Modeling magnetostrictive generation of elastic waves in steel pipes,II. Comparison to experiment

Abstract

This paper describes continued investigation of magnetostrictive generation of elastic waves in steel pipes via alternating current through a coil about the pipe in the presence of a longitudinal static magnetic field. In paper I, electromagnetic theory was used to find solutions for changing electromagnetic fields induced in the pipe. The solutions were used to obtain magnetostrictive forcing terms in an elastic wave equation for solutions appropriate to continuity of normal stresses across cylindrical boundaries. It was found that longitudinal {\rm L}(0,1) and {\rm L}(0,2) elastic wave modes could be propagated for the frequency range considered. The amplitudes of these waves were dependent on the magnetostrictive forcing terms, which were in turn attributable to the alternating electromagnetic fields. In this paper, measurements are reported for the a.c. magnetic permeability of a steel pipe as a function of frequency and static magnetic field. These values are inserted into the model, and after other appropriate substitutions, predictions for wave amplitudes generated in the pipe are compared against experimental measurements.