Granular Explosives Research Articles

Application features of granular explosives in underground mining in Oktyabrsky Mine

Application features of granular explosives in underground mining in Oktyabrsky Mine

Size-dependent shock response mechanisms in nanogranular RDX: a reactive molecular dynamics study.

Understanding the shock initiation mechanisms of explosives is pivotal for advancing physicochemical theories and enhancing experimental methodologies. This study delves into the size-dependent shock responses of nanogranular hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) through nonequilibrium reactive molecular dynamics simulations. Utilizing the ReaxFF-lg force field, we examine the influence of the particle size on the decomposition dynamics of RDX under varying shock velocities. Our findings reveal that larger particles promote more significant RDX decomposition at lower velocities due to fluid jet formation and gas compression during void collapse. Conversely, smaller particles exhibit a higher average temperature and a faster decomposition rate under high-velocity shocks, attributed to their increased specific surface area. Detailed chemical reaction pathways are analyzed to elucidate the growth and initiation of reactions during shock waves. The results contribute to resolving the discrepancies observed in experimental studies of shocked granular explosives and provide a deeper understanding of the underlying mechanisms governing their behavior. This research offers valuable insights into the design and control of nano- and submicron-sized explosives with tailored sensitivity to external stimuli.

Исследования техногенного воздействия взрывного разрушения горных пород при освоении месторождений полезных ископаемых открытым способом

The topicality of this research is defined by the increasing volume of mining operations near settlements and production infrastructure, as well as by the increasing unit capacity of mining and haulage equipment and, consequently, by the growing volume of rock mass simultaneously blasted and prepared for excavation. Changes in the mining conditions at the operations of UK Kuzbassrazrezugol JSC have been analyzed. A brief analysis of research results on various factors affecting the degree of man-made impact of the blasting operations is presented. One of the ways to safely increase the volume of simultaneously blasted rock mass is the introduction of energy-saving environmentally friendly technologies in production and use of plastic explosives, which would ensure higher completeness of chemical transformations and the efficiency of the blast through the use of special fuel mixtures containing surfactants instead of diesel fuel in the compositions of granular industrial explosives. This will increase the contact surface area of the fuel and the oxidizer by several orders of magnitude as well as the stability and the energy-output ratio of the blasting charges with the zero oxygen-combustible balance. Reducing the consumption of explosives, energy intensity of mining, the man-made impact of blasting operations on the environment, the seismic action of the blast, the radius of the hazardous zone - all of this can be achieved by using charges placed in hoses of variable diameter when blasting wet and dry rock masses. The article shows the dependence of changes in the load on the atmosphere with increasing distance from the blast epicenter and with increasing weight of simultaneously detonated explosives in surface mining operations, as well as the dependence between the yield of fines and the size of the gap between the charge and the charging chamber.

The minimum entropy principle for a two‐phase flow model

Bounded entropy solutions of the Baer–Nunziato model of two‐phase flows are proved to satisfy the minimum entropy principle; that is, the spatial infimum of the specific entropy is an increasing function of time. The model was derived for the study of deflagration‐to‐detonation transition in granular explosives and consists of seven nonlinear partial differential equations with nonconservative source terms. Apparently, we will also show that the generalized entropy inequality can be reduced in the usual divergence form for standard entropy pairs in gas dynamics equations.

Assessment of the Parameters of a Shock Wave on the Wall of an Explosion Cavity with the Refraction of a Detonation Wave of Emulsion Explosives

At present, studying the parameters of shock waves at pressures up to 20 GPa entails a number of practical difficulties. In order to describe the propagation of shock waves, their initial parameters on the wall of the explosion cavity need to be known. With the determination of initial parameters, pressures in the near zone of the explosion can be calculated, and the choice of explosives can be substantiated. Therefore, developing a method for estimating shock wave parameters on an explosion cavity wall during the refraction of a detonation wave is an important problem in blast mining. This article proposes a method based on the theory of breakdown of an arbitrary discontinuity (the Riemann problem) to determine the shock wave parameters on the wall of the explosion cavity. Two possible variants of detonation wave refraction on the explosion cavity wall are described. This manuscript compares the parameters on the explosion cavity wall when using emulsion explosives with those obtained using cheap granular ANFO explosives. The detonative decomposition of emulsion explosives is also considered, and an equation of state for gaseous explosion products is proposed, which enables the estimation of detonation parameters while accounting for the incompressible volume of molecules (covolume) at the Chapman–Jouguet point.

