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ICF13A

13th International Conference on Fracture June 16–21, 2013, Beijing, China -7- In SCK specimen, SIF due to remote load F is independent on crack length in the crack size range 0.15 0.4 cr W   and simply related to the applied load ( F , 0B , eB , and W are specified in Figure 5):   6.56 I eff F K K F B W      . (19) The Green’s function for SIF due to self-equilibrated double forces applied to the crack faces in SCK specimen is obtained by introducing a correction factor to the Green’s function of semi-infinite crack in an infinite solid ( 2 semi G x  ): 1 2 3 2 2 2 ( , , ) SCK G x LW x x x L L       . (20) where x is the distance from the tip of crack layer (CL), L is CL length ( cr pz L  ) Thus, the SIF due to dr  is obtained by integrating the Green’s function over the PZ size and the total SIF tot K is obtained by tot dr K K K    . 4.2. COD Formula Based on numerical analysis of SCK specimens with different geometries ( pz L0.1, 0.2, 0.25, 0.3; and LW0.2, 0.25, 0.3, 0.35), the COD  and dr  at a point x due to the remote load F and dr  respectively can be presented in the following forms: 2 2 0 8 e F x x x E L L L BB                  and 2 2 8 ' ' ' ' dr dr pz pz pz W x x x E                  (21) The coefficients , , and are functions of only one variable L/W and the coefficients  ,  , and  are simple functions of pz , L and W. The total opening is: tot dr       . The same approach is readily applicable to other specimen geometries. Thus, the evaluation of CL parameters is the building block for calculation of CL driving forces and simulation of CL growth. 5. Examples of Crack Layer Growth Simulation The process zone driving force PZ X monotonically decreases with increase of PZ size. The equilibrium PZ size eq pz corresponds to vanishing of the corresponding thermodynamic force: 2 0 ' pz PZ tr tot PZ x K V E        . (22) The experimental determination of the equilibrium PZ size is conducted by direct observations of striations of fracture surface in discontinuous CL growth. A comparison of calculated equilibrium PZ size eq pz with experimental data (Figure 4 (a)) at elevated temperature is shown in Figure 4 (b).

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