Semisoft elasticity and director reorientation in stretched sheets of nematic elastomers.

A two-dimensional effective model for the semisoft elastic behavior of nematic elastomers is derived in the thin film limit. The model is used to investigate numerically the force-stretch curves and the deformed shape, and to resolve the local patterns in the director orientation in a stretching experiment. From the force-stretch curves we recover the two critical stretches which mark the transition from hard to soft and back to hard response. We present an analytical model for their dependence on the aspect ratio of the sample, and compare it with numerical results.