Quantitative analysis on low cycle fatigue damage: a microstructural model for the prediction of fatigue life

A study has been made to develop a model predicting the low cycle fatigue life of a material in relation to its microstructural variables. To achieve this goal, the concept of damage accumulation by multiple surface cracks has been adopted. An equation for stage I crack growth suggested by Tomkins was modified to consider the effect of grain size on the crack growth rate at early stage, and statistical analysis was carried out to calculate the final crack length for fatal failure. A concept of equivalent crack length has been used to present the quantitative description of crack growth rate when multiple cracks grow at the same time. To verify the suggested model, low cycle fatigue tests were conducted for the polycrystalline single-phase steel with the various grain sizes. The results showed a good agreement between the experimental data and the predicted curve.