Technical Reports

Ultrasonic Instrumentation to Measure Hoop Stress in Cast-Steel Railroad Wheel Rims

  • 01
  • Mar
  • 1998
AUTHOR: Raymond E. Schramm
SUBJECT: Evaluation
KEYWORDS: EMAT, Instrumentation, Nondestructive Testing, Railroad Wheel, Residual Stress, Ultrasonic
ABSTRACT: This is Report No. 32 in a series covering research done by hte National Institute of Standards and Technology for the Federal Railroad Administration. We report on a project by the Materials Reliability Division to develop and test an ultrasonic instrument package for measuring residual stress in the rims of railroad wheels. Stress, residual or applied, has an acoustoelastic effect. Measuring acoustic birefringence (the samll change in velocity with direction of polarization) is a method for nondestrcutive evaluation (NDE) of stress. We have previously shown the viability of this approach for inspecting the rims of cast-steel railroad wheels. While the effect of metallurgical texture will preclude measurements of high accuracy, this ultrasonic method should be useful as a screening tool to find those wheels that have potentially dangerous tensile stresses. The current effort has been to develop instrumentation for use in the field. The factors considered were size and compactness, ease of use, and automoation. In the present unit, most of th electronics are commercial, off-the-shelf items. There are two computer plug-in boards (pulser/receiver and ADC) in a "lunchbox" computer. The probe is an electromagnetic acoustic transducer (EMAT) in a case designed to fit the front rim face (frf) with the necessary precision. A software program collects digital signal information and analyszes it withot operator invtervention. In its present form, this package should be able to collect enough statistically significant information for determining stress in less than 30 seconds.