V. S. Kuksenko

Diagnostics and forecasting of breakage of large-scale objects

Using a kinetic approach to the breakage of solids, a two-stage model of breakage is constructed. The model is invariant for objects of various scale. A physical approach to forecasting the final stage of macroscopic breakage is developed. The applicability of the methods devised is tested on laboratory samples, industrial constructions, and large-scale objects.

Dynamics of microcracks and time dependences of surface deformation of a heterogeneous body (granite) under an impact

The dynamics of fractoluminescence flashes and the time dependences of surface deformation of granite with different sizes of feldspar grains under an impact on samples by a metal pin have been studied with a 10 ns resolution. A band at ∼1.9 eV has been observed in the fractoluminescence spectra, which means that, under the influence of mechanical stresses, Si-O-Si bonds are broken and ≡ SiO⊙ free radicals are formed. The fractoluminescence has the form of flashes with a duration of ∼10 ns. It has been assumed that each of them corresponds to the nucleation of a microcrack. From the flash intensities and the elastic wave velocity, the linear size of microcracks has been estimated to be from ∼8 to 30 μm. Microcracks are mainly generated during passage of a deformation wave through feldspar grains. An impact causes the appearance of eigenvibrations of the entire sample, and cracking of grains gives rise to eigenvibrations of grains.

Luminescence of quartz under the action of a shock wave

Upon fracture of quartz under the action of a shock wave caused by an electric explosion, a plasma jet is formed. An analysis of the luminescence spectra shows that the jet consists of atoms and cations of the elements contained in quartz and impurities in it.

Fracture features of granite under various deformation conditions

Fracture mechanisms of dry and water-saturated granite samples and slip (displacement) along a ready fault have been studied by measuring acoustic emission signals. It has been found that disperse defect formation is observed in dry samples under mechanical load, then localization occurs, and a fracture source is formed, whose development results in macrofault formation. In water saturated samples, chaotic defect formation occurs in the entire volume, which leads to a high degree of material damage. At the closing deformation stage, several fault source zones are formed in which main cracks develop. In the case of slip along a ready fault, stoppers at crack edges are broken.

Emission of plasma escaping from a heterogeneous solid (granite) under an electric discharge near its surface

The electrical breakdown of air near a granite plate causes sequential release of several hundred plasma jets consisting of electrons, positively charged ions, and Si, O, and other atoms. The release duration of each jet does not exceed ∼10 ns, and the interval between them varies from ∼10 to ∼300 μs. It is assumed that the shock wave increases the lattice strain in dislocation pile-ups to such values at which the ground and excited state levels begin to cross. This leads to transitions between electronic levels, breaking of interatomic bonds, and emission of positively charged ions and electrons.

Dynamics of the deformation and destruction of a heterogeneous body (granite) under the influence of an electric discharge

The device is constructed, which makes it possible to simultaneously detect, with a time resolution of 10 ns, fractoluminescence as well as electromagnetic emission and surface deformation observed in a solid during its destruction under the effect of a shock wave. Using this device, time dependences of deformation and destruction of the granite plate caused by an electric breakdown with an energy of 0.2 J in air near its surface are investigated. It is found that the breakdown causes the appearance of a shock wave in granite, the velocity of which is ∼5 km/s. The shock wave stimulates emission of a plasma consisting of atoms and ions, which enter into the graphite composition, from the granite surface. It is assumed that the appearance of the plasma is caused by cumulation of the shock wave energy in micropores contained in graphite.

Formation of power-law size distributions of defects during fracture of materials

The experimental data on the surface relief of loaded ribbons of an amorphous alloy have been obtained. The distributions of surface defects formed under loading have been analyzed using the wavelet transform and box counting method. Moreover, the data on the time accumulation of microcracks in the volume of a loaded granite specimen have been examined. It has been shown that power-law size distributions of defects (scaling) appear on the surface and in the bulk before fracture. It has been revealed that the appearance of the power-law distributions is one of the indications of the formation of the self-organized critical state. The formation of the self-organized critical state in the bulk and on the surface of the material has been considered. It has been established that the formation of the self-organized critical state precedes the fracture of a solid.

Physical and methodological principles of rock burst prediction

Conclusions1.The fracturing of rocks is a process evolving in time on the basis of a stochastic accumulation and development of cracks.2.Acoustic emissions allow monitoring the accumulation of the number of cracks and evaluating their sizes.3.For monitoring the emission of elastic energy, computerized systems are necessary, capable of real-time recording of all acoustic signals above a desired threshold and measuring their amplitude and time parameters.4.The formation and development of a fracturing source can be detected reliably by variations of the amplitude-time spectra of AE and the variation of the statistical parameters of AE.5.The similarities of the fracturing processes at different size scales allows using the predictive features detected to forecast rock bursts.

The mechanism and dynamics of rock fracture upon mechanical impact and electric discharge

The mechanism and dynamics of the deformation and fracture of quartz, granite, and marble samples under the striker blow on their surface and electric discharge inside them are studied by the fractoluminescence (FL), electromagnetic (EME), and acoustic emission (AE) methods with 10-ns resolution. The impact excites a forced deformation wave with a velocity within 0.8 to 2 km/s depending on the mineral. The atomic bonds rupture and microcracks are formed at the nodes of the wave, which leads to the emergence of the FL flashes and disruption of the time dependences of EME. Based on the intensity of the flashes, the dimensions of microcracks are estimated to vary from 2 to 70 µm depending on the mineral. In turn, the emergence of microcracks initiates additional deformation waves.The discharge inside the studied samples excites a pressure shock wave which transforms into the tension wave after reflection from the surface. According to the analysis of FL spectra, this leads to the breakdown of the rocks into positively charged ions and electrons. The shock wave velocity in granites is measured at 4.8 km/s, which is close to the velocity of the longitudinal acoustic vibrations ~5 km/s. The microcracks in the rock have not enough time to form with this loading velocity. It is supposed that the shock wave stretches the deformed interatomic bonds at the dislocation nuclei in the crystal lattices of the minerals up to their breakdown into positively charged ions.

Dynamics of fractoluminescence and electromagnetic and acoustic emission upon an impact against the marble surface

The blow of a steel striker against the marble surface induces strain waves and electromagnetic emission. Simultaneously, microcracks appear in the marble single crystal with excited free CO2− radicals at the microcrack banks. Relaxation of electronic excitation leads to the emergence of fractoluminescence bursts. The burst intensity is proportional to the area of the microcrack surfaces. Measurements show that the linear size of the microcracks varies from ∼2 to ∼47 μm.