Interface debonding ahead of a primary crack

The debonding of an interface between two elastic materials is assumed to occur ahead of a primary crack lying in material 1. Conditions for such a mechanism are derived from an asymptotic analysis and depend on the elastic mismatch between the two materials as well as on material 1 and interface toughnesses. The ligament width between the primary crack tip and the interface and the debond nucleation length can be determined if the interface strength is known. A similar mechanism involving a crack nucleation ahead of the primary crack in material 2 is also examined. Deflection prediction is derived from an energetic criterion which is in general more favourable to deflection than the He and Hutchinson one. The former decreases asymptotically towards the latter. Moreover, if the crack lies in the stiffest material, results show that these nucleation mechanisms are highly improbable. If material 2 and interface strengths are known, a stress criterion is naturally derived, The presented analysis is independent of the applied loads and of the geometry of the specimen. (C) 2000 Elsevier Science Ltd. All rights reserved.