Strain rate dependent compressive properties of glass microballoon epoxy syntactic foams

Lightweight glass microballoon epoxy syntactic foams have a high strength-to-weight ratio, making them attractive for transport applications. A better understanding of the compressive properties of such foams is required to improve predictive modelling tools and develop novel formulations. In this study, the response of a foam to compressive loading was experimentally investigated over strain rates from 0.001 to 4000 s−1. The stress-strain response, deformation/damage history and volume change were examined quantitatively and/or qualitatively; all of these parameters exhibit strain rate sensitivity. Combined finite element stress analysis and microscopic observations reveal that heterogeneous (localised) damage arises in the foam due to the coexistence of two failure modes: (i) crushing of glass microballoons dominating in the central part and (ii) shear cracking of the epoxy matrix that forms and propagates from the corners. As the strength of the epoxy matrix increases with increasing strain rate, cracking of glass microballoons begins to dominate over the matrix/microballoon debonding, resulting in macroscopic strain rate dependency of compressive properties.