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ORIGINAL ARTICLE

Fatigue surface crack growth behavior in flat plate and out‑of‑plane gusset‑welded joints under biaxial cyclic loads with different phases Mizuki Morishita1 · Koji Gotoh2   · Yosuke Anai3 · Shuichi Tsumura3 · Toshio Niwa4 Received: 3 March 2020 / Accepted: 13 August 2020 © The Japan Society of Naval Architects and Ocean Engineers (JASNAOE) 2020

Abstract Although many in-service welded built-up structures, which contain many welded joints as fatigue crack initiation sites, are subjected to many types of loading, their structural integrities are evaluated according to design codes based on theoretical and experimental investigations under uniaxial loading conditions. Additionally, most of these codes implement the S–N curves approach. This study highlights the biaxial cyclic loading with different phases. The fracture mechanics approach toward fatigue life evaluation can obtain the fatigue crack growth history. This paper confirms the applicability of the previously proposed numerical simulation method for obtaining the fatigue crack propagation histories of a cracked plate subjected to biaxial loads with a phase difference for each loading component. A fracture mechanic approach was used to establish the proposed method. The fatigue surface crack growth behavior of a flat plate and an out-of-plane gusset-welded joint under biaxial cyclic loadings with different phases was investigated by extending the applicability of the proposed method to a through-thickness crack. Comparisons between the measured crack evolution and the numerical simulation results were carried out to validate our fatigue crack growth simulation for flat plane and welded joints. Keywords  Fatigue · Biaxial cyclic loading with phase difference · Numerical simulation of fatigue crack growth · RPG stress · Out-of-plane gusset-welded joints

1 Introduction Most in-service welded structures, such as ships and offshore structures, contain many welded joints that can become fatigue crack initiation sites. Additionally, these structures are subjected to many types of loading. However, the structural integrity of most working structures and vehicles is

* Koji Gotoh [email protected]‑u.ac.jp 1



Department of Civil and Structural Engineering, Graduate School of Engineering, Kyushu University, 744 Motooka, Nishi‑ku, Fukuoka 819‑0395, Japan

2



Department of Marine Systems Engineering, Faculty of Engineering, Kyushu University, 744 Motooka, Nishi‑ku, Fukuoka 819‑0395, Japan

3

Physical System Research Group, Industrial System Engineering Department, National Maritime Research Institute, 6‑38‑1, Shinkawa, Mitaka, Tokyo 181‑0004, Japan

4

Industrial System Engineering Department, National Maritime Research Institute, 6‑38‑1, Shinkawa, Mitaka, Tokyo 181‑0004, Japan





assessed using design codes based on theoretical and experimental investigations under uniaxial loading conditions from a practical viewpoint. The objective of this study was to highlight the biaxial cyclic loading with different phases. The fatigue strength under bi