Acoustic Emission and Barkhausen Pulses
The acoustic emission technique is considered as one of the non-destructive testing methods for materials and devices (Beattie, 1976; Dunegan and Hart-man, 1981; Wadley and Scruby, 1981; Wadley et al., 1981; Beattie, 1983). Different from most other methods, no external fields, radiation or sound waves are applied as inherent part of the method. All acoustic signals occurring at the surface of the sample originate from its interior. On the other hand acoustic emissions are only generated, if the material is loaded by some external forces, be they mechanical, electrical, magnetic, or thermal. All detectable interior changes of the material have to occur abruptly to induce a pulse of acoustic waves. The frequencies may be very low, like when considering the earths crust as a large sample and moving internal faults generating earthquakes as the acoustic emission events (Aki and Richards, 1980), but in technical systems ultrasonic frequencies are always encountered.
KeywordsFatigue Anisotropy Zirconia Titanate Barium
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