Low-frequency Vibration Inspection of Sandwich Composites

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One-sided in-service inspection of certain composite structures (honeycomb-, balsa- and foam-core sandwich) can be successful using a low-frequency vibration method but defect detection is limited, and classification of defects is not currently supported. Data-acquisition equipment had hardly advanced in 20 years, bar moving from analogue to digital, until the new 'Bondcheck' bond testing system from Baugh and Weedon. This offers full-waveform capture at every location, with the potential to expand to an array of sensors, opening up greater potential for structure analysis algorithms and comparison with modelled responses.Prior work has showed the potential for improved pitch-catch probe design to enhance the resolution and frequency range, whilst the use of full-frequency capture offered the potential for defect classification, depth and size estimation. This project will use low-frequency vibration to classify defects in sandwich composites and determine their depth, location and size, based on comparison with the modelled low-frequency (5 kHz -100 kHz) responses of a range of structures with different defect types. Bristol has considerable experience of both acoustic modelling and inversion methods using modelled responses. For this project a database method coupled with multi-dimensional optimisation to invert the data and determine the type and 3D location of defects will be used initially, with potential for refinement of the method in a variety of ways.The student will be based at the Ultrasonics and Non-Destructive Testing Group at the University of Bristol before relocating to the Baugh & Weedon's offices in Hereford.