Chapter 30 - Case History: Bonded Composite Reinforcement of the F/A-18 Y470.5 Centre Fuselage Bulkhead

Abstract

This chapter summarizes a work program aimed at development and validation of a bonded composite reinforcement for the Y470.5 bulkhead crotch region. Both a finite element (FE) analysis and an experimental test program were undertaken to determine the suitability of a bonded reinforcement for the bulkhead. A representative structural detail test specimen the curved beam specimen (CBS) was designed to identify the stress state in the joint and in conjunction with FE analysis, to determine the through-thickness stresses in the adhesive. The static and fatigue testing of this specimen were used to validate the reinforcement for the bulkhead. The reinforcement to the F/A-18 Y470.5 bulkhead crotch region was limited by the existence of through-thickness adhesive stresses resulting from the curvature of the region. Through-thickness stresses in bonded joints, or stresses normal to the plane of the adhesive layer, generally arise from out-of-plane loading in the joint. These stresses are called peel, tension, tearing, or normal stresses and usually result from the shear stresses developed during load transfer and from the development of secondary bending under non-axial loading. Less commonly they arise in joints with a high degree of curvature. Through-thickness stresses play no part in the desired load transfer in the joint, but can cause failure since adhesives (and composite adherends) have relatively low peel strengths.