Effect of temperature on the static response of bonded structural patch repairs

Abstract

Aircraft and automotive structures are often subjected to stresses that can lead to damage or weakening over time, particularly in aging systems. To repair such damage, adhesively bonded composite patches have been used as an efficient temporary repair method, offering reduced stress concentration relative to mechanically fastened repairs and enabling continued operation of the structure until a permanent repair can be implemented. This study examines the static performance of cracked aluminum and steel specimens repaired with glass-fiber/epoxy and carbon-fiber/epoxy patches, focusing on the effects of patch type, patch thickness, substrate thickness, and environmental conditions. Damage was introduced into the specimens by generating a central fatigue crack, after which they were repaired using epoxy-bonded patches and tested under static loading at different temperatures: room-temperature (70 °F), high-temperature (145 °F), and low-temperature (−60 °F). As expected, the experimental results showed that patched specimens exhibited a higher load-carrying capacity than those without patches. While temperature did not significantly affect the unpatched specimens, the load-carrying capacity of the patched specimens was reduced at high temperature due to adhesive softening, with a reduction of approximately 13–18 % relative to room temperature across all material and patch combinations. In contrast, low-temperature conditions resulted in a smaller reduction of approximately 2–8 % compared to room temperature. In addition to the experiments, finite element (FE) models were developed in ABAQUS© to predict failure loads using a stress intensity factor (SIF) approach and to interpret the experimental results. The FE predictions showed close agreement with the experimental results with prediction errors ranging from approximately 1.5 %–10.9 % across all materials and patch combinations at different temperatures. These findings confirm that bonded composite patch repair improves the strength of damaged structures and that finite element modeling can accurately predict their performance at different temperatures.