AMPLITUDE DEPENDENT DAMPING IN VINYL-POLYMERS

The damping behaviour of several vinyl polymers-poly(methyl methacryla te) (PMMA), poly(vinyl chloride) (PVC), polystyrene (PS) and impact po lystyrene (PSi)-was studied both as a function of temperature and stra in 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 temp erature, with values much larger than those given by the usual mechani cal tests (tensile, creep and stress relaxation). It is suggested that the nonlinear effects are related to the alpha relaxation in these ma terials, since the activation enthalpy is quite similar to the one obt ained from the maxima of this relaxation.