Modelling the mechanical performance of structural adhesive layers with process-induced viscous fingers using mesh-based and material-based approaches

Viscous fingering is a phenomenon occurring inside an adhesive layer when the adherends are separated from each other while the adhesive is still in its viscous state. This leads to a decreased joint performance. In this work, modelling approaches for adhesive bondlines affected by viscous fingering are investigated using a trilinear cohesive zone model: The first one is a surface-based approach where the material parameters are decreased with respect to the remaining bondline surface. The second approach is a material-based approach. Using Tapered-Double-Cantilever-Beam (TDCB) specimens and Linear-Butt-Bonded (LBB) specimens with defined viscous elongations, the material parameters for the traction separation law are directly determined. The third approach is a mesh-based approach, where the thin branches of the interfacial structure are modelled using a very fine finite element mesh. Using a line laser, a scan of the fracture pattern is performed and analyzed by a python script that creates an orphan mesh of the surface topography for further numerical investigations. The presented modelling approaches with their specific inputs are explained in detail and compared to each other regarding the accuracy of the numerical predictions by comparing experimental and numerical data of a TDCB specimen with viscous fingering. A combination of a mesh- and material-based approach shows the best accuracy in the investigations whereas a purely surface based approach is insufficient.