Arrest, deflection, penetration and reinitiation of cracks in brittle layers across adhesive interlayers

A layer structure consisting of two glass plates bonded with polymer-based adhesives and loaded at the upper surface with a line-wedge indenter is used to evaluate crack containment. Two adhesives are used, a low-modulus epoxy resin and a particle-filled composite. The adhesives arrest indentation-induced transverse cracks at the first interface. A substantially higher load is required to resume propagation beyond the second interface in the second glass layer. Delamination is not a principal failure mode. Nor is the operative mode of failure one of continuous crack penetration through the adhesive, but rather reinitiation of a secondary crack in the glass ahead of the arrested primary crack. A fracture mechanics analysis, in conjunction with finite element modeling, is presented to account for the essential elements of crack inhibition, and to identify critical material and layer thickness variables. It is confirmed that adhesives with lower modulus and higher thickness are most effective as crack arresters.