Adhesive bonding of aircraft structures

Adhesive bonding of aircraft primary structures has been in use for over 50 years and is still in use on current aircraft projects as a direct alternative to riveting. Bonding of stringers to skins for both fuselage and wing construction and of metallic honeycomb to skins for elevators, ailerons, tabs and spoilers are the main uses for adhesives. Details of the historical use of adhesive bonding on commercial aircraft and how the adhesive materials developed are given. Assessment of bonded structures are made by carrying out routine tensile lap shear (pr EN 2243-1) and peel tests (BS EN 2243-2 for metal to metal and BS EN 2243-3 for metal to metal honeycomb) to determine the strength. In addition, early bond loads of a particular assembly are assessed for a long period of time by tensile lap shear and pull test pieces based on the component adherend form. Qualification of new adhesives is far more protracted and involves fluid immersion, accelerated ageing, high, low and cyclic temperature testing followed, if successful, by structural fatigue and static buckling tests on bonded structure. The importance of the phenolic/polyvinyl formal adhesive Hexcel Redux 775 to British Aerospace bonding programmes is noted.