Deformation of thermoplastic vulcanizates

The stress-strain behavior of thermoplastic vulcanizate (TPV) materials is studied experimentally; a constitutive model for the behavior is proposed and found to successfully predict the important features of the observed stress-strain behavior. TPVs are a relatively new class of elastomer-like material consisting of a rather high-volume fraction of elastomeric particles (0.40 < <upsilon>(p) < 0.90) embedded in a continuous thermoplastic matrix. The uniaxial and plane strain compressive behavior of a series of TPV materials is studied where <upsilon>(p) is progressively increased from 0.0 to 1.0. The influence of upsilon (p) on the various features of the stress-strain behavior is identified from small to large strain. A constitutive model is proposed which acts to provide a simplified representation of the effective contribution of the thermoplastic phase and the elastomeric phase to the overall composite macroscopic behavior. The model is found to successfully capture and predict the significant features of the stress-strain behavior during loading including a relatively stiff initial response, followed by a yield-like event, followed by strain hardening and strain stiffening. The model also captures basic features of the unloading behavior, including the enhanced stiffness upon initial load reversal followed by the nonlinear unloading behavior which leads to the extensive recovery of these materials and their elastomeric-like behavior. Although the magnitude of the hysteresis loop is poorly predicted, the increase in recovery with increase in elastomer content is captured. (C) 2001 Elsevier Science Ltd. All rights reserved.