13th International Conference on Fracture June 16–21, 2013, Beijing, China -8- For⎯Sa = 1.1·σD (Fig. 8a), the calculated lifetimes for the Rbl ratios 1 and 10 are within the scatter band. For Rbl = 100 only the results of the original and modified Palmgren-Miner’s rule are within the scatter band. The approach by Liu/Zenner always provides the most conservative results, which strongly increase with increasing Rbl-ratio. In comparison, for⎯Sa = 1.2·σD (Fig. 8b), all approaches provide approximately the same results for the lowest ratio Rbl = 1. The higher the Rbl-ratio is, the more the original PM approach overestimates the lifetime and the values are outside the scatter band. Thus, the low load amplitudes contribute to fatigue damage, if the high block loading is high enough with respect to the lower amplitudes and if the high blocks occur less frequently. The lifetimes obtained by Liu/Zenner for the Rbl-ratios of 1 and 10 provide good results. At a ratio of 100 it is again conservative. None of the approaches give suitable results for all three Rbl-ratios. In Fig. 9 the calculated fatigue life Nf,calc for the investigated load-time history FELIX is compared with the experimental mean fatigue life Nf,exp of the three different reconstructed load sequences. For the investigated load sequences FELIX 11 and FELIX 12 the original Palmgren-Miner‘s rule provides results within the scatter band. The approach slightly overestimates the fatigue life of FELIX 10. The elementary Palmgren-Miner’s rule as well as the approach by Liu/Zenner for FELIX 10 and FELIX 11 lead to conservative results, where again the approach by Liu/Zenner is the most conservative one. However, it is observable that each approach leads to the same calculated lifetimes Nf,calc independent of the used reconstructed load sequence, while the experimental lifetimes Nf,exp clearly differ. 1.0E+07 1.0E+08 1.0E+09 1.0E+07 1.0E+08 1.0E+09 Nf,calc (log) Nf,exp(log) PM-original PM-elementar PM-modified Liu-Zenner FELIX 10 FELIX 11 FELIX 12 Figure 9. Comparison of different reconstructed load sequences (FELIX) with calculated fatigue life using Palmgren-Miner’s rule with a damage sum of 1
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