Effects of debonds and face sheet damage in GRP sandwich panels in naval ships

Sandwich construction with face sheets of fibre-reinforced plastics (FRP) and a core of polymer foam or balsa wood offer a lightweight construction that is well suited to naval and other vessels for high-speed operation or where payload considerations require that the structural weight be minimised. Some of these applications involve the use of highly optimised sandwich solutions. Studies are under way to establish how the structural performance is influenced by the presence of production defects or in-service damage. Previous work to establish the local strength reductions caused by face-core debonds and face sheet impact damage is being extended to cover sandwich lay-ups with non-crimp glass reinforcements, vinylester matrix materials and foam cores of both PVC and PMI. Cases with both compressive and (for face sheet impact damage) tensile loading are considered. Modelling approaches and failure criteria are discussed. Tentative strength reduction curves are presented, but uncertainty concerning the intact strengths of the materials used needs to be removed before these can be used with confidence.