FAILURE CRITERION FOR THICK MULTIFASTENER GRAPHITE-EPOXY COMPOSITE JOINTS

A method for accurately predicting the strength of multifastener, thic k composite joints is discussed. The method is based on the average st ress criterion applied around the hole circumference. Basic laminate s trength data are obtained from single-fastener and reduced-section not ched specimens. Using ABAQUS finite element analyses (FEA), the stress -field distribution around the fastener-loaded hole in both the single -fastener and multifastener joints is determined. The single-fastener test data in conjunction with this FEA and the average stress criterio n are then used to predict the multifastener joint strength. Multifast ener joint strength of three different laminate lay-ups is predicted t o within 1% accuracy. However, the results show that the average stres s criterion cannot accurately predict the location of failure initiati on. In the current investigation, the maximum strain criterion is used to locate possible sites of failure initiation. When this information is used in conjunction with the average stress criterion, the predict ed multifastener joint strength based on single-fastener net-tension d ata is reasonably accurate.