Experimental observations of detonation in ammonium-nitrate-fuel-oil (ANFO) surrounded by a high-sound-speed, shockless, aluminum confiner

Detonations in explosive mixtures of ammonium-nitrate-fuel-oil (ANFO) confined by aluminum allow for transport of detonation energy ahead of the detonation front due to the aluminum sound-speed exceeding the detonation velocity. The net effect of this energy transport on the detonation is unclear. It could enhance the detonation by precompressing the explosive near the wall. Alternatively, it could decrease the explosive performance by crushing porosity required for initiation by shock compression or destroying confinement ahead of the detonation. At present, these phenomena are not well understood. But with slowly detonating, non-ideal high explosive (NIHE) systems becoming increasing prevalent, proper understanding and prediction of the performance of these metal-confined NIHE systems is desirable. Experiments are discussed that measured the effect of ANFO detonation energy transported upstream of the front by a 76-mm-inner-diameter aluminum confining tube. Detonation velocity, detonation front-shape, and aluminum response are recorded as a function of confiner wall thickness and length. Detonation shape profiles display little curvature near the confining surface, which is attributed to energy transported upstream modifying the flow. Average detonation velocities were seen to increase with increasing confiner thickness, while wavefront curvature decreased due to the stiffer, subsonic confinement. Significant radial sidewall tube motion was observed immediately ahead of the detonation. Axial motion was also detected, which interfered with the front-shape measurements in some cases. It was concluded that the confiner was able to transport energy ahead of the detonation and that this transport has a definite effect on the detonation by modifying its characteristic shape.     

Detonation performance of the CL-20-based explosive LX-19

The generation of constitutive detonation performance model components for high explosives (HEs) invariably involves reference to experiment, as reliable first-principles determinations of these models are beyond our current capability. Whatever its form or complexity, the detonation performance model must be able to accurately capture the detonation wave timing and the energy release that it triggers upon arrival. Specifically, the HE products equation-of-state (EOS), which largely determines the detonating HE’s ability to do useful work on its surroundings, is typically inferred from cylinder expansion tests where metal-confined HE cylinders are detonated and the ensuing outer confiner wall-expansion trajectory is recorded. Expensive, iterative comparisons to multimaterial hydrodynamic (or “hydrocode”) simulations of these experiments are then used to constrain the parameters of the chosen EOS form. Here, we report on new detonation performance experiments produced for the highly-ideal, plastic-bonded explosive and CL-20-based LX-19 which are used to produce a new sub-scale detonation performance model for the explosive. This includes new products EOS and a new Detonation Shock Dynamics front propagation law. We also confirm the capability of two new, non-hydrocode-based products EOS generation techniques to accelerate the HE model parameterization process. This latter development is particularly significant for detonation performance modeling of new HE formulations.     

A particle level-set based Eulerian method for multi-material detonation simulation of high explosive and metal confinements

The multi-material numerical simulation for energetic system that consists of a high explosive charge and an inert confinement is carried out with an accurate and state-of-the-art Eulerian method. An explosively driven copper tube results in a state of extreme temperature and pressure, coupled to a high speed structural response of metal due to a detonating high explosive (HE). We use the experimentally tuned Ignition and Growth (or JWL++) rate equation for the HE while the elasto-plastic response of inert is modeled by the Mie–Gruneisen equation of state (EOS) and the Johnson–Cook strength model. A new particle level-set based reactive Ghost Fluid Method (GFM) that imposes exact boundary conditions at the material’s interface according to physical restraints is developed to simulate the multi-material detonation problem. Our calculations reproduce the experimental data of both unconfined and confined rate stick problems, suggesting that the method is suitable for detonation simulation of energetic systems.     

Explosive compositions based on the mechanoactivated metal-oxidizer mixtures

Detonation-like regimes in mechanoactivated energetic composites (MAECs) were experimentally studied. The test MAECs consisted of layers of a metal (Al, Mg) and Teflon mixed at the submicron and nano levels. The systems reacted to form solid final products. MAECs are appreciably superior to ordinary mixtures in chemical transformation rate. The burning of MAECs occurs in an explosive regime at a velocity of 300–400 m/s, with the temperature of the products being as high as 4000 K. When initiated with a HE charge, porous MAECs detonate in the steady regime. Depending on the composition and density of the samples, the detonation velocity varies from 700 to 1300 m/s, values markedly higher than the speed of sound in the initial mixture. Detonation is controlled by a hot spot mechanism, more specifically, by relay reaction propagation by jets of products.     

