• Engineer, Bhavin
• Courtney, Charles
• Hernandez-Crespo, Borja

Abstract

In recent years, guided wave technology has been successfully used to inspect and monitor metallic structures, such as pipes, in order to detect cracks and corrosion. Commercial systems have been released to assess the integrity of metallic (isotropic) structures; however commercial applications for anisotropic materials, such as composites, have not been widely established. The increase of complexity of the wave propagation and the fact that composite structures are composed by areas of different lay-ups, different material properties and thicknesses hinders its applicability.<br/>Guided waves are ultrasonic elastic waves that propagate in solid media. The phase and group velocity of these waves are not necessarily the same and they can vary according to the frequency, thickness and material properties. This relationship between velocity and frequency for a given structure is commonly displayed in graphs called dispersion curves. Dispersion curves are an important tool for the analysis and design of any guided wave application. These curves provide key information about the propagation characteristics of each wave mode and enable the study of signal processing techniques, the creation of new transducer arrays and the development of damage detection techniques. Therefore, the first step for the deployment of any guided wave application is to know the dispersion curves of the structure to inspect. For the case of complex anisotropic structures, like wind turbine blades, the theoretical creation of dispersion curves is challenging and time-consuming. So in this paper, a new experimental methodology is presented to create the dispersion curves directly from the specimen that is going to be inspected. A phased array is developed as a pulser/receiver in order to determine the phase velocity of the fundamental wave modes. The proposed technique is explained in detail and analytical and experimental analyses are presented for an aluminium plate in order to validate the method with a simple structure. Using this method for composite structures and its feasibility is also discussed.<br/>

Topics

• impedance spectroscopy
• dispersion
• corrosion
• phase
• aluminium
• crack
• anisotropic
• composite
• ultrasonic
• isotropic
• ultraviolet photoelectron spectroscopy