Verification of an experimental method to measure the stress-elongation law for an adhesive layer using a DCB-specimen

A method to measure the stress-elongation law for a thin adhesive layer is presented. It is noted that the experimental results give a law that resemble the cohesive law that has been used ad hoc in general investigations of fracture and specifically in numerical simulations of adhesive bonds. The method is based on the balance of energetic forces and a direct measurement of the elongation of the adhesive at the start of the layer. In the experiments, only the surfaces of the adherends are accessible for measurement. However, due to anticlastic deformation, the elongation at the interior is larger than at the surface. The method is also based on the assumption of linear elastic adherends. Influences of these prerequisites are studied using the finite element method. Experimental and simulated results compare well up to the initiation of crack propagation. After this point, the simulations give, as expected, a constant J, while the experiments show a rapidly decreasing J. Similarly, the force-displacement records agree well up to the start of crack propagation. However, the experiments show a more rapidly decreasing force after this point than the simulations.