13th International Conference on Fracture June 16–21, 2013, Beijing, China -7- ratio was deduced to compute the equivalent pure shear strain for Rε = 0. The 0.8% uniaxial strain range is equivalent in shear to 1 (1 ) (1 )0.8% (1 0.3989)0.8% 1.119% eq (15) Thus, the upper and lower faces were displaced in shear up to a nominal shear strain of 1.119% for equivalence in this particular case. The Poisson„s ratio was deduced using an elastic model with cubic symmetry, i.e., 12 11 66.3 0.399 166.2 C C (16) 3.2 Crack growth vs cycles for smooth specimens Smooth specimens were employed to simulate shear and tension-compression straining at 650°C for under three strain ratios Rε = min max / = -1, Rε = 0 and Rε = 0.5, all undergoing an equivalent nominal strain range of 0.8% at 0.05%/s strain rate. For each loading condition, a total of 10 equivalent microstructure realizations were simulated. The simulations considered unidirectional periodic boundary conditions, with lateral faces free of traction. Figure 3 presents crack length vs. life on a semi-log scale. Each data point corresponds to extending the crack by one grain and only lives below 109 are considered (otherwise considered as crack arrest, giving rise to run-out Figure 2. Example of voxellated meshes representing the explicit polycrystalline microstructure for axial straining of smooth (top) and notched (bottom) specimens. Triangular straining sequence is applied by displacing the upper and bottom faces of the meshes at 0.05%/s strain rate.
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