Fatigue Notch Factors for Structural Details

The use of fatigue notch factors is proposed for specifying the relationship between the allowable stress range and the number of loading cycles. This is done by premultiplying the stress range with a fatigue notch factor which accounts for the severity of the detail's stress concentration. The method simplifies the manner in which fatigue specifications are written, and it conveys the idea of classification of details by severity of stress concentrations; it is most suitable for use in computer-aided analysis and design. The proposed equations for redundant load path structures give stress range values closer to those corresponding to the lower confidence limit at two standard deviations of the mean than the rounded off values in the specifications. The proposed equations for nonredundant load path structures are set at a uniform 5.5 standard deviations below the mean.