Waveform-Based Ultrasonics for Characterization of Elastodynamic Anisotropy and Acoustic Emission Sources in Thick Plates: Theory and Experiment.
Traditional, narrow-bandwidth approaches to acoustic emission (AE) studies and ultrasonic materials characterization utilize only a portion of the information contained in ultrasonic signals. Even in very quantitative studies the sample is typically characterized at a single or very few ultrasonic frequencies. The reason for the reduction of ultrasonic data may well lie in the lack of robust representation for the behavior of transient, wideband signals in anisotropic solids. With the exception of isotropic solids exhibiting simple geometries such as thin plates or half-spaces, models capable of predicting or explaining the complex waveforms detected in such studies have been unavailable. A new, powerful and computationally efficient representation of the elastodynamic Green's function for anisotropic solids make such interpretation possible. Using appropriate acoustic sources the resultant transient displacements can be efficiently and accurately predicted. Ultimately these processes can be used for either materials characterization or source characterization of AE events. Problems arise, however, in both the optimum source of the signal and in the detection of such signals since most sensors distort or modify the actual ultrasonic displacements. In order to insure the fidelity of the waveform measurements, a significant portion of this work focuses on the characterization and optimization of both wideband transient sources and particle displacement sensors. Criteria for selection of sources will originate both from the scope of the new theoretical representation and from the requirements of acoustic emission simulation. The performance of potential detectors will be evaluated theoretically and experimentally. Once the ability to generate suitable acoustic signals has been established and a high-sensitivity, high -fidelity sensor chosen, predictions and measurements of transient, wideband signals are made on aluminum, lucite and composite plates. Significant agreement between theory and experiment is achieved. Deviations between theory and experiment are identified and discussed and the potential of inversion methods is presented.
- Pub Date:
- Engineering: Materials Science; Physics: Acoustics