| Abstract: | The solid-phase rheology of a thermotropic polyester which is liquid crystalline in the melt (Vectra A) was studied for one-dimensional finite-amplitude deformations, including step-strain and recovery, step-stress and recovery, and step-strain followed by small-amplitude oscillations. The rheology is complex, and cannot be described by existing models. Below a critical strain, which is history-dependent, Vectra A deforms as a linear viscoelastic solid. Above the critical strain the deformation is both viscoplastic and viscoelastic. There appears to be a maximum recoverable strain of about 0.03, beyond which all deformation is nonrecoverable. A large number of relaxation modes is required to describe the stress, and one time scale is inadequate to describe the time-dependence of yielding and plastic flow. |
