THE EFFECTS OF MICROSTRUCTURE ON THE RESPONSE OF ALUMINUM E-127 CALIBRATION STANDARDS

摘要

Attenuation measurements show a smaller anisotropy than might be expected based on the highly elongated state of the microstructure, with significant variation from sample to sample. The samples studied provide an example of a case in which a flaw would be oversized in a production plate when the reference flat-bottom hole signal was obtained from a calibration sample. Backscattering showed much greater anisotropy than attenuation. This fact, combined with the significant fluctuations in back-surface echo strength for waves propagating parallel to the long dimensions of grains, and the observation that, in sample T3, the direction of highest backscattering was the direction of lowest attenuation, suggests that mechanisms other than scattering, e.g., phase distortion, are making significant contributions to the attenuation. The better understanding of these phenomena is important to the proper use of standards as references in flaw sizing as well as for the development of improved techniques for microstructural characterization.