Part of the outer edge showed signs of erosion in the form of a chamfer (Ch), followed by a smooth region and a set of crack arrest arcs (arrows). The final part of the surface showed a cusp of material rising above the plane of the surface (C). Detailed optical inspection revealed at least eleven crack arrest arcs. However several of the arcs represented single cracks, so there were only seven major crack growth events. In the same study, one crack could be seen growing parallel to the long axis of the tube. Interpretation suggested that the sample failed from this point (O) in the eroded edge of the junction and grew in a series of steps to the final cusp.
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