A “Toolbox” for Forensic Engineers

Failure Due to Manufacturing Faults 161
Figure 5.23 Side view of broken claw.
Figure 5.24 Unbroken claw at opposite end of guard rail.
within the section, because it exists as uniformly distributed tiny holes of
rounded shape that do not exert any serious localized stress-raising effect
likely to initiate fatigue.
A section had already been cut from the fracture for microstructural
examination and presumably the evidence of porosity had provided the basis
for the allegation of manufacturing defect. However, close study of the fracture
revealed that the claw had broken in a sideways movement, forcing it to
open it up as it was twisted off the frame tube. Shallow lips at the edges of
the fracture indicated it had started where the microsection had been cut out
and progressed across the section to finish at the opposite edge. Aluminum
castings have low ductility, usually between 1 and 4% in the sand cast condition,
even when they are free of gas porosity, so not much deformation is