Foreword
Bolted connections are a crucial assembly method in wind turbine generator assembly, affecting almost all components. Therefore, the selection and strength verification of bolts are essential guarantees for the reliability of wind turbine generators.
With the rapid development of my country's wind power industry and the continuous decline in wind power generation costs, the price of wind turbine units has also decreased, leading to a fierce price war among major wind power equipment assembly companies. Ensuring the quality of wind turbine units while reducing costs has become a critical issue for all wind power companies. Bolts, as essential connecting components in wind power equipment, present one of the main challenges to cost reduction in the design process of wind turbine units due to the inherent uncertainties in their characteristics.
1. Current status of bolted connections
Currently, bolt failure issues in my country's wind turbines are already evident in the high-strength bolts connecting the tower flanges. The main failure modes are: stripping, twisting, yielding, and even tensile breakage during installation; bolt breakage during equipment operation, threatening turbine operation, and in severe cases, even causing the wind turbine to collapse. (Wind power materials and equipment)
The reasons for these problems with high-strength bolts in towers, besides the substandard quality of the bolts themselves, also include insufficient theoretical and practical knowledge in the design process.
2. Main methods of bolt verification
At present, people mainly use two methods to design and verify the reliability of bolts: finite element software analysis and scientific calculation.
In the process of analysis using finite element software [1], we can apply preload through direct loading, equivalent force, equivalent strain, and equivalent temperature methods. However, these loading methods either cannot transfer shear stress, cannot simulate the frictional behavior between bolts and connected parts in reality, and cannot consider the preload loss caused by nut loosening. This results in excessive bolt stress in actual finite element simulations, and therefore, they are generally not used as a means of checking the bolt structure of wind turbine generators.
