Non-ideal Explosives Research Articles

Effect of aluminum content on detonation velocity and density of emulsion explosives.

The performance of nonideal explosives, such as emulsion explosives, can be altered by metal powders like aluminum (Al) while keeping their other components the same. The high demand of emulsions coupled with various specific requirements, recommends a study on the performance of explosives. A research study on the detonation velocity of emulsion explosives variation with varying Al content in the emulsion matrix was carried out. The Al content in the emulsion matrix was varied from 0 to 20% and the corresponding density and detonation velocity (confined and unconfined) were measured. The misfire of emulsion explosives occurred at 20% Al content both in confined and unconfined conditions. The paper also focuses on the emulsion's density dependence on different Al content. The variation of density observed was in the range from 1.16 to 1.42g/cc. The results obtained can be used by blasting engineers to design higher explosives.

Explosion of aluminized mixtures in bubble column as a method of underwater compression wave enhancement

The results of experimental investigations of underwater explosions of ideally and nonideally detonating charges in continuous water and in water containing air bubbles are reported. Charges few tens of grams in weight were exploded in a metal reservoir filled with water. Parameters of compression waves generated by explosions in the reservoir were monitored. Based on the experimental data obtained the mechanism and the main stages of nonideal explosions as well as the nature of the effect of enhanced directed impact of blast waves on targets attained with the aid of bubble arrays are discussed.

Pressure Load Characteristics of Nonideal Explosives in a Simulation Cabin

In this study, an aluminum‐containing charge was exploded in an enclosed simulation cabin to explore the characteristics of two types of damaging pressure loads formed by internal explosions: the first incident shock wave and the quasistatic pressure. A high‐frequency piezoelectric sensor was used to measure the first incident shock wave and a low‐frequency piezoresistive sensor was used to measure the quasistatic pressure. After obtaining effective experimental data, the experimental results were compared with the values obtained by the classical calculation model. The results show that the pressure loads generated by the internal explosions from the ideal explosive and the aluminum‐containing explosive share similar load characteristics, given the same mass and benchmark explosive. The difference between the two explosives primarily lies in the amplitude of the load parameters. The aluminum‐containing explosive has lower first incident shock wave and higher quasistatic pressure than that of the ideal explosive. For the peak overpressure of the first incident shock wave, the explosion shock wave load parameters of the aluminum‐containing explosive, which are calculated based on the explosion heat theory, are higher than the measured values. The peak quasistatic overpressure is directly related to the total energy released by the explosion; however, they are hardly correlated with the reaction process. Therefore, the aerobic postcombustion reaction of the aluminum‐containing explosive does not affect the analysis and calculation of the peak quasistatic overpressure. As a result, given the heat value of the explosive, the peak quasistatic overpressure of the explosive can accurately be obtained.

The evolution of the temperature field during cavity collapse in liquid nitromethane. Part II: reactive case

This work is concerned with the effect of cavity collapse in non-ideal explosives as a means of controlling their sensitivity. The main objective is to understand the origin of localised temperature peaks (hot spots) which play a leading order role at the early stages of ignition. To this end, we perform two- and three-dimensional numerical simulations of shock-induced single gas-cavity collapse in liquid nitromethane. Ignition is the result of a complex interplay between fluid dynamics and exothermic chemical reaction. In the first part of this work, we focused on the hydrodynamic effects in the collapse process by switching off the reaction terms in the mathematical formulation. In this part, we reinstate the reactive terms and study the collapse of the cavity in the presence of chemical reactions. By using a multi-phase formulation which overcomes current challenges of cavity collapse modelling in reactive media, we account for the large density difference across the material interface without generating spurious temperature peaks, thus allowing the use of a temperature-based reaction rate law. The mathematical and physical models are validated against experimental and analytic data. In Part I, we demonstrated that, compared to experiments, the generated hot spots have a more complex topological structure and that additional hot spots arise in regions away from the cavity centreline. Here, we extend this by identifying which of the previously determined high-temperature regions in fact lead to ignition and comment on the reactive strength and reaction growth rate in the distinct hot spots. We demonstrate and quantify the sensitisation of nitromethane by the collapse of the isolated cavity by comparing the ignition times of nitromethane due to cavity collapse and the ignition time of the neat material. The ignition in both the centreline hot spots and the hot spots generated by Mach stems occurs in less than half the ignition time of the neat material. We compare two- and three-dimensional simulations to examine the change in topology, temperatures, and reactive strength of the hot spots by the third dimension. It is apparent that belated ignition times can be avoided by the use of three-dimensional simulations. The effect of the chemical reactions on the topology and strength of the hot spots in the timescales considered is also studied, in a comparison between inert and reactive simulations where maximum temperature fields and their growth rates are examined.

