In connection with the problem of forecasting rock bursts, methods permitting the investigation of the kinetics of destruction of rock masses are undergoing intensive search at this time. Acoustic (AE) and electromagnetic (EMP) emissions accompanying all stages of material deformation and destruction are the most extensively utilized methods.A theoretical electromagnetic emission model is proposed and verified experimentally in this paper, as accompanying the process of crack generation and jumplike development in rock masses with conductivity less than 10 -2 fl'Z-m'1. This model permits the prediction of the recordable parameters of EMP generation in solid bodies in terms of known parameters of crack motion.
INITIAL HYPOTHESESPulsed electromagnetic emission has been thoroughly studied in alkali-halide crystals (AHC) over the frequency range i01-i0 ~ Hz [1][2][3]. It is related to two mechanisms: the formarion of dislocation slip lines [i] at early stages of the microplastic deformation and the generation or jumplike propagation of cracks [3]. Only these two mechanisms under consideration are capable of producing fields close to those recorded in intensity [I].The effect of charging spell surfaces in a lithium fluoride crystal was investigated in [2]. It was established that the spell edges carry charges of opposite sign over their whole extent, with the charge relaxing continuously in time during crack growth. Localization of the bulk charge being formed occurs in a very small neighborhood of the destruction surface [2]. The theoretical foundation for this effect is [4] that because of asymmetry of the elastic field near the crack apex and the presence of tangential stress in the normal direction to the destruction plane, transverse slip of the charged dislocations occurs, i.e., separation of the charges between the crack edges. It is impossible to exclude the possibility also of the appearance of fluctuating charges due to r_he presence of cation and anion vacancies and impurity ions in a narrow domain near the crack apex since thermodynamic conditions near the destruction surface differ substantially from those in the remaining body bulk.The majority of massive rocks are of heterogeneous structure containing mineral grains with ionic bonding, consequently separation of the charges on the edges of the ruptures during crack formation can occur in an analogous manner.Identity of the momentum modes during crack formation in massive rocks and ionic crystals is established in [3], which permitted a deduction to be made about the excitation EMP by the motion of the oppositely charged crack edges.A Fourier analysis of the EMP spectrum shows that the main fraction, by weight of the frequencies is in the 10z-10~-Hz range, where the upper limit of the EMP frequency band is determined by the charge relaxation time T, i.e., ~max = T-z, which corresponds to the electromagnetic radiation wavelength range A -3.10~-30 m. Therefore, the quasistationarity condition [5] is satisfied at the distance R << A from the radiation sour...
The main requirement to the materials used to make membranes polymer electrolyte membrane fuel cells (PEM FC) is the combination of high proton conductivity and resistance to the FC operation conditions. Thus, the search for inexpensive and high-performance non-fluorinated or partially fluorinated materials for use as FC membranes is an actual task today, since the use of membranes based on perfluorosulfonate acid has a number of disadvantages limiting their application. The aim of this study is the investigation of sulfonated polyimide (SPI) and materials for use as FC membranes. The relevance of research stems from the fact that the use of the SPI will allow to increase the resistance of the membrane to the constantly changing environment in which PEM operates. The objects of research are sulfonated polyimides. SPIs, especially aromatic SPIs, are attractive to researchers, because of the possibility of obtaining a wide variety of chemical structures and also due to their excellent thermal, mechanical properties and high resistance to aggressive media. The results of this study will be methods of obtaining and evaluating the advantages and disadvantages of SPI-based materials. For the first time, special attention will be paid to advanced development based on SPI with the addition of crown-ether fragments.
The thermofluctuation strength theory of S. N. Zhurkov [1] provides the basis of the kinetic concept of solids in a field of mechanical stresses.According to this theory, the time until body destruction ~" for stretching stress o and absolute temperature T obeys the equationwhere U 0 is the interatomic binding energy, ~'0 is the period of atomic oscillations, and v is the activation volume.A detailed study of the destruction process [2] has shown that cracks are generated in the body after time 7" at a rate A stationary accumulation of cracks (1~ = const) is realized only up to a certain boundary N*, behind which follows the phase of accelerated accumulation, complete by rupture of the sample [2].It has been established experimentally that the boundary value N* obeys the concentration criterion N*-Va l L = K* .
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