  The 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 distinct 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.
