Fatigue damage in marine structures is generally assessed by means of stress−number of cycles (S−N) curves. These curves are obtained from many experimental tests on structural components. Fracture mechanics (FM), using the crack propagation method is also a practical technique. In this approach, fatigue damage is estimated based on crack propagation from an initial crack size through the surface and depth of structural members. In this paper, S−N curves based on FM were compared with S−N curves obtained following two standards: DNVGL-RP-C203 and API-RP2A-WSD. The results showed that the curves did not agree well. Therefore, to obtain better fitting, calibration factors are needed. From S−N curves established for two stages, two calibration factors – α₁ (for the first stage) and α₂ (for the second stage) – are proposed for fitting S−N curves based on the FM approach with the DNV GL and the API S−N curves. The wall thickness, the initial crack depth and the critical crack depth were found to have a significant effect on determination of the calibration factors.

中文翻译：

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海上结构疲劳损伤校准因素研究

海洋结构中的疲劳损伤通常通过应力-循环次数 ( S - N ) 曲线进行评估。这些曲线是从对结构部件的许多实验测试中获得的。使用裂纹扩展方法的断裂力学 (FM) 也是一种实用技术。在这种方法中，疲劳损伤是根据从初始裂纹尺寸到结构构件表面和深度的裂纹扩展来估计的。本文将基于 FM 的S − N曲线与S − N曲线获得以下两个标准：DNVGL-RP-C203 和 API-RP2A-WSD。结果表明曲线不一致。因此，为了获得更好的拟合，需要校准因子。从小号- ñ -为两个阶段，两个校准因子建立曲线α ₁（第一级）和α ₂（用于第二级） -提出用于装配小号- ñ基于与DNV GL和FM的方法的曲线API S - N曲线。发现壁厚、初始裂纹深度和临界裂纹深度对校准因子的确定有显着影响。