Fatigue and fracture of ultrasonically welded aluminum alloys to carbon fiber reinforced thermoplastics

Abstract

This work evaluates the fatigue behavior of ultrasonically welded aluminum AA5024) to fiber reinforced thermoplastic (PEEK) joints at a stress ratio of R > 0. Initial load increase tests were carried out and, based on a detected material reaction caused by fatigue damage, the load horizon for subsequent constant amplitude tests was derived. After identifying characteristic stress level, microscopic investigations of hybrid fracture surfaces were carried out. Damage behavior and failure mechanisms in comparison to monotonic tensile tests were investigated and discussed in detail. For a fatigue limit of 2·106 cycles, the applied maximum force corresponds to 35% of the maximum lap shear force for monotonic testing. A drop in stiffness to 88% close to failure was observed.