Remaining life assessment method of fatigue crack propagation in a double hull ship structure

船舶结构构件在服役检查中可能会发现疲劳裂纹，为了防止船舶的瞬时失效以及关键舱室的油和/或水密性等使用性能的丧失，对其适用性进行了研究。讨论了双层船体结构的疲劳裂纹扩展特性和剩余寿命评估。为了检验从业人员计算的局部应力可能发生的变化，对船舶结构细节进行了有限元比较研究。结果表明，壳单元模型计算结果具有较高的相关性，但其局部应力值明显低于试验和实体单元计算结果。针对三维疲劳裂纹的分析，提出了一种新的数值与解析相结合的权函数法来确定船舶结构细部的应力强度因子，该方法被证明是一种更为有效的疲劳裂纹分析方法。讨论了一种先进的剩余寿命评估数值模拟方法，该方法精确地考虑了焊接残余应力、结构冗余和弯曲裂纹扩展的影响。模拟的裂纹路径和疲劳裂纹扩展寿命与试验结果吻合较好。对双层底部结构内底板关键部位检测到的裂纹进行了疲劳剩余寿命评估，并基于断裂力学方法计算了其剩余寿命。为了实现疲劳强度分析和疲劳裂纹扩展分析所必需的高效、鲁棒的有限元网格生成，采用了铺装法和区域组成法。此外，还提出了一种预测弯曲裂纹扩展的先进计算方法。为了提高在役船舶的安全性和维护性，提出了船舶结构损伤信息系统的概念。少

The fitness for serviceability of structural members of ships, in which fatigue cracks could be found during in-service inspection, is investigated in order to prevent instantaneous failures of ships as well as the loss of serviceability such as oil and/or water tightness of critical compartments. The characteristics of fatigue crack propagation and the remaining life assessment of double hull ship structures are discussed.A finite element comparative study of ship structural detail has been carried out in order to examine the possible variations of calculated local stress by practitioners. It is found that the results of shell element models have high correlation with each other, but give significantly lower local stress than experimental and solid element results. With regard to the analysis of 3-D cracks, a new combined numerical and analytical weight function method is proposed for the determination of stress intensity factors in ship structural details, which is proved to be a ver … More y efficient method for fatigue crack analysis. Discussions are also made for an advanced numerical simulation method for the remaining life assessment, in which the effects of welding residual stresses, structural redundancy, and curved crack propagation are precisely taken into account. The simulated crack paths and the fatigue crack propagation lives are in fairly good agreement with the experimental results.The fatigue remaining life assessment is demonstrated for cracks detected in the critical parts of the inner bottom plate of a double bottom structure, where the remaining life is calculated based on the fracture mechanics approach. The paving method and the domain composition method are implemented for the efficient and robust finite element mesh generation which is essential for fatigue strength analysis and fatigue crack propagation analyis. Also, an advanced computational method has been developed for the prediction of curved crack growth. A concept of the information system for damages of ship structures is proposed for the improved safety and maintenance of ships in service. Less