Crack propagation in adhesively bonded steel assemblies

The adhesive strength of steel/polymer/steel assemblies has been measured by using a wedge test. An original device developed in the laboratory allows the introduction of the wedge into the assembly at a controlled speed and for the crack propagation to be followed with a camera-equipped microscope. The aim of this study was to analyse the influence of the wedge introduction speed V, both on the adherence energy G and of the crack propagation rate. The results show that firstly, when the introduction speed increases the adherence energy globally increases and a transition is observed on the G versus V curve. Secondly, when the wedge introduction rate is increased, the global crack propagation rate is reduced. Furthermore, a two step evolution is observed for the crack propagation. During the first step, the crack propagates rapidly. The crack velocity is then slower during the second step, and is inversely proportional to the wedge introduction speed.