Stress has subtle effects on acoustic properties and exploiting these may lead to a field-usable system to detect and measure residual stress in the rims of railroad wheels. Acoustic birefringence is the underlying principle of operation. This is a measure of the relative difference in the propagation times of two shear waves polarized in radial and circumferential directions. The ultrasonic probe here is an EMAT (electromagnetic-acoustic transducer). This type of transducer requires little or no surface preparation and no acoustic couplant. The system operates in a pulse-echo mode. A short burst of shear horizontal waves travels through the rim thickness. The rotation of the EMAT determines the orientation of the polarization vector, radial or circumferential. Precise timing of echoes in both directions reveals the degree of birefringence. Changes are due to both stress state and metallurgical texture. Initial tests indicate it may be possible to separate these two. The Federal Railroad Administration now has this instrumentation for field tests.
Ultrasonic measurements of residual stress in railroad wheels
Ultraschallmessung der Eigenspannungen in Eisenbahnrädern
1991
7 Seiten, 6 Bilder, 9 Quellen
Conference paper
English
Ultrasonic measurement of residual stress in cast steel railroad wheels
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