© 2013 Siemens Energy, Inc. All rights reserved. ( ) ( ) ( ) 2 3 4 3/2 2 0.886 4.64 13.32 14.72 5.6 1 P K B W α α α α α α + Δ Δ = + − + − − (1) where / a W α= , a is computed crack length, W takes a constant value of 40, and P is the applied load. 3. Results and discussion Three types of specimens with different orientations were machined from cast plates. Figure 1 indicates the schematic images of these three types of CT specimens, where the different-color cylinders indicate crystal grains. Totally 12 specimens were tested at T0 and T0+250 0C, with crack growth in longitudinal, transverse and diagonal directions, respectively. Figure 1. Schematic images of three types of C(T) specimens 3.1. Effect of orientation on FCG rates The overall crack growth rate versus stress intensity factor values in Paris regime, i.e., / da dN K −Δ curves, are depicted in Figure 2, from which one can conclude that the orientation dependence is very weak, i.e., crack growth data in all orientations fall into one narrow [1/3, 3] band. Meanwhile, when using Paris law to obtain linear regression of all crack growth data, the correlation coefficient can be up to 0.88.
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