Fatigue Growth Behaviour of Two Interacting Cracks with Different Crack Offset.

Under cyclic fatigue load, multiple cracks would significantly deteriorate the service life of the components with respect to the case of a single crack owing to the crack interaction. The present study aims to explore the effect of crack interaction on the fatigue growth behaviour of samples with different crack offset. In this study, fatigue crack growth tests were performed for samples containing a single crack and non-collinear cracks of different crack offset in an aluminum-lithium alloy. It was shown that the two facing non-collinear cracks changed their growth direction when the cracks were overlapped, resulting in load mode transfers from mode I to I + II mixed mode. Then, the interaction behaviour was studied by establishing the finite element models to calculate the stress intensity factor K of samples with different crack offset. The results indicated that the K decreased, largely owing to the shielding effect as the two cracks overlapped, leading to retardation of crack growth in the position of overlap, especially for the specimens with a small crack offset. It was also shown that the interaction effect could change from positive to negative during the process of the multiple cracks' growth, thus leading to the acceleration or deceleration of crack growth rates, suggesting that the influence of interaction on cracks' growth behaviour could vary with the different stages of crack growth.