Fatigue Anecdote

Of the wide variety of materials-related topics, BMC has in-depth experience with fatigue failures, including diagnosis, rigorous analysis, subsequent design changes, and inspection mitigation. In this case, a component that failed could have been catastrophic, but fortunately, it was not. It was imperative to discover the root cause as well as the prior analysis and material selection to avoid such a failure, especially given the criticality of the part.

After routine failure analysis observations, BMC determined the mechanism was fatigued as the part was a cantilevered shaft that came to a very sharp corner radius. On the surface, the obvious oversight was the lack of radius, and with a simple design change, the situation was easily improved.

Our philosophy is to go the extra mile.

However, BMC’s philosophy is to go the extra mile where appropriate; in this case, further inspection unearthed unexpected part conditions. Analysis suggested longer life than realized, and the temptation was to assume it was due to the sharp corner radius, which it was–-in part. BMC discovered pitting corrosion that accelerated crack growth, exacerbating poorer-than-expected fatigue life. While the conclusion to add more corner stress relief was correct, it took extra consideration and experience to recognize the relevant risks (crevice and pitting corrosion in a marine environment) and consider the complete mitigation strategy.