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.
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.
Photograph B Failed wheel stud fractures.
A close-up view of the failed stud denoted "I” in photograph B is shown in Photograph C.
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.
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 SEM. An SEM map of the areas on the fracture surface which were examined are shown in Photograph E.
Photograph E Failed wheel stud I with locations marked where SEM.
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 (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 proved that the service facility that had changed the tire over tightened the wheel studs. 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.