Magneto-mechanical damping and Delta E-effect in ferritic steel at different levels of ultrasound strain amplitudes

The magneto-mechanical damping and Young's modulus (Delta E-effect) of reac tor pressure vessel steels were investigated in a wide amplitude range for both amplitude-independent (AID) and amplitude-dependent (ADD) damping rang es. Two JRQ (Japanese reference quality) steel samples, one in the as-recei ved and the other in the thermally aged condition were used in the experime nts. The measurements were made using the composite oscillator technique at resonance frequencies of about 100 kHz. Longitudinal vibrations of the rod samples were used. Magnetic field up to 26,000 A/m was applied along the l ength of the rod. Amplitude and field dependencies of the damping and reson ant frequencies (Young's modulus) have been measured. Computer controlled a coustic measurements were made simultaneously at two amplitude levels. The data about the influence of high amplitude ultrasonic excitation (HAUE) of the samples (with the amplitudes in the ADD range) on hysteretic field beha viour of AID, ADD and resonant frequencies (Delta E-effects) have been obta ined. The experiments showed that the Delta E-effect at low amplitudes (AID range) was qualitatively changed by HAUE, whereas the AID remained almost the same during the experiments with and without HAUE. It was found that an nealing of the JRQ steel for 3 years at 300 degrees C slightly increased ma gneto-mechanical damping and Delta E-effects for both AID and ADD ranges, b ut it qualitatively changed neither amplitude nor magnetic field dependenci es. The analysis of the experimental data shows that the influence of annea ling can be explained by relaxation of internal stresses in the sample mate rial. This is confirmed by the higher level of flow stresses for the 'as re ceived' sample as compared with the stresses for the 'thermally aged' one. The newly found effect of HAUE is supposed to be caused by reversible chang es (due to high vibrational amplitude) of the internal stresses as well. (C ) 2000 Elsevier Science S.A. All rights reserved.