A Prediction of the Fatigue Crack Propagation Curve Considering the Effect of Mean Stress

概要

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Previously the authors proposed a four stages classification of the fatigue crack propagation, namely the initial, the tensile mode, the shear mode and the final propagation stage. In this report, a method for calculating the crack propagation is proposed based on the authors' classification. A new model is introduced considering the effective stress intensity factor. The initial crack propagation is affected by the compressive stress on the fatigue crack inner surfaces. The propagation in the tensile mode and the shear model stages is mainly controlled by the effective stress intensity factor ΔK_e=K_<max>-αK_<min>, and the value of α is expressed by stress ratio, and is independent of the fatigue crack propagation rate and the applied stress amplitudes. The results of this calculation agree well with the experimental results. The usefulness of this calculation in the initial stage is qualitatively shown for the study of non-propagating crack, crack propagation influenced by residual stress and the crack propagation behavior by programed load.
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