船体の寿命評価技術に関する研究

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This report is a summary of SRI research project entitled "Study on Life Estimation of Hull Structures". In 1990's, serious accidents of aged bulk carriers and fatigue damage of single hull VLCC side longitudinals occurred frequently. Then, the research which focused it on the design method based on fatigue life, the evaluation method of corrosion and diminution and the inspection method which can be applied to PSC was started. In advanced fatigue design of hull structures, rational estimation of ship loads and development of exact method of fatigue life estimation: Estimation methods of wave-induced loads based on the concept of "the worst short-term sea condition" , the impulsive pressure on the surface of the water and inertia loads acting on the cargo holds by liquid or granular cargo were proposed. And a new structure analyzing system and the results of fatigue tests of the 1/3-scaled bilge knuckle models of double hull tankers were displayed. Advanced estimation methods for fatigue strength of structural members: first, the effects of construction factors, such as welding conditions, configurations of weld zone, weld deformation, residual stresses etc., on structural strength were examined, then bi-axial fatigue behavior of a box-welded (wrap-around) steel joint was experimentally studied, and finally the fatigue life assessment method to evaluate the influence of structural mean stress on fatigue strength in design stage was proposed. In study on durability of ship hull materials, corrosion and corrosion fatigue tests were performed under seawater and dilute sulfuric acids pH4 and pH2. Data bases of corrosion speeds, crack propagation characteristics and fatigue crack initiation lives were prepared. Three types of fatigue crack initiation life of notched specimens are summarized by S-N curves for nominal stress, Seq-N curves for an equivalent stress at notch roots using modified MIL HDBK-5 and ΔK-N curves using stress intensity factors at notch roots. Deterioration of paint films under immersion tests in seawater was also studied. The present state of hull inspection techniques and hull inspection scenes were investigated in order to pick up inspection techniques to be improved or developed. Research on ultrasonic thickness measurement error caused by roughness of corroded plates and the error reduction methods, quantitative inspection by hammering test, application of hull deformation measurement to evaluation of full strength were carried out experimentally.
独立行政法人海上技術安全研究所の論文
2003-01-24

船体の寿命評価技術に関する研究

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