Two-phase crack propagation approach to fatigue life prediction of preloaded notched members

Abstract Experiments with preloaded notched members of 2024-T3 aluminum alloy have shown that preloads in a wide range, even including those which create overall yielding, increase the fatigue lives of the members. Evidence suggests that the extended fatigue life is primarily due to the residual compressive stress generated at the notch root which retards the propagation of small cracks. The finite-element method (FEM) was employed to evaluate the residual compressive stress at preloaded notches. Prediction of fatigue lives of preloaded notch specimens was based on the crack propagation with two phases: small-crack propagation within the notch stress field resulting from the preloads and crack propagation outside the notch field. The effective stress-intensity-factor range for small cracks was calculated using the local stress at the notch field obtained by FEM. The theoretical values based on this model are in good agreement with experimental data.

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