Peculiarities of britlle and ductile materials destruction and deformation during the explosion of industrial shaped charges

Purpose. To study the laws of deformation and destruction of brittle and ductile rocks and concretes under explosion of industrial shaped charges. Methods. In experiments, the following methods of investigation were used: method of contact sensors for determination of jet velocity; determination of the ultrasonic wave velocity in the concrete samples; methods of optical and electronic microscopy; X-ray phase analysis; measuring and visual analysis of the dimensions and nature of deformation and destruction zones. Findings. The work describes the experimental data on the destruction of barriers made of concrete, granite, steel ST 3, AMC-n alloy, and zinc by the explosions of shaped charges of serial production with porous liners. Calculation formulas for estimating the radius of a destruction zone of geomaterials and rocks in case of a semi-infinite barrier are suggested. The calculation method is based on the estimation of energy impact on the rock by jet penetration velocity into the barrier. Jet velocities are determined experimentally and by engineering methods. The reasons for deviations in the hole shape and deflection of the destruction zone from the symmetry axis were determined. Originality. The modes of penetration of shaped jets into rocks of different porosity, the size of the fracture zone around the hole and the causes and mechanisms of the deviations of the hole shape from the symmetric one are established. Practical implications. The results of the research will be used to design blasting-and-perforation operations in geotechnological wells and can be used to design initiating devices for borehole charges.Мета. Дослідження закономірностей деформування й руйнування крихких і пластичних гірських порід та бетонів при вибуху промислових кумулятивних зарядів. Методика. Метод контактних датчиків для визначення швидкості струменя; визначення швидкості ультразвукових хвиль у зразках бетону; оптична та електронна мікроскопія; рентгенофазний аналіз; вимірювання й візуальний аналіз розмірів та характеру зон деформування і руйнування. Результати. В роботі описані експериментальні дані про деформацію та руйнування перешкод з бетону, граніту, пінобетону, сталі Ст 3, сплаву АМЦ-н і цинку вибухами кумулятивних зарядів серійного виробництва з пористим облицюванням. Запропоновано розрахункові формули для оцінки радіусу зони руйнування геоматеріалів і гірських порід у разі напівнескінченної перешкоди. Визначено причини відхилень форми отвору і зони руйнування від осі симетрії. Наукова новизна. Визначено режими проникнення кумулятивних струменів у породи різної пористості, розміри зони руйнування навколо отвору, а також причини і механізми відхилення форми отвору від симетричної. Практична значимість. Результати досліджень будуть використані для проектування вибухо-прострілочних робіт у геотехнологічних свердловинах і можуть бути використані для конструювання ініціюючих пристроїв свердловинних зарядів.Цель. Исследование закономерностей деформирования и разрушения хрупких и пластичных горных пород и бетонов при взрыве промышленных кумулятивных зарядов. Методика. Метод контактных датчиков для определения скорости струи; определение скорости ультразвуковых волн в образцах бетона; оптическая и электронная микроскопия; рентгенофазный анализ; измерение и визуальный анализ размеров и характера зон деформирования и разрушения. Результаты. В работе описаны экспериментальные данные о деформировании и разрушении преград из бетона, гранита, пенобетона, стали Ст 3, сплава АМЦ-н и цинка взрывами кумулятивных зарядов серийного производства с пористыми облицовками. Предложены расчетные формулы для оценки радиуса зоны разрушения геоматериалов и горных пород в случае полубесконечной преграды. Определены причины отклонений формы отверстия и зоны разрушения от оси симметрии. Научная новизна. Определены режимы проникания кумулятивных струй в породы различной пористости, размеры зоны разрушения вокруг отверстия, а также причины и механизмы отклонения формы отверстия от симметричной. Практическая значимость. Результаты исследований будут использованы для проектирования взрыво-прострелочных работ в геотехнологических скважинах и могут быть использованы для конструирования инициирующих устройств скважинных зарядов.The authors extend their sincere gratitude to the staff of Scientific Research Centre “Materialoobrobka vybukhom” (Processing Materials by Explosion) of the Paton Institute of Electric Welding affiliated with the National Academy of Sciences of Ukraine for the assistance in organization and conducting of the research. We would like to express special thanks to S.I. Kochetkov for the provided data on the velocity of longitudinal sound in solid sandy rocks, and to V.P. Bugaits for the assistance in experiments

Dynamically dominant magnetic fields in the diffuse interstellar medium

Observations show that magnetic fields in the interstellar medium (ISM) often do not respond to increases in gas density as would be naively expected for a frozen-in field. This may suggest that the magnetic field in the diffuse gas becomes detached from dense clouds as they form. We have investigated this possibility using theoretical estimates, a simple magneto-hydrodynamic model of a flow without mass conservation and numerical simulations of a thermally unstable flow. Our results show that significant magnetic flux can be shed from dense clouds as they form in the diffuse ISM, leaving behind a magnetically dominated diffuse gas.Comment: 2 pages, 1 figure. In proceedings of IAU Symposium 259: "Cosmic magnetic fields: from planets to stars and galaxies", eds. K.G. Strassmeier, A.G. Kosovichev & J.E. Beckman in pres

