Electromagnetic Effects Resulted from Natural Disasters - Ultra and Extremely Low Frequency Electromagnetic Fields - page 370

Fig. 10.2 A schematic plot of macroscopic crack surrounding by the cloud of microcracks.
A craze/plastic zone is restricted by dashed line . Adapted from Surkov ( 2000a )
Fig. 10.3 Electric charges at the surfaces of microcracks. The lines show the directions of
conduction currents that lead to the charge relaxation. The electric dipole moments of the
microcracks are shown with arrows . Adapted from Surkov ( 2000a )
Laboratory tests have shown that the microcracks are formed in the so-called
craze/plastic zones at the crack tip or in the vicinity of crack walls where the micro-
failure remains trapped (Fig. 10.2 ). The formation and relaxation of electric charges
on the sides of microcracks result in the excitation of wide-band electromagnetic
noise and currents which are dissipated in the conducting media thereby trans-
forming into ULF vibrations bounded above by the frequency 1 Hz. The theory
assumes that the sides of microcracks are homogeneously charged: one of them
positively while the other negatively. The charges on the crack walls are situated in
such a way that the vectors of electric dipole moments of all the microcracks are
approximately parallel to each other as schematically shown in Fig. 10.3 .Herea
mechanism of the charge generation is not specific while the charge relaxation is
assumed to be due to electric currents.