Fatigue Life Prediction Using Strain Intensity Factor and Equivalent Initial Flaw Size

In this paper, an effective approach is developed to evaluate fatigue life of smooth specimens of 316 austenitic stainless steel under the fully reversed loading condition based on strain intensity factor and the equivalent initial flaw size (EIFS) concept. The strain intensity factor is indicated to be a better driving parameter to correlate with the fatigue crack growth rate, especially for the fully reversed load condition and the low cycle fatigue region. EIFS is an effective approach to account for complex process of the crack initiation and small crack propagation, which can be calculated by correlating the fatigue limit strain with fatigue threshold strain intensity factor. The fatigue limit strain is obtained from experimental data by analyzing the asymptotic behavior of the fatigue life curve. The driving force of crack growth is expressed in strain intensity factor. Then the fatigue life could be calculated by integrating the crack growth rate from integral lower limit EIFS to integral upper limit critical crack length a_c. The experimental data of 316 austenitic stainless steel are employed to validate the proposed model. The good agreements are observed. It has shown that strain-intensity-factor-based approach could be a good method for fatigue life evaluation.