Experimental Investigation of Failure Behaviors of CFRP–Al Lap Joints with Various Configurations Under High- and Low-Temperature Conditions

The failure behaviors of CFR-aluminum lap joints with diverse configurations through quasi-static tensile tests were conducted at -40 °C, 25 °C, and 80 °C. Four specimen types were examined: CFRP-aluminum alloy two-bolt single-lap joints (TBSL), two-bolt double-lap joints (TBDL), two-bolt bonded-bolted hybrid single-lap joints (BBSL), and two-bolt bonded-bolted hybrid double-lap joints (BBDL). The analysis reveals that double-lap joints possess a markedly higher strength than single-lap joints. The ultimate loads of the TBSL (single-lap joints) at temperatures of -40 °C and 25 °C are 29.5% and 26.20% lower, respectively, than those of the TBDL (double-lap joints). Similarly, the ultimate loads of the BBSL (hybrid single-lap joints) at -40 °C, 25 °C, and 80 °C are 19.8%, 31.66%, and 40.05% lower, respectively, compared to the corresponding data of the TBDL. In bolted-bonded hybrid connections, the adhesive layer enhances the joint's overall stiffness but exhibits significant temperature dependence. At room and low temperatures, the ultimate loads of the BBDL are 46.97 kN at -40 °C and 50.30 kN at 25 °C, which are significantly higher than those of the TBDL (42.24 kN and 44.63 kN, respectively). However, at high temperatures, the load-displacement curves of the BBDL and TBDL are nearly identical. This suggests that the adhesive layers are unable to provide a sufficient shear-bearing capacity due to their low modulus at elevated temperatures. This research provides valuable insights for designing composite-metal connections in aircraft structures, highlighting the impacts of different joint configurations and temperature conditions on failure modes and load-bearing capacities.