Determination of True Stress-True Strain Curves of Auto-body Plastics

Abstract

This paper is concerned with tensile characteristics of auto-body plastics at various strain rates ranging from 0.001/sec to 100/sec. Tensile characteristics at the high strain rate are important in prediction of deformation modes of plastic components which undergo the high-speed deformation during car crash. Uniaxial tensile tests at the quasi-static strain rate were conducted at strain rates ranging from 0.001/sec to 0.01/sec by using a tensile testing machine, INTRON 5583. Uniaxial tensile tests at intermediate strain rates were conducted at strain rates ranging from 0.1/sec to 100/sec by using a high-speed material testing machine developed. Since the deformation of plastics is accompanied with localized deformation and a conventional extensometry method(CEM) is no longer valid for strain measurement, a force equilibrium grid method(FEGM) is newly proposed in order to acquire accurate true stress-true strain curves of plastics. FEGM is utilized with image capture of non-uniform distribution of deformation at each elongation stage from a high speed camera in aids of grid methods. The relation between true stress and true strain at the designated strain rate and increment were obtained by collecting the load data by the equilibrium and the deformation images.