A Study of the Nonlinear Attenuation Behavior of Preload in the Bolt Fastening Process for Offshore Wind Turbine Blades Using Ultrasonic Technology

Jia Han, Ke Xie, Zhaohui Yang (), Lin’an Li and Ming Zhao
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Jia Han: CSSC Haizhuang Wind Power Co., Ltd., Chongqing 401122, China
Ke Xie: CSSC Haizhuang Wind Power Co., Ltd., Chongqing 401122, China
Zhaohui Yang: School of Aeronautics, Northwestern Polytechnical University, Xi’an 710072, China
Lin’an Li: School of Mechanical Engineering, Tianjin University, Tianjin 300072, China
Ming Zhao: School of Mechanical Engineering, Tianjin University, Tianjin 300072, China

Energies, 2025, vol. 18, issue 12, 1-15

Abstract: The attenuation of bolt preload is a critical factor leading to bolt fatigue failure, whereas the study of the nonlinear attenuation behavior of preload and its mechanism during installation is an inevitable challenge in engineering practice. The attenuation of the preload of a bolt is mainly related to the stiffness of the bolt body as well as the stiffness of the connected parts. This study aimed to develop an experimental system to analyze the nonlinear attenuation behavior of preload during bolt tightening. First, a simulation system replicating the bolt installation process was constructed in a laboratory setting, incorporating blade and pitch bearing specimens identical to those used in a 10 MW wind turbine, restoring the stiffness coupling characteristics of the “composite-metal bearing” heterogeneous interface at the blade root through a 1:1 full-scale simulation system for the first time. Second, ultrasonic preload measurement equipment was employed to monitor preload variations during the bolt tightening process. Finally, the instantaneous preload decay rate of the wind turbine blade-root bolts and the over-draw coefficient were quantified. Experiments have shown that the preload decay rate of commonly used M36 leaf root bolts is 11–16%. If a more precise value is required, each bolt needs to be calibrated. These findings provide valuable insights for optimizing bolt installation procedures, enabling precise preload control to mitigate fatigue failures caused by abnormal preload attenuation.

Keywords: blade-root bolt; preload; instantaneous preload decay rate; over-draw coefficient (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2025
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