The evolution of the temperature field during cavity collapse in liquid nitromethane. Part I: inert case

This work is concerned with the effect of cavity collapse in non-ideal explosives as a means of controlling their sensitivity. The main objective is to understand the origin of localised temperature peaks (hot spots) which play a leading order role at the early stages of ignition. To this end, we perform two- and three-dimensional numerical simulations of shock-induced single gas-cavity collapse in liquid nitromethane. Ignition is the result of a complex interplay between fluid dynamics and exothermic chemical reaction. In order to understand the relative contribution between these two processes, we consider in this first part of the work the evolution of the physical system in the absence of chemical reactions. We employ a multi-phase mathematical formulation which can account for the large density difference across the gas–liquid material interface without generating spurious temperature peaks. The mathematical and physical models are validated against experimental, analytic, and numerical data. Previous inert studies have identified the impact of the upwind (relative to the direction of the incident shock wave) side of the cavity wall to the downwind one as the main reason for the generation of a hot spot outside of the cavity, something which is also observed in this work. However, it is also apparent that the topology of the temperature field is more complex than previously thought and additional hot spot locations exist, which arise from the generation of Mach stems rather than jet impact. To explain the generation mechanisms and topology of the hot spots, we carefully follow the complex wave patterns generated in the collapse process and identify specifically the temperature elevation or reduction generated by each wave. This enables tracking each hot spot back to its origins. It is shown that the highest hot spot temperatures can be more than twice the post-incident shock temperature of the neat material and can thus lead to ignition. By comparing two-dimensional and three-dimensional simulation results in the context of the maximum temperature observed in the domain, it is apparent that three-dimensional calculations are necessary in order to avoid belated ignition times in reactive scenarios.

A complete equation of state for non-ideal condensed phase explosives

The objective of this work is to improve the robustness and accuracy of numerical simulations of both ideal and non-ideal explosives by introducing temperature dependence in mechanical equations of state for reactants and products. To this end, we modify existing mechanical equations of state to appropriately approximate the temperature in the reaction zone. Mechanical equations of state of the Mie-Grüneisen form are developed with extensions, which allow the temperature to be evaluated appropriately and the temperature equilibrium condition to be applied robustly. Furthermore, the snow plow model is used to capture the effect of porosity on the reactant equation of state. We apply the methodology to predict the velocity of compliantly confined detonation waves. Once reaction rates are calibrated for unconfined detonation velocities, simulations of confined rate sticks and slabs are performed, and the experimental detonation velocities are matched without further parameter alteration, demonstrating the predictive capability of our simulations. We apply the same methodology to both ideal (PBX9502, a high explosive with principal ingredient TATB) and non-ideal (EM120D, an ANE or ammonium nitrate based emulsion) explosives.

A Simple Method for Calculating the Detonation Pressure of Ideal and Non-Ideal Explosives Containing Aluminum and Ammonium Nitrate

A Simple Method for Calculating the Detonation Pressure of Ideal and Non-Ideal Explosives Containing Aluminum and Ammonium Nitrate

The dependence of Ammonium-Nitrate Fuel-Oil (ANFO) detonation on confinement

As detonation is a coupled fluid-chemical process, flow divergence inside the detonation reaction zone can strongly influence detonation velocity and energy release. Such divergence is responsible for the diameter-effect and failure-diameter phenomena in condensed-phase explosives and particularly dominant in detonation of nonideal explosives such as Ammonium Nitrate and Fuel Oil (ANFO). In this study, the effect of reaction zone flow divergence on ANFO detonation was explored through variation of the inert confinement and explosive diameter in the rate-stick geometry with cylinder expansion experiments. New tests are discussed and compared to prior experiments. Presented results include the detonation velocity as a function of diameter and confinement, reaction zone times, detonation product isentropes and energies, as well as sonic surface pressures and velocities. Product energy densities and isentropes were found to increase with detonation velocity, indicating more complete chemical reaction with increased detonation velocity. Detonation reaction zone times were found to scale with the acoustic transit time of the confiner wall and used to show that the ANFO diameter effect scaled with the reaction zone time for a particle along the flow centerline, regardless of the confinement. Such a result indicates that the ANFO reaction mechanisms are sufficiently slow that the centerline fluid expansion timescale is a limiting factor controlling detonation velocity and energy release.

