X-ray microtomography and finite element modelling of compressive failure mechanism in cenosphere epoxy syntactic foams

The X-ray microtomography with interrupted uniaxial compression was performed on cenosphere epoxy syntactic foams to directly observe the internal microstructural change of the constituents during the failure process. Finite element modelling of the full scale foam specimen was developed and experimentally validated to predict the localised stress, fracture of cenospheres and deformation in the matrix. The finite element predictions were related to the X-ray microtomographic observations to analyse the underlying mechanisms of internal 3D failure process in the plateau region of the foam. The compressive failure process in microscopic scale consists of (1) the crushing of cenospheres and (2) the plastic deformation and fracture of the matrix. The failure mechanisms in the two constituents are determined by the localised stress state and the stress transfer between the constituents, and govern the different strain stages of bulk stress-strain behaviour of the foam. The maximum tensile stress concentration near the equator causes the earlier vertical splitting fracture of largest cenospheres. The localisation of stresses in the connection zone between adjacent cenospheres results in the formation of micro-cracks, which then propagate preferentially diagonally to form the macro-cracks by joining other micro-cracks and the voids left by crushed cenospheres.