© 2013 Siemens Energy, Inc. All rights reserved. Figure 2. Fatigue crack growth behaviors for all DS specimens in Region II Figure 3 shows the crack growth behaviors for the three types of specimens tested at T0. Generally, comparable crack growth rate data can be found in longitudinal and transverse directions, while those in diagonal direction seem to be lower, especially in the high- KΔ regime. That’s to say, there is no significant difference between crack growth rate in longitudinal and transverse directions, while specimens in diagonal direction have a much lower crack growth rate, and the difference becomes larger when it is up to the high- KΔ regime. Figure 3. Crack growth behaviors of three types of specimens tested at T0 However, at T0+250 0C, the orientation dependence becomes even weaker, as can be seen in Figure 4. Cracks that travel in longitudinal and transverse directions also have a comparable crack growth rate; but different with those at T0, cracks in diagonal directions still travel with a comparable rate, and no obvious difference can be found, even in the high- KΔ regime. Figure 4. Crack growth behaviors of three types of specimens tested at T0+250 0C
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