Corner fatigue cracking behavior of hybrid laser AA7020 welds by synchrotron X-ray computed microtomography

To elucidate the fatigue corner cracking behaviors related with gas pores of hybrid laser arc welded 7020-T651 alloys, both high-resolution in situ synchrotron X-ray computed microtomography and finite element based predictions containing the closure effect or significant plasticity have been undertaken in the domain of fracture mechanics. It is found that fatigue cracks are preferentially initiated from a pore intersecting with the corner free surface and that it steadily propagates inside the weld with a quarter elliptical shape. Moreover, the fatigue corner crack exhibits a very complex morphology. A quantitative agreement between the experiment and prediction of crack shape under executed loading cycles is observed. By using the critical stress intensity factor along the crack line, the modified fracture toughness of a given hybrid laser weld can also be determined numerically for three-dimensional non-penetration curved fatigue cracks.