Issue 48

A. Takahashi et alii, Frattura ed Integrità Strutturale, 48 (2018) 473-480; DOI: 10.3221/IGF-ESIS.48.45 478 As shown in Fig. 3 and 5, the alignment rule in the FFS code is established with the horizontal and vertical distance of two non-coplanar cracks. However, the unit of the horizontal and vertical distance is defined as mm. Therefore, there is a question on the validity of the application of the alignment rule to the other size of cracks. To check if it is valid to apply the same alignment rule to the other size of cracks, fatigue crack growth simulations of two non-coplanar cracks of 2 c =10 mm with various horizontal and vertical distances are performed. The results are shown in Fig. 6. In the figure, the solid and dotted lines are taken from respectively the JSME FFS code and experimental data obtained by Ando et al. [3]. In Fig. 5 where the crack size is 2 c =5 mm, the numerical results are fully covered by the dotted line taken from the experimental data. However, in Fig. 6, the some of the numerical results are over the dotted line. Therefore, the categorization of the fatigue crack growth behavior of two non-coplanar cracks has a dependence on the initial crack size. Thus, the alignment rule is not applicable to arbitrary size of embedded cracks. To remove the dependence of the categorization on the initial crack size shown in Fig. 6, the horizontal and vertical distance of two non-coplanar cracks are normalized by the half of the initial crack size c . The result is shown in Fig. 7. As a result of the normalization of the horizontal and vertical distances by the half of the initial crack size, the categorizations of the fatigue crack growth behavior of two non-coplanar cracks with 2 c =5 mm and 10 mm become almost identical. Thus, the results suggest that the horizontal and vertical distance of two non-coplanar cracks should be normalized by the initial crack size to apply the alignment rule to arbitrary size of cracks. Figure 6 : Interaction map of two non-coplanar embedded cracks obtained by the s-FEM simulations. The initial crack size is 2 c =10mm. The plot is based on the real length of H and S . The borders determined by the JSME and Ando et al. are also plotted. (a) (b) Figure 7 : Interaction map of two non-coplanar embedded cracks obtained by the s-FEM simulations. The initial crack sizes are (a) 2 c =5mm and (b) 2 c =10mm. The plot is based on the length of H and S normalized by the half size of crack c . The borders determined by the JSME and Ando et al. are also plotted.