13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Analysis of Crack Retardation Effects and Crack Path in Ship Structure Members on Different Routes Fredhi Agung Prasetyo 1,* , Wengang Mao 2 , Tomohei Kobayashi 1 , Naoki Osawa 1 , Jonas W Ringsberg 2 1 Department of Naval Architecture & Ocean Engineering, Osaka University, Suita Osaka 5650871, Japan 2 Department of Shipping and Marine Technology, Chalmers University of Technology, Gothenburg, Sweden * Corresponding author: Fredhi_Agung@naoe.eng.osaka-u.ac.jp Abstract The ship size has been rapidly increased in recent years. Consequently, many aspects of ship structural safety have been concerned, i.e. fatigue strength. Since fatigue cracks are found in the early stage of a ship’s service life, it might be that the classical cumulative fatigue rule is insufficient to consider the effects of many uncertain factors, such as variable wave environment loads. The wave load history hinges on the short-sea history. It means that the accuracy of fatigue assessment is affected by the used wave model. There are several established wave models, which could be used to simulate wave load history as in the real ocean conditions. In this paper, wave load histories of a 2800TEU container ship are generated by two different wave models. It is used for crack propagation analysis in the changing routes and trades. The result in the simulated crack propagation lives is examined and discussed. Keywords fatigue crack propagation, fatigue damage sensor, hindcast data, ship structures 1. Introduction Fatigue is an important issue for maritime industry. Large ship designers must consider the fatigue strength of ship structures. The traditional ship fatigue assessment is conducted by using a simplified method, in which Palmgren-Miner linear cumulative law and S-N curves are used. In this method, all parameters are provided by classification societies' rules. A comparative study shows that this method gives wide scatter of fatigue life predictions [1]. Thus, fatigue cracks are observed much earlier than expected, challenge the safety of structural integrity and final failure in shipping. This is caused by many uncertain factors, e.g. chosen S-N parameters, load spectrum range, fatigue assessment method, etc. The solving alternately starts from how to get the structural stress history for various sea-states. A sea-state is characterized by its energy spectra, which is a function of significant wave height (Hw) and mean wave period (Tw). The transfer function of structural stress response, also known as RAOs, is obtained from a direct calculation by considering wave loads for all loading conditions, ship speeds, and heading angles. It can be combined with the wave energy spectrum of a sea state to compute the stress spectrum. The fatigue crack propagation theory is capable to predict fatigue crack propagation length in a real service voyage [1][2]. The accuracy of fatigue propagation analysis hinges on the load sequence's reproducibility of the actual sea-state history. Ship owners' concern about fatigue damage is growing, and the ship operation / route is changed constantly according to the weather condition. The load sequence obtained from the wave scatter diagram in classification society rules may be different from that of the actual load [3]. This may affect the accuracy of the crack propagation analysis.