  Through 2D granular Couette flow experiments, we probe failure and
deformation of disordered solids under shear. Shear produces smooth affine
deformations in such a solid and also irresversible so-called non-affine
particle displacements. We examine both processes. We show that the non-affine
part is associated with diffusion, and also can be used to define a granular
temperature. Distributions for single particle non-affine displacements,
$\dri$, satisfy $P_1(\dri) \propto \exp [-|\dri/\Delta r|^{\alpha}]$ ($\alpha
\stackrel{<}{\sim} 2$). We suggest that the shear band forms due to a radially
outward diffusive flux/non-affine motion which is balanced in the steady state
by inward diffusion due to density gradients.
