Amplitude Dependent Damping in Vinyl Polymers

The damping behaviour of several vinyl polymers-poly(methy1 methacrylate) (PMMA), poly(viny1 chloride) (PVC), polystyrene (PS) and impact polystyrene (Psi)-was studied both as a funtion of temperature and strain amplitude. The measurements were performed from room temperature up to the glass transition temperature and shows amplitude dependence at frequencies of the order of 50 kHz. The data are interpreted in terms of a hyperbolic sine stress dependence of the strain rate, including an effective stress. The activation volume was found to depend on temperature, with values much larger than those given by the usual mechanical tests (tensile, creep and stress relaxation). It is suggested that the nonlinear effects are related to the a relaxation in these materials, since the activation enthalpy is quite similar to the one obtained from the maxima of this relaxation.