A New Approach to Fatigue Life Prediction Based on Nucleation and Growth (Preprint)
SOUTHWEST RESEARCH INST SAN ANTONIO TX DEPT OF MATERIALS AND MECHANICS
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Prediction of total fatigue life in components is often performed by summing initiation and propagation life phases, where initiation life is based on stress-life or strain-life methods calibrated to smooth specimen fatigue tests. An engineering size crack e.g., 0.030 or 1 mm is often used as the transition between initiation and propagation analyses. However, these methods commonly fail to give accurate predictions for problems with significant stress gradients. A new approach to fatigue life prediction has been developed to address this shortcoming. The approach employs traditional smooth specimen and fatigue crack growth data but applies them in novel ways. The first step is to generate nucleation curves to a designated small crack size from smooth specimen data by subtracting calculated crack growth life including small-crack corrections in the smooth specimen from the total smooth specimen life. The second step is to apply these nucleation curves to predict the nucleation life to the same initial crack size in a feature of interest, equating the stress at the nucleation length in the feature geometry with the uniform stress in a corresponding virtual smooth specimen. The feature crack growth life is calculated from this crack size to failure, and then nucleation and growth lives are summed to obtain the total fatigue life. The approach has been demonstrated for Ti-6Al-4V using available data from smooth specimen and fatigue crack growth tests to predict total fatigue lives in double-edge notched fatigue specimens at three different stress ratios.
- Statistics and Probability
- Test Facilities, Equipment and Methods
- Properties of Metals and Alloys