Joining-technique selection for complex multi-material structures focusing on the mechanical behaviour of adhesive joints

Abstract

The trend to use multi-material structures in automotive lightweight design leads to an increasing diversity of joining techniques being applied. In structural components, these often can be combined in a large number of possible joining-technique configurations. This poses a challenge for engineers to choose the optimal configuration. The vision is to automate and facilitate the selection of a mechanically optimal joining-technique configuration in a software environment. Since adhesive solutions are crucial to multi-material designs, the initial focus of the current studies is on epoxy and polyurethane adhesive bonds. As a basis, a universal application-oriented characterization approach for adhesive bonds, developed at DLR, is used. Aiming at full-scale crash models, this approach incorporates cohesive-zone elements due to their high computation efficiency. To optimize the joining configuration, validation starts at the single configuration, proceeding to the optimization process. The cohesive-zone simulation method is applied to develop a validation specimen that exhibits non-trivial deformation during testing. Compared to structural applications, for research purposes, this multiple-joint specimen reduces complexity in the optimization process. It comprises three joints into one sample; for each joint two different adhesives can be chosen. The specimen is shown in the figure. In a tensile test, each joint is dominated by a different stress state - normal, shear and peeling. In that way a complex load case is achieved, for which the first-failing joint and the optimal joining-technique configuration is determined in simulation and validated by experiments.