Kh. F. Makhmudov

Electromagnetic phenomena entailed by deformation and fracture of dielectric solids

Mechanoelectric effects caused by elastic deformation of glasses and marbles are studied in a neutral environment and with weak electric polarization of samples. It is found that the electric potentials that are produced by bending a sample are opposite in sign in compressed and stretched regions. The mechanoelectric effects increase or decrease depending on the direction of the electric field applied to the sample. It is concluded that the electric polarization and the polarization induced by mechanical deformation are of a common nature. Electromagnetic precursors of earthquakes are discussed.

Relaxation of electric fields induced by mechanical loading in natural dielectrics

An investigation is made of electric fields induced in natural dielectrics by mechanical loading and electrical polarization. It is shown that the relaxation of the polarization is identical in nature for both cases and is basically a thermally activated process. The temperature dependence is obtained for the relaxation time of the electric fields. Also estimated is the activation energy for motion of charge carriers leading to the relaxation of these fields.

Thermoactivation mechanism of relaxation of the mechanoelectric effects in solid dielectrics

The mechanoelectric effects under weak electric polarization and elastic deformation of glass and marble samples are investigated. The electric potentials of no relation to the piezoelectric effect are measured. The induced electric potential relaxation is studied and the activation energy of this process is estimated. The induced potential relaxation mechanism is proposed. The electric field potentials in the sample are measured by the contactless method with a specially constructed electrometer of a high input voltage.

Predicting the loss of stability of loaded structural elements using the method of acoustic emission

In experiment, a reinforcing steel rod was placed into concrete prior to casting. After solidification, the rod was pulled out of the sample structure at a constant velocity of the clamp. During withdrawal of the rod, the loading force and the clamp velocity were measured and the accompanying acoustic emission was monitored. It is established that the intensity of acoustic emission exhibits a sharp increase before the onset of the macroscopic loss of stability. It is concluded that the macroscopic fracture of loaded reinforced-concrete structures can be, in principle, predicted using acoustic emission measurements.

On wave and rheidity properties of the Earth’s crust

The properties of the Earth’s solid crust have been studied on the assumption that this crust has a block structure. According to the rotation model, the motion of such a medium (geomedium) follows the angular momentum conservation law and can be described in the scope of the classical elasticity theory with a symmetric stress tensor. A geomedium motion is characterized by two types of rotation waves with shortand long-range actions. The first type includes slow solitons with velocities of 0 ≤ Vsol ≤ c0, max = 1–10 cm s–1; the second type, fast excitons with V0 ≤ Vex ≤ VS–VP. The exciton minimal velocity (V0 = 0) depends on the energy of the collective excitation of all seismically active belt blocks proportional to the Earth’s pole vibration frequency (the Chandler vibration frequency). The exciton maximal velocity depends on the velocities of S (VS ≈ 4 km s–1) and/or P (VP ≈ 8 km s–1) seismic (acoustic) waves. According to the rotation model, a geomedium is characterized by the property physically close to the corpuscular–wave interaction between blocks that compose this medium. The possible collective wave motion of geomedium blocks can be responsible for the geomedium rheidity property, i.e., a superplastic volume flow. A superplastic motion of a quantum fluid can be the physical analog of the geomedium rheid motion.

Dynamics of the nanosecond destruction of stressed granite during shock loading

The method of luminescence with a time resolution of 2 ns has been applied to studying the dynamics of the surface destruction of uniaxially compressed granite by a shock wave caused by electric discharge in air near its surface. The shock impact causes emission of jets of positively charged ions from the most strongly distorted regions on the sample surface. It has been discovered that, when the compressing stress reaches ~0.92–0.95 times the sample’s breaking stress, two maxima can be observed on the time dependence of the jet intensity. The first maximum corresponds to the shock wave reaching the sample surface and the second maximum corresponds to the crack destroying the sample.

The influence of stress on electron emission initiated by a shock wave from a heterogeneous material (granite)

An electrical breakdown of the air near the surface of a compressed granite plate initiates a shock wave in it. Having reached the back side of the plate, the shock wave causes successive (with an interval of ~50 ns) emission of plasma jets presumably consisting of positively charged ions. The intensities of the jets are distributed exponentially. While the compression pressure P does not exceed ~0.9–0.95 of the failure pressure Pf, it does not affect the number and efficiency of the radiation sources. At P ≈ (0.9–0.95)Pf, the shock wave causes the emergence of a crack destructing the sample. Simultaneously, the number and efficiency of ion sources increase 3–4-fold. This phenomenon is explained by an increase in the concentration of clusters of dislocations upon the creep of the sample.

Effect of mechanical stress on the polarization of natural dielectrics (Rocks)

A sample of marble not possessing piezoelectric properties was subjected to uniaxial compressive loading and the response electric field potential was measured by a contactless method using a high-sensitivity electrometer. In the second experiment, weak electric potentials were applied via special electrodes to the opposite sides of the sample subjected to the same mechanical load. The electric potentials measured under the conditions of mechanical loading significantly change upon weak electrostatic polarization of the sample.

Mechanically-induced electrical effects in natural dielectrics

An investigation is made of the generation and relaxation of an electric field in natural dielectrics exposed to mechanical loading and applied electric potentials. It is shown that these processes are identical.

Mechanism and Dynamics of Fracture of the Stressed Granite Surface by a Shock Wave

The dynamics of emission of positively charged ions from the granite surfaces containing different concentrations of quartz and feldspar under the action of a shock wave is investigated with a time resolution of 2 ns. The ions are assumed to be emitted at the instants of emergence of dislocations moving in intersecting glide planes at the sample surface. Defects in the form of extended “grooves” are formed in the region of emergence of dislocations. A compressive load suppresses the defect formation.