| Research Abstract |
The procedure, by which real local crack driving forces (Modes I,II and III crack driving forced along crack front) can be measured in 3D, in-situ and in high density (at intervals less than 1 micron) via the sub-micrometer ultra-high resolution synchrotron radiation X-ray computed tomography (CT, hereinafter), has been developed in this study. This has been realized by microstructural tracking of several hundred features, and this can be further extended to several ten thousand features level. Measurements, which had been available only on specimen surface by the special material test procedures such as photoelasticity, Moire interferometry and caustics, have been readily applied to material interior. In general, the local crack driving forces are intricately and remarkably affected not only by macroscopic applied stress, but also by various crack shielding/anti-shielding effects, such as crack deflection, damage evolution and crack closure phenomenon, due to microstructures of the actual materials. The procedure developed has been applied to fatigue cracks propagating in aluminum alloys. The experiments were performed at the imaging beam lines BL20B2 and BL47XU of the SPring-8 and ID19 of the ESRF, and its feasibility was verified. By analyzing mechanisms of real local crack driving forces at each crack-tip point, the contributions by various crack shielding/anti-shielding effects, such as crack deflection, damage evolution and crack closure phenomenon, could be quantitatively clarified.
By doping Ga into nano-scopic structures such as grain boundaries, they could be visualized. The visualization of the grain boundary has been succeeded in casting materials, wrought materials and porous aluminum materials, which indicates the effectiveness of the technique developed.
|
