High resolution magnetic Barkhausen noise measurements of slit defects in steel
- Queen`s Univ., Kingston, Ontario (Canada). Dept. of Physics
During the magnetization process of a ferromagnetic material magnetic Barkhausen noise (MBN) occurs as a consequence of either (1) irreversible domain wall motion or (2) irreversible rotation of the domain vector magnetization. Conventionally, MBN measurements for NDT applications are performed with a pick-up coil and U core magnet applied to the surface of the sample. The pick-up coil is constructed by winding fine wire around a small cylindrical bobbin. Placed on a steel surface the pick-up coil senses perpendicular changes in flux from the induced voltages. Given that the diameter of the pick-up coil may be of the order of 10 mm and that the changing magnetic fields which the coil detects fall off as 1/r{sup 3}, where r is the distance from the center of the coil, high resolution in the MBN signal cannot be expected from this method. Read head technology in contrast, attempts to localize the measurement of the signal to as small a region as possible and, therefore, maximize the resolutions. This is accomplished by coupling the ``demagnetization`` fields, that are produced by the medium to be measured and that extend above the surface, through a narrow slit into the read head. MBN signals are detected by the abrupt localized changes of flux which produce voltages in pick-up coils threading the read head. In an effort to localize the range over which MBN signals are measured, and, therefore, increase the resolution of the MBN signal a small magnetic disk read head was mounted within a laminate U shaped sweep field core. When this was placed on a ferromagnetic test piece the application of a sweep field to the U core magnet induced MBN within the sample. The resolution of the read head device was tested by performing measurements across various slits and through cuts in several steel samples. The depression of the MBN signal in the vicinity of the slit or through cut was interpreted in terms of the corresponding depression of the magnetic fields in their vicinity.
- OSTI ID:
- 64648
- Report Number(s):
- CONF-931193-; ISBN 0-931403-23-5; TRN: IM9528%%308
- Resource Relation:
- Conference: American Society for Nondestructive Testing (ASNT) fall conference and quality testing show: NDT - a partner in engineering innovation, Long Beach, CA (United States), 8-12 Nov 1993; Other Information: PBD: 1993; Related Information: Is Part Of ASNT 1993 fall conference and quality testing show. NDT: A partner in engineering innovation; PB: 193 p.
- Country of Publication:
- United States
- Language:
- English
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