Effect of Cutouts on Strength of GRP (Glass Reinforced Plastic) for Naval Ship Hulls

摘要

The effects of cutouts on the strength of glass reinforced plastic (GRP) for use in naval ship hulls have been studied. Experiments were conducted on an E-glass fiber/polyester resin laminate provided by the U.S. Navy Minesweeper Hunter (MSH) shipbuilder in 48 in. x 15 in. panels. Tensile tests were run on full-sized panels with circular cutouts of 3.75 to 7.50 inch diameter with and without edge notches; conventional tensile and fracture toughness tests were also run. Three theoretical models were evaluated. First, the notch sensitive, so that models which include stress concentration effects are required. A simple stress concentration model appears valid, but can only provide an accurate prediction when the measured tensile strength is increased by a factor to represent the actual local strenth at the cutout edge. Linear elastic fracture mechanics provides strenth predictions reasonably close to the experimental results when cracks are present at the edge of the cutout. In addition to the direct experimental results of the study, the effects of a seawater environment and cyclic fatigue loading are estimated based onearlier studies. The overall effects on ship hull design safety factors are calculated. The required safety factors are excessively high unless cutouts are reinforced to eliminate the stress concentration effect. Detailed recommendations for further research and development needed to advance failure analysis in GRP hulls are provided.