Nucleation and propagation of an edge crack in a uniformly cooled epoxy/glass bimaterial

An epoxy/glass bimaterial beam test configuration has been used to study cooling-induced crack nucleation and propagation. This effort extends a nucleation criterion, previously applied to tensile-loaded, adhesively bonded butt joints, to another geometry and type of loading. Loading by thermally induced straining complicates the application of a nucleation criterion based upon parameters defining the asymptotic stress fields at the interface edge (i.e. at the edge discontinuity defined by the intersection of the interface and stress-free boundary). In contrast to the tensile-loaded butt joint, where the magnitude of asymptotic stress state is fully characterized by a single interface-edge stress intensity factor K a, an additional, non-negligible r-independent regular term K a0 always exists for thermally induced strains. In the present work, a direct extension of the previously used nucleation criterion is applied: crack nucleation occurs when K a= K ac, but with the stipulation that interface-edge toughness K ac depends on K a0.