A “Toolbox” for Forensic Engineers

222 Forensic Materials Engineering: Case Studies
Figure 7.5 External view of the critical crack running along an external corner,
the ends shown by arrows.
Figure 7.6 Internal view of the crack showing weld line at left.
bracket used for attachment of other engine parts. The arrow at left indicates
the tide marks formed when the leakage occurred. Because they ran in one
particular direction from one end of the crack, it could be inferred that the
box was oriented vertically in the engine compartment with the lower end
at the right in Figure 7.3. The crack was about 65 mm long, running through
the wall of the tank. Inside the box, the crack possessed the same shape and
dimensions as externally, but ran from or into a different feature known as
a weld line (Figure 7.6). Weld lines are regular features found in moldings,
normally where the molten polymer is forced around a core (to form a hole
in the final product, for example) and the streams have to rejoin. The unusual
position of this weld line is that it falls nowhere near such a design detail.
The fact that the crack also lay very close to the weld line must surely provide
some further clue to its origin.