Interfacial Layers in Brittle Cracks

A study has been made of interfacial layers that form within cracks in mica and silicate glass. The layers are the result of interactions with environmental species behind the crack tip. Deposition processes are associated with precipitation from aqueous solutions and corrosion of the crack walls. The level of precipitation depends on such factors as "impurity" content, temperature, etc. It is demonstrated that the layers can bridge the interface and thereby significantly increase the apparent toughness and the strength. These retardation effects are modeled as an "internal"(negative) contribution to the net stress intensity factor on the crack from closure tractions over a near-tip area of the interface. The results highlight the potential importance of surface chemistry as a determinant of both equilibrium and kinetic fracture properties.