Repair of Damage to Marine Sandwich Structures: Part II - Fatigue Testing

Sandwich construction panels, comprising glass reinforced polymer (GRP) composite skins and PVC foam core, are in use in the current generation of naval vessels of the mine hunting class. Such structures will inevitably be subjected to damage and any repair techniques need to ensure that the strength, stiffness and resistance to fatigue crack initiation of the structure are restored. In a previous study the recommended techniques, outlined in Defence Instruction (Navy) ABR 5803 for the repair of sandwich structures, have been evaluated under static four-point bending and deficiencies in the repair techniques which affected sandwich strength and stiffness were identified. A modified repair technique was proposed to simplify the repair procedure for GRP sandwich panels and to overcome the problems associated with the RAN repair technique. In this study the repair techniques were scrutinized by measuring the cracking resistance of repaired sandwich panels under fatigue loading. The modified repair technique, in comparison with the RAN repair technique, was found to fully restore the fatigue cracking resistance of sandwich construction panels to the level observed for the undamaged panels.