Cohesive zone modelling of adhesive joints employing a unified and simplified testing program for material characterization

Abstract

In automotive engineering, it is state of the art to use high-strength, toughness-modified epoxy adhesives (EP) combined with spot-welding in the assembly of the metallic body-in-white. Modern multi-material structures contribute to changes in the requirements on advanced adhesive joining techniques. In recent applications a trend towards more flexible adhesives can be observed, particularly the usage of polyurethane adhesives (PU). Both types of adhesives (EP and PU) have to be modeled in structural simulations. Considering full-scale crash models, cohesive zone elements are suitable due to their high computation efficiency. A universal characterization approach for both types of adhesive joints based on cohesive zone modelling is introduced. In recent research work at DLR, one main challenge is to identify a common testing program for the characterization of EP- and PU-adhesives. First, a state of the art testing program using specific specimen geometries for epoxy adhesives as TDCB (for Mode-I) and TENF (for Mode-II) is investigated. As a second step, this experimental methodology is transferred to the group of polyurethane adhesives. For this purpose, the Mode-II specimen geometry has to be changed due to the high compliance of PU-adhesives. Therefor the pursued approach is to replace Mode-II by Mode-III. In further steps, the Mode-I and Mode-III specimen geometries can be simplified in a manner that the same adherends can be used for both crack modes and both adhesive groups. The experimental and numerical results of the suggested material characterization program are shown to verify the approaches of unification and simplification.