Custom made electrostatic transducers were used for ultrasonic investigations of damaged CFRP. These investigations resulted in identification of non-linear ultrasonic responses due to the presence of damage. The broadband nature of electrostatic transducers is essential for this work to scan a wide range of frequencies to identify non-linear responses. These non-linear response frequencies were used with an electrostatic transducer to induce thermosonic heating at the damage which was measured with an IR camera. The use of non-linear response frequencies reduces the power required to produce thermosonic heating. Travelling guided waves (Lamb waves) allow excitation of the damage at a distance from the excitation source allowing large samples to be studied. This provides a completely non-contact measurement for NDE which shows promise for future composite inspection systems.
A commercially-available air coupled piezoelectric array was used to induce thermosonic heating in damaged CFRP. Themosonic heating of the damage has been observed with an IR camera. The intensity of the thermosonic heating decreased with the increased distance of the ultrasonic excitation from the damage, as would be expected with energy dissipation into the CFRP. The use of an array allowed scanning of the focal point across a sample to locate and image areas of damage, without moving either the array or the camera. This scanning capability could increase the speed at which composites can be inspected, reducing the current laborious contact transducer methods.
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