Impact rupture of structural adhesive joints under different stress combinations

The paper reports the results of an experimental study on bonded joints, carried out by means of an instrumented impact pendulum, equipped to load overlap specimens in shear. Such testing configuration is the most adequate and natural to study the possible modifications of the behavior of the joint, changing from static to dynamic loading condition, keeping the same specimen type. The specimens were steel strips bonded by an epoxy adhesive (Hysol 3425). Several values of lap length, adhesive and adherends thickness were adopted, to achieve rupture under different peel and shear stress combinations. The stress state at rupture has been calculated by means of a structural solution. The results show that the failure points, in a chart having as axes the maximum values of peel and shear structural stress, lie outside the rectangular limit zone previously obtained under static conditions. Therefore, in spite of the concerns associated with the impact condition, the strength of the tested adhesive does not decrease with respect to the case of static loading. In alternative, also the evaluation of the stress intensity factor proves to be effective to predict failure in the considered cases.