抄録
The resolution of three-dimensional (3-D) imaging using the synchrotron radiation has been dramatically improved, enabling the high resolution observations of microstructure and damage inside bulk materials in 3-D. In the present study, high resolution phase contrast microtomography (μ-CT) technique has been applied to obtain clear crack images together with the details of microstructural features in a cast aluminum alloy. Crack opening/closure, crack extension and damage evolution in the vicinity of a crack-tip is observed. 3-D image analysis is performed to evaluate void initiation and growth near the crack-tip. The information on physical displacement of each microstructural feature is provided for analyzing local crack driving forces at crack front. A 3-D measurement procedure for local crack-tip opening displacement is proposed using a set of 3-D tomographic volume. Inhomogeneous 3-D crack propagation behaviors are analyzed using the data obtained by means of the techniques. For example, local fracture toughness values in both ductile α-aluminium and less ductile Al-Si eutectic phases are evaluated using the techniques. It has been clarified that the local fracture toughness is several times higher in the α phase than that in the eutectic phase. The crack-tip driving force reaches the maximum just before the onset of crack propagation and decreases during the propagation. Overall, these techniques have been identified to provide a unique possibility to quantitatively interpret the 3-D cracking behavior in bulk materials.
