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As any structure ages, its structural characteristics will also change. The goal of this work was to determine if modal response data from a wind turbine could be used in the detection of damage. The input stimuli to the wind turbine were fiom traditional modal hammer input and natural wind excitation. The structural response data was acquired using accelerometers mounted on the rotor of a parked and undamaged horizontal-axis wind turbine. The bolts at the root of one of the three blades were then loosened to simulate a damaged blade. The structural response data of the rotor was again recorded. The undamaged and damage-simulated datasets were compared using existing damage detection algorithms. Also, a novel algorithm for combining the results of different damage detection algorithms was utilized in the assessment of the data. This paper summarizes the code development and discusses some preliminary damage detection results.

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Bolted connections are the most common method used to fasten together two or more structural elements. After fatigue, self-loosening is the most frequent cause of failure of dynamically loaded bolted connections. Bolted connections experience self-loosening due to relative motion between the thread flanks and between other contact surfaces of the clamped or clamping elements. If the relative motions are eliminated, then no dynamic self-loosening can occur. It is found that the relative transverse motion d at a bolted connection is directly related to the preload Q and the transverse force F applied to the bolt. As a basis for the study of bolt self-loosening, a model of thread slipping is established, and relationships between Q, F and d are theoretically derived. It is found that the stiffness of the bolt threads is approximately parabolic. Due to this nonlinear relationship between Q and d, it is found that the relationship between F and d is also nonlinear. For a given set of geometrical and material parameters, the critical transverse force Fcr (i.e., the minimum force needed to make the threads slip) can be predicted. Experiments are run and though the results are obscured by the presence of other effects including sliding friction between the clamped parts and bending of the bolt body, it seems that qualitative agreement exists between the theoretical model and a physical system. The results presented in this work serve as the preliminaries to the development of a model of the dynamic self-loosening of bolted connections and, as such, offer an insight into the mechanisms that lead to self-loosening. Additionally, these results offer clues regarding methods that could be used to prevent bolted connection failures.