Local shear strength distribution of ultrasonically welded hybrid Aluminium to CFRP joints

This paper presents an approach to evaluate the local distribution of lap shear strength in the joining zone of ultrasonically welded single lap joints of aluminum and fiber-reinforced thermoplastics, which also show a sufficient resistance against ageing or galvanic corrosion. Both the characteristics of the process and the microscopic evaluation of the fracture surfaces suggest that the strength is distributed inhomogeneously over the joining area and is composed of adhesive and cohesive fractions. For this evaluation, two procedures were developed to subdivide the joining zone into sections and to investigate them separately. Subsequently, a local strength distribution in the joining area can be determined using mathematical operations. With the help of this interpretation, different bonding mechanisms can be identified and assigned. Additionally to mechanical investigation, Finite Element simulations were used to calculate the stress distribution of the joints depending on the carrying cross section to validate the experimental data. Despite the change of the geometry e.g. due to drilling, the calculated stress distribution pattern did not change.