Behaviour of sandwich structures with cork compound cores subjected to blast waves

Sandwich structures can often sustain large deformations under constant load enabling them to absorb significant amounts of energy. The mechanical properties of cork (e.g. low density and high specific stiffness and strength) suggest that this material—and its compounds—may have excellent properties when acting as core in energy absorbing sandwich systems and structures. Cork is a natural material with a cellular structure (closed cell). After reaching yield stress, cork exhibits a region of almost constant stress for increasing strains until densification is reached, allowing it to absorb considerable amounts of energy. Within the scope of the present work, two micro-agglomerated cork (MAC) compounds are incorporated as cores in sandwich structures with 5754-H22 aluminium alloy face sheets. Samples with constant thickness of the face sheets and different core thicknesses are tested. These structures are fixed on a 4-cable ballistic pendulum and subjected to blast waves originated from the detonation of 30 g of high explosive (C4) at a fixed stand-off distance (300 mm). The deflection of the front and back face sheets is measured as well as the transmitted impulse and movement of the pendulum. The effects on the structural response of the core thicknesses and core densities are determined. A linear dependence between the relative core thickness reduction and the initial core thickness is determined for both MAC compounds. A value of ≈11% was obtained for the relative thickness reduction, strongly indicating the possibility of energy dissipation by the core, most probably due to crushing of the cellular structure of cork.