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positive ions, and X-ray radiation have been observed under fast plastic deformation
of metals and alloys. It is conceivable that so high energy of electrons is due
to the electric field originated from the electric charges accumulated at the crack
tip and from the opposite charges distributed on the crack sides. This field is
able to accelerate the free electrons in parallel with the crack surface. Besides,
one may suppose that the intensive deformation of matter near the crack tip
leads to the excitation and ionization of inner atomic shells, which in turn results
the emission of both 100 keV electrons and characteristic X-ray radiation. The
experimental evidence points to the presence of gas-discharge micro-plasma and
electrical discharges between sides of the growing cracks. The duration of the
discharges was estimated to be 0:1 s and their linear sizes were of the order of
10
2
-10
3
cm. Optical measurements have shown that we observe the light flashes
frequently during the destruction of different materials in vacuum and air. The flash
duration varies from 0.1-1 s for metals to 20 ms for the samples of granite and
basalt. The light is radiated by at least two sites which are the fracture zone and the
dusty streams flowing from the fracture zone. The sources of emissions are assumed
to be the ionized and excited atoms of the fractured matter as well as the atmospheric
gases.
The electromagnetic perturbations have been shown to connect with acoustic
emissions of the fractured sample. The laboratory tests using a hydraulic machine
have demonstrated that there arise the electric pulses only during the stress increase
and the amplitude of the signals enhances with the increase of the loading rate. There
is a few indirect evidence that the source of electromagnetic pulses is the tension
microcracks rather than the shear ones. This is consistent with the observation that
the buildup of the tension microcracks around the tip of main shear crack is typical
for the preliminary stage of sample fracture. It is interesting to note further that
the intensity of electromagnetic signals was higher at the early stage of the loading
whereas the acoustic emission increases just before the moment of total sample
destruction. This suggests that the same effects can be observed during large-scale
tectonic processes associated with EQs, volcano eruptions and etc. However, in
contrast to the laboratory tests, the range of typical frequencies is found to shift
to the low frequency region; firstly because of the large sizes of the fractured zones
located in the EQ focal area; and secondly due to the strong absorption of high
frequency electromagnetic emission by the conducting layer of the ground.
References
Abramova KB, Valitskiy VP, Zlatin IA, Peregud BP, Pukhonto IYa (1971) Radiation caused by
fast deformation and fracture of metals. Rep USSR Acad Sci (Doklady Akademii Nauk SSSR)
201(6):1322-1325 (in Russian)
Alekseev OG, Lazarev SG, Priemskiy DG (1984) On the theory of electromagnetic effects followed
dynamical deformation of metals. J Appl Mech Tech Phys (Zhurnal Prikladnoi Mekhaniki i
Tekhnicheskoi Fiziki) 4:145-147 (in Russian)
Allison FE (1965) Shock induced polarization in plastics. 1. Theory. J Appl Phys 36:2111-2113
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