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Expedition Rollover
The rollover of a 1998 Ford
Expedition resulted in fatal injuries. A
non-destructive metallurgical evaluation was
required, including examination of the subject
vehicle in a salvage holding yard. An overall view
of the subject vehicle is shown in Photograph A.
Photograph A: Overall view of the subject
vehicle.
An overall view of the axle
attachment plate is shown in Photograph B.
Photograph B: Overall view of the axle
attachment
plate.
The axle plate was removed for
field stereomicroscopic inspection. Upon removal,
the upper two attachment bolt holes were noted to
be distorted and "out of round." The removed axle
plate is shown in Photograph C.
Photograph C: Close-up view of failed axle. Note
oval distortion of bolts holes.
A profile view of the axle
assembly after removal of the axle wheel bearing is
shown in Photograph D.
Photograph D: Profile view of the axle assembly
after removal of axle wheel bearing.
The right rear wheel and tire
provided additional information. The wheel rim was
fractured from about the 3 o'clock to the 6 o'clock
position. This area also contained heavy soil
residue. The overall view of the tire and wheel rim
are shown in Photograph E.
Photograph E: Overall view of the tire and wheel
rim.
The peeled back portion of the
fracture axle, the last portion of the axle to
fail, is located at about the 10:30 o'clock
position in Photograph E.
A close-up view of the fracture
surface, after light cleaning, is shown in
Photograph F.
Photograph F: Close-up view of the fractured
axle
after light cleaning
Automobile and truck axles have a
case hardened zone on the surface, for wear
resistance, and a soft axle core so that the axle can
twist and take up engine torque applied by the engine
to the wheels. These two zones show
up distinctively in that
chevrons are
observed in the case hardened zone. In Photograph F,
the chevrons point, on each side of the case
hardened zone (at 3 o'clock and 9 o'clock), toward
the 6 o'clock area of the fracture. This then is
where the axle fracture initiated. Visually, there
does not appear to be any metallurgical flaw or
defect at the 6 o'clock origin area. The final
fracture (as the axle is presently oriented) is in
the "tear back" area (shown in Photograph D).
The axle failure in question was
the result of the rollover of the Ford Expedition
during the accident. The Expedition rollover was not
the result of a metallurgical
failure that initiated the accident.
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Dr.
R. Craig Jerner, Ph.D., PE specializes in accident
investigation and metallurgical failure analysis,
with over 30 years experience as a metallurgical
consultant and accident investigator. He has
testified as a metallurgical expert in over 250
depositions and more than 70 court appearances. If you or someone you know should need the services of Dr. Jerner and J.E.I. Metallurgical, please visit our web site at the buttons below, or e-mail Dr. Jerner --- 