Detailed inspection of the upper portion of the crack (Figure 2, rotated to an orientation about halfway between the left and right views of Figure 1) revealed a ridge pattern with finer steps merging to coarser ones from bottom to top (equivalent to left to right on Figure 1). This would indicate crack growth opposite of the beach-mark theory and in line with the swoop theory. I kept looking, despite having concluded that this portion of the crack was due to a separate loading event. It was probably the last portion to separate and unrelated to either the beach marks or the swoop!
Zooming in on the features at the 6 o’clock position of the left side of Figure 1, we have the bottom view of Figure 2. This ridge pattern shows a crack-growth direction consistent with the beach marks, not the swoop. This tells us that the beach marks and the lower step are all likely part of the main crack.
We have not investigated the tooling material quality or the quality of the heat treating. We have not tested for the presence of grinding burn. We don’t know if there was a lubrication failure. Was there something stuck on the end of the punch that increased the bending forces over time? The overall smoothness of the crack indicates that it took some time to propagate.
The uncertainty remaining in my analysis, a permanent condition, results from the missing beach-mark initiation area. This mini fracture analysis fits right in with the general atmosphere of 2020, blanketed by the trauma and uncertainty associated with COVID-19.
Perhaps it’s a bad idea for a failure-analysis expert to admit uncertainty, but sometimes that is the most honest action we can take. In addition, one of the great techniques to increase our creative skills is learning to tolerate uncertainty. If we don’t think we already have the answer, we have a greater chance of recognizing either the answer itself – or the next hint on the path toward figuring it out – should it show up at a later time.