A “Toolbox” for Forensic Engineers

A “Toolbox” for Forensic Engineers 89
occurred. Laboratory examination of the fractured carrier bar would not
have identified the cause of failure, and would be quite irrelevant as the
solution to the problem lay in circumstances prior to failure.
Visual observation can be used as a comparator. The following case
illustrates how simple comparative observations can be used in a manner
similar to fingerprint identification. A stolen Jaguar was recovered. In the
course of the theft, the car had sustained damage to the windows, roof and
bodywork. In addition, the hubcaps for all four steel road wheels were
missing. However, the owner stated that the steel road wheels had been
substituted for his original alloy wheels, an expensive “extra” for that make
of vehicle. He submitted a substantial claim to his insurers for bodywork
repairs, and for purchase of new alloy road wheels to replace those stolen
from his vehicle.
Similar to fingerprints, the observation of “hub-prints” (the impressed
markings from the wheel hub into the wheel rim, and vice versa) can identify
mating surfaces that have been in intimate contact for extended periods of
time. Examination was restricted to one side of the Jaguar. Road wheels on
the opposite side were left untouched to facilitate a similar investigation by
other interested parties.
Initial observation of the wheel rims revealed no finger markings in the
wheel grime (Figure 4.2A). As the inner surface of the rim contains a deep
well, it is natural to hold or grasp the wheel with your fingers in this well to
take the weight of the wheel, and provide a balanced lift. Lack of any markings
in the road grime was indicative of wheels that had not been removed for
some considerable period of time and travel.
Arc lengths generated from bolting the wheel rim to the hub (Figure
4.2B) were measured and a match was observed between the flange and rim.
In addition, machining marks from the flange had been impressed onto the
wheel rim, and were clearly seen within the arc markings. The pitch of these
machining marks was identical on both flange and wheel rim.
Seven additional matching features were found on each wheel, verifying
the initial observation that the steel road wheels had been on the vehicle and
not removed for a substantial amount of time and mileage. The claim was
undoubtedly fraudulent. When advised of the criminal nature of fraud, the
Jaguar owner rapidly withdrew his claim. Furthermore, the insurers advised
him that they would not cover repair costs for damage sustained during the
theft, nor would they insure him at any future time.
4.3 Assessing the Situation
When undertaking any failure analysis the initial evidence from the scene of
an accident has to be evaluated by visual observation, based on a common