In situ observation of ductile fracture using X-ray tomography technique

Fast microtomography combined with local crack driving force analysis has been employed to analyze crack-tip stress/strain singularities in an aluminum alloy. The application of fast microtomography has made it possible to observe real crack initiation and propagation behaviors without intermediate unloading. The details of a crack and its local propagation behaviors are readily observed with this technique along with evidence of microstructure/crack interactions. After a preliminary investigation of the achieved spatial resolution, we show that conventional stationary and growing crack singularities can be quantitatively validated by deriving the local crack opening displacement. This is to our knowledge the first three-dimensional validation of conventional fracture mechanics during a real time continuous experiment that has been mainly developed via surface observations so far. We also reveal that there is a spatial transition from a stationary crack singularity to a growing crack singularity in addition to the well-known temporal transition that occurs with the onset of crack propagation. Local crack propagation behaviors are also discussed on the basis of this validation. To separate the effects of complex crack geometry from those of microstructure, we also perform an image-based numerical simulation. (c) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.