Model of non-ideal detonation of condensed high explosives

The Zeldovich-Neumann-Doering theory of ideal detonation allows one to describe adequately the detonation of charges with near-critical diameter. For smaller diameters, detonation velocity can differ significantly from an ideal value expected based on equilibrium chemical thermodynamics. This difference is quite evident when using non-ideal explosives; in certain cases, this value can be up to one third of ideal detonation velocity. Numerical simulation of these systems is a very labor-consuming process because one needs to compute the states inside the chemical reaction zone, as well as to obtain data on the equation of state of high-explosive detonation products mixture and on the velocity of chemical reaction; however, these characteristics are poorly studied today. For practical purposes, one can use the detonation shock dynamics model based on interrelation between local velocity of the front and its local curvature. This interrelation depends on both the equation of state of explosion products, and the reaction velocity; but the explicit definition of these characteristics is not needed. In this paper, experimental results are analyzed. They demonstrate interrelation between the local curvature of detonation front and the detonation velocity. Equation of detonation front shape is found. This equation allows us to predict detonation velocity and shape of detonation wave front in arbitrary geometry by integrating ordinary differential equation for the front shape with a boundary condition at the charge edge. The results confirm that the model of detonation shock dynamics can be used to describe detonation processes in non-ideal explosives.

Numerical and experimental study on cyclotrimethylenetrinitramine/aluminum explosives in underwater explosions

Underwater explosion experiments were conducted to determine the optimal performance of cyclotrimethylenetrinitramine (RDX)-based aluminized explosives with an aluminum content of 0%, 15%, and 30%. Free-field blast output energies of the three types of explosives were measured between 0.3 and 0.8 m. The shock wave energy, bubble energy, detonation energy, and energy heat release rate were measured. A new calculation method was based on the experimental results to simulate the bubble pulse process and pressure changes inside the bubbles of non-ideal explosives. The specific distance at which maximum total energy was achieved for the underwater explosion was determined.

Modelling of complex blast

There is an extensive hierarchy of models for the prediction of free-field blast wave propagation and loading. As one begins to move to more complex scenarios (e.g. near-field blast, non-ideal explosives, internal blast or buried charges), there is a need for more detailed understanding and modelling. In this article, we discuss a range of sub-models for the components of complex blast which can be used in hydrocode modelling of the loading of targets or structures. Many explosives are fuel-rich and thus have the capacity to undergo secondary combustion after detonation (afterburn). Even in the free field, this mechanism affects the wave profile and we illustrate the errors associated with simpler models, even for the case of detonation of a sphere of 2,4,6-trinitrotoluene (TNT) in the free field. We identify why these effects should be accounted for in any analysis of later time reflections in more complex targets and discuss how the effects of complex blast are also important in assessing human injury. We also report some engineering models which we have developed based on parameter studies using hydrocode models. The effects of any casing surrounding the explosive charge also influence the loading on a target, both by taking energy out of the blast wave and by accelerating fragments which produce a heterogeneous loading on a structure. Some blast mitigation concepts also make use of the transfer of energy to powder, liquid or foam surrounds. Buried charges can also behave in a similar manner to powder-based blast mitigants and lead to fast moving fingers of solid material which can produce localised loadings on structures. We identify how recent studies in these areas are influencing complex blast calculations.

