Calculation Example: Fatigue Failure Basics
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A steel mechanical component has a rotary-beam test endurance limit () of . If the actual component has a machined surface, which corresponds to a Surface Condition Factor () of , calculate the modified endurance limit () to be used for evaluating fatigue failure.
The calculation result shows that the endurance limit to be used in actual design () is reduced to only MPa from the original 250 MPa.
The reason for the decrease in fatigue strength is that the actual surface is rough (having a factor ), unlike the highly polished test specimen. This roughness acts as tiny flaws that cause stress concentration, which is the starting point for fatigue cracks. Therefore, engineers must always use this reduced value in their design calculations for safety.