Acoustical birefringence and the use of ultrasonic waves for experimental stress analysis |
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Authors: | Nelson N Hsu |
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Institution: | (1) Department of Engineering Mechanics, University of Kentucky, 40506 Lexington, KY |
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Abstract: | Stress-induced optical birefringence in transparent materials has long been a common technique of stress analysis. Although
stress-induced acoustic birefringence was discovered more than 20 years ago, its development and actual applications are still
limited. This paper will look at the similarities and differences between the propagation of light waves in photoelastic materials
and the propagation of ultrasonic waves in deformed solids. Critical comparisons of the experimental methods employed in photoelasticity
with those available in modern ultrasonic measuring technique show why previous studies on ultrasonic measurement of stresses
were not very successful.
A new experimental technique is devised for using ultrasonic waves for stress analysis. The technique employs a single rotatable
10-MHz shear transducer as the transmitter and receiver of ultrasonic pulses. The enlarged display of the 10-MHz modulated-pulse
pattern of reflected echoes provides a convenient way to determine the directions of principal axis of the stress within ±3
deg. The pulse-echo-overlap method is used to measure the absolute velocities of the two principal shear waves. The difference
in principal stresses is then calculated from the velocity measurements. Test results of common structural-aluminum and steel
specimens under uniaxial compression show a linear relation between the velocity changes and the applied stress. Ultrasonic
measurements of stress distribution in a 6.35-cm diameter, 1.9-cm-thick aluminum disk under diametric compression are also
reported.
Paper was presented at Third SESA International Congress on Experimental Mechanics held in Los Angeles, CA on May 13–18, 1973. |
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