The use of bolted joints to connect the transition piece and monopile is nowadays widely applied in the offshore wind industry. Traditionally, grouted connections were used in the early generation of offshore wind turbines, but the experienced failures in such connections led to an increased tendency towards bolted flange connections to join the transition piece and monopile in the new generation of offshore wind turbines. The bolts used for this purpose have high strength and huge sizes, and are subjected to a preload that is applied during the tightening process. The present study is focused on the analysis of preload effects on stress distribution in M72 bolted connections by considering different friction coefficients between the bolt and nut threads. The bolt is considered to be made of grade 10.9 steel, whereas the nut is assumed to be made of grade 8.8 steel, which is a softer material. Using the finite element commercial software package Abaqus, numerical models were developed and analysed to establish trends for stress distribution and plastic strains during the bolt tightening process, and to quantify stress concentration factors in individual engaged threads.

中文翻译：

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海上风力发电机M72螺栓连接应力分布的数值分析

如今，使用螺栓连接来连接过渡件和单体桩已广泛应用于海上风电行业。传统上，灌浆连接被用于早期的海上风力涡轮机中，但是这种连接中经历的故障导致了螺栓法兰连接越来越多地趋向于连接过渡件并在新一代海上风力涡轮机中独占。用于此目的的螺栓具有很高的强度和较大的尺寸，并承受在拧紧过程中施加的预紧力。本研究着重于通过考虑螺栓和螺母螺纹之间的不同摩擦系数来分析预紧力对M72螺栓连接中应力分布的影响。该螺栓被认为由10.9级钢制成，假定螺母是由8.8级钢制成的，这是一种较软的材料。使用有限元商业软件包Abaqus，开发并分析了数值模型，以建立螺栓拧紧过程中应力分布和塑性应变的趋势，并量化各个啮合螺纹中的应力集中系数。