Modeling and Lowering Residual Stresses in Bonded Composite Patch Repairs of Metallic Aircraft Stuctures

摘要

The technology in using composite patches to repair cracked aging aircraft structures has been proven to be efficient and economical. One of the problems resulting from bonding of a composite patch to the metallic host structure is thermal stresses induced from bonding the patch to the host structure at elevated temperatures. The main objective of this research was to develop multi-step curing procedures in order to reduce the level of thermal residual stresses and increase the fatigue life of the composite repair. Several efficient two-step cure temperature cycles have been obtained for the film adhesive FM73. Experiments were performed to verify the significant reduction of thermal stresses resulting from the use of these two-step cure cycles. The effect of reduced thermal stresses on the fatigue life of a cracked aluminum plate repaired with symmetrical composite patches was investigated experimentally and analytically. An analytical model was developed for the optimal design of two-step cure cycles.