Failure Investigation of the Wind Turbine Blade Root Bolt
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TECHNICAL ARTICLE—PEER-REVIEWED
Failure Investigation of the Wind Turbine Blade Root Bolt Donghuan Liu • Xinchun Shang
Submitted: 22 October 2012 / in revised form: 22 January 2013 / Published online: 15 March 2013 ASM International 2013
Abstract The failure analysis of the high-strength bolt at root position of the wind turbine blade was conducted to find the cause of fracture. Detailed investigations using several characterization techniques such as stress calculation, chemical composition test, mechanical property test, metallurgical investigation, and fractography analysis were performed to identify the cause of the bolt failure. Based on the theoretical calculation and failure analysis, it could be concluded that the bolt failed by fatigue accelerated by stress concentration while under low temperature. Practical suggestions were also given to avoid similar failures. Keywords Failure analysis High-strength bolt Wind turbine blade Fractography Stress concentration
Introduction Wind power generation has rapidly spread in recent years as one of the clean energy resources. The sizes of the wind turbines have become larger and larger because of the low energy density of the wind. At the same time, the wind turbines have been installed on the sea or mountainous areas, where the temperature is very low at winter seasons, to increase the efficiency. This tendency creates difficulties in the maintenance of the turbines and the bolts that connect the turbine blades with the flanges [1]. The reported failures of the wind turbine blade root bolts in this article occurred at a wind farm of Inner Mongolia province of the
D. Liu (&) X. Shang Department of Applied Mechanics, University of Science and Technology Beijing, Beijing 100083, People’s Republic of China e-mail: [email protected]
People’s Republic of China. After just 3 years of performance, the root bolts of the turbine blade suddenly were broken, and the blade fell off to the ground. The components of the blade/bearing/hub bolted joint are shown in Fig. 1. The dimension of the blade bearing is 945 mm 9 1255 mm 9 130 mm, and it is assembled to the blade by means of M24 10.9 class bolts equally distributed along its inner ring. The total number of the bolts is 48. The bearing’s inner ring bolts connect the blade, the bearing’s inner ring, the torque plate, and the stiffening plate. Many researchers have devoted a great deal of time to the failure analysis of bolts and such engineering components. The application of both optical microscopy and scanning electron microscopy (SEM) has been quite useful in characterizing microstructures of failed engineering components during recent years [2–10]. This article describes the failure analysis of the turbine blade root highstrength bolt. The main purpose of this article is to find the root cause of the fracture and make suggestions to avoid similar accidents.
Stress Analysis Stress calculation and analysis of bolts under working conditions are given in this section. Blade Force Analysis The blade and its 48 M2
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