The rollover of a Ford Expedition resulted in fatal injuries. A non-destructive metallurgical evaluation was requested, including examination of the subject vehicle in a salvage yard. An overall view of the subject vehicle is shown in Photograph A.
Photograph A Overall view of the subject SUV.
An overall view of the axle attachment plate is shown in Photograph B.
Photograph B Overall view of the SUV axle attachment plate.
The axle plate was removed for field stereo microscopic inspection. Upon removal, the upper two attachment bolt holes were noted to be distorted and out of round. The removed SUV axle plate and axle are shown in Photograph C.
Photograph C View of failed SUV 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 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 is 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 View of the fractured axle after light cleaning.
Automobile and truck axles have a case hardened zone on the axle surface, for wear resistance. A soft axle core is present to allow the axle to twist and absorb engine torque applied to the wheels. These two fracture zones show up distinctively in that chevrons are observed in the outer 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 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. This Expedition rollover accident was not the result of a metallurgical defect.