5.3 Critical crack
The critical crack was found at one end of the reservoir, as shown by the arrows in Figures 2 and 4 in Paper 3. It was a single brittle crack that adjoined an external bracket used for attachment of other engine parts. The arrow on the left indicates the tide marks formed when the leakage occurred. As they ran in one particular direction from one end of the crack, it was inferred that the reservoir was oriented vertically with the lower end being that shown in Figure 2, Paper 3. The detailed view of the crack in Figure 4, Paper 3 is approximately life-size, so the crack was about 65 mm long, running lengthwise along the side of the reservoir, along a corner of an external buttress.
Inside the reservoir, the crack possessed the same shape and dimensions as externally, but ran from or into a different feature, known as a weld line (Figure 5, Paper 3). Weld lines in general are a regular and normal feature found in mouldings, normally where the molten polymer is forced around a core – to form a hole in the final product, for example. The unusual property of this weld line was that it fell nowhere near such a design detail. The fact the crack also lay very close provided a further clue to its origin.