NEW METHODS FOR ULTRASONIC NDE OF DIFFICULT MATERIALS

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In many engineering applications, materials that exhibit heterogeneous or otherwise acoustically scattering microstructure are employed, examples include austenitic steels and alloys, concrete and fibre reinforced composites. In ultrasonic non destructive evaluation (NDE) of such highly scattering media, the defect target signal is frequently obscured by clutter echoes, caused by numerous, relatively small (relative to the ultrasonic wavelengths), stationary reflectors, which form part of the internal microstructure of the material. The extent of this clutter can be significant and even defects that are larger than these randomly scattering regions can be difficult to detect. This type of time-invariant clutter noise cannot be reduced by the standard time averaging or correlation techniques that are used to reduce time varying random electrical noise. Accordingly, defect identification invariably involves a compromise between achievable resolution, which is determined partly by wavelength in the material, and the noise arising from scattering in the propagation medium. This project will investigate a range of methods for improved ultrasonic NDE of difficult materials. The approach will involve a combination of ultrasonic beam modelling, novel transducer design and array signal processing methods.