This paper presents the experimental results of active-sensing structural health monitoring (SHM) techniques, which utilize piezoelectric transducers as sensors and actuators, for determining the structural integrity of wind turbine blades. Specifically, Lamb wave propagations and frequency response functions at high frequency ranges are used to estimate the condition of wind turbine blades. For experiments, a 1？m section of a CX-100 blade is used. The goal of this study is to assess and compare the performance of each method in identifying incipient damage with a consideration given to field deployability. Overall, these methods yielded a sufficient damage detection capability to warrant further investigation. This paper also summarizes the SHM results of a full-scale fatigue test of a 9？m CX-100 blade using piezoelectric active sensors. This paper outlines considerations needed to design such SHM systems, experimental procedures and results, and additional issues that can be used as guidelines for future investigations. 1. Introduction Wind turbines are becoming a larger source of renewable energy in the world. The US government projects that 20% of the US electrical supply could be produced via wind power by 2030 . To achieve this goal, the turbine manufacturers have been increasing the size of the turbine blades, often made of composite materials, to maximize power output. As a result of severe wind loadings and the material level flaws in composite structures, blade failure has been a more common occurrence in the wind industry. Monitoring the structural health of the turbine blades is particularly important as they account for 15–20% of the total turbine cost. In addition, blade damage is the most expensive type of damage to repair and can cause serious secondary damage to the wind turbine system due to rotating imbalance created during blade failure. Therefore, it is imperative that a structural health monitoring (SHM) system be incorporated into the design of the wind turbines in order to monitor flaws before they lead to a catastrophic failure. There has been a considerable research effort focused on applying SHM techniques on wind turbine blades [2, 3]. However, most of these studies focus on a single technique for damage detection; consequently very little work has been done to compare the results of multiple active-sensing techniques. Thus, the goal of this study is to assess the relative performance of high-frequency SHM techniques, namely, Lamb wave propagation and frequency response functions (FRFs), as a way to nondestructively
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