Direct measurement procedure for three-dimensional local crack driving force using synchrotron X-ray microtomography

X-ray microtomography has been utilized for the observation of ductile fractures in an aluminum alloy with an Al/Al–Si dual phase structure. A procedure for analyzing a series of tomographic images is proposed for extracting the variation in the local crack-tip opening displacement (CTOD), and its feasibility is confirmed. Complicated crack growth behavior and the formation of uncracked ligaments ahead of a crack tip are observed in the alloy owing to the marked difference in local fracture toughness between the two phases. The proposed technique has provided a quantitative interpretation for such phenomena. It is clarified that a conventional measurement significantly overestimates the CTOD level. The transition behavior in CTOD has been revealed over a certain distance across an interface between the two phases, suggesting the existence of scaling effects that influence the microstructure/fracture relationship. Overall the current method could offer a highly effective way of assessing three-dimensional local fracture behavior.