Micromagnetic surface studies of materials for nondestructive evaluation
A system which employs the magnetic Barkhausen effect to measure micromagnetic Barkhausen emissions (E) in ferromagnetic materials using a time varying magnetic field was developed. A patent application was made (US patent application temporary no. 754,904 pending). It was observed that E is dependent on microstructure in different Fe, Ni, Co alloys, steel, and rare earth-Fe alloys. The ac excitation field used in the present developed system is essential, since superposition of ac excitation field on quasi dc field gives cleaner, more reproducible magnetic Barkhausen pulse waveforms. 30 Hz was found optimal for the excitation frequency, for very fast in situ measurements. E can be generated at different depths in the material by altering the excitation frequency; using a band pass filter, E can be detected over different frequency ranges. Instead of conventional count rate, techniques for analyzing the E were developed: pulse height spectrum analysis, frequency spectrum analysis, RMS voltage analysis, and pulse waveform analysis. A model was developed for the magnetic Barkhausen effect.
- Research Organization:
- Ames Lab., IA (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- W-7405-ENG-82
- OSTI ID:
- 10124503
- Report Number(s):
- IS-T-1634; ON: DE93006303
- Resource Relation:
- Other Information: TH: Thesis (M.S.); PBD: 25 Nov 1992
- Country of Publication:
- United States
- Language:
- English
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