Tensile failure behaviors of composite-aluminum alloy double-bolt double-lap bolted-bonded hybrid structures under high and low temperature environments

During service, aircrafts will inevitably experience harsh environments such as high temperature and low temperature. The high and low temperature environments may have an impact on the mechanical properties and load-bearing capacity of the connection structure of aircraft, which will threaten the safety, stability and service life of the structure. Therefore, this paper took the composite-aluminum alloy double-bolt double-lap bolted-bonded hybrid structure as the research object, and studied the influences of high and low temperature environment on the tensile strengths and failure behaviors of the bolted-bonded hybrid connection joints through experiments and numerical simulations. The Micro-CT and SEM damage characterization techniques were used to observe and analyze damage modes of composite laminates at the surrounding area of bolt holes. Meanwhile, a progressive damage failure model of composite material based on the 3D Hashin criterion and cohesive element analysis method was used to simulate and analyze the failure process of connection structures. The results show that the ultimate loads of the bolted-bonded hybrid joints at 80℃, 25℃ and −40℃ environments increase by 5.1%, 27.5% and 17.2% respectively, compared with the pure bolted joints. Moreover, compared to the room temperature environment, the ultimate load of the bolted-bonded hybrid joint at the 80℃ environment decreases by 24.6%, while the ultimate load of the bolted-bonded hybrid joint at −40℃ environment increases by 3.5%. As the strength of the resin usually decreases with the increase of the environment temperature, the high temperature will soften the resin and reduce the bearing capacity of the composite material, while the low temperature environment will make the resin hard and brittle. Therefore, with the increase of environment temperature, the bearing capacity of the bolted-bonded hybrid joint will decrease. The damage propagation trends and final failure modes of the composites under these three temperature environments are basically consistent. The failure modes are fan-shaped tensile fracture failure at the edge of the hole and local compression failure around the hole. The research results can provide theoretical guidance and reference for the design of composite-metal connected structures of aircraft at high and low temperature environment.