Damage detection in a laboratory wind turbine blade using techniques of ultrasonic NDT and SHM

Abstract

This paper presents a case study in the use of ultrasonic NDE/SHM techniques for detecting and locating damage in a real (but small) wind turbine blade.Two techniques are considered: (1) non-linear acoustics, and (2) guided-wave "pitch-catch" SHM. While the non-linear acoustics approach proved disappointingly insensitive to damage induced experimentally in the blade, the guided-wave approach not only detected the damage but also proved capable of locating it, using a "network of novelty detectors" methodology. A first, slightly ill-conceived, programme of guided-wave tests actually provided valuable insight into attenuation of waves in the structure of interest and supported the idea that actuator-sensor networks of a feasible density could be used for wind turbine blade SHM. KEYWORDS guided wave-based SHM, non-linear acoustics, structural health monitoring (SHM), wind turbine blades Strain. 2018;54:e12290.wileyonlinelibrary.com/journal/str of the total electricity costs from a wind turbine. One effective way forward is to reduce the life cycle costs and to extend the life of the wind turbine structure by the application of SHM.The second reason for the choice of structure here relates to a serious issue in the application of ultrasonic wave-based SHM to WT blades. WT blades are very large structures, with current generations of blades approaching 100 m in length. Furthermore, blades are typically manufactured from composite materials, which are known to have high levels of attenuation for ultrasonic waves. Clearly, a limitation of the use of guided-wave SHM is the density of the sensor/actuator network needed; if too high a sensor/actuator density is needed, then ultrasonic SHM is infeasible. This project allowed an investigation into the degree of attenuation experienced by a guided-wave SHM system implemented on a structure manufactured from realistic material.Another difference in the current study was the damage mechanism investigated. In Yang et al., [2,3] single fatigue cracks were initiated and propagated in the glass and composite plates under fairly ideal laboratory fatigue test conditions. In the current study, it was decided to generate the damage via a more realistic mechanism. It is widely accepted that fibre-reinforced polymer-based wind turbine blades are susceptible to low velocity impact damage, e.g., from hail or birdstrike. The low velocity impact often causes internal damage and is usually barely detectable by eye. This damage although small may propagate to more severe damage and eventually cause failure of the structure without warning. The damage in the WT blade of this study was generated using a hammer impact.In summary, this paper presents damage detection on an wind turbine blade exposed to impact, by using modal analysis, non-linear acoustics, and guided-wave SHM. The layout of the paper is as follows. Section 2 presents the results of an experimental modal analysis of the WT blade; this provided useful information in designing the subsequent programme of SHM activity. Section 3 prese...

A Comprehensive Analysis of Wind Turbine Blade Damage

“…For the detection of faults, several mathematical and, recently, artificial intelligence methods have been proposed, aiming to overcome the noise introduced by the composite material and, of course, the complex geometry. The most popular studies are based on wavelet transform and pattern recognition [84], guided wave with signal processing [85], signal-to-noise processing [86] and simple harmonic motion analysis [87].…”

A Robot-Assisted Large-Scale Inspection of Wind Turbine Blades in Manufacturing Using an Autonomous Mobile Manipulator

“…The cells at positions (9,4) and (7,8) are left-hand driving cells. The cells at (8,4) and (8,8) do not feature a specific type, since they had no neighbored cell of interest when they were expanded. In Figure 5b, the The start cell for the planning procedure is set to the middle of the corridor zone.…”

“…Imperfections in the alignment of the structure or during the fiber reinforcement change the structural properties and thus reduce the quality of the composite material. Currently, such imperfections are detected with help of ultrasonic [4,5], thermal [6,7], or radar [8,9] techniques, whereby a differentiation has to be made in pre-and post-resin-injection inspections. If an imperfection is detected after the resin injection, no corrections are possible, and the component is, therefore, a reject.…”

Analysis of Modal Parameters Using a Statistical Approach for Condition Monitoring of the Wind Turbine Blade

“…[16,17]. Many of these methods are only applicable in laboratory conditions due to the high accuracy of the measurement, time-consumption of the measurement and calculation or complex measurement equipment required [18].…”