Propagation of gaseous detonation across inert layers

In rotating detonation engines and explosion accidents, detonation may propagate in an inhomogeneous mixture with inert layers. This study focuses on detonation propagation in a stoichiometric H₂/O₂/N₂ mixture with multiple inert layers normal to the detonation propagation direction. One- and two-dimensional simulations considering detailed chemistry are conducted. The emphasis is placed on assessing the effects of inert layer on detonation reinitiation/failure, detonation propagation speed, detonation cell structure and cell size. Specifically, the inert layer thickness and the spacing between two consecutive inert layers are varied. Either detonation reinitiation or failure across the inert layers is observed. It is found that successful detonation reinitiation occurs only at relatively small values of the inert layer thickness and spacing. For each given value of the inert layer spacing, there is a critical inert layer thickness above which detonation fails after crossing the inert layers. This critical inert layer thickness is found to decrease as the inert layer spacing increases. The detailed process of detonation reinitiation across the inert layers is analyzed. The interaction between the transverse shock waves is shown to induce local autoignition/explosion and eventually over-driven detonation development in the reactive layer. The averaged detonation propagation speed in the inhomogeneous mixture is compared to the CJ speed and very good agreement is achieved. This indicates that the inert layer does not affect the detonation propagation speed once successful detonation reinitiation happens. Unlike the detonation speed, the detonation cell structure and cell size are greatly affected by the inert layer results. For the first time, large cellular structure with size linearly proportional to the inert layer spacing is observed for detonation propagation across inert layers. Besides, a double cellular structure is observed for relatively large spacing between inert layers. The formation of double cellular structure is interpreted.     

钝感炸药爆轰驱动研究

 对两种典型的钝感炸药（IHE）的爆轰驱动模型进行了实验研究。一种是点爆散心波驱动，另一种是滑移爆轰驱动。并在同一条件下做了非钝感炸药（HE）的爆轰驱动实验，以比较IHE和HE驱动规律的异同。对实验模型用二维数值模拟及拟合公式进行了计算，最后给出了在本实验条件下两种炸药驱动规律差异，也对计算偏差范围作了估计。     

180°圆弧形钝感炸药的爆轰波传播

 采用贴体坐标下与Level Set方法相结合的爆轰冲击波动力学（DSD）计算方法,研究了180°圆弧形钝感炸药中非理想爆轰波的传播过程。通过数值模拟计算和实验测量的对比分析,得到了180°圆弧形炸药中爆轰波传播的一些规律：圆弧形钝感炸药可以实现定常爆轰,即在极坐标中整个爆轰波以固定角速度转动。这种定常阵面的形状和角速度与圆弧的外半径无关,定常体系依赖于圆弧形炸药的内半径和覆盖圆弧的外壳物质。对描述圆弧形炸药中爆轰波传播规律的经验公式进行了研究,结果表明这些经验公式能够准确描述爆轰波速度的变化,在实验测量和预估方面具有一定的参考价值。     

Experimental and modeling analysis of detonation in circular arcs of the conventional high explosive PBX 9501

We examine the diffraction dynamics of a two-dimensional (2D) detonation in a circular arc of the conventional HMX-based, high performance, solid explosive PBX 9501, for which the detonation reaction zone length scale is estimated to be of the order of 100–150 µm. In this configuration, a steady propagating detonation will develop, sweeping around the arc with constant angular speed. We report on results from three PBX 9501 arc experiments, exploring the variation in linear speed on the inner and outer arc surfaces for the steady wave along with the structure of the curved detonation front, as a function of varying inner surface radius and arc thickness. Comparisons of the properties of the motion of the steady wave for each arc configuration are then made with a spatially-distributed PBX 9501 reactive burn model, calibrated to detonation performance properties in a 2D planar slab geometry. We show that geometry-induced curvature of the detonation near the inner arc surface has a significant effect on the detonation motion even for conventional high explosives. We also examine the detonation driving zone structure for each arc case, and thus the subsonic regions of the flow that determine the influence of the arc geometry on the detonation propagation. In addition, streamline paths and reaction progress isolines are calculated. We conclude that a common approximation for modeling conventional high explosive detonation, wherein the shock-normal detonation speed is assumed equal to the Chapman–Jouguet speed, can lead to significant errors in describing the speed at which the detonation propagates.     

