Effects of strain rate and density on tensile behavior of polypropylene syntactic foam with polymer microballoons

The objective is to characterize the effects of local strain rate and density on the mechanical properties of the thermoplastic syntactic foams at the intermediate and high strain rates. Tensile tests are conducted at the nominal strain rates from 10^-1 to 10² s^-1. Finite element analyses are conducted on the microstructural models to estimate the local strain rate. When the local strain rates are considered, the relative elastic moduli are classified into two groups by the nominal strain rates below 10 and above 50 s^-1. This is because the matrix material at the cell edge is rubber phase leading to small local bending stiffness at the nominal strain rate below 10 s^-1. At the nominal strain rate above 50 s^-1, the relative elastic moduli can follow the equation proposed by Gibson and Ashby, while the relative yield stress is plotted in one group, leading to follow Gibson and Ashby law.