Tractor Trailer Wheel Failure

A metallurgical failure analysis of the right rear inside tandem wheels on a tractor trailer was requested after a trailer wheel failure. The rear tandem wheels exited the trailer and struck an oncoming vehicle.  The fifth axle hub, onto which the wheels had been mounted was lost (opening the issue of spoliation), leaving only  the failed wheel available for metallurgical failure analysis.

A metallurgical failure analysis was requested including both visual and stereomicroscopic examinations. Visual examination revealed the existence of a weld nugget on the wheel rim. This weld nugget was the result of an attempt to weld repair a previous crack and/or localized damage or defect in the wheel rim.  The failed trailer wheel exhibited a circumferential fracture, as a result of metal fatigue, of the wheel rim traversing each of the ten wheel stud holes.

The fatigue crack, once initiated at the weld nugget on trailer wheel, grew circumferentially as a result of normal (or possibly abnormal) operating stress until final separation of the dual wheels from the subject vehicle's fifth axle hub. Weld repair nugget is denoted by a white arrow in photograph of wheel rim shown below in Photograph A.

 
Photograph A  Failed truck wheel rim. Repair weld was placed on the truck wheel rim by an unknown welder. This improper weld repair led to truck wheel rim failure as a result of metal fatigue. White arrow denotes location of weld nugget.

A close-up examination revealed the presence/remnants of a weld repair nugget between lug bolt holes denoted "C" and "D". A close-up view of the area containing the weld repair nugget is shown below in Photograph B.

 
Photograph B  Close-up view of remnants of weld repair nugget between the lug holes denoted C and D. White arrow denotes repair weld nugget.

Microscopic view of the weld nugget area shown above confirms the presence of the repair weld nugget. Weld repair (which is strictly forbidden by the U.S. DOT codes and standards) was evidently attempted. The result of this truck wheel rim weld repair was initiation of a fatigue crack which propagated to the C and D lug holes. The fatigue crack then circumferentially propagated around the rim and through the adjacent lug stud holes, as the truck was used. A close-up view of the weld repair is shown in Photograph C.

 
Photograph C  Microscopic view of repair weld nugget used to repair a crack/defect in the subject truck rim.

The matter was resolved when evidence of welding on the heat treated truck wheel rim was identified.

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