Ultrasonic Characterization of Residual Stress and Texture in Cast Steel Railroad Wheels
An ultrasonic technique has been used to characterize the state of residual stress and texture in the rims of cast steel railroad wheels. Orthogonally polarized shear-horizontal (SH) waves are propagated through the thickness of the rim in pulse-echo mode. The (normalized) difference of arrival times of these waves (acoustic birefringence) depends upon both texture and stress. The birefringence, B, was measured with two transducers: an electromagnetic-acoustic transducer (EMAT) and a piezoelectric transducer made of PZT.
Two wheels were tested. The first wheel had a sawcut, which locally relieved the residual (hoop) stress. Measurement of the birefringence at the sawcut allowed us to estimate the contribution of texture, which we subtracted from values of B at stressed locations. Values of hoop stress obtained with the EMAT and PZT transducer agreed to within 10 MPa, for transducers placed on the center of the back face of the rim.
The second (uncut) wheel had been heat treated and air quenched, giving a different microstructure. Measurements of B were made with both transducers at different radial and circumferential locations. We estimate that the values of hoop stress obtained with the two transducers will differ by less than 25 MPa for this wheel. Furthermore, the EMAT required less surface preparation of the rim than the PZT transducer, indicating the potential for use of EMATs for residual stress measurements in the field.
KeywordsResidual Stress Principal Stress Piezoelectric Transducer Hoop Stress Surface Preparation
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