Adhesively bonded repairs to primary aircraft structure

The design of bonded repairs to flight critical aircraft structure places great demands on the ability of the adhesive to withstand the operating environment over long periods of time. The structural loads in a repair may be significantly greater than those in similar bonded joints in the original aircraft due to the greater design freedom available during manufacture. A test specimen has been developed to generate design data for the fatigue endurance of the adhesives used in bonded repairs, and both shear strain range and strain energy release rate have been investigated as parameters to describe the fatigue behaviour. This information has been used in the development of an adhesively bonded composite repair for a 48 mm long crack in the lower wing skin of an F-lll aircraft. Since this crack was in primary structure and above critical length, a rigorous test and analysis program was undertaken to demonstrate that the repair was capable of restoring the static and fatigue strengths of the structure to design ultimate values. Tests on full-scale specimens and a range of coupon tests have verified that the repair is capable of restoring residual static strength and will reduce the crack growth rate by approximately two orders of magnitude. (C) 1999 Aeronautical gr Maritime Research Laboratory. Published by Elsevier Science Ltd. All rights reserved.