Thick weldments used in offshore structures frequently act as fatigue crack initiation sites due to stress concentration at weld toe as well as weld residual stress fields. This paper investigates the cyclic deformation behavior of S355 G10+M steel, which is predominantly used in offshore wind applications. Owing to the vast size difference of monopile structure and weld cross‐section, a global–local finite element (FE) method was used, and the weld geometry was adopted from circumferential weld joints used in offshore wind turbine monopile foundations. Realistic service loads collected using supervisory control and data acquisition (SCADA) and wave buoy techniques were used in the FE model. A nonlinear isotropic–kinematic hardening model was calibrated using the strain controlled cyclic deformation results obtained from base metal (BM) as well as cross‐weld specimen tests. The tests revealed that the S355 G10+M BM and weld metal (WM) undergo continuous cyclic stress relaxation. Fatigue damage over a period of 20 years of operation was predicted using the local stress at the root of the weldments as the life limiting criterion. This study helps in quantifying the level of conservatism in the current monopile design approaches and has implications towards making wind energy more economic.

中文翻译：

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单桩焊件在工况下的性能及疲劳损伤预测

由于在焊趾处的应力集中以及焊缝残余应力场，用于海上结构的厚焊件经常充当疲劳裂纹的起始点。本文研究了主要用于海上风力发电的S355 G10 + M钢的循环变形行为。由于单体桩结构和焊缝横截面的尺寸差异很大，因此采用了全局局部有限元（FE）方法，并且采用了海上风力发电机单体桩基础中使用的圆周焊缝的焊缝几何形状。在有限元模型中使用了通过监督控制和数据采集（SCADA）以及浮标技术收集的实际服务负荷。使用从母材（BM）以及交叉焊接试样测试获得的应变控制的循环变形结果，校准了非线性各向同性的运动硬化模型。测试表明，S355 G10 + M BM和焊接金属（WM）经历了连续的循环应力松弛。使用焊件根部的局部应力作为寿命限制标准，可以预测在使用20年后的疲劳损伤。这项研究有助于量化当前单桩设计方法中的保守程度，并且对使风能更经济具有启示意义。使用焊件根部的局部应力作为寿命限制标准，可以预测在使用20年后的疲劳损伤。这项研究有助于量化当前单桩设计方法中的保守程度，并且对使风能更经济具有启示意义。使用焊件根部的局部应力作为寿命限制标准，可以预测在使用20年后的疲劳损伤。这项研究有助于量化当前单桩设计方法中的保守程度，并且对使风能更经济具有启示意义。