Schmid Factor. The Schmid Factor was estimated to be 0.48 for the ultrafine-grained pillar and 0.47 for the nanocrystalline pillar. The critical resolved shear stress τ^sub r^ was calculated to be 248 MPa and 334 MPa for the ultrafine-grained and nanocrystalline copper pillars, respectively. The resolved shear stress from a theoretical model developed by I. Gutkin et al.16 is estimated to be 100 MPa and energy-based calculations carried out by S, Kibey et al.17 to be 120 MPa for copper. Y.T.