Overload Fracture of Cast Aluminum Wheel

The right-rear wheel of a full-size pickup truck involved in a single-vehicle accident was alleged to have fractured, leading to loss of vehicle control. The wheel was found fractured and partially separated from the vehicle by a distance of approximately 200 feet from the final resting point of the vehicle. The wheel was manufactured using a common casting procedure utilizing aluminum alloy A356 in the T6 condition. In subsequent litigation, the presence of porosity in the wheel was alleged to have precipitated the failure. Radiographic inspection of the wheel displayed the presence of shrinkage porosity in a quantity less than the maximum allowed according to the part specification. The recovered portions of the right-rear wheel exhibited evidence of impact overload fracture, including significant deformation. Inspection of the remaining artifacts also revealed that the right-front wheel exhibited a similar fracture as the rear.