 years, plastic deformation in crystals has been understood to be governed by dislocations.  Despite several decades of work, a coherent picture of plasticity in amorphous materials has only recently begun to emerge.  This picture is based on local zones which are particularly susceptible to shear; so-called shear transformation zones (STZs).  The visco-plastic response of a host of amorphous solids ranging from metallic glasses, to granular materials, to soft matter such as foams and emulsions are believed to be governed by this same underlying STZ mechanism. 

I will discuss computer simulations of various model systems which probe the complex spatio-temporal activity exhibited by these shear zones.  In particular, I will show how correlated avalanches of shear zones can give rise to a system-size dependent diffusion constant in sheared 2D Lennard-Jones glasses.  I will also discuss how this picture is modified near the random close packing point in repulsive systems.