Reduction of residual thermal stresses during bonded composite patch repair

An increasingly attractive technology for life extension of ageing aircraft is the use of bonded composite patches for repair and local strengthening of metallic structures.; The objective of the work was to develop improved process cycles to reduce residual stresses while minimizing process cycle time and still achieving a high final degree of cure. A repair was simulated using a pre-cured composite patch bonded to an aluminum substrate using FM 73 adhesive.; Investigation of standard single-step cycles confirmed the expectations of improved final adhesive characteristics and lowered process times when curing at maximum temperature levels.; A two-step curing strategy was successful in maximizing final cure properties and reducing residual stresses.; Finally, with the use of multi-step cure cycles a good compromise was achieved between lowered residual stresses and maximized adhesive properties. (Abstract shortened by UMI.)...