Static and dynamic observations of dislocations and other defects in smectic Cano wedges

We study the role of defects in the flow properties of a thermotropic smect ic (iri Cane wedge geometry) by in situ deformation experiments in an optic al polarizing microscope. The motion of the edge dislocation array is studi ed for imposed strain rates and their climb velocity is measured. At a stre ss close to 3000 dyn/ cm(2) a jerky climb of edges is observed implying the existence of screw dislocations which hinder the free motion of the farmer . At a stress close to 5000 dyn/ cm(2)a Viscous motion of edges is evidence d for which we confirm the validity of the Orowan relation, established for solid crystals.