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Loading Analysis of Composite Wind Turbine Blade for Fatigue Life Prediction of Adhesively Bonded Root Joint Davood Salimi-Majd & Vahid Azimzadeh & Bijan Mohammadi

# Springer Science+Business Media Dordrecht 2014

Abstract Nowadays wind energy is widely used as a non-polluting cost-effective renewable energy resource. During the lifetime of a composite wind turbine which is about 20 years, the rotor blades are subjected to different cyclic loads such as aerodynamics, centrifugal and gravitational forces. These loading conditions, cause to fatigue failure of the blade at the adhesively bonded root joint, where the highest bending moments will occur and consequently, is the most critical zone of the blade. So it is important to estimate the fatigue life of the root joint. The cohesive zone model is one of the best methods for prediction of initiation and propagation of debonding at the root joint. The advantage of this method is the possibility of modeling the debonding without any requirement to the remeshing. However in order to use this approach, it is necessary to analyze the cyclic loading condition at the root joint. For this purpose after implementing a cohesive interface element in the Ansys finite element software, one blade of a horizontal axis wind turbine with 46 m rotor diameter was modelled in full scale. Then after applying loads on the blade under different condition of the blade in a full rotation, the critical condition of the blade is obtained based on the delamination index and also the load ratio on the root joint in fatigue cycles is calculated. These data are the inputs for fatigue damage growth analysis of the root joint by using CZM approach that will be investigated in future work. Keywords Wind turbine blade . Delaminationindex . Cohesive zone model . Fatigue debonding . Load ratio

1 Introduction The size of wind turbine blades has been increased in the past decade due to improve efficiency. The increasing of resulting mass leads to high bending moments at the inner part of the blade. Composite materials due to high strength and stiffness to their weight ratio are commonly used in wind turbine blade structures. So that blades of horizontal axis wind turbines (HAWT) are now completely made of composites. It is approximated that 108 load cycles will happen in the prospected lifetime of a composite wind turbine which is about D. Salimi-Majd : V. Azimzadeh : B. Mohammadi (*) School of Mechanical Engineering, Iran University of Science & Technology, Tehran, Iran e-mail: [email protected]

Appl Compos Mater

20 years. During the life of a composite wind turbine, the rotor blades are subjected to different cyclic loads such as aerodynamics, gyroscopic, centrifugal and gravitational forces. The details of calculating these loads can be found in Rajadurai et al. researches [1–3]. These loading conditions, cause to fatigue failure of the composite blade and its adhesively bonded root joint. So in order to estimate the cost effectiveness of a wind turbine, the fatigue life of wind turbine