Abstract
The Dugdale strip yield model for crack tip plasticity has been modified in this paper to take into account the influence of biaxial stress fields on the yield condition of the material such that the role played by loads that are applied in a direction parallel to the crack plane is no longer taken to be incidental. The von Mises yield criterion, which has recently proved by S. T. Chen in a rational way, is adopted instead of the Tresca yield criterion. Effects of unloading and repeated loadings are also considered. The modified model predicts that cyclic deformation behaviors at a crack tip are dependent not only on the amplitude of load fluctuations but also on the mean level at which the load is being cycled, in contrast to other investigators' results which are based essentially on the virgin unmodified Dugdale model, revealing that at least two parameters are necessitated if the rate of fatigue crack propagation is to be predicted more accurately.
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