| The purpose of the present research is to develop a model predicting the high cycle fatigue life in relation to the microstructural variable, especially, grain size. In order to achieve this goal, the concept of small crack propagation has been adopted since it is thought that the fatigue crack initiation is similar to the propagation of small crack, which is greatly influenced by the microstructural variables. It is assumed that the whole fatigue crack initiation process can be represented by the microcrack propagation through one grain and one barrier, i.e., consisting of two steps, the propagation through one grain and the arrest at a barrier. For the first step, a modified small crack growth law has been used to consider the influence of grain size on the resolved shear stress, which is the major driving force for the small crack propagation. For the second one, the concept of strain accumulation criterion has been used to calculate the cycles required in overcoming a harrier. Reasonable agreement is found between the experimental data and the predicted curve. |
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