*5.3. Results of Fatigue Life Simulations*

Figure 15 shows the simulated stress field in porous specimens, S1 through S7, using ABAQUS and the fatigue life predicted by Fe-safe. The scale used for fatigue life is Log10 life, i.e., 1 million cycles are represented by 6 on this scale. As mentioned earlier, a node spacing of 1 mm is found to show good agreemen<sup>t</sup> between the measured and the predicted fatigue lives. A complex stress field is developed due to porosity upon loading each specimen. It is observed that area with stress concentrations experienced the shortest lives. Moreover, for each specimen, the least number of cycles to failure is predicted on the surface. This shortest life predicted is considered to be the fatigue life for that specimen. A

summary of simulated stress, measured and predicted fatigue life for each specimens, is presented in Table 5.

**Figure 15.** ABAQUS stress analysis and fatigue life prediction from Fe-safe.


**Table 5.** Summary of simulated and experimental results of fatigue testing for steel specimens.

The experimental and simulated S-N curve are presented in Figure 16. Simulation results shows two specimens to experience the infinite life where the predicted number of cycles to failure are beyond the runout condition, i.e., 10<sup>6</sup> cycles. For a better understanding of experimental and simulated results, the measured and simulated lives for all specimens are compared in Figure 17. A line of perfect correspondence is provided in the figure to determine if a prediction is non-conservative (above the line) or conservative (below the line). It can be observed that six out of seven specimens are within a factor of 10 of the test results, which can be considered as a good agreemen<sup>t</sup> in fatigue life prediction [18]. The specimen S1 is found to have a relatively bad agreemen<sup>t</sup> since the predicted fatigue life is slightly more than the factor of 10 of the test result. In general, the overall results for fatigue life prediction are encouraging, however, the overall nature of predictions are found to be non-conservative in steel specimens.

**Figure 16.** Simulated and experimental S-N curve for steel specimens.

**Figure 17.** Measured and predicted fatigue lives of steel specimens.
