Influence of Ammonium Nitrate Prills' Properties on Detonation Velocity of ANFO

Prilled/granulated ammonium nitrate is commonly used as a fertilizer and a basic ingredient of industrial explosives, especially of ANFO. One of the most important factors that affect the explosive properties of ANFO is the porosity of the prills/granules. This paper describes an attempt to manufacture ammonium nitrate prills of determined porosity in order to investigate its influence on the ANFO detonation velocity. A method of manufacturing porous ammonium nitrate prills with a high‐level of oil absorption (up to 20% by volume) was developed. The relations between porosity and granulometric distribution of ammonium nitrate prills versus the detonation velocity of ANFO were examined. It has been proved that the detonation velocity of ANFO increases significantly with higher porosity and smaller size of ammonium nitrate prills/granules. The influence of ANFO oxygen balance (researched by changing the content of fuel oil in the mixture) on detonation velocity has been determined for two kinds of ammonium nitrate prills–one with a low and another one with a high level of porosity.     

An empirical confinement model for ANFO explosive

Ammonium-nitrate-fuel-oil (ANFO) explosive, one of the most used mining explosives, exhibits highly non-ideal behaviour. The non-ideality of the detonation is manifested in the strong dependence of the detonation velocity on the charge radius and existence and the characteristics of confinement. This can lead to the detonation velocities as low as one-third of the ideal velocity. The literature reported experimental detonation velocities of cylindrical ANFO charges confined in different confiners (aluminium, copper, steel, polymethyl methacrylate, and polyvinyl chloride) are analysed in this paper. An empirical confinement model, which relates the detonation velocity to the charge radius and the mass of the confiner to the mass of explosive ratio per unit length, is proposed. The model predicts the detonation velocity of unconfined and confined ANFO charges with a mean average percentage error of 8.8 %.     

Calculation of the Energy of Explosives with a Partial Reaction Model. Comparison with Cylinder Test Data

The energy delivered by explosives is described by means of the useful expansion work along the isentrope of the detonation products. A thermodynamic code (W‐DETCOM) is used, in which a partial reaction model has been implemented. In this model, the reacted fraction of the explosive in the detonation state is used as a fitting factor so that the calculated detonation velocity meets the experimental value. Calculations based on such a model have been carried out for a number of commercial explosives of ANFO and emulsion types. The BKW (Becker‐Kistiakowsky‐Wilson) equation of state is used for the detonation gases with the Sandia parameter set (BKWS). The energy delivered in the expansion (useful work) is calculated, and the values obtained are compared with the Gurney energies from cylinder test data at various expansion ratios. The expansion work values obtained are much more realistic than those from an ideal detonation calculation and, in most cases, the values predicted by the calculation are in good agreement with the experimental ones.     

Analytic Model of Reactive Flow

A simple analytic model allows prediction of rate constants and size effect behavior before a hydrocode run, if size effect data exist. It utilizes detonation velocity, average detonation rate, pressure and energy at infinite radius. This allows the derivation of a generalized radius, which becomes larger as the explosive becomes more non‐ideal. The model is applied to near‐ideal PBX 9404, in‐between ANFO and most non‐ideal AN. The power of the pressure declines from 2.3, and 1.5 to 0.8 across this set. The power of the burn fraction, F, is 0.8, 0 and 0, so that an F‐term is important only for the ideal explosives. The size effect shapes change from concave‐down to nearly straight to concave‐up. Failure is associated with ideal explosives when the calculated detonation velocity turns in a double‐valued way. The effect of the power of the pressure may be simulated by including a pressure cut‐off in the detonation rate. The model allows comparison of a wide spectrum of explosives providing that a single detonation rate is feasible.     

Performance Properties of Commercial Explosives

The aquarium test is a proven means of obtaining nonidial performance property data for commercial blasting agents. Optical data on the detonation velocity, shock wave in water, and expansion rate of the pipe enclosing the detonation products (in combination with the equilibrium thermodynamic chemistry code BKW) give the C-J state and degree of chemical reaction at the detonation front, as well as information on additional chemical reaction that occurs as the detonation products expand. Specific explosive systems that are studied are ammonium nitrate-fuel oil mixture (ANFO), aluminized ANFO, flaked trinitrotoluene (TNT), and several other commercial products in 10-cm-diam and 20-cm-diam pipes of Plexiglas and clay. Experimental shock pressure data are obtained with lithium niobate transducers placed in the water surrounding the explosive charge. These data show that the addition of ∼ 100-μm aluminum particles to ANFO significantly increases the initial peak shock pressure delivered to the surrounding medium. Peak shock pressures in the water, calculated from the shock-wave orientation, are also useful in comparing performance properties of various commercial explosives.     

