13th International Conference on Fracture June 16–21, 2013, Beijing, China -9- 4 Discussion and conclusions The simulations showed quantitatively the detrimental effects of higher strain ratios, which change orders of magnitude the cycles required to grow a crack of similar lengths. Furthermore, in all cases tension-compression straining was more damaging than shear straining, which has been reported in the literature for other materials [14][15]. The results for smooth specimens exhibited a spread of fatigue life over three orders of magnitude for strain ratios between Rε = 0.5 and Rε = -1, for shear and tension-compression loading. Notched specimens under tension-compression loading showed a smaller spread, which is explained by a reduction of the variability in nucleating a crack. This effect dominates over the reduction of the highly strained volume around the notch. In the case of notches under shear, the cracks nucleated within the bulk of the specimen (not at the notch), and the results are comparable to those found for smooth specimens. Figure 4. Stress-strain responses of a smooth specimen microstructure realization and three strain ratios over 20 uniaxial straining cycles. Figure 5. Comparison of the results for strain ratios Rε = 0, Rε = 0.5 and Rε = -1 on a logarithmic scale for notched specimens undergoing an equivalent nominal strain range of 0.8%.
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