Sophie Arweiler-Böllert, Moritz Liesegang, Tilmann Beck, Julia Jungbluth, Sebastian Schmeer

• The reliable use of ultrasonic metal welding requires a thorough understanding of the relevant bonding mechanisms. This article presents an approach to systematically investigate the relation between the mechanical properties and the interface of selected Al/Cu and Al/GFRP joints. The hypothesis is that the microstructure and tensile shear strength of the specimen can be related to their interface properties presented by contact stiffness and damage initiation traction. For this purpose, the mentioned hybrid material systems were ultrasonically welded using specific parameters to achieve defined levels of mechanical joint strengths. Micro sections and fracture surfaces were characterized to identify the interface geometry at certain strength levels. The main findings were different shares of bonded areas in the interface and characteristic micro geometries. Microscale finite element models of representative samples were developed to determine the stress and deformation behavior in the interface under tensile shear load and to compare the influence of the interface geometry on contact conditions to a simplified model. The simulations provide information about the influence of different damage initiation tractions and geometrical characteristics in the joints’ interfaces, as well as their contribution to the overall joint strength. For prospective industrial applications, they can serve as basis for further development of a contact model on component scale.