This paper provides a guideline to the literature of magnetic techniques for nondestructive evaluation. Compared with other NDE methods such as ultrasonics or eddy currents, the literature for magnetic methods is relatively small, but one of the difficulties is that it is widely scattered. This review therefore presents a fairly comprehensive summary of works on Barkhausen effect, magnetoacoustic emission, magtenic hysteresis, residual field and magnetically induced velocity change methods that have appeared to date.

Review of magnetic methods for nondestructive evaluation

Recent progress of residual stress measurement methods: A review

Nondestructive evaluation of steels using acoustic and magnetic barkhausen signals—I. Effect of carbide precipitation and hardness

The effects of carbon on the magnetic properties of steel have been of great interest over the years both because of the great commercial importance of steel and because it is known that carbon is the most important single factor affecting the magnetic properties of steel. Slight changes in the amount and distribution of the carbon content can completely mask any changes due to grain size, stress, and the effects of other impurities. The magnetic properties of several specimens of steel in which the carbon content has been deliberately reduced are investigated so that the more subtle effects on magnetic properties caused by these other factors can be determined. The results presented include magnetic Barkhausen measurements, magnetoacoustic emission measurements, and magnetization data. The grain structure of each specimen was closely monitored and the resulting magnetization data correlated with the microstructure.

Magnetic properties of decarburized steels: An investigation of the effects of grain size and carbon content

Metal magnetic memory technique has provided a new arena for assessing stress status, especially for detecting early damage in ferromagnetic materials. To investigate the magnetomechanical effect of metal magnetic memory phenomenon, the rotary bending fatigue experiments under different stress levels were conducted. The normal components of magnetic field intensities induced by cyclic bending stresses on the surfaces of 45-steel specimens were measured throughout the fatigue process. The results show that surface magnetic fields generated contains reversible and irreversible process prior to failure, while there is a substantial increase just before fracture. Possible reasons for the variations of magnetic fields and corresponding signal characteristics to identify damage zones were discussed.

Magnetic field variation induced by cyclic bending stress

The effect of stress on the magnitude of acoustic emission during magnetization of mild steel and nickel has been investigated. It has become clear that the magnitude of acoustic emission during magnetization shows a strong dependence on stress. This effect should have nondestructive testing applications suited for field inspection.

H. Kusanagi

Papers

Stress effect on the magnitude of acoustic emission during magnetization of ferromagnetic materials