Mechanical Behaviour of a Mineral Filled Elastomer Modified Polypropylene Compound - An Experimental-Numerical Investigation

Abstract

The present work is concerned with the mechanical behaviour of the mineral filled elastomer modified polypropylene compound found in the frontal bumper covering of the BMW 5-series (G30).

Material tests machined from injection moulded plates were used to characterise the elasto-viscoplastic behaviour. The material showed rate-sensitivity, pressure-sensitivity and significant volume changes. Tensile specimens machined from components were used to investigate the reproducibility of the mechanical properties. The general tendencies were reproducible, but there was a scatter in both stress level and in failure strain. The scatter in failure strain is thought to be a result of inhomogeneous distribution of particle reinforcements.

The SIMLab Polymer Model was applied in the numerical work. A separate calibration was made for plates and for components, due to differences discovered in the experimental work. Validation with numerical material tests showed excellent results. Furthermore, a probabilistic approach was applied on the damage model, in order to account for the experimentally observed scatter in failure strain. The critical damage was introduced as a pseudo-random independent variable which followed a Weibull distribution. The scatter was adequately reproduced through Monte-Carlo simulations, though some non-physical effects were discovered. These were a consequence of the assumed statistical independence between integration points and between elements.

Finally, the capabilities of the material model were investigated in full scale crash simulations. The agreement between SPM and the currently applied material model in BMW Group was excellent. The probabilistic approach could however not be evaluated in the applied load case, as the material was too ductile to reach failure.