Reactive flow modeling of small scale detonation failure experiments for a baseline non-ideal explosive

Small scale characterization experiments using only 1–5 g of a baseline ammonium nitrate plus fuel oil (ANFO) explosive are discussed and simulated using an ignition and growth reactive flow model. There exists a strong need for the small scale characterization of non-ideal explosives in order to adequately survey the wide parameter space in sample composition, density, and microstructure of these materials. However, it is largely unknown in the scientific community whether any useful or meaningful result may be obtained from detonation failure, and whether a minimum sample size or level of confinement exists for the experiments. In this work, it is shown that the parameters of an ignition and growth rate law may be calibrated using the small scale data, which is obtained from a 35 GHz microwave interferometer. Calibration is feasible when the samples are heavily confined and overdriven; this conclusion is supported with detailed simulation output, including pressure and reaction contours inside the ANFO samples. The resulting shock wave velocity is most likely a combined chemical-mechanical response, and simulations of these experiments require an accurate unreacted equation of state (EOS) in addition to the calibrated reaction rate. Other experiments are proposed to gain further insight into the detonation failure data, as well as to help discriminate between the role of the EOS and reaction rate in predicting the measured outcome.

The Use of the Propellant Specific Impulse for the Prediction of the Prompt and Terminal Gurney Velocity of High Explosives

Simple relationships are presented for the calculation of both prompt and terminal Gurney velocity of chemical high explosives. By considering that a given explosive behaves like a propellant, its specific impulse was calculated using Mader’s ISPBKW code; it was found that the density impulse (where is the explosive density and is an empirically optimized variable) performance factor correlates well with the terminal Gurney velocity of both ideal and nonideal explosives. Furthermore, the cylinder wall energy can be computed from (from which the prompt Gurney velocity can be obtained through the application of the Gurney’s cylinder equation. It was concluded that ( is a powerful factor for the prediction of the Gurney velocities, especially for nonideal compositions.

Three-Tier Strategy for Screening High-Energy Molecules Using Structure–Property Relationship Modeling Approaches

Experimental determination of the explosive properties of chemicals is a tedious, time- and resource-intensive, and involved risk. In this study, we have established a three-tier structure–property relationship (SPR) modeling strategy for screening the chemicals for their explosive behavior. Accordingly, qualitative (ternary classification: nonexplosive, ideal and nonideal explosive), semiquantitative (binary classification: industrial and high explosive), and quantitative SPR models based on decision tree forest (DTF) and decision tree boost (DTB) algorithms were developed for discriminating the chemicals in different categories and predicting the detonation velocity (DV) of ideal and lower flammability limit (LFL) of nonideal explosives in accordance with the OECD guidelines. The statistical quality and external predictive power of the developed SPR models were evaluated through the internal and external validation procedures. In the test set, the qualitative and semiquantitative SPR models (DTF, DTB) r...

An Improved Simple Method for the Calculation of the Detonation Performance of CHNOFCl, Aluminized and Ammonium Nitrate Explosives

An improved simple method is presented for calculation of the detonation velocity of CHNO and CHNOFCl explosives, as well as non-ideal explosives containing aluminum (Al) and ammonium nitrate (AN) additives. In contrast to the available complex computer codes, where the estimated detonation velocities of non-ideal explosives for equilibrium and steady state calculations show significant differences from the measured data, this simple method gives more reliable results. Suitable decomposition paths are suggested in which the partial interaction of Al with the gaseous products and the decomposition of AN are assumed for composite explosives containing Al/AN additives. The predicted detonation velocities using the new method are good compared to those from one of the well-known empirical methods and from computer codes using full and partial equilibrium of Al/AN.

Scaling of detonation velocity in cylinder and slab geometries for ideal, insensitive and non-ideal explosives

Experiments were conducted to characterize the detonation phase-velocity dependence on charge thickness for two-dimensional detonation in condensed-phase explosive slabs of PBX 9501, PBX 9502 and ANFO. In combination with previous diameter-effect measurements from a cylindrical rate-stick geometry, these data permit examination of the relative scaling of detonation phase velocity between axisymmetric and two-dimensional detonation. We find that the ratio of cylinder radius ($R$) to slab thickness ($T$) at each detonation phase velocity ($D_{0}$) is such that$R(D_{0})/T(D_{0})<1$. The variation in the$R(D_{0})/T(D_{0})$scaling is investigated with two detonation shock dynamics (DSD) models: a lower-order model relates the normal detonation velocity to local shock curvature, while a higher-order model includes the effect of front acceleration and transverse flow. The experimentally observed$R(D_{0})/T(D_{0})$(${<}1$) scaling behaviour for PBX 9501 and PBX 9502 is captured by the lower-order DSD theory, revealing that the variation in the scale factor is due to a difference in the slab and axisymmetric components of the curvature along the shock in the cylindrical geometry. The higher-order DSD theory is required to capture the observed$R(D_{0})/T(D_{0})$(${<}1$) scaling behaviour for ANFO. An asymptotic analysis of the lower-order DSD formulation describes the geometric scaling of the detonation phase velocity between the cylinder and slab geometries as the detonation phase velocity approaches the Chapman–Jouguet value.

