Prediction of impact performance of plastics mouldings Part 1: Materials models and determination of properties

Abstract

Measurements have been made of true stress v. true strain curves under tension, compression and shear on a rubber toughened, propylene–ethylene copolymer used for the manufacture of motor vehicle interior door trim. Results are analysed to determine the properties and parameters required by selected elastic–plastic models for the simulation of impact performance using finite element methods. For this purpose, measurements are required out to large strains and over a wide range of strain rate which includes very high rates ( ∼ 1000 s⁻¹) associated with impact events. The determination of properties at high strain rates is achieved by modelling measurements at low and moderate strain rates and calculating the behaviour at high strain rates by extrapolation. Measurements of stress–strain curves under tension, shear and compression and of Poisson's ratio with strain are used to derive parameters for the von Mises and linear Drucker–Prager models and for a new model that takes account of the influence of cavitation on plastic deformation. Limitations in the applicability of the first two models for describing the deformation behaviour of the copolymer are demonstrated. In Part 2 of this paper, the results reported here are used in finite element analyses to predict the deformation of subcomponents cut from door trim mouldings. These predictions are compared with experimental measurements.