Abstract
Abstract— The propagation behaviour of fatigue cracks emanating from pre‐cracks was numerically simulated to evaluate the development of crack closure with crack growth. The crack opening stress intensity factor at the threshold was approximated as a function of the applied stress and the amount of crack extension. Pre‐cracked specimens of a medium‐carbon steel with a small surface crack and a single‐edge crack were fatigued to investigate experimentally the initiation and propagation of cracks from pre‐cracks. Crack closure was dynamically measured by using an interferometric strain/displacement gauge. The threshold condition of crack initiation from pre‐cracks was given by a constant value of the effective stress intensity range which was equal to the threshold value for long cracks. The cyclic R‐curve was constructed in terms of the threshold value of the maximum stress intensity factor as a function of crack extension approximated on the basis of the experimental and numerical results. The cyclic R‐curve method was used to predict the fatigue thresholds of pre‐cracked specimens. The predicted values of the fatigue limits for crack initiation and fracture, and the length of non‐propagating cracks agreed very well with the experimental results.
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