Issue 48

A. Takahashi et alii, Frattura ed Integrità Strutturale, 48 (2018) 473-480; DOI: 10.3221/IGF-ESIS.48.45 480 C ONCLUSIONS atigue crack growth simulations of two non-coplanar embedded cracks are performed using the s-FEM, and the fatigue crack growth behavior is evaluated by the visual inspection and the ratio of stress intensity factor. The s- FEM has a great advantage in the fatigue crack growth simulation, because the cracks can be modelled as local meshes separately from the global mesh, which is for the geometry and boundary conditions of structures. Using the s- FEM, the fatigue crack growth simulation could be performed automatically. We need to prepare only the global mesh and the crack front information, which is the number of segments along the crack tip. The complex non-planar behavior of two non-coplanar embedded cracks could be simulated with the s-FEM. Then, the fatigue crack growth behavior was categorized into five patterns to discuss the similarity of the fatigue crack growth behavior of embedded cracks and that of surface cracks. The results suggest that the location and shape of the boundary between the pattern C and D, which corresponds to the criteria for the application of the alignment rule, is very similar to those for the surface cracks. Therefore, the existing alignment rule is applicable to the embedded cracks, although the rule is established based on the numerical and experimental results of surface cracks. However, because the horizontal and vertical distance of two cracks are described with a mm unit, the alignment rule gives different results to different initial size of cracks. To remove the dependence of the alignment rule on the initial crack size, the horizontal and vertical distance of two cracks should be normalized by the half size of initial crack. Finally, the stress intensity factor of two non-coplanar embedded cracks and single cracks is calculated. Then, it could be found that the ratio of the maximum stress intensity factor of two non-coplanar embedded cracks to the stress intensity factor of the single crack can be a parameter to determine the fatigue crack growth pattern and the criteria for the application of the alignment rule. R EFERENCES [1] Brighenti R., Carpinteri A. (2013). Surface cracks in fatigued structural components: a review, Fatigue Frac. Eng. Mat. Struct., 36, pp. 1209-1222. [2] Rozumek D., Faszynka S. (2017). Fatigue crack growth in 2017A-T4 alloy subjected to proportional bending with torsion, Frattura ed Integrità Strutturale, 42, pp. 23-29 [3] Sniezek L, Slezak T, Grzelak K, Hutsaylyuk V. (2016). An experimental investigation of propagation the semi-elliptical surface cracks in an austenitic steel. Int. J. Pressure Vessels and Piping, 144, pp. 35–44. [4] Codes for Nuclear Power Generation Facilities, Rules on Fitness-for-Service for Nuclear Power Plants, JSME, (2016). [5] Kamaya, M., Miyokawa, M., Kikuchi, M. (2010). Growth prediction of interacting surface cracks of dissimilar sizes, Eng. Frac. Mech., 77, pp. 3120-3131. [6] Ando, K., Hirata, T., Iida, K. (1983). An Evaluation Technique for Fatigue Life of Multiple Surface Cracks: Part 2: A Problem of Multiple Parallel Surface Cracks, J. Marine Sci. Tech., (in Japanese), 153, pp. 352-363. [7] Fish, J., Markolefas, S., Guttal, R., Nayak, P. (1994). On adaptive multilevel superposition of finite element meshes, Appl. Numer. Math., 14, pp. 135-164. [8] Okada, H., Higashi, M., Kikuchi, M., Fukui, Y., Kumazawa, N. (2005). Three dimensional virtual crack closure-integral method (VCCM) with skewed and non-symmetric mesh arrangement at the crack front, Eng. Frac. Mech., 72, pp. 1717- 1737. [9] Paris, P., Erdogan, F. (1963). A Critical Analysis of Crack Propagation Laws, J. Basic Eng., Trans. American Society of Mechanical Engineers, pp. 528-534 [10] Richard, H.A., Fulland, M., Sander, M. (2005). Theoretical crack path prediction, Fatigue & Frac. Eng. Mater. Sci. 28, pp. 3-12. F