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RESEARCH PAPERS: Gas Turbines: Manufacturing and Materials

Calibrating Ultrasonic Images for the NDE of Structural Materials

[+] Author and Article Information
R. S. Gilmore

GE Corporate R&D, Schenectady, NY 12301

A. M. Glaeser

University of California, Berkeley, CA 94720

J. C. Wade

Garrett APD, Phoenix, AZ 85034

J. Eng. Gas Turbines Power 116(3), 640-646 (Jul 01, 1994) (7 pages) doi:10.1115/1.2906868 History: Received March 10, 1993; Online April 24, 2008

Abstract

Ultrasonic imaging is taking a larger and larger role in the NDE of turbine engine materials and in support of fracture mechanics calculations. It is also playing an increasing role in quality and process control. For most fracture toughness calculations, it is necessary to establish the accuracy with which a flaw’s size and shape are imaged, whether single or multiple flaws are involved, and the spacing of multiple flaws. Because of these requirements, resolution, as well as detection sensitivity, has become an issue. There are a number of resolution targets that can provide this type of calibration information for an ultrasonic imaging system. A fused quartz USAF 1951 target, similar to the patterns used in this work, was first used by Gilmore (1986), but Gilmore’s pattern was superficial and subsurface evaluations were limited to focusing on the pattern from the opposite side of the blank and monitoring the reflection from what is now the target backwall. Work by Paton (1977) did produce buried targets in titanium samples, but there was no practical method to produce buried targets in high-temperature ceramics until the techniques developed by Rodel and Glaeser (1987) were used to produce the targets described in this paper. Optically transparent resolution targets make it feasible to verify visually that the resolution target has been correctly fabricated. An image of the target with a candidate ultrasonic transducer then permits quantitative image resolution estimates to be made even when the interrogating acoustic beam contains significant refractive aberration. This is important because useful subsurface images can be acquired with the use of acoustic beams that are aberrant to the point that diffraction-limited beam-width calculations are meaningless. This work also demonstrates how the interdisciplinary skills of manufacturing companies can be combined with those of universities to produce results that any one of the individual members of the team could not have produced alone, without significant increases in labor, time, and cost.

Copyright © 1994 by The American Society of Mechanical Engineers
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