Numerical modelling of underwater detonation of non-ideal condensed-phase explosives

The interest in underwater detonation tests originated from the military, since the expansion and subsequent collapse of the explosive bubble can cause considerable damage to surrounding structures or vessels. In military applications, the explosive is typically represented as a pre-burned material under high pressure, a reasonable assumption due to the short reaction zone lengths, and complete detonation of the unreacted explosive. Hence, numerical simulations of underwater detonation tests have been primarily concerned with the prediction of target loading and the damage incurred rather than the accurate modelling of the underwater detonation process. The mining industry in contrast has adopted the underwater detonation test as a means to experimentally characterise the energy output of their highly non-ideal explosives depending on explosive type and charge configuration. This characterisation requires a good understanding of how the charge shape, pond topography, charge depth, and additional charge confinement affect the energy release, some of which can be successfully quantified with the support of accurate numerical simulations. In this work, we propose a numerical framework which is able to capture the non-ideal explosive behaviour and in addition is capable of capturing both length scales: the reaction zone and the pond domain. The length scale problem is overcome with adaptive mesh refinement, which, along with the explosive model, is validated against experimental data of various TNT underwater detonations. The variety of detonation and bubble behaviour observed in non-ideal detonations is demonstrated in a parameter study over the reactivity of TNT. A representative underwater mining test containing an ammonium-nitrate fuel-oil ratestick charge is carried out to demonstrate that the presented method can be readily applied alongside experimental underwater detonation tests.

The Experimental Research of Air Explosion of Non-Ideal Explosives

The relationship of shock wave peak overpressure and the positive impulse of 10kg TNT, PW0,PW20,PW30 high energy explosives with different Al content and distance were studied through air explosion experiments. Besides, the damage of 140kg explosives to concrete and human being were analysized and calculated based on the fitted formulas, which shows that the damage area of PW20 is larger than other explosives.

Experimental measurement of the scaling of the diameter- and thickness-effect curves for ideal, insensitive, and non-ideal explosives

Numerous two-dimensional high-explosive slab tests were fielded for explosives that exhibit ideal (PBX 9501), slightly non-ideal (PBX 9502), and highly non-ideal (ANFO) detonation. Detonation velocity versus slab thickness t (thickness-effect curves) are compared to previous diameter-effect measurements obtained by varying the diameter d of cylindrical rate sticks. The scale factors d/t necessary to overlay the diameter- and thickness-effect curves were computed for each explosive formulation. We observe that the scale factor varies with detonation velocity (or level of detonation "ideality"). The measured scale factors range from 1.89–2.20, 1.25–1.87, and 1.79–1.05 for PBX 9501, PBX 9502, and ANFO formulations, respectively, as detonation velocity varies from the (near failure) critical velocity to the Chapman-Jouguet velocity. These results support our previous theoretical prediction that the scale factor relating the diameter- and thickness-effect curves will increasingly deviate from two as the detonation structure becomes increasingly non-ideal.

Measurements of near-field blast effects using kinetic plates

Few tests have been designed to measure the near-field blast impulse of ideal and non-ideal explosives, mostly because of the inherent experimental difficulties due to non-transparent fireballs and thermal effects on gauges. In order to measure blast impulse in the near-field, a new test has been developed by firing spherical charges at 152 mm (6 in) from steel plates and probing acceleration using laser velocimetry. Tests measure the velocity imparted to the steel plate in the 50 – 300 μs timeframe, and are compared with free-field overpressure measurements at 1.52 m (5 ft) and ms timescales using piezoelectric pencil gauges. Specifically, tests have been performed with C4 to probe the contributions of ideal explosives and charge size effects. Non-ideal aluminized explosive formulations have been studied to explore the role of aluminum in near-field blast effects and far-field pressure, and are compared with formulations using LiF as an inert surrogate replacement for Al. The results are compared with other near-field blast tests and cylinder tests, and the validity of this test is explored with modeling and basic theory.