Ultrasonic Measurement of Stress in Railroad Wheels

Published

February 1, 1999

Author(s)

R E. Schramm

Abstract

Acoustic birefringence is the relative change in sound velocity with polarized direction. While the effect is small (usually parts in 10⁴), this is a useful tool to probe stress and metallurgical texture since these generate anisotropic changes in the elastic constants. Piezoelectric transducers usually require a fluid couplant that might vary in thinkness and introduce timing errors. An electromagnetic-acoustic transducer (EMAT) eliminates this problem. Methods of changing the polarization vector include rotating the probe mechanically, using separt but close probes, or stacking orthogonal piezoelectric elements or EMAT coils. Because of its simplicity, we use the latter design. Field use requires automation in data collection and analysis. The instrument described here digitizes an echo, locks onto a cycle, and calculates the time when it crosses zero amplitude. Signal averaging yields the arrival time of a signal at about 90 υs with a standard deviation of 2 ns to 4 ns. In screening the residual stress in the rims of cast-steel railroad wheels, this system has a total error of [approximately equal to] {+or-}60 Mpa; most of this is due to varibility of the metallurgical texture. Most components in this equipment are commercially available.

Citation

Review of Scientific Instruments

Volume

70

Issue

No. 2

Pub Type

Journals

Keywords

EMAT, instrumentation, nondestructive testing, railroad wheel, residual stress, ultrasonic

Citation

Schramm, R. (1999), Ultrasonic Measurement of Stress in Railroad Wheels, Review of Scientific Instruments (Accessed November 8, 2024)