Development of high performance lightweight aluminum alloy/SiC hollow sphere syntactic foams and compressive characterization at quasi-static and high strain rates

Aluminum alloy A356 filled with silicon carbide hollow spheres (SiC _HS) is investigated for quasi-static (10^-3 s^-1) and high strain rate (up to 1520 s^-1) compressive properties. Such closed cell composite foams, called syntactic foams, are of interest in weight sensitive structural applications. The present work is focused on understanding the compressive failure mechanism and relating them with the material microstructure. The compressive and plateau strengths of syntactic foams with SiC_HS are found to be 163 and 110 MPa, respectively. The measured properties are considerably higher than the existing fly ash cenosphere filled aluminum matrix syntactic foams. Compressive failure mechanisms are studied for A356/SiC_HS syntactic foams and direct evidence of hollow sphere crushing at the end of the elastic regions is obtained. The predictions of compressive strength obtained from an existing model are validated with the experimental results. Extensive analysis of data on open and closed cell foams containing gas porosity and syntactic foams is presented. A clear advantage in terms of low density and high yield strength is observed in A356/SiC _HS syntactic foams compared to other foams. Yield strength of aluminum foams may be different at high strain rate compression compared to quasi-static values but most of the foams do not show strong evidence of strain rate sensitivity within the high strain rate regime.