用光电法研究钝感炸药JB-9014反应区结构

 报道了用光电法研究炸药反应区结构的原理、实验方法和钝感炸药JB-9014的反应区结构。研究结果表明，密度为1.894 g/cm³的JB-9014炸药在平面一维定常爆轰时，其Neumann峰压力为36.5 GPa，反应区宽度为1.75 mm，反应过程时间为0.31 μs；装药密度减少时，Neumann峰压力、反应区宽度和反应过程时间均减小。     

Characteristics analysis of hybrid plasmonic waveguide for low-loss lightwave guiding

It has been experimentally demonstrated that a low-loss guided hybrid mode is supported if a metal strip is embedded in a low index polymer layer surrounded by two high index slabs. In this paper, further numerical analyses on the guided hybrid modes are reported to fully elucidate the characteristics of the hybrid plasmonic waveguide. For a one-dimensional slab structure with a metal film of infinite width, simulation results exhibit that low-loss guided hybrid modes are associated with surface plasmon modes and dual dielectric slab modes. The optical properties of the guided modes are improved by increasing the field intensity which is confined into lossless dielectric layers by decreasing the metal film thickness and increasing the refractive index and thickness of the high-index slabs. The finite element method is used to investigate the lateral mode confinement of the optical guided modes by the corresponding metal strip. By reducing the metal film width, the guided modes are confined in the plane transverse to the direction of propagation and the characteristics are significantly improved. The hybrid plasmonic waveguide can be exploited for long-range propagation-based application such as optical interconnection.     

Detonation propagation with velocity deficits in narrow channels

Propagation limits of detonations in narrow channels have been studied with a focus on velocity deficits and variation in cell widths. A channel was formed by a pair of metal plates of 1500 mm length which were inserted in a detonation tube of 50.5 mm inner diameter. Test gases were hydrogen–oxygen mixtures diluted with argon or nitrogen, which were selected as representatives of regular and irregular mixture systems. The velocity deficits predicted using the concept of negative boundary layer displacement thickness were compared to those obtained experimentally. From good agreement between the predicted and the experimental velocity deficits, the cell width enlarged in the channel was calculated using the induction zone length behind the decelerated leading shock front. Although this calculation underestimates the cell widths, the calculated cell widths were found to be well predicted when they were multiplied by an appropriate proportionality factor. It is found that for given mixtures, a combination of the calculated velocity deficit and the number of cells in a channel contributes to the prediction of propagation limits of detonations.     

Modeling of electrically actuated elastomer structures for electro-optical modulation

A transparent elastomer layer sandwiched between two metal electrodes deforms upon voltage application due to electrostatic forces. This structure can be used as tunable waveguide. We investigate structures of a polydimethylsiloxane (PDMS) layer with 1–30 μm thickness and 40 nm gold electrodes. For extended electrodes the effect size may be calculated analytically as a function of the Poisson ratio. A fully coupled finite-element method (FEM) is used for calculation of the position-dependent deformation in case of structured electrodes. Different geometries are compared concerning actuation effect size and homogeneity. Structuring of the top electrode results in high effect magnitude, but non-uniform deformation concentrated at the electrode edges. Structured bottom electrodes provide good compromise between effect size and homogeneity for electrode widths of 2.75 times the elastomer thickness.     

Convective burning and detonability of aluminum-rich ammonium perchlorate-aluminum-nitromethane mixtures: 1. Experiment

The initiation and propagation of low-velocity detonation in ammonium perchlorate (AP)-aluminum-nitromethane (NM) mixtures with Al: AP ratios of 1: 1 to 2.5: 1 and porosities from 40 (10 wt % HM) to 0% (40 wt % NM) in strong steel shells (in the air) and plastic shells submerged in water are experimentally studied. The optimum contents of the components that provide reliable initiation of steady detonation (at velocities from 2 to 5 km/s) by weak explosive sources in mixtures with an Al: AP ratio of 1: 1 and above are determined. The selected mixtures reproducibly detonate in plastic shells surrounded by a 30-cm-thick layer of water at velocities somewhat lower than in strong steel shells in the air.     

Peculiarities of propagation of acoustic excitations through an imperfect 1D-superlattice

Virtual crystal approximation is adapted to address peculiarities of propagation of acoustic waves through a 1D ‘sandwich’ superstructure consisting of alternating layers of two types randomly substituted by foreign layers of the third type. Same-parity layers are of the same width and constitute a sublattice. Dependence of the lowest forbidden acoustic zone width of the described structure on concentrations of impurity layers in the two sublattices is numerically evaluated for longitudinal and transverse excitations. Values of substitute concentrations making the structure completely transparent prove to be independent of the relative widths of the 1st and 2nd type layers.     

