A “Toolbox” for Forensic Engineers

232 Forensic Materials Engineering: Case Studies
Figure 7.15 Base of polypropylene traction battery case showing oval burn.
Figure 7.16 Close-up of hole with brittle crack in the bottom running through
to the interior.
was quite unexpected, but could be explained by the presence of an aluminum-silicon
alloy stud in the container holding the traction batteries. If the
stud had been present when the battery was first inserted, it is likely that the
base impacted the stud and initiated a brittle crack. When the crack penetrated
the wall, sulfuric acid would have leaked and reacted with the light
metal, igniting the plastic at the base (Figure 7.17). The small fire was quickly
extinguished by the liquid acid, leaving the shape of the stud impressed in
the base. The problem could thus be attributed to the installer rather than
the battery maker. The design was not at fault, and greater care should have