New highly-sensitive and non-contact methods for acoustic recognition and imaging of defects in composites

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The requirements and standards of quality assurance for materials and industrial components continue to be upgraded constantly to meet the ever-growing demands for reliability and safety in modern engineering systems.The project is aimed at enhancing efficiency and sensitivity of acoustic NDT techniques by using the concept of a local resonance of defects. The novelty of the proposed approach is that it provides a selective acoustic excitation and energy delivery from the wave directly to the defect via its mechanical resonance. By frequency match between a probing ultrasonic wave and the defect resonance, a substantial enhancement in efficiency and sensitivity of ultrasonic NDT techniques is validated. A significant improvement is expected for the family of prospective ultrasound-activated effects (nonlinear, thermal, etc.) which are usually comparatively inefficient so that the corresponding NDT and imaging techniques require an elevated acoustic power and specific instrumentation adapted to high-power ultrasonics. The project is concerned with development of the resonance and non-contact versions for the techniques of nonlinear ultrasonics and ultrasonic thermography (thermosonics) with advanced efficiency that enables to avoid high-power apparatuses and use conventional low-energy NDT equipment instead.To this end, a detailed theoretical analysis and numerical modelling of the local resonance-induced phenomena will be given for basic types of defects in composite materials. The simulation will include both linear and nonlinear resonant modes of defects to be applied for a comprehensive vibration spectrum analysis, the models of frictional heating to address a resonant acousto-thermal conversion.The experimental methodologies to be used for recognition of the defect resonance combine an acoustic (both contact and non/contact) excitation with monitoring a local vibration pattern and a defect thermal response by means of scanning laser vibrometry and IR-camera. A resonance amplification of defect vibrations results in a strong nonlinear defect response and a local spectral conversion. The nonlinear resonance modes to be studied and applied for a highly-sensitive defect recognition and imaging will include sub- and super-harmonic parametric resonances. The advantages of resonance ultrasonic thermography with an enhanced thermal response of defects will be elaborated and experimentally analysed for both linear and nonlinear vibration modes. A special emphasis will be given to investigation of non-contact resonance techniques with objective to create the methods which combine benefits of resonant approach with simplicity of conventional ultrasonic probing.The implementation of the project will result in substantial improvement of acoustic technologies for NDT and imaging of flaws in composite materials relevant to automotive, aviation and aerospace industries.