A 3D measurement procedure for internal local crack driving forces via synchrotron X-ray microtomography

Abstract

Synchrotron X-ray microtomography has been utilized for the in situ observation of fatigue crack opening/closure during load cycles. High-resolution phase contrast imaging technique has enabled the reconstruction of clear crack images together with the details of microstructural features. Physical displacements of micro-pores in a crack-tip stress field are used to obtain local mixed-mode crack driving forces along a crack front, and its feasibility is confirmed. Complicated crack closure behaviour are observed due to the combined effects of local modes II and III displacements. The technique used provides a highly effective way of assessing local crack driving forces together with supplementary ways of verifying and interpreting it by visualising and quantifying various forms of crack-tip shielding behaviour. The proposed technique is clearly advantageous compared to the limited procedures available in the current literature, where detailed internal information can only be achieved for limited types of material.

Three dimensional experimental and numerical multiscale analysis of a fatigue crack

“…Compared to this earlier work, the approach presented herein has the advantage of being fully automatic and much less local. Moreover, the DIC analysis provides sub-voxel displacement values in the micrometer range close to those measured by Toda et al [68]. It is worth noting that the sample studied herein has a larger cross section (i.e., 3 times larger) than the one used by Toda et al [68], which paves the way for performing crack closure measurements with an increased confidence.…”

“…Moreover, the DIC analysis provides sub-voxel displacement values in the micrometer range close to those measured by Toda et al [68]. It is worth noting that the sample studied herein has a larger cross section (i.e., 3 times larger) than the one used by Toda et al [68], which paves the way for performing crack closure measurements with an increased confidence. Interestingly, the same authors measured a significant contribution of mode III for the opening of their crack macroscopically loaded in mode I.…”

“…Experimentally determined values of SIF along a crack front had been obtained in the past from the analysis of high resolution (voxel size of 0.7 µm) 3D tomographic images [68,69]. In that case, small porosities close to the tip of a crack were used as markers for "manual" tracking of the displacement field at the crack tip.…”

Four-Dimensional Annihilation Behaviors of Micro Pores during Surface Cold Working

“…This technique is excellent in that it allows not only the four-dimensional (i.e., three-dimensional time evolution) observation of the inside of a material but also the highdensity mapping of internal mechanical quantities by tracing the physical displacement of dispersion particles. [11][12][13] 2. Experimental Method…”

High-resolution Observation of Steel Using X-ray Tomography Technique

“…It has been well documented in the literature that such scattered closure patches contribute effectively to fatigue crack growth resistance. 18,19) Crack extension varied to some extent along the crack front line. A few retarded sections of the crack front are seen periodically, as indicated by white arrows in Fig.…”