Investigations on the energy balance in TDCB tests

The Tapered Double Cantilever Beam (TDCB) test is an established method to determine the critical strain energy release rate of adhesives in mode I. Provided that the adherends stay elastic, that the adhesive layer is not too flexible and that inertia effects can be neglected, the experiment allows to identify the work required by the adhesive layer per area of crack growth. The evaluation according to the standard does not permit to distinguish between different sources of dissipation in the adhesive layer or at the adhesive-adherend interfaces, though. This paper proposes two approaches to gain a more detailed understanding of the dissipation in mode I crack growth of adhesive layers. The first investigation method uses detailed finite element simulations of the TDCB test based on an elastic-plastic adhesive material model derived from tests on bulk specimens. The simulation is used to distinguish between the work required for the plastic deformation of the entire adhesive layer and the work consumed by the crack and the adhesive in its vicinity. The dependence of this distribution of work on the adhesive layer thickness is studied. The second approach adds a temperature measurement by an infrared camera to the TDCB test. This measurement allows observation of the thermo-elastic effect in the adhesive layer and of the heat generation at the crack. Finally, the results of the two approaches are employed to estimate the energy balance in the TDCB test. The application to a ductile epoxy adhesive shows the feasibility of the proposed methods.