where \(S\) and\(\ \sigma\ \)represent the fatigue limit of structural components and material when the stress ratio R is -1 respectively.\(\ K_{T}\) is the stress concentration coefficient. ε is the size effect coefficient. βis the surface quality coefficient.\(\ C_{L}\)is loading method.
In order to obtain more accurate stress-life relationship of structural parts, S-N curve of material parts should be modified. The stress concentration factor (SCF) had a great influence on the fatigue of structural components [37], which could be simulated and solved by the finite element formula[38].The stress concentration coefficient can be defined as