A “Toolbox” for Forensic Engineers

Establishing the Load Transfer Path 79
Figure 3.13 Close view of the clamp to the sidecar chassis showing the sheared
lug. Notice the left end of the clamp has lifted off the chassis tube under the
same force system that sheared the lug weld.
cracking to propagate through the rest of the joint until it was no
longer capable of withstanding the service loadings.
3. Entrapment of residual zinc plating solution in crevices behind the
clamp lug brazed joints had caused stress corrosion cracking of the
bronze alloy over a period of time and had reached the stage where
four of the eight lugs were so weakened that they cracked open on
the last occasion the bolts were tightened. This loosened the attachment
of the bracket and allowed the sidecar wheel to move backward
and become misaligned.
In a nutshell, this expert had advised the rider’s legal representatives that
the accident was caused by sudden, final fracture of the hub weld as the
machine rounded the curve, allowing the sidecar wheel to become misaligned
and finishing off the loose clamp lugs. The tire rubbed against the chassis
frame, causing the machine to become tail light and somersault.
The defendant’s engineer was not impressed by these assertions, and was
confident he could rebut all three on technical grounds. However, he first
wished to examine the axle, which appeared to be bent slightly downward,
as suggested by the small gap that had opened up at the top of the hub,
indicated by the arrow in Figure 3.14. Figure 3.15 is a view with the sidecar
wheel laid flat below the chassis. It seemed from the damage to the clamp
still remaining on the chassis that a considerable downward force had acted
to cause much deformation damage to the bracket and fracture of the hub.
Accordingly, a joint investigation, attended by the manufacturer and the
claimant’s legal representative, was carried out during which the position of