FINITE ELEMENT MODELLING The three dimensional finite element mesh used to analyse the crack tip deformation of a typical compact tension specimen is shown in Fig. 3. A crack length of a = 15.6 mm and a crack length-to-specimen width ratio of a/W=0.6 were used. Here, the specimen thickness and height are 12.5 mm and 31.2 mm, respectively, and the notch radius is 1.3 µm. [010] [100] [001] a Figure 3: Finite element mesh of the CT specimen The plane of the specimen is normal to the [001] crystallographic axis and the crack faces lie normal to the [010] axis. Note also that, due to the symmetries of the lattice and the specimen, only 1/4th of the specimen needs to be modelled. In total, 14000 linear brick elements are used in the analysis, with a focused mesh at the crack tip. The smallest element size in the model is 1.0 µm (or ∼6×10−5a). 1 2 3 0.00 3.00E-3 5.83E-3 8.67E-3 1.15E-2 1.43E-2 1.72E-2 2.00E-2 8.71E-1 [010] [100] [001] f = 0.68 (b) 20 m 1 2 3 0.00 3.00E-3 5.83E-3 8.67E-3 1.15E-2 1.43E-2 1.72E-2 2.00E-2 2.46E-0 [010] [100] [001] f = 0.58 (a) 20 m p p V V Figure 4: Contours of accumulated inelastic strain near the notch tip for: (a) 58% and (b) 68%γ’ volume fraction after 320 hours exposure at 850◦C 4
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