Experimental measures of affine and nonaffine deformation in granular shear

Through 2D granular Couette flow experiments, we probe failure and deformation of disordered solids under shear. Shear produces a mean azimuthal flow, smooth affine deformations, and irreversible so-called nonaffine particle displacements. We find that these processes are all of comparable magnitude and depend on the local shear rate. We compute the parameter of Falk and Langer characterizing nonaffine motion, D-min(2), and find that it is reasonably well described in terms of collections of single particles making locally nearly isotropic random steps, delta r(i). Distributions for single particle nonaffine displacements, delta r(i), satisfy P-1(delta r(i)) proportional to exp[-|delta r(i)/Delta r|(alpha)] (alpha less than or similar to 2).