The Ultrasonic Measurement of Stress on Ferrous Plate using Pulsed Electromagnet Magnetostrictive Emat Probes

  • S. J. Wormley
  • R. B. Thompson
  • Yan Li
Chapter

Abstract

Last year we finished the design and assembly of a semi-automatic system for the measurement of stress in textured ferritic steel[2], Magneto- strictive EMATs, which have no contributions generated by Lorentz force, were used on ferrous alloys since the absence of the Lorentz force mechanism precludes any velocity errors that might be produced by interference of Lorentz force and magnetostrictively generated signals. Phase shifts due to lift-off were solved by driving the transmitter EMAT’s in series. To make reliable wave-speed measurements in an industrial environment with an economical sampling period of 100 nanoseconds, a Fourier Transform-Phase-Slope technique was implemented which not only solves the zero-crossing problem[1,2], but achieves accuracy approaching the Cramer-Rao bound[3], Initial data are improved over the previous year’s work, however, further refinements are required to archive the expected error bound of ± 2 ksi. These refinements take the form of reducing the effects of temperature induced velocity changes during the measurement process.

Keywords

Radar Hull Acoustics EMAT 

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Copyright information

© Plenum Press, New York 1991

Authors and Affiliations

  • S. J. Wormley
    • 1
  • R. B. Thompson
    • 1
  • Yan Li
    • 1
  1. 1.Center for Nondestructive EvaluationIowa State UniversityAmesUSA

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