Résumé
This ultrasonic sensor made of a copper delay line operates in dry coupling configuration to detect modifications of the contact quality between two materials under compressive stress by measuring the acoustic energy reflected on the air volumes trapped at the interface. Frequency domain analysis of the first delay line round trip echo is useful to operate with harmonics for different selectivities to the interface properties but, pressed on a unpolished copper plate, the sensitivity of acoustic reflection to contact quality vanishes for high roughness level. To overpass this limitation, measurement with the sixth delay line echo has been successfully performed to investigate the stress dependence of the contact quality between a copper plane surface and rugged industrial materials such as amorphous carbon and carbon-carbon composite. This acoustic method, associated with an electric contact resistance measure, has given a direct insight of the deformability of the interface depending on the roughness and the mechanical properties of the two materials involved in the connection. Plasticity, anelasticty effects are observed. Acoustic waves and electromagnetic ones are also not perturbed in the same way by the gas interface modification versus mechanical loading.