A study on the failure mode and load of the composite key joint

Abstract

The joining of composite materials has traditionally been achieved by adhesive bonding or mechanical fastening. Mechanical fastenings require little or no surface preparation, and are easy to inspect for joint quality. However, they require machining of holes that interrupt the fiber continuity and may reduce the strength of the adherend. We proposed the new composite key joint to minimize the fiber discontinuity and strength degradation of adherend. Mechanical key joints with three different d/ t (slot depth to thickness) ratios and two different e/ w (edge length to width) ratios were manufactured and tested. Carbon-epoxy unidirectional prepreg (USN125) and plain weave prepreg (HPW193) were used for the composite key joints. Tensile tests were performed on the composite key joints and their failure modes were evaluated. Finite element analyses for the mechanical key joints were performed and the stresses around the key slot were calculated. From the tests, it could be concluded that the failure load of the key joints was about two times larger than those of a mechanical joint for the investigated composite joints.