Realisation of 3D In-situ Assessment of Local Crack Driving Forces via Ultra-high Resolution Synchrotron X-ray CT

该程序，通过该程序真实的局部裂纹驱动力（模式I，II和III裂纹驱动力沿着裂纹前沿），可以在三维，原位和高密度（间隔小于1微米），通过亚微米超高分辨率同步辐射X射线计算机断层扫描（CT，下文），在这项研究中已经开发。这已经通过几百个特征的微结构跟踪来实现，并且这可以进一步扩展到几万个特征水平。光弹性、云纹干涉法、焦散线等特殊材料试验方法只能在试件表面进行测量，而这些方法已很容易地应用于材料内部。一般而言，局部裂纹驱动力不仅受宏观应力的影响，而且受实际材料微观结构所引起的裂纹偏转、损伤演化和裂纹闭合等裂纹屏蔽/反屏蔽效应的影响。所开发的程序已被应用于铝合金中的疲劳裂纹扩展。在ESRF的SPring-8和ID 19的成像光束线BL 20 B2和BL 47 XU上进行了实验，验证了其可行性。通过分析裂纹尖端各点处真实的局部裂纹驱动力的作用机制，可以定量地阐明裂纹偏转、损伤演化和裂纹闭合等各种裂纹屏蔽/反屏蔽效应的贡献，并通过在晶界等纳米结构中掺杂Ga，将其可视化。在铸造材料、变形材料和多孔铝材料的晶界显示中取得了成功，表明了该技术的有效性。

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.