Health Monitoring of Composite Structures by Combining Ultrasonic Wave Data

With the growing size of large-scale structures, composite materials are being increasingly used due to their high strength-to-weight ratio. As structures get larger, so too does the necessity for a robust health monitoring system; a well-founded and reliable method of doing so is by monitoring acoustic emissions. However, such a method encounters significant problems when employed on composite structures; such as high dispersion of extensional modes, propagation distance-dependent wave velocity and highly subjective characteristic frequencies of failure modes. Ultrasonic guided waves offer the abilities of location and severity detection to a more accurate level, whereas acoustic emission involves a more efficient passive approach. By analysis of ultrasonic waves in a carbon-fibre-reinforced-polymer (CFRP) plate, information is show here that will provide the stepping stones for the development of a robust health monitoring system for composite structures using ultrasonic guided waves. Advanced signal processing is used to show information on selected features of an acoustic burst as it propagates through the composite material, as well as how damage affects these features. It was found that both the energy of the burst and the first asymmetric mode are affected by the orientation of fibres in a composite, although in differing ways. However, the time of flight of an acoustic burst is unaffected. Subsequently, damage affects all of the above mentioned features, and this knowledge can be utilised to identify damage. Finally, the one-dimensional propagation of a wave along the length of the fibres is tested against various statistical-based models to showcase the potential of this method for use in modelling the propagation of an acoustic wave in a composite material.