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Truck Wheel Stud Failure
A tractor trailer was traveling
from Houston, Texas to a small city in another state
outside Texas. About 75 miles into the trip the left
front outer drive axle tire on the tractor blew out and had to be
replaced. All of the wheel lug studs were replaced
when the tire was replaced. After traveling another
250 miles the same left front tire which had just
been replaced departed the
vehicle as it was crossing a two lane
bridge. A passenger vehicle, traveling in the
opposite direction on the bridge was struck by the
tire and a passenger was very seriously injured. An
overall view of the truck wheel and tire is shown in Photograph A.
Photograph A Overall view of truck wheel
following wheel stud failure and subsequent
accident.
Analysis of the wheel studs which remained with
the inner wheel of the vehicle was requested. A close-up view of the
wheel stud fractures is shown in Photograph B.
Photograph B Overall view of failed wheel
stud fractures on the subject accident truck
wheel.
A close-up view of the failed stud denoted “ I”
in photograph B is shown in Photograph C.
Photograph C Close-up view of failed
truck wheel stud denoted " I".
Although the truck had traveled only
250 miles since the tire/wheel stud replacement the
failed wheel stud fracture surface exhibited considerable mechanical
damage. A close-up view, after removal from the
wheel, of
the failed " I" wheel stud is shown in Photograph D.
Photograph D Close-up view of failed
truck
wheel stud " I"
after removal from truck wheel.
Although much of the wheel stud
fracture had been mechanically damaged, the subject
stud was examined in the
SEM. An SEM map of the
areas on the fracture surface which were examined
are shown on Photograph E.
Photograph E Overall view of
failed wheel
stud " I"
with locations marked where SEM
examinations were conducted.
The very high magnification SEM examination revealed that individual
fatigue striations on the wheel stud fracture could be counted.
That is, the separation or distance between fatigue
striations could be measured. One area
of the wheel stud fracture examined is shown in Photograph F.
Photograph F Scanning electron
micrograph
(magnification 10,000x) of fatigue striations.
Yellow line marker indicates the distance between fatigue
striations.
A determination of the spacing between the fatigue striations
revealed that one
fatigue striation was created for every wheel
revolution. This proved that the service facility that had
changed the tire and the
wheel lugs had been over tightened. The
overtightening of wheel studs thereby set up and
initiated the fatigue
crack
failure. Knowing the exact number of wheel
revolutions from the time of the tire/wheel stud
change corresponded to the number of fatigue striations that
should be present. Upon completion of the fatigue analysis
the matter was resolved.
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