Nonlinear bonding strength of aluminum alloy scarf-bonded joints: effects of adhesive thickness, scarf angle, and temperature

To elucidate the nonlinear dependence of bonding strength on adhesive thickness, scarf angle, and temperature, uniaxial tensile tests were conducted on cylindrical aluminum alloy scarf joints. Load–displacement curves, fracture surface morphologies, and stress–strain data were systematically analyzed to evaluate the effects of adhesive thickness (t a , 100–1000 μm), scarf angle (θ, 15°–90°), and temperature (T t , 20–60 °C) on joint mechanical performance. The present work demonstrates that the relationships between these parameters and bonding strength are strongly nonlinear. Results show that reducing t a from 1000 μm to 100 μm increases peak load by approximately 83.7% and fracture displacement by about 60%, with the failure mode transitioning from interfacial debonding to cohesive failure. Decreasing θ increases the peak load but reduces the bonding strength per unit area, with the strength failure surface gradually deviating from a perfect circular arc. As the temperature rises to 60°C, the peak load decreases by 20–30% on average; however, the degradation is significantly less than that of the bulk adhesive. Moreover, increasing t a or θ mitigates high-temperature strength loss, with thicker adhesive layers providing buffering against thermal degradation. This study quantitatively characterizes the nonlinear bonding behavior of aluminum alloy scarf joints under the coupled influence of geometric and thermal factors, providing valuable insights for adhesive joint design, interface optimization, and the calibration and validation of cohesive zone models.