Damage interaction in fully-backed composite sandwich beams subject to time dependent moving loads

The paper deals with the interaction of multiple damage mechanisms in composite sandwich beams subject to static and dynamic out-of-plane loading, due for instance to high velocity impact or water slamming. A sandwich beam continuously supported by a rigid plane is considered and the damage mechanisms for skin delamination and core crushing are studied. Under quasi static loading conditions the core shields the stress field at the tip of delaminations in the skin from the applied load and induces local energy barriers to crack propagation. The constitutive and geometric parameters can be tailored to improve shielding and reduce damage growth in beams with elastic cores, for instance by increasing the stiffness of the core; however, core crushing, which reduces the shielding of the fracture parameters, can be favoured for properties that have been optimized in the elastic regime. The optimal design of the system must account for the interaction of the different mechanisms. Similar effects are observed under dynamic loading, where core crushing increases the displacements in the skin and consequently the energy release rate during the loading phase. In the free oscillation phase that follows the application of a pulse load the skin-core interaction generates delamination openings that are not present under quasi-static loading and give rise to a mode I component of the energy release rate that can dominate crack propagation; energy dissipation due to core crushing reduces this effect.