ASYMPTOTIC INTERFACE CORNER SOLUTIONS FOR BUTT TENSILE JOINTS

In previous work, the intensity of the stress singularity of type r(delta) (delta < 0) found at the interface comer between a thin elastic adhesive layer and one of a pair of rigid adherends was fully determined for a butt tensile joint. This stress intensity factor, referred to here as the free-edge stress intensity factor K(f), can be applied to both plane strain and axisymmetric geometries. This study investigates the potential application of a K(f)-based failure criterion to butt tensile joints. Detailed elastic-plastic finite element calculations for adhesive properties representative of a high strength epoxy indicate that when residual cure stress can be neglected (1) the region dominated by the interface comer singularity is reasonably large relative to adhesive layer thickness, (2) the plastic yield zone is contained within the singular field at nominal failure loads, and (3) the plastic zone size is characterized by K(f) and displays the expected load level and layer thickness dependence. The way uniform adhesive shrinkage (thermal contraction) during cure alters interface comer stress fields is also discussed. When adhesive shrinkage is present, both constant and singular terms must be included in the asymptotic solution to get good agreement with full field finite element results. In general, there is no unique relation between the size of the interface corner yield zone and K(f), although for a prescribed shrinkage strain, K(f) does characterize the extent of plastic yielding. Calculated results suggest that the presence of residual stress can have a considerable effect on the relation between bond thickness and joint strength.