Fatigue of structural adhesives under stress concentrations: Notch effect on fatigue strength, crack initiation and damage evolution

The effect of stress concentrations on the fatigue behaviour of two structural adhesives, relevant materials in lightweight applications, was investigated regarding fatigue strength, crack initiation lifetime, damage evolution and fracture behaviour. Internally and externally notched adhesive bulk specimens were tested under constant amplitude loading with a stress ratio of 0.1. Majority of fatigue lifetime (60-95%) was spent on crack initiation, which was shortened by an increasing stress concentration factor. Crack initiation causes a sudden damage increase near to failure. A model was proposed correlating the fatigue strength of notched specimens with highly stressed region and stress concentration factor.