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Truck Wheel Stud Failure

A tractor trailer was traveling out-of-state from Houston, Texas. About 75 miles into the trip, the left front outer drive axle tire on a tractor trailer 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.

Truck wheel and tire from an accident
Photograph A.  Truck wheel following wheel stud failure.

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, with each stud labeled with letters A through J.

Overall view of failed wheel stud fractures
Photograph B.  Failed wheel stud fractures.

A close-up view of the failed stud denoted "I” in photograph B is shown in Photograph C.

Close-up view of failed wheel stud
Photograph C.  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.

Wheel stud after it was removed
Photograph D.  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 scanning electron microscope (SEM). An SEM map of the examined areas on the undamaged fracture surface is shown in Photograph E.

SEM Map of the fracture surface
Photograph E.  Failed wheel stud "I" with locations marked where SEM examination was 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.

SEM of fatigue striations
Photograph F.  Scanning electron micrograph (SEM) (mag 10,000x) of fatigue striations.

A determination of the spacing between the fatigue striations revealed that one fatigue striation was created for every wheel revolution. This fact proved that the service facility, which changed the tire, over-tightened the wheel studs. Overtightening of the wheel studs set up and initiated the fatigue crack failure. Theoretically, 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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J.E.I. Metallurgical, Inc.

5514 Harbor Town
Dallas, Texas 75287

Phone: (972) 934-0493
Fax: (469) 737-3938

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