Effect of stress concentrations on the fatigue behaviour of structural adhesives

Aim of the present research is to investigate the effect of stress concentrations on the fatigue behaviour of structural adhesives using numerical and experimental approaches with focus on the prediction of fatigue lifetime of notched specimens. A model was proposed to explain the behaviour of SN curves of notched specimens in which the slope is controlled by the size of the highly stressed region and the stress concentration factor translates the position of the curve. The SN curves for crack initiation lifetime of both adhesives have indicated that most of the fatigue lifetime was spent on the crack initiation phase. A method for lifetime prediction based on the stress-life approach and the Theory of Critical Distances to account for the effects of stress concentrations on the fatigue lifetime was proposed. The critical distance length was obtained through a calibration. The effectiveness of the proposed method in predicting the fatigue lifetime of notched specimens was evidenced by the good accuracy obtained with regards to experimental results (relative error less than 12%) for different notched specimens and different structural adhesives.