Magnetomechanical damping in iron

Abstract

We have carried out a complete, detailed study of magnetomechanical damping on a set of annealed and deformed iron specimens. The results for macroeddy-current and microeddy-current damping are consistent with previous data on iron. The macroeddy peak gives a good indicator of achieving saturation. The microeddy damping offers a usable method for estimating domain size. The slope of damping versus amplitude in the hysteretic Rayleigh region is inversely proportional to the square of a measure of internal stress, as predicted by Smith and Birchak (SB). At higher amplitudes, in annealed and slightly deformed specimens, the damping increases more rapidly than in the Rayleigh region, a phenomenon not previously recognized, and contrary to existing models. The very long straight line in the Rayleigh region, implying a lack of any linear scale for the hysteresis, suggests that there is a fractal nature to the process. This suggestion is consistent with the SB theory. A possible model for the elementary hysteretic event is the reorientation of a quadrupole as the local stress changes sign; if this process involves a random sampling of the internal stress field, the lack of scale can be accounted for.

Review on Structural Health Evaluation with Acoustic Emission

“…Serious evaluation of these diverging results has not been conducted so far, but Papadakis' data are more reliable as he used directly bonded quartz disc transducers, while later studies used damped ultrasonic transducers and water immersion [68][69][70][71]. Magnetic effects could be a factor, but are less than 10 dB/m at 1 MHz and not large enough [73,74]. Most of the references dealt with the longitudinal wave attenuation.…”

Internal friction and magnetic properties of thermally aged Fe–1 wt.% Cu alloys

“…Since similar phenomena have been reported in ferromagnetic metals measured without magnetic field [9,11], the observed IF comes mainly from the loss of magnetic origins. Comparing two specimens, the IF of aged specimen was larger than that of unaged one, which suggests a larger magnetic energy loss of aged specimen rather than a mechanical energy loss due to motion of dislocations.…”

“…In most of the IF studies, a magnetic field was intentionally applied during the measurement for elimination of magnetic effects in order to highlight the interaction between dislocation and solute atoms. Since the IF of ferromagnetic metals is also influenced by magnetic domain wall movement and magnetization rotation [11], elucidation of magnetic effects on IF of Cu precipitated metals is definitely needed for establishing the fundamentals as an NDE method.…”

Influences of Heat Treatment and Grain Size on the Damping Capacity of an Fe-Cr-Al Alloy

“…Approximately, it can be stated that the dissipated energy accompanying the magnetic domain wall movements is associated with domain wall mobility. Therefore, in addition to the structure and size of magnetic domains and domain walls, obstacles (such as grain boundaries, dislocations, precipitation, and stress), which retard domain wall movements, may also influence the magnetomechanical damping [1][2][3][4]. Extensive studies have been conducted on this subject, and indeed many important results have been obtained that are critical for engineering applications.…”