A staggered-projection Godunov-type method for the Baer-Nunziato two-phase model

When describing the deflagration-to-detonation transition in solid granular explosives mixed with gaseous products of combustion, a well-developed two-phase mixture model is the compressible Baer-Nunziato (BN) model of flows containing solid and gas phases. As this model is numerically simulated by a conservative Godunov-type scheme, spurious oscillations are likely to generate from porosity interfaces, and may result from the average process of conservative variables that violates the continuity of Riemann invariants across porosity interfaces. In order to reduce numerical oscillations, this paper proposes a staggered-projection Godunov-type scheme over a fixed gas-solid staggered grid, by enforcing that compaction waves with porosity jumps are always inside gaseous grid cells and other discontinuities appear at gaseous cell interfaces. The scheme is based on a standard Godunov scheme for the Baer-Nunziato model on gaseous cells and guarantees the continuity of the Riemann invariants associated with the compaction waves across porosity jumps. While porosity interfaces are moving, a projection process fully takes into account the continuity of associated Riemann invariants and ensures that porosity jumps remain inside gaseous cells. Furthermore, the generalized Riemann problem (GRP) solver is applied, not only to achieve second-order accuracy, reduce numerical oscillations, but guarantees the well-balanced property of the resulting scheme as well.

Shock structure for the seven-equation, two-phase continuum-mixture model

Continuum models of two-phase flow have been employed to investigate a wide variety of physical phenomena, ranging from bubbly-gas and solid-loaded liquid flows to detonation waves in granular explosives. The set of governing equations consists of mass, momentum and energy balance for each phase, and an equation for the evolution of volume fraction of either phase. The set is closed by providing an equation of state for each phase and by specifying the inter-phase interaction terms. Examination of the time scales associated with the interaction terms shows that in many regions of the flow, the pressures and velocities equilibrate rapidly, which has led to the development of a single-pressure and single-velocity reduced, 5-equation model. Such a reduction is incomplete in that it omits thin shock-like regions (inner layers) where pressure and velocity changes can remain. To regularise the reduced model, a number of studies have added dissipative terms which smoothen and thereby resolve these thin shock-like regions. However, the sensitivity of the solution to the choice of regularisation has not been investigated. Further, although the 5-equation model has been used extensively in the literature for numerical computations, its regularisation is often left to the numerical method employed. This study carries out a systematic analysis of the structure of this thin shock-like inner layer, with emphasis on the dependence of the structure of the layer and of the jumps across it on system parameters. The results are compared with those obtained via computations with the parent, 7-equation model.

Influence of Particle Size of Explosive on Ignition Mechanism Under Low Velocity Impact

AbstractDrop‐weight impact experiments are performed on different particle size Octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine (HMX) granular explosives. The drop‐weight impact machine is equipped with the high‐speed photographic systems for obtaining a mechanical‐chemical image of the impact process. The experimental image shows that the small particles of 700 μm have melted for a long time and over a large area during the loading process. HMX particle size affects the ignition mechanism. For a single particle, the ignition mechanism changes from friction to viscous heating with the decrease of particle size. The ignition mechanism of 6000 μm and 1800 μm HMX particles is friction work. The ignition mechanism of HMX small particles of 700 μm includes friction work and viscous heat under drop weight impact.

Cover Picture: Nonlinear Resonant Ultrasound Spectroscopy for Predicting Sensitivity to Initiation in Granular High Explosives (Prop., Explos., Pyrotech. 3/2020)

Cover Picture: Nonlinear Resonant Ultrasound Spectroscopy for Predicting Sensitivity to Initiation in Granular High Explosives (Prop., Explos., Pyrotech. 3/2020)

Deflagration-to-detonation transition in hot HMX and HMX-based polymer-bonded explosives

The deflagration-to-detonation transition (DDT) in hot, thermally damaged HMX (δ-phase) and HMX-based polymer-bonded explosives (PBX 9501, LX-14, LX-10 and PBX 9012) differs in some respects from what has been observed in similar tests (DDT tube experiments) with room temperature granular explosives. We provide streak images with other observations and demonstrate the behavior can be binned according to the degree of porosity evolved from physical and chemical damage to the compositions. In each bin, the DDT behavior eventually organizes to resemble Type I DDT, but differs in the early-stage burn phenomena and how a propulsive thermal explosion event arises. We argue that the hot explosive properties, such as permeability and compressibility, and the morphological characteristics of the thermal damage, control the physical mechanism for establishment of the thermal explosion. In some cases, these observations may need to be carefully implemented in numerical models to increase predictive value for these materials at elevated temperature. With high-porosity (ϕ ≈ 20–50%), the PBXs behaved like granular beds. At intermediate levels of porosity (ϕ ≈ 4–20%), the transition occurred over longer distances and the process is characterized by a weak, slow convective burn precursor that sets up thermal runaway to explosion behind the flame infiltration front. In the low-porosity bin (ϕ ≈ 0–4%), where run lengths were short, the thermal explosion is the result of compressive, and possibly also, deconsolidative burning. It is clear that the high-temperature conditions imposed in these experiments caused sensitization towards DDT and this effect was most apparent in tests where the explosive was heated until runaway and auto-ignition where transition distances were among the shortest measured. Practical findings include there being some safety benefit for having binders in HMX formulations, especially when the binder is thermally stable.

