Indentation and face-wrinkling of a damaged sandwich beam with a compressive yielding core and cohesive interfaces

In composite sandwich beams, the presence of damage or thickness imperfections in the skin and the interaction between progressive yielding of the core and cohesive fracture at the core/face interface may influence the failure modes for indentation and face wrinkling. The problem is investigated using the one-dimensional representation of the skin as a beam/beam-column on a Winkler foundation that is elastic-plastic in compression and elastic-softening in tension; the skin damage is accounted for through local reductions of the beam flexural stiffness. First results on the indentation response and collapse load show that upper and lower threshold solutions correspond to the fully intact and fully damaged beams and the transition between the limiting solutions depends on the size, entity and position of the damage; characteristic lengths define the minimum size of the damage that has the strongest effect on the solution and the minimum distance between load and damage for which the damage has no effect.