Reduction of strength of GFRP sandwich panels in naval ships by face sheet holes, cracks and impact damage

Extensive studies have been previously carried out on the effects of various types of local damage on the performance of sandwich panels used in the hull structures of naval ships. More recently, the approach was adapted for application on board a specific ship series. Strength reduction data were obtained for a set of sandwich materials that were representative for the vessels in question. The face sheet materials were glass fibre-reinforced plastics with non-crimp fabrics and two different types of vinylester resin. The core materials were PVC foams. Tests were performed on laminate specimens with and without circular holes under tensile loading and on sandwich face sheets with holes, cracks and impact damage under compressive loading. The strength reductions caused by impacts with sharp and blunt objects were compared with those caused by machined cracks and circular holes, respectively, and with Whitney and Nuismer’s point stress and average stress models for infinitely large laminates with cracks and holes. It was found that strength reductions due to impact damage can be estimated using tests on specimens with machined cracks and holes, and also with the average stress models if appropriate values of characteristic length are assumed. Special attention is paid to the need to take account of the geometry and the finite size of tested specimens.