Steering Gear Component Failure

It was reported that a vehicle lost steering after making a slight steering maneuver. This steering maneuver loads the steering gear well below its maximum load-carrying capacity and therefore is not expected to cause a sudden fracture of any steering component. Examination of the steering gear did reveal a broken part critical to the steering mechanism.

Evaluation of the fractured surfaces, of the broken part, was required to accurately determine the cause of the failure. Visual and scanning electron microscopic examination revealed the sequence of failure. However, this particular sequence rarely occurs and could be misinterpreted without an accurate knowledge of fracture features. Process knowledge of the component allowed the root cause to be determined and properly focused the investigation to avoid further accidents.

Figure 1 shows the fractured surface and the interpretation of the fracture features are described in the caption.

Skill set needed to analyze problem: Failure analysis of heat treated steels and knowledge of case hardening processes, and manufacturing experience with hydraulic rods.

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