Issue 48

A. Takahashi et alii, Frattura ed Integrità Strutturale, 48 (2018) 473-480; DOI: 10.3221/IGF-ESIS.48.45 473 Focussed on “Crack Paths” Fatigue crack growth simulation of two non-coplanar embedded cracks using s-version finite element method Akiyuki Takahashi, Ayaka Suzuki, Masanori Kikuchi Tokyo University of Science, Japan takahash@rs.noda.tus.ac.jp, 7516629@ed.tus.ac.jp, kik@rs.noda.tus.ac.jp A BSTRACT . In this paper, the fatigue crack growth simulation of two non- coplanar embedded cracks using the s-version finite element method is presented, and the validity and reliability of the alignment rule for two non- coplanar cracks are evaluated. According to the previous numerical and experimental studies on two non-coplanar surface cracks, the simulated fatigue crack growth behavior is categorized into five patterns to discuss the criteria for the application of the alignment rule. The results suggest that the strength of interaction between the non-coplanar embedded cracks is similar to that between non-coplanar surface cracks. Finally, the interaction of the cracks is evaluated by the stress intensity factor, and the categorization of the fatigue crack growth behavior is discussed by the stress intensity factor. It can be found that the boundary corresponding to the criteria of the application of the alignment rule can be determined as the ratio of the stress intensity factor is 4%. Thus, instead of making a decision of the fatigue crack growth pattern based on the visual inspection, the ratio of the stress intensity factor can be used, and should give more quantitative evaluation of the interaction of two non-coplanar embedded cracks. K EYWORDS . Non-coplanar embedded cracks; Fatigue crack growth; Stress intensity factor; Alignment rule; S-version finite element method. Citation: Takahashi, A., Suzuki, A., Kikuchi, M., Fatigue crack growth simulation of two non-coplanar embedded cracks using s- version finite element method, Frattura ed Integrità Strutturale, 48 (2019) 473-480. Received: 23.11.2018 Accepted: 12.12.2018 Published: 01.04.2019 Copyright: © 2019 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. I NTRODUCTION atigue crack growth is a classical but critical issue to ensure the structural reliability. Up till now, many experimental and numerical studies on the fatigue crack growth of surface cracks have been conducted to model the complex behavior of fatigue crack growth and establish an accurate evaluation method of the residual fatigue life [1-3]. In the fitness-for service (FFS) code for nuclear power plants, flaws detected in structural components are assumed to be simple elliptical cracks and are evaluated using well-established stress intensity factor calculation methods for the simple elliptical cracks [4]. If two non-coplanar cracks appear and are detected in their close vicinity, according to the alignment rule in the FFS code, one of the cracks is projected onto the plane of the other crack. Furthermore, if the projected crack touches or overlaps with the other crack, the cracks are combined into a simple elliptical crack. The combination of cracks is controlled F