The Dead-Pressing Phenomenon in an ANFO Explosive

The dead-pressing phenomenon or pressure desensitization in ANFO as well as in other civil explosives is well-known. However, to our knowledge, the detailed study of this phenomenon in ANFO has not been carried out or reported. Therefore, such a study was planned in a SveDeFo research program. Blasting experiments in iron pipes were performed. Mainly, the density of dead-pressing and the transmission distance of detonation in the dead-pressed ANFO were studied. The results show that the dead-pressing density of the tested ANFO, Prillit A (a trademark of Nitro Nobel AB in Sweden), in diameters 45 mm, 60 mm and 75 mm of steel pipes is respectively 1.35, 1.39 and 1.43 [g/cm³]. The dependence of the detonation transmission distance on the density of the ANFO has also been outlined.     

Simulation of Explosive Welding with ANFO Mixtures

The work described here arose from a study into explosive welding. As part of that study, the impact velocity of stainless steel and titanium plates to grazing detonation of ANFO/perlite, the velocity of detonation were measured. Computer simulation required a new model which copes with an equation of state of low explosives.     

改性铵油炸药连续爆速实验研究

采用连续速度探针研究改性铵油炸药在不同起爆条件下爆速和爆轰成长的连续变化.在起爆条件分别为雷管/160g起爆药柱、雷管/160g起爆药柱/有机玻璃隔板和仅采用雷管时,改性铵油炸药在稳定爆轰阶段的稳定爆速分别为4569m/s、4496m/、4559m/s,爆轰成长距离分别为3.5、7.3和20cm,爆轰成长时间分别为0.01、0.025和0.06ms.结果表明,在相同的装药约束条件下,起爆能量越大,改性铵油炸药爆轰成长时间和爆轰成长距离越短,即越容易发展为稳定爆轰.     

Dead Zones in LX‐17 and PBX 9502

Pin and X‐ray corner turning data have been taken on ambient LX‐17 and PBX 9052, and the results are listed in tables as an aid to future modeling. The results have been modeled at 4 zones/mm with a reactive flow approach that varies the burn rate as a function of pressure. A single rate format is used to simulate failure and detonation in different pressure regimes. A pressure cut‐off must also be reached to initiate the burn. Corner turning and failure are modeled using an intermediate pressure rate region, and detonation occurs at high pressure. The TATB booster is also modeled using reactive flow, and X‐ray tomography is used to partition the ram‐pressed hemisphere into five different density regions. The model reasonably fits the bare corner turning experiment but predicts a smaller dead zone with steel confinement, in contradiction with experiment. The same model also calculates the confined and unconfined cylinder detonation velocities and predicts the failure of the unconfined cylinder at 3.75 mm radius. The PBX 9502 shows a smaller dead zone than LX‐17. An old experiment that showed a large apparent dead zone in Composition B was repeated with X‐ray transmission and no dead zone was seen. This confirms the idea that a variable burn rate is the key to modeling. The model also produces initiation delays, which are shorter than those found in time‐to‐detonation.     

Detonation Wave Propagation in Double‐layer Cylindrical High Explosive Charges

The flow fields associated with regular and irregular reflections of detonation waves in double‐layer cylindrical (DLC) high explosives (HE) are analyzed, and an analytical model for predicting the detonation wave configurations is proposed. Regular reflection and three‐shock Mach reflection during detonation wave propagation are discussed. Calculated results of pressure, flow velocity, and specific volume are presented and the Mach stem height is also determined based on mass conservation. The corresponding numerical simulation based on the Lee–Tarver model is developed to generate data comparable with an ordinary cylindrical charge. It is shown that steady convergent detonation wave propagation occurs in the DLC charge. The maximum pressure up to 4.0 times of Chapman–Jouguet (CJ) pressure is reached at the collision point related to the Mach reflection, and the predictions based on the proposed model correlate well with corresponding numerical results.     

Detonation Performance of TATP/AN‐Based Explosives

The detonation velocity and performance were determined for four mixtures of triacetone triperoxide (3,3,6,6,9,9‐hexamethyl‐1,2,4,5,7,8‐hexoxonane, TATP), ammonium nitrate (AN) and water (W) by cylinder expansion tests. The composition of these mixtures varied in the following ranges: 21–31% TATP, 37–54% AN and 19–32% W. The obtained results were compared with those of powdery 2,4,6‐trinitrotoluene (TNT), AN‐fuel oil explosive (ANFO) and emulsion explosive. It was found that the tested TATP/AN/W mixtures represent typical non‐ideal explosives with relatively low critical diameter and with high sensitivity to initiation despite the high content of water due to the presence of the primary explosive (TATP). The detonation velocity is comparable to that of powdery TNT (at similar density). However, the acceleration ability is significantly lower than that of powdery TNT.     

