The standard error SE of log_{10}(N) is used to adjust the fatigue life or the damage predicted to any given **probability of survival**. Fatigue life data always include some scatter, and at any given level of stress, the distribution of fatigue lives is assumed to be a log-normal distribution. Or stated differently, a Normal or Gauss distribution of the logarithm of the fatigue life.

# Category: Material Fatigue

## Surface Roughness Factor KR for Fatigue

Fatigue tests of specimens are usually done on components with mirror polished surfaces. However, a component with a larger surface roughness will have a reduced fatigue strength. To account for the effect of this surface roughness to the fatigue strength of a material, a **roughness factor K _{R}** is used. This surface roughness factor is used to adjust the material S-N curve. This article describes the FKM method for obtaining the surface roughness factor and how to apply this factor to the S-N curve.

## What is Material Fatigue?

Material failure due to **structural fatigue **is an important cause of structural failure. But what is metal fatigue exactly? And which factors influence the fatigue strength of components?