Fatigue life prediction of surface notched specimens with finite residual thickness based on the theory of critical distances
DING Mingchao
BIAN Shuguang
WANG Liming
HUANG Jiaxing
YANG Lipo
CAI Long
Abstract：[Objective]To address the overestimation issue of the classical theory of critical distances(TCD)in predicting the fatigue life of surface notched components with finite residual thickness,the influence of finite residual thickness on the stress fields and fatigue life was investigated.[Methods]Firstly,surface notched specimens with various finite residual thicknesses were designed,and room-temperature axial tensile fatigue tests were conducted.Linear elastic finite element analysis was performed to extract the stress field curves along the thickness direction.Then,based on the fundamental concepts of the point method(PM)and line method(LM)in TCD,an intersection method(IM)and a total stress field method(TSFM)were proposed for equivalent stress evaluation and lifetime prediction in combination with the material S-N curve.[Results]Test verification indicates that the prediction results of traditional TCD methods fall outside the 2-fold scatter band.In contrast,the proposed intersection method,incorporating an intersection stress correction factor(0.855 76 for TC4 titanium alloy),significantly enhances the prediction accuracy to within the 1.5-fold scatter band.The total stress field method,which integrates the stress field over the entire remaining thickness range,yields predictions predominantly within the 2-fold scatter band and exhibits superior applicability for specimens with higher stress concentration(Kt>2.1).Both methods require only the linear elastic stress field curves and the material S-N curve,offering high accuracy and simplified operations.
Keywords：Theory of critical distancesSurface notchThicknessFatigue life predictionIntersection-point methodFull stress field method
Publication Date：2026-07-31
Online Publishing Date：2026-09-12(First online date of this platform, not the publication date of the document)
Pages：9( 23-31 )