The supernova-regulated ISM. II. The mean magnetic field

The origin and structure of the magnetic fields in the interstellar medium of spiral galaxies is investigated with 3D, non-ideal, compressible MHD simulations, including stratification in the galactic gravity field, differential rotation and radiative cooling. A rectangular domain, 1x1x2 kpc^{3} in size, spans both sides of the galactic mid-plane. Supernova explosions drive transonic turbulence. A seed magnetic field grows exponentially to reach a statistically steady state within 1.6 Gyr. Following Germano (1992) we use volume averaging with a Gaussian kernel to separate magnetic field into a mean field and fluctuations. Such averaging does not satisfy all Reynolds rules, yet allows a formulation of mean-field theory. The mean field thus obtained varies in both space and time. Growth rates differ for the mean-field and fluctuating field and there is clear scale separation between the two elements, whose integral scales are about 0.7 kpc and 0.3 kpc, respectively.Comment: 5 pages, 10 figures, submitted to Monthly Notices Letter

Magnetic fields and spiral arms in the galaxy M51

(Abridged) We use new multi-wavelength radio observations, made with the VLA and Effelsberg telescopes, to study the magnetic field of the nearby galaxy M51 on scales from 200\pc to several \kpc. Interferometric and single dish data are combined to obtain new maps at \wwav{3}{6} in total and polarized emission, and earlier \wav{20} data are re-reduced. We compare the spatial distribution of the radio emission with observations of the neutral gas, derive radio spectral index and Faraday depolarization maps, and model the large-scale variation in Faraday rotation in order to deduce the structure of the regular magnetic field. We find that the \wav{20} emission from the disc is severely depolarized and that a dominating fraction of the observed polarized emission at \wav{6} must be due to anisotropic small-scale magnetic fields. Taking this into account, we derive two components for the regular magnetic field in this galaxy: the disc is dominated by a combination of azimuthal modes, $m=0+2$, but in the halo only an $m=1$ mode is required to fit the observations. We disuss how the observed arm-interarm contrast in radio intensities can be reconciled with evidence for strong gas compression in the spiral shocks. The average arm--interam contrast, representative of the radii r>2\kpc where the spiral arms are broader, is not compatible with straightforward compression: lower arm--interarm contrasts than expected may be due to resolution effects and \emph{decompression} of the magnetic field as it leaves the arms. We suggest a simple method to estimate the turbulent scale in the magneto-ionic medium from the dependence of the standard deviation of the observed Faraday rotation measure on resolution. We thus obtain an estimate of 50\pc for the size of the turbulent eddies.Comment: 21 pages, 18 figures (some at lower resolution than submitted version), accepted for publication in MNRA

The supernova-regulated ISM. I. The multi-phase structure

We simulate the multi-phase interstellar medium randomly heated and stirred by supernovae, with gravity, differential rotation and other parameters of the solar neighbourhood. Here we describe in detail both numerical and physical aspects of the model, including injection of thermal and kinetic energy by SN explosions, radiative cooling, photoelectric heating and various transport processes. With 3D domain extending 1 kpc^2 horizontally and 2 kpc vertically, the model routinely spans gas number densities 10^-5 - 10^2 cm^-3, temperatures 10-10^8 K, local velocities up to 10^3 km s^-1 (with Mach number up to 25). The thermal structure of the modelled ISM is classified by inspection of the joint probability density of the gas number density and temperature. We confirm that most of the complexity can be captured in terms of just three phases, separated by temperature borderlines at about 10^3 K and 5x10^5 K. The probability distribution of gas density within each phase is approximately lognormal. We clarify the connection between the fractional volume of a phase and its various proxies, and derive an exact relation between the fractional volume and the filling factors defined in terms of the volume and probabilistic averages. These results are discussed in both observational and computational contexts. The correlation scale of the random flows is calculated from the velocity autocorrelation function; it is of order 100 pc and tends to grow with distance from the mid-plane. We use two distinct parameterizations of radiative cooling to show that the multi-phase structure of the gas is robust, as it does not depend significantly on this choice.Comment: 28 pages, 22 figures and 8 table

Evolving turbulence and magnetic fields in galaxy clusters

We discuss, using simple analytical models and MHD simulations, the origin and parameters of turbulence and magnetic fields in galaxy clusters. Three physically distinct regimes can be identified in the evolution of cluster turbulence and magnetic fields. Firstly, the fluctuation dynamo will produce microgauss-strong, random magnetic fields during cluster formation and major mergers. Turbulent velocity of about 300 km/s can be maintained at scales 100-200 kpc. The magnetic field is intermittent, has a smaller scale of 20-30 kpc and average strength of 2 microgauss. Secondly, when major mergers end, turbulent speed and magnetic field undergo a power-law decay, decreasing in strength but increasing in scale by a factor of about two. Thirdly, smaller-mass subclusters and cluster galaxies produce turbulent wakes, with turbulent speeds and magnetic field strengths similar to those quoted above. The velocity scales are about 200 kpc and 10 kpc respectively, and the magnetic field scale is about 6 times smaller. Although these wakes may fill only a small fraction of the cluster volume, their area covering factor can be close to unity. So one can potentially reconcile observations that indicate the coexistence of turbulence with ordered filamentary gas structures, as in the Perseus cluster. Random Faraday rotation measure is estimated to be typically 100-200 rad/m^2, in agreement with observations. We predict detectable synchrotron polarization from cluster radio halos at wavelengths 3-6 cm, if observed at sufficiently high resolution (abridged).Comment: 20 pages, 9 figures, Replaced to match version accepted by MNRA