Evaluation of Dynamic Tensile Characteristics of Polypropylene Composites with Temperature Variation

Abstract

This article suggests two useful methods to obtain true stress-strain curves with the variation of the strain rate ranging from 0.001 to 200/s using a finite element technique and optimization for two typical polymers: a polypropylene; and a polypropylene composite. The polypropylene is adopted as a core material of a vehicle's instrument panel and the polypropylene composite sustains the passenger-side air bag module (PAB module) as a structural member. Their dynamic tensile characteristics are important to predict deformation modes of the PAB module which undergoes high speed deformation during air bag expansion. Since the polymers are temperature sensitive materials, the dynamic tensile tests were performed at the three levels of temperature: the low temperature (-30 degrees C); the room temperature (21 degrees C); the high temperature (85 degrees C). During tensile tests of two polypropylene composites, the gage region in the specimen of the polypropylene composite elongates uniformly while that of the polypropylene does not elongate uniformly. In the case of the polypropylene, experimental stress-strain curves were modified by enforcing the load response calculated by finite element analysis coincident with that of the experiment. In the case of the polypropylene composite, experimental stress-strain curves were scaled by applying change rate of the gage length. Stress-strain curves of both cases provide excellent performance in their numerical response with the finite element analysis. The material properties obtained are indispensible to estimate the high speed deformation mode during air bag expansion at both normal and harsh operating conditions.