10 Tips for Designing Against Fatigue

Roof of AZ stadium collapsed due to fatigue.

Do you want to be responsible for accidents like this? I guess not. To avoid such misery it is always good to keep some elementary things in mind.

Things to keep in mind when designing against fatigue

  • Always remember: fatigue is caused by cyclic stresses.
  • Do recognize that cracks initiate at locations with high stresses, i.e. stress concentrations. The sharper the discontinuity, the higher the stress concentration factor.
  • Provide a smooth flow of stresses.
  • Improve surface finish, cracks almost always initiate at the surface.
  • Consider surface hardening by carburization or nitriding, this improves the fatigue properties at the surface.
  • Increase the fatigue performance by means of residual compression stresses on the surface. Note that residual tensile stresses are unfavorable for fatigue.
  • Know that fatigue life analyses are inherently inaccurate. Simplifications in your analysis increase the inaccuracy.
  • Fatigue testing helps to validate your analysis and to optimize your design.
  • Be aware of disturbance loads; not only operational loads contribute to fatigue.
  • “If you think safety is expensive, try accident”, i.e. ignore your manager.

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