Magnetomechanical Acoustic Emission of Iron and Steels.
CALIFORNIA UNIV LOS ANGELES DEPT OF MATERIALS
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The motion of magnetic domain walls in ferromagnetic materials produces acoustic emission AE. This type of AE was detected during magnetization of a nickel and during elastic loading of iron. Recently, this was also found to depend on applied stress. Varying AE outputs were observed on several ferromagnetic materials under alternating magnetic field. This magnetomechanical AE phenomenon has a potential of performing nondestructive measurements of residual stresses in structures, components and weldments, and we examined systematically effects of applied stress and magnetic field strength in ferritic steels. This measurements of residual stresses in structures, components and weldments, and we examined systematically effects of applied stress and magnetic field strength in ferritic steels. Several carbon steels, A 533 B steel and commercially pure iron were tested in annealed or normalized condition. By employing two AE transducers of different resonant frequencies, rms voltages were measured at two frequency ranges. Maximum stress level was 350 MPa. It was found that 1020 steel shows the highest AE response among the materials tested. Residual stress levels can be determined by monitoring the ratio of the outputs of two AE transducers for a given material condition. The amount of prior cold work and the difference in heat treatment can also be determined by monitoring this AE phenomenon. Several exploratory experiments for the developing a new method of nondestructive evaluation of residual stress and material conditions have also been conducted. Results of these experiments are described and discussed in detail. Author
- Metallurgy and Metallography
- Test Facilities, Equipment and Methods