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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