Cold impact performance of polypropylene (PP)

Abstract

In this thesis, the ability of the SIMLab polymer model to represent the material behaviour of polypropylene used in the Toyota Yaris door trim, under impact loading, has been investigated. The overall goal was to attempt to replicate an experimental drop test on the door trim at −30◦C through a finite element simulation. Thus, the polymer model had to be calibrated using various experimental uniaxial stress tests. It was then validated by comparing numerical simulations to experimental results of the uniaxial tests, and additionally a Charpy V-notch impact test.

The main source of test specimens for both the uniaxial stress tests and the Charpy tests, were injection moulded material sample plates. The material was found to be quite ductile, uniform, isotropic and otherwise performing with only small variances with respect to stress, strain and fracture behaviour. A secondary specimen source was the door trim itself. It was studied if the material in the sample plates were in fact representative to that of the door trim. Results showed that their behaviour was identical, except for strain at fracture, which varied immensely.

The Charpy impact test showed that the material behaved in a brittle fashion for higher strain rate. The initial choice of fracture criterion was not able to represent the transition from ductile to brittle material behaviour. Two different attempts circumvent this problem was made, including inverse modelling of the main fracture parameter such that experimental and numerical simulations coincided.

Experimental drop tests on the Yaris door trim were performed at Toyota s European headquarters in Zaventem, Belgium. Results of the simulations showed that the model estimated a too brittle response. A thorough sensitivity study was thus performed. The effects of the parameter central for the fracture criterion was found to be the most critical.