Both halves of a gray cast iron transmission housing from a 50-ton dump truck were found to contain numerous cracks. The housing material was possibly G3000 grade designation for automotive gray cast iron. No service duration or material specifications were provided. Investigation (visual inspection, tensile testing, 2% nital etched 59x cross sections, and metallographic analysis) supported the conclusion that failure was due to applied stresses sufficient to fracture the castings which exhibited brittle overload cracks at highly stressed locations. No recommendations were made.

A stick-shift from an automobile transmission failed in service. Failure occurred by stable fatigue crack propagation at locations R and L. Plausibly, the crack initiated at location R due to maximum tensile stress, which was perhaps further concentrated by a surface imperfection. As the crack progressed, the service load shifted to the section marked L. This overload on location L appears to have caused another fatigue crack that propagated first over the smooth-banded region. Catastrophic failure occurred when the component became unstable under the applied load.

An AISI 4320 H transfer gear shaft that was part of a transmission sustained severe surface damage after 12 h of dynamometer testing at various gearing and torque loads. The damage was characterized by generalized wear and spalling. Examination of a cross section of the shaft that intersected undamaged, burnished, and surface-spalled zones revealed no anomalies in the chemistry, microstructure, or hardness that could have caused the damage. The physical evidence suggested that the operable mechanism was contact fatigue caused by misalignment of the shaft in the assembly.