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