Bonded joints with through-thickness adhesive stresses – reinforcing the F/A-18 Y470.5 bulkhead

Abstract

A bonded composite reinforcement is being developed for the Royal Australian Air Force F/A-18 Y470.5 bulkhead crotch region. Due to the curvature of the surface in this area any bonded reinforcement was predicted to have high through-thickness stresses present in the adhesive under load. A representative specimen, the “curved beam specimen” (CBS) was designed using finite element analysis to identify the stress state in the joint and determine the through-thickness stresses in the adhesive. The specimen was then mechanically tested to failure under static loads and also under spectrum fatigue loading to determine the viability of the repair. The data from the above program was used to determine an estimate for the through-thickness stress design allowable for the structural film adhesive Cytec FM73. It is suggested that the CBS will prove to be a suitable specimen for providing generic data on the through-thickness static and fatigue strength of adhesives.