ЗАВИСИМОСТЬ ЭЛЕКТРОСТАТИЧЕСКОГО ПОТЕНЦИАЛА ОТ СКОРОСТИ ТРАНСПОРТИРОВАНИЯ ПРИ ПНЕВМОЗАРЯЖАНИИ

The wide use of pneumatic method of loading and portage of granular explosives (ВВ) at the conduct of mountain works specifies on the necessity of researches of defects concomitant to this method: namely an origin of electrification in a charge hose. Electric potential and charge are the basic parameters of the energy distinguished at a digit, the amount of warmth of thatgoes to the warming-up of VV. In the total, knowing the minimum temperatures of selfignition of a erodredges, it is possible to control the size ofelectric charge and exceeding of that conduces to the unplanned explosion.

An HLLC-type Riemann solver and high-resolution Godunov method for a two-phase model of reactive flow with general equations of state

A high-resolution Godunov method is developed for a two-phase model of reactive flow. The model considers general equations of state of Mie-Grüneisen form and different choices for the reaction rate, both relevant for simulations of the dynamical behavior of detonations in PBX-type granular explosives. The numerical approach employs a Riemann solver, and various options ranging from an exact solver to an approximate solver of HLLC type are described. A principal aim of the paper is an assessment of the approximate Riemann solvers in terms of the accuracy and efficiency of numerical solutions of the two-phase model. In particular, this study considers the state-sensitive behavior in different regimes of the solutions in a reverse-impact configuration, including compaction, run to detonation, and the evolution to compaction-led and reaction-led steady detonations. For these regimes, the convergence properties of the numerical approach are examined for the different choices of the Riemann solver, as is the error in the solutions at lower grid resolution. Finally, the computational performance of the time-stepping scheme is assessed for the different solvers.

Nonlinear Resonant Ultrasound Spectroscopy for Predicting Sensitivity to Initiation in Granular High Explosives

AbstractNonlinear Resonant Ultrasound Spectroscopy (NRUS) is a technique that can measure bulk nonlinear coefficients of the nonlinear elastic modulus for a material. NRUS has been used to identify damage in a variety of granular materials including rocks and concrete. Some energetic materials, such as Pentaerythritol Tetranitrate (PETN), are commonly fielded as pressed granular compacts. It is well known that the sensitivity to initiation of these materials is heavily dependent on their microstructure, and that microstructure changes naturally (becomes damaged) over time. In this study, we examine the use of NRUS to identify changes in microstructure between pristine and thermally aged PETN pellets. In particular, we examine the relationship between the bulk hysteretic nonlinearity, α, of the pellets and time spent at temperature, powder specific surface area (SSA), and sensitivity to initiation. We find that, in general, α does not increase uniformly for all pellets within a single thermal aging condition. However, when the pellets are test fired to determine sensitivity to initiation, there is a strong correlation between α and firing voltage threshold. NRUS‐measured α has the added benefit that the measurements can be made in situ and on benchtop scales.

Impact of surface energy on the shock properties of granular explosives.

This paper presents the first part of a two-fold molecular dynamics study of the impact of the granularity on the shock properties of high explosives. Recent experimental studies show that the granularity can have a substantial impact on the properties of detonation products {i.e., variations in the size distributions of detonation nanodiamonds [V. Pichot et al., Sci. Rep. 3, 2159 (2013)]}. These variations can have two origins: the surface energy, which is a priori enhanced from micro- to nano-scale, and the porosity induced by the granular structure. In this first report, we study the impact of the surface-energy contribution on the inert shock compression of TATB, TNT, α-RDX, and β-HMX nano-grains (triaminotrinitrobenzene, trinitrotoluene, hexogen and octogen, respectively). We compute the radius-dependent surface energy and combine it with an ab initio-based equation of state in order to obtain the resulting shock properties through the Rankine-Hugoniot relations. We find that the enhancement of the surface energy results in a moderate overheating under shock compression. This contribution is minor with respect to porosity, when compared to a simple macroscopic model. This result motivates further atomistic studies on the impact of nanoporosity networks on the shock properties.

