Effects of local strain rate and micro-porous morphology on tensile mechanical properties in PP/EPR blend syntactic foams

This study characterizes the effects of local strain rate and micro-porous shape on the tensile mechanical properties at the intermediate and high strain rates in the thermoplastic polymer syntactic foams. Four types of syntactic polypropylene (PP)/ethylene propylene rubber (EPR) blend foams are developed with respect to the micro-porous morphologies. Tensile tests are conducted at the nominal strain rates from 0.3 to 100 s−1. Finite element (FE) models are constructed based on the morphological pictures. The corresponding tensile test simulation is conducted on the microstructural FE models to estimate the local strain rate and investigate the relation between the micro-porous morphology and the local strain rate. It is found that the local strain-rate distribution gets broader in the spherical-shape porous foams than the elliptical-shape porous foams. The strain-rate dependencies of the apparent elastic modulus and the yield stress of the syntactic foams are mainly caused by the matrix materialʹs properties. The magnitude of the yield stress is dependent on the micro-porous shape although that of the apparent elastic modulus is not influenced by the porous morphology. When the local strain rate is taken into account, the yield stress can be predicted by the simple rule of mixture in the spherical shape of the syntactic foams.