含對接銲道缺陷之散裝貨輪疲勞強度分析

Study on Fatigue Strength of Bulk Carrier with Defect in Butt Welded Joints

本文探討一艘十多萬噸散裝貨輪，該船在某次航行過程中，於某含缺陷對接銲外板處發生疲勞破壞。文中將日本造船研究協會所建義之「尖峰比率法」的精神，應用於散裝貨輪之疲勞強度分析，包括耐航性能分析、負荷長期分佈統計、有限元素分析、應力長短期分佈計算、疲勞壽命預估與裂縫進展等。此外，配合採用正規頻譜分析法進行之應力分析結果，及針對該含缺陷銲道外板試驗片進行疲勞試驗之結果[1]，分析該艘散裝貨輪銲道裂縫處之長期疲勞壽命及在惡劣海況下（假設有義波高8m）之短期疲勞壽命，並利用da/dN曲線略估該銲道裂縫處在惡劣海況下，裂縫進展至500mm所需時間，以建立一套完整疲勞強度分析流程。 In this paper, we investigate on a more than 100.000 DWI bulk carrier. There was a fatigue crack appearing in a butt welded outer plate during a sail. According to the spirit of the ”Peak Rate Method” of SR (Japan), it is applied to the analysis of fatigue strength of the bulk carrier, including the seakeeping analysis, long-term distribution of load, finite element analysis, long-term distribution of stress, and estimation of the fatigue life. In addition, in order to build up a complete analysis procedure of fatigue strength. we combined the result of the analysis of fatigue strength which coordinates with the normal spectrum method, with the results of fatigue tests focusing on the welded outer plate specimen with fatigue crack to analyze the long-term fatigue life of the welded breach of the bulk carrier and the short-term fatigue life under the abominable sea voyage (if the wave-high is 8m high). Then we can calculate the time of the welded crack expand to 500mm under the abominable sea voyage by using the da/dN curve.