Abstract

Simultaneous Probing of the Nonlinear Effect of a Plane Unbonded Interface on Incident Longitudinal and Shear Acoustic Waves as a Function of Amplitude and Pressure

T.P.Berndt (NASA Langley Research Center, Hampton, Virginia, USA); B.O'Neill (Department of Physics, University of Windsor, Windsor, Ontario, Canada)

e-mail: t.p.berndt@larc.nasa.gov

Nonlinear acoustic harmonic generation at plane surfaces between two identical materials is being investigated experimentally as a function of contact pressure and ultrasonic input amplitude for normally incident longitudinal and shear waves. In our experimental setup, both types of waves probe the same interfacial region under identical conditions, and the transmitted as well as the reflected wave components are detected almost simultaneously. In addition, the feasibility of using a single transducer to probe both, second- and third-order nonlinear longitudinal and shear wave harmonics, with a pulse-echo configuration is demonstrated. For both types of wave polarization, characteristic amplitude variations in the spectrum of higher harmonics have been observed as a function of contact pressure. In the case of shear wave propagation, the data appears to confirm a recently developed model [B. O.Neill, R. Gr. Maev, and F. Severin, Rev. Progr. QNDE 20 (2000)] that predicts the absence of even-order harmonics in the spectrum of higher harmonics, generated at friction-coupled interfaces. Furthermore, because a varying interfacial contact pressure is impractical for nondestructive materials characterization, ultrasonic amplitude scanning is investigated and proposed as a more suitable testing method. This approach is shown to have the potential of determining different contact pressures.

Section : 3