Failure Transition in Fatigue Crack Propagation of Epoxy Adhesives under Mode I Loading. Effect of Stress Singularity at the Interfacial Edges of DCB Specimens on Failure Transition.

Abstract

Fatigue crack initiation and propagation behaviors in DCB specimens were investigated using a rubber modified epoxy as adhesive. Glass substrates were used to observe the failure transition (cohesive→interfaicial) in fatigue crack growth. In order to know the effect of stress singularity at the interface edges on the failure transition, tapered and chamfered DCB specimens. (S55C substrates) having nominaly zero/greatly reduced stress singularities were also used. The experimental results revealed that a cohesive fatigue crack in the adhesive layer once stopped with decreasing a strain energy release rate range. Simultaneously a new interfacial crack initiated and propagated near the arrested crack tip. Tapering and chamfering the edges of DCB adherends delayed the interfacial crack initiation. It was found that the interfacial crack initiation due to stress singularity at the interfacial edges was the major driving force for failure transiton.