| Summary: | This thesis investigates guided wave ultrasonic damage detection under different environments relevant to aerospace applications. The survivability of airborne SHM components are investigated, and damage detection techniques for a range of extreme environmental conditions are proposed, with emphasis on carbon fibre reinforced polymers (CFRP) and piezoelectric transducers. To assess the robustness and integrity of the transducers, a set of environmental test profiles are developed which are relevant to airborne electronics. The performance of commercially available and manufactured transducers are investigated when exposed to the test profiles. Transducer types found to be robust to these conditions are used for developing damage localisation approaches under extreme conditions. Transducer arrangement is also an important factor in accurate damage localisation. A method for optimal transducer placement is presented, finding the largest coverage area with a limited number of transducers while still achieving accurate damage localisation. The main novelties are the ability to account for the presence of stiffeners, incorporating different damage types and transducer failure. Two methods for damage detection under varying operational conditions are presented: instantaneous baseline and temperature compensation. Both developed methods use the delay-and-sum approach, without the need for a large library of baseline signals. The developed temperature compensation method, reduces the non-damage related environmental residual by applying stretch based correction. The novelty is in accurate damage localisation over a large temperature range with only one baseline by using a range of stretch factors. The instantaneous baseline method exploits symmetry of the transducer network to record baselines at the same instant as interrogation, under the same conditions. This allows accurate damage localisation without the need for sets of baseline signals or temperature compensation in isotropic and quasi-isotropic material. Both of these methods are verified experimentally for detection of a crack in an aluminium plate, barely visible impact damage (BVID) in CFRP plates and a stiffened fuselage panel.
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