Vapor pressure and residual stress effects on the toughness of polymeric adhesive joints

Parallel debonding along the two interfaces formed by a ductile polymeric film joining elastic substrates is studied. The film is taken to be elastic-plastic. The film-substrate interface is modeled by a strip of cells that incorporates vapor pressure effects on void growth and coalescence through a Gurson porous material relation. Thermal expansion mismatch between the film and the substrates is treated as an initial residual stress in the film. When residual stress is combined with high vapor pressure, interface cracking of the joint exhibits brittle-like characteristics with joint toughness reduced significantly. Other factors affecting joint toughness, such as initial porosity of the interface as well as strain hardening and thickness of the film are also discussed.