Investigation and mapping of toxic fumes produced by detonation of ANFO explosives in underground space

Post-blast fumes are hazardous and known to cause severe health related issues of workers. Further, these harmful gases have a significant impact on the surrounding environment. Thus, it is imperative to have an in-depth understanding of the real time detonation fume generation in underground space to avoid hazardous health risk of the worker. In this context, the mapping of toxic fume concentrations generated by the detonation of ANFO explosives in the actual field is a fascinating area of research that has a great environmental impact. This article examined the real-time analysis of toxic fumes generated by ammonium nitrate fuel oil (ANFO) explosives at various locations of a metalliferous underground mine. Furthermore, detonation parameters of various ANFO explosive compositions were also studied at the mining site. On-site blasting studies were performed with ANFO explosives, and post-detonation fume measurements enabled us to map the CO and NO_x concentrations in underground spaces. Toxic fumes like CO and NO_x were analyzed before and after each blasting operation at different intervals, and found within the allowed limit as per the Directorate General of Mines Safety guidelines. Additionally, an empirical correlation has been established to evaluate the maximum detonation velocity based on the alteration of ammonium nitrate and fuel oil composition.     

Calculation of Detonation Properties of Gaseous Explosives Using Generalized Reduced Gradient Nonlinear Optimization

In this paper, a study on the development of a numerical modeling of the detonation of C H N O‐based gaseous explosives is presented. In accordance with the numerical model, a FORTRAN computer code named GasPX has been developed to compute both the detonation point and the detonation properties on the basis of Chapman–Jouguet (C‐J) theory. The determination of the detonation properties in GasPX is performed in chemical equilibrium and steady‐state conditions. GasPX has two improvements over other thermodynamic equilibrium codes, which predict steady‐state detonation properties of gaseous explosives. First, GasPX employs a nonlinear optimization code based on Generalized Reduced Gradient (GRG) algorithm to compute the equilibrium composition of the detonation products. This optimization code provides a higher level of robustness of the solutions and global optimum determination efficiency. Second, GasPX can calculate the solid carbon formation in the products for gaseous explosives with high carbon content. Detonation properties such as detonation pressure, detonation temperature, detonation energy, mole fractions of species at the detonation point, etc. have been calculated by GasPX for many gaseous explosives. The comparison between the results from this study and those of CEA code by NASA and the experimental studies in the literature are in good agreement.     

Numerical Investigation of Case Hardening of Plant Tissue During Drying and Its Influence on the Cellular-Level Shrinkage

Dried plant food materials are one of the major contributors to the global food industry. Widening the fundamental understanding of different mechanisms of food material alterations during drying assists the development of novel dried food products and processing techniques. In this regard, case hardening is an important phenomenon, commonly observed during the drying processes of plant food materials, which significantly influences the product quality and process performance. In this work, a mesh-free-based 2D numerical model developed by the authors is further improved and used to simulate the influence of case hardening on shrinkage characteristics of plant tissues during drying. In order to model the fluid mechanisms of plant cells, smoothed particle hydrodynamics (SPH), which is a popular mesh-free technique used to solve hydrodynamics problems, is used. The cell wall mechanisms are modeled using the discrete element method (DEM). The model is fundamentally more capable of simulating large deformations of multiphase materials compared to conventional grid-based modeling techniques such as finite element methods (FEM) or finite difference methods (FDM). Case hardening is implemented by maintaining distinct moisture levels in the different cell layers of a given tissue. In order to compare and investigate different factors influencing tissue deformation under case hardening, four different plant tissue varieties (apple, potato, carrot, and grape) are studied. The simulation results indicate that the inner cells of any given tissue undergo limited shrinkage and cell wall wrinkling, compared to the case-hardened outer cell layers of the tissues. For a given dried tissue condition, the case-hardened cellular deformations are highly influenced by the unique characteristics of the different tissues, such as cell size, cell fluid turgor pressure, and cell wall properties.     

