Increasing Strength of Graphite/Epoxy Bolted Joints by Introducing an Adhesively Bonded Metallic Insert

摘要

A method to increase the failure load in graphite/epoxy bolted joints where the failure mode is bearing strength is proposed by bonding a metallic insert in the hole. In order to design test specimens with significantly reduced compressive stresses at the hole boundary, finite element (FE) analyses were performed. The FE-analyses reveal the possibility to reduce the compressive stresses at the hole boundary in quasi-isotropic laminate by 50 percent, if a 10 mm hole is enlarged to 14 mm and a 2 mm thick metallic insert is adhesively bonded in the hole. Experiment results show an increase in failure load of up to 55 percent when using an aluminum insert and of 30 percent when using steel insert, the steel insert also giving a 13 percent stiffer joint. The adhesively bonded insert alters the failure mode to failure in the adhesive combined with net tension failure of the composite member. Studies of FE-results explain the difference in failure load when using a steel or aluminum insert respectively by the fact that the stiffer steel insert causes higher tension stresses in the adhesive, which lead to a primary tension failure in the adhesive.