Chemical compatibility of granular explosives and sulfide ore in a sealed ampoule

Chemical compatibility of granular explosives and sulfide ore in a sealed ampoule

The behavior limestone under explosive load

Limestone behavior under explosive loading was investigated. The behavior of the limestone by the action of the three types of explosives, including granular, ammonite and emulsion explosives was studied in detail. The shape and diameter of the explosion craters were obtained. The observed fragments after the blast have been classified as large, medium and small fragments. Three full-scale experiments were carried out. The research results can be used as a qualitative test for the approbation of numerical methods.

Numerical simulation of deflagration to detonation transition in granular HMX explosives under thermal ignition

To study the deflagration to detonation transition process in granular explosive under thermal ignition condition, the conductive burning is introduced into the classical model. The novel space–time conservation element and solution element method is applied to solve the mathematical governing equations. The transition process in granular HMX bed which is packed to 85 % of theoretical maximum density is simulated. The development of conductive burning, convective burning and detonation is analyzed. In the early stage, the combustion propagates slowly. It moves no more than 0.2 mm within 8.16 ms. After onset of convective burning, it takes only 20 μs to form a steady detonation with the velocity of 8165 m s−1. The time to detonation increases with the decrease in particle diameter.

Analysis of microstructure-dependent shock dissipation and hot-spot formation in granular metalized explosive

Variations in the microstructure of granular explosives (i.e., particle packing density, size, shape, and composition) can affect their shock sensitivity by altering thermomechanical fields at the particle-scale during pore collapse within shocks. If the deformation rate is fast, hot-spots can form, ignite, and interact, resulting in burn at the macro-scale. In this study, a two-dimensional finite and discrete element technique is used to simulate and examine shock-induced dissipation and hot-spot formation within low density explosives (68%–84% theoretical maximum density (TMD)) consisting of large ensembles of HMX (C4H8N8O8) and aluminum (Al) particles (size ∼60–360 μm). Emphasis is placed on identifying how the inclusion of Al influences effective shock dissipation and hot-spot fields relative to equivalent ensembles of neat/pure HMX for shocks that are sufficiently strong to eliminate porosity. Spatially distributed hot-spot fields are characterized by their number density and area fraction enabling their dynamics to be described in terms of nucleation, growth, and agglomeration-dominated phases with increasing shock strength. For fixed shock particle speed, predictions indicate that decreasing packing density enhances shock dissipation and hot-spot formation, and that the inclusion of Al increases dissipation relative to neat HMX by pressure enhanced compaction resulting in fewer but larger HMX hot-spots. Ensembles having bimodal particle sizes are shown to significantly affect hot-spot dynamics by altering the spatial distribution of hot-spots behind shocks.

Compaction shock dissipation in low density granular explosive

The microstructure of granular explosives can affect dissipative heating within compaction shocks that can trigger combustion and initiate detonation. Because initiation occurs over distances that are much larger than the mean particle size, homogenized (macroscale) theories are often used to describe local thermodynamic states within and behind shocks that are regarded as the average manifestation of thermodynamic fields at the particle scale. In this paper, mesoscale modeling and simulation are used to examine how the initial packing density of granular HMX (C4H8N8O8) C4H8N8O8 having a narrow particle size distribution influences dissipation within resolved, planar compaction shocks. The model tracks the evolution of thermomechanical fields within large ensembles of particles due to pore collapse. Effective shock profiles, obtained by averaging mesoscale fields over space and time, are compared with those given by an independent macroscale compaction theory that predicts the variation in effective thermomechanical fields within shocks due to an imbalance between the solid pressure and a configurational stress. Reducing packing density is shown to reduce the dissipation rate within shocks but increase the integrated dissipated work over shock rise times, which is indicative of enhanced sensitivity. In all cases, dissipated work is related to shock pressure by a density-dependent power law, and shock rise time is related to pressure by a power law having an exponent of negative one.

Mesoscale thermal-mechanical analysis of impacted granular and polymer-bonded explosives

Localized deformation within energetic materials under impact loading may lead to the formation of hot spots, which can cause initiation or detonation of energetic materials. In this work, the thermal-mechanical response of cyclotetramethylene-tetranitramine (HMX) based granular explosives (GXs) and polymer-bonded explosives (PBXs) under impact loading has been investigated using finite element software ABAQUS. A series of three-dimensional mesoscale calculations is performed at impact velocities from 100m/s to 500m/s using a crystal plasticity constitutive model for HMX crystals that accounts for nonlinear, anisotropic thermoelasticity and for crystal plasticity. For PBX simulations, a viscoelasticity model is used for the polymer binder. Results show that the average and localized stress and temperature field, which are greatly affected by crystal anisotropy and polymer binder, of GXs are larger than those of PBXs. Qualitative agreement with Pop Plots from the experiments shows that GXs are more sensitive than PBXs.