海洋结构物疲劳裂纹扩展寿命的一种工程预报方法

海洋结构物疲劳寿命的准确预报对海洋结构安全具有重要意义。基于裂纹扩展的寿命预报相比于常规的基于累积损伤理论的寿命预报方法，能够考虑载荷次序、初始缺陷等重要因素的影响，各大船级社极力推进裂纹扩展理论在海洋工程中的应用。文章从裂纹扩展法则、应力强度因子求解、疲劳载荷谱模拟上对裂纹扩展理论的工程应用进行研究，试图找出准确、合理且相对简单的方法。结合裂纹扩展的单一曲线模型、基于有限元子模型技术的应力强度因子求法以及基于谱分析的疲劳载荷谱产生方法，对某半潜式钻井平台典型焊接节点进行基于裂纹扩展疲劳寿命预报，并讨论了初始裂纹尺寸对疲劳寿命的影响。结果表明，该半潜平台焊接结构符合设计寿命的要求，初始裂纹尺寸对疲劳寿命影响很大，可为海洋结构物基于裂纹扩展的疲劳寿命预报提供参考。

An Engineering Method to Predict Fatigue Crack Propagation Life for Marine Structures

Accurate prediction of fatigue life is important for the safety of marine structures. Com-paring with traditional methods based on Cumulative Fatigue Damage (CFD) theory, life prediction based on Fatigue Crack Propagation (FCP) can take the key factors, like load sequence and initial defects, into consideration. This makes the major classification societies strongly promote the appli-cation of FCP theory in ocean engineering. This paper investigated the engineering method of fatigue life prediction based on FCP from three aspects, namely crack propagation law, calculation of Stress Intensity Factor (SIF) and generation of fatigue load spectrum. The aim was to find an accurate, ra-tional and relatively simple method. By using the unique curve model, the technology of sub-model to calculate SIF and the method to generate fatigue load spectrum based on spectral analysis, the crack propagation life of a typical fatigue hot spot of a semi-submersible platform was predicted and then the effect of initial crack size was discussed. The results showed the discussed hot spot met the requirement of design life. And initial crack size of the surface crack affected the fatigue life a lot. The method proposed in this paper may provide a reference for accurate prediction of fatigue life of marine structures.