Acousto-Ultrasonics: Theory and ApplicationJ. Duke Finding and slzmg cracks and other crack-like discontinuities has been the center of attention for scientists and engineers developing and using nondestructive evaluation (NDE) technology. However, with advanced mate rials being "engineered" and used in critical structural components, a new for NDE has emerged. Whereas many traditional engineering materi challenge als fail due to the initiation and self-similar propagation of a crack, reinforced composite materials degrade and fail in a manner more analogously to the collapse of a structure. Consequently the NDE of such materials involves assessing the combined effect of the material's damaged condition rather than identifying and sizing single critical imperfection. In 1979 Alex Vary, seeking to address the challenge confronting the NDE of advanced fiber reinforced composite materials began work on a new method of materials characterization. Focusing on the problem of evaluating graphite fiber reinforcedl epoxy laminated plates; Vary used a piezoelectric transducer to excite a mechanical disturbance in a plate and, with a sensi tive piezoelectric transducer monitored the disturbance on the same surface of the plate. (Placing the transducers on the same surface was primarily for practical purpose but their displacement in the direction of anticipated service load was of fundamental significance!) To quantify this observation, he counted the number of excursions, of the resulting electrical signal, above a arbitrary voltage threshold; a procedure frequently used for acoustic emission signal analysis. |
Contents
The AcoustoUltrasonic Approach | 1 |
Interaction of Ultrasonic Waves with Layered Media 233 | 23 |
Diffuse Waves for Materials NDE | 35 |
Copyright | |
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acoustic emission acousto-ultrasonic acousto-ultrasonic technique analysis applications attenuation backscatter Beta distribution cepstrum characteristics Characterization coefficient components composite laminates composite materials composite plates correlation couplant coupling delay line density detection digitized dispersion curves displacement E. G. Henneke effect elastic EMAT energy epoxy experimental fiber direction fiber reinforced composite flexural waves glass graphite/epoxy impact damage incidence inhomogeneity interface J. C. Duke Lamb wave laser layer load longitudinal wave matrix mechanical method mode NASA Nondestructive Evaluation Nondestructive Testing normal obtained optical fiber parameters peak amplitude phase velocity piezoelectric polar porosity probe properties pulse received signal receiving transducer reflection resin ringdown sample scattering self-coupling transducer shear wave shown in Fig shows specimen spectral stiffness strength stress wave factor structure surface waves SWF measurements thickness threshold tion transmission transverse cracks transversely isotropic ultrasonic waves ultrasound unidirectional variations voltage wave propagation waveform wavelength