Material BehaviourMechanical response and microstructure investigation of a mineral and rubber modified polypropylene

The paper presents an experimental investigation of a semi-ductile rubber-modified polypropylene reinforced by mineral particles. The behaviour of the material is investigated by performing tension, shear and compression tests at quasi-static and dynamic strain rates, applying digital image correlation for full-field strain measurements. Subsequently, scanning electron microscopy is used to analyse the fracture surfaces of the tension and compression test samples, and to relate the observed mechanical response to the evolution of the microstructure. The experimental study shows that the material is highly pressure and strain rate sensitive, and that the rate sensitivity seems to be more pronounced with increasing pressure from tension via shear to compression. It also exhibits significant volume change, which is mainly ascribed to a cavitation process appearing during tensile deformation. Assuming matrix-mineral particle debonding immediately after yielding and self cavitation of rubber particles, both kinds of particles might be the source of initial cavities. From the study of the fracture surfaces in tension it appears that the fracture process is less ductile at high strain rates than under quasi-static conditions, while the micrographs taken of compression samples show that the size of the cavities is much smaller than in tension.