High strain rate compressive response of syntactic foams: Trends in mechanical properties and failure mechanisms

Syntactic foams are composite materials comprising hollow particles dispersed in a matrix material. Available studies on high strain rate compressive response of polymer matrix syntactic foams are critically analyzed to identify the strain rate effects with respect to the material composition. Syntactic foams reinforced with micro- and nano-sized fibers and particles are also covered in the study. Polymer matrix syntactic foams demonstrate strain rate sensitivity in compressive strength over a wide range of strain rates. The compressive strength in the strain rate range of 500-1500s^-1 is usually seen to be higher than the quasi-static strength. Reinforced syntactic foams also show similar trends. Compared to the quasi-static compressive failure mechanism of shear cracking, the high strain rate failure occurs by crack propagation in the direction of compression. Compressive properties are not available for syntactic foams in the intermediate strain rate range of 1-400s^-1 due to a lack of appropriate test methods for this range. Absence of modeling and simulation of high strain rate properties of syntactic foams in the published literature is noted. Increasing applications of syntactic foams in automobiles and potential applications in armor structures can benefit by these findings because the mechanical properties and failure criteria selected in the design process should account for the strain rate sensitivity.