Course of SN-curves especially in the high-cycle fatigue regime with regard to component design and safety

Conventional design codes base their recommendations still on the common prejudice that an “endurance limit” exists. However, several investigations prove clearly that in the high-cycle regime a decrease of fatigue strength with increased number of cycles still occurs, even if corrosion or temperature effects are excluded. Therefore, the fatigue design of components submitted to loadings below the knee point of the SN-curve must consider this fact in order to avoid failures. With regard to the course of the SN-curve in the very high-cycle area, material and manufacturing dependent recommendations are given.