| Abstract [eng] |
In most industrial and household applications, such as renewable energy applications (wind and tidal power plants), pipelines and storage tanks, construction industry, structures in the ground, water and aerospace applications are constructed from composite materials. Composite materials are used rather intensively due to their lightweight, high compressive and tensile strengths, high stiffness and low density, flexibility, lower maintenance and non-corrosive nature. In spite of all favorable features and a wide range of applications the composites contain, the failure in the components of composite structures may occur either in-service or during the manufacturing procedures. Many non-destructive testing (NDT) methods have been developed for the identification, location and estimation of defects in structures such as ultrasonic testing, radiographic testing, electromagnetic testing, etc. Among all the available NDT techniques, ultrasonic guided wave (GW) testing has been the most promising due to its high sensitivity to the defects and wide coverage region The possible mechanisms that may occur during the interaction of ultrasonic GW with the layered structure of composites are reflection or refraction of wave modes, scattering and mode conversions. It increases the complexity in the received ultrasonic signals so that the extraction of defects-related information becomes very complicated which can be overcome by applying an appropriate measurement and signal processing techniques. Two flexible and cost-effective contact-type measurement techniques in pitch-catch mode and based on short-distance and long-distance GWs for the detection and estimation of the disbond-type defects in smaller and larger multi-layered composite structures. Moreover, the application of a particular set of various signal-processing techniques for de-noising and post-processing the experimental signals are also proposed which improves the accuracy of defect estimation. There are very innovative and novel results in the dissertations which are according to me are as follows: The developed measurement techniques enabling to detect disbond type defects in multi-layered composite materials. The proposed 2D analytical model allows obtaining directivity patterns of contact type ultrasonic transducers at any distance in dispersive media. The signal processing techniques enabling the extraction of defect parameters from a single experimental B-scan. The developed ultrasonic non-destructive testing technique which enables to detect the defect as small as 2 mm using guided waves. The critical evaluation of the research work was presented during the period of dissertation by the scientific community have been certified by 11 publications: 7 articles are published in international journals referred in Thomson Reuters ISI Web of Science (with impact factor), while other 4 publications are published in the reviewed proceedings of international conferences indexed in Thomson Reuters ISI Web of Science (without impact factor). |
