Rubber toughening of plastics - Part XIII - Dilatational yielding in PA6.6/EPR blends

Tensile tests were carried out at both constant stress and constant extensi on rate on polyamide 6.6 blends containing 0-20 wt% of maleinated ethylene- propylene rubber (EPR-g-ma), using specimens conditioned at 50% RH. Longitu dinal and lateral strain measurements on creep specimens showed that blends containing EPR-g-ma exhibited dilatation at tensile stresses above 27 MPa. This observation is consistent with the predictions of the particle cavita tion model proposed in an earlier paper (A. Lazzeri and C. B. Bucknall, J. Mater. Sci. 28 (1993) 6799). In standard tensile tests on PA6.6/EPR-g-ma bl ends, cavitation preceded yielding (defined by the 1% offset strain). Creep and yield data obtained over a range of temperatures and strain rates were correlated using the Eyring equation. The onset of dilatation in these PA6 .6/EPR blends was marked by a change in deformation kinetics, which is anal ysed using a modified version of Gurson's equation. (C) 2000 Kluwer Academi c Publishers.