Torsional fatigue life evaluation for steel thin-wall specimens considering crack initiation phase

In this paper, a new model for fatigue life evaluation of a steel thin-wall tubular specimen based on critical plane theory is presented. the fatigue model incorporates the crack initiation phase in the life prediction model. the total fatigue life is the sum of both crack initiation and propagation lives. initial crack length is not applied priory, but is calculated within the model. the crack initiation life is evaluated using a critical plane approach base on a modified smith-watson-topper and the fatemi- socie criteria. the evaluated fatigue lives are validated by experimental results for a thin-wall tubular specimen. both critical plane criteria have resulted in similar fatigue lives, with the fatemi-socie criteria giving a slightly more accurate initiation life. the model absolute error is high without consideration of the crack initiation phase. the proposed model indicates that a correct determination of the fatigue life requires consideration of the crack initiation phase.