Predicting Detonation Performance of CHNOFCl and Aluminized Explosives

A new “hand‐calculated” method is introduced for prediction of detonation pressure of explosive and mixture of explosives with general formula CHNOFClAl. Suitable decomposition paths are used to estimate heat of detonation and detonation pressure. These decomposition paths are based on the distribution of oxygen atoms between carbon and hydrogen atoms as well as the degree of oxidation of aluminum. For CHNOFCl explosives, it is shown that the predicted detonation pressures with the new method are more reliable with respect to one of the best available empirical methods for loading densities greater than or equal 0.8 g cm⁻³. Since aluminized explosives have non‐ideal behavior, the new method does not require using full or partial oxidation of aluminum, which is usually required by a computer code. The predicted results of the new model also provide more reliable results than outputs of complex computer code with the BKWS equation of state.     

Modeling Hydrodynamic Behaviors in Detonation

A multistage reaction model developed for general use from initiation through detonation of heterogeneous high explosives is used to specifically simulate the interface vclocimetry and plate push experiments of a triamino-trinitrobenzene-based explosive in detonation. A simplification of the unified model leads to a rate relation that ineludes only two dominant stages: a fast one that represents the major portion of reaction dictated by propagation and decomposition, and a slow one that reflects probably the formation of large carbon molecules. The apparent more energetic behavior of the equation of state near the detonation front is actually due to the slow reaction process.     

Detonation Failure Characterization of Homemade Explosives

Typically characterizing home made explosives (HMEs) requires many large scale experiments, which is prohibitive given the large number of materials in use. A small scale experiment was developed to characterize HMEs such as ammonium nitrate‐fuel oil mixtures. A microwave interferometer is applied to small scale confined transient experiments, yielding time resolved characterization of a failing detonation that is initiated with an ideal explosive booster charge. Experiments were performed with ammonium nitrate and two fuel compositions (diesel fuel and mineral oil). It was observed that the failure dynamics were influenced by factors such as the chemical composition, confiner thickness, and applied shock wave strength. Thin steel walled confiners with 0.71 mm wall thickness experienced detonation failure and decoupling of the shock wave from the reaction zone. Confiners with a wall thickness of 34.9 mm showed a decrease in propagation speed and a steady reactive wave was achieved. Varying the applied shock strength by using an attenuator showed corresponding changes in the initial overdriven reactive wave velocity in the HMEs. The distance to detonation failure was also shown to depend on the attenuator length when thin wall confinement was used. This experimental method is shown to be repeatable and can be performed with little required material (about 2 g). The data obtained could be useful to model development and validation, as well as quantifying detonability of materials.     

光滑粒子动力学方法在复杂流动中的研究进展

光滑粒子动力学（smoothed particle hydrodynamics,SPH）是一种纯粹的拉格朗日型无网格数值方法,尤其在处理包含自由表面或多相运动界面的复杂流动问题方面具有独特优势。随着计算精度和稳定性等方面的不断完善,SPH方法已被广泛应用于科学和工程的众多领域。介绍了SPH基础理论的最新成果,重点分析了其在界面流、流固耦合、非牛顿流体等领域的研究进展,并对未来发展进行了展望。     

LX-04炸药大隔板试验的数值模拟

为研究不同条件下LX--04（HMX／氟橡胶／85／15）大隔板试验（LSGT）的冲击波感度G。,运用ANSYS／LS．DYNA对整个爆炸冲击波传爆过程进行了数值模拟,观察了LSGT中爆轰冲击波的传播过程,分别讨论了主发炸药PE4、TNT、B炸药产生的爆轰波经过有机玻璃隔板、铝隔板、钢隔板衰减后的冲击波压力变化情况,最终找出了3种不同主发炸药和3种隔板下LX-04冲击波感度G50。同时,定性地分析了3种隔板对爆炸冲击波的衰减系数。其中,铝隔板的衰减系数最大,有机玻璃隔板的衰减系数最小。     

LX‐17 Corner‐Turning

We have performed a series of highly‐instrumented experiments examining corner‐turning of detonation. A TATB booster is inset 15 mm into LX‐17 (92.5% TATB, 7.5% kel‐F) so that the detonation must turn a right angle around an air well. An optical pin located at the edge of the TATB gives the start time of the corner‐turn. The breakout time on the side and back edges is measured with streak cameras. Three high‐resolution X‐ray images were taken on each experiment to examine the details of the detonation. We have concluded that the detonation cannot turn the corner and subsequently fails, but the shock wave continues to propagate in the unreacted explosive, leaving behind a dead zone. The detonation front farther out from the corner slowly turns and eventually reaches the air well edge 180° from its original direction. The dead zone is stable and persists 7.7 μs after the corner‐turn, although it has drifted into the original air well area. Our regular reactive flow computer models sometimes show temporary failure but they recover quickly and are unable to model the dead zones. We present a failure model that cuts off the reaction rate below certain detonation velocities and reproduces the qualitative features of the corner‐turning failure.