Evaluation of Dynamic Tensile Characteristics of Polyprophylene with Temperature Variation

Abstract

This paper deals with dynamic tensile characteristics for the polyprophylene used in an IP(Instrument Panel). This polyprophylene is adopted in the dash board of a car, especially PAB(Passenger Air Bag) module. The dynamic tensile characteristics are important because the PAB module undergoes high speed deformation during the airbag expansion. The operating temperature of a car varies from −40°C to 90°C according to the specification. The dynamic tensile tests are performed at the low temperature(−30°C), room temperature(21°C) and high temperature(85°C). The tensile tests are carried out at strain rates of six intervals ranged from 0.001/sec to 100/sec. The flow stress increases as the strain rate becomes higher. The flow stress decreases at the high temperature while the strain rate sensitivity increases. Tensile tests of polymers are rather tricky since polymer does not elongate uniformly right after the onset of yielding unlike the conventional steel. A new method is suggested to get the stress-strain curve accurately. The stress-strain curves were modified on the basis of the nominal stress-strain curves obtained from the experiment. Finite element analysis of the tensile test with the special specimen was carried out with modified stress-strain curve obtained from the ASTM IV specimen. The optimization method produced a good stress-strain curves which is in good coincidence with the stress-strain curve obtained from the experiment. The material properties obtained from this research will be useful to estimate the airbag expansion at the normal and harsh operating conditions respectively.