Numerical Analysis of Multilayer Waveguides Using Effective Refractive Index Method

With the help of the effective refractive index method we have numerically analyzed a multilayer planar waveguide structure and calculated the propagation constants, confinement factors, and transverse electric (TE) modes. A five-layer waveguide model has been provided to analyze the electro-magne tic wave propagation process. The analysis method has been applied to the 980 nm laser with active layer of GaInAs/GaInAsP strained quantum wells, GaInAsP confinement layers and GaInP cap layers. By changing the thickness of confinement layers, we obtained confinement factor as high as 95% with higher TE modes TE1 and TE2. The results are in good agreement with the experiment by A. Al-Muhanna et al. and give the new idea to enhance output power of semiconductor lasers. The analysis method can also be extended to any other slab multilayer waveguide structures, and the results are useful to the fabrication of optic-electronic devices.     

超压爆轰产物声速以及热力学CJ点的实验研究

超压爆轰产物声速是建立超压爆轰产物状态方程的基础性实验数据,而CJ点数据是反映炸药爆轰性能的重要参数。利用稀疏波追赶技术,通过光纤探针监测三氯甲烷中稀疏波追赶向前冲击波的过程,测量了不同压力点下JB-9014炸药超压爆轰产物的声速,得到了拉格朗日声速随粒子速度的变化曲线,由Lc线与稳定爆速D的交点确定了热力学CJ点,对JB-9014炸药所得到的CJ压力为28.8 GPa,与通常测量值28.5 GPa仅相差0.3 GPa。介绍了应用光纤探针测量爆轰驱动飞片的速度和平面性的方法,应用该方法得到了飞片的击靶速度和形状,此方法具有较高的测量精度。     

炸药爆轰驱动超高速击波管的数值摸拟

 高能炸药（HE）柱壳沿轴向传播的稳定态爆轰，在置于炸药柱壳内部的泡沫塑料（工作流体）中产生很强的轴向击波，达到极高的压力和能量密度。适当设计，可使工作流体的流动接近一稳定态，与炸药爆轰以相同的相速度前进。击波阵面后的工作流体可用Nozzle流动方程很好地描述^[1]，Nozzle收缩段中的流动不受散开段流动的影响。利用这一性质，可以设计出达到极高压力和能量密度的超高速击波管，并且不受管壁物质强度的限制。数值模拟计算给出了上述稳定态物理图象，并显示出开始阶段轴向击波的形成过程及其后对稳定态的逼近，计算结果及物理图象与理论分析符合得很好。     

Effects of heat loss and viscosity friction at walls on flame acceleration and deflagration to detonation transition

The coupled effect of wall heat loss and viscosity friction on flame propagation and deflagration to detonation transition(DDT) in micro-scale channel is investigated by high-resolution numerical simulations.The results show that when the heat loss at walls is considered, the oscillating flame presents a reciprocating motion of the flame front.The channel width and Boit number are varied to understand the effect of heat loss on the oscillating flame and DDT.It is found that the oscillating propagation is determined by the competition between wall heat loss and viscous friction.The flame retreat is led by the adverse pressure gradient caused by thermal contraction, while it is inhibited by the viscous effects of wall friction and flame boundary layer.The adverse pressure gradient formed in front of a flame, caused by the heat loss and thermal contraction, is the main reason for the flame retreat.Furthermore, the oscillating flame can develop to a detonation due to the pressure rise by thermal expansion and wall friction.The transition to detonation depends non-monotonically on the channel width.     

Detonation propagation across a stratified layer with a diffuse interface

A study was conducted to examine detonation propagation in a stratified layer of hydrogen-oxygen-nitrogen above an inert gas in a horizontal narrow channel. The stratified layer was produced by a gravity current, generated by retracting a door initially separating a hydrogen-oxygen-nitrogen mixture in the predetonator and a heavier inert gas in the test-section. A steady detonation wave generated in the predetonator was transmitted into the stratified layer. The reactivity of the predetonator mixture was varied via the hydrogen-oxygen equivalence ratio and the amount of nitrogen dilution. Schlieren photography was used to visualize the detonation front in the test-section, and soot foils were used to obtain the cellular structure. Schlieren imaging showed a curved detonation front that decoupled at about mid channel height, into a shock wave and trailing contact surface. Both the hydrogen-oxygen-nitrogen reactivity and the type of inert gas initially in the test-section affected the distance travelled by the detonation wave in the stratified layer. The mixture composition distribution within the test-section before ignition was obtained via a three-dimensional CFD simulation. The lateral extent of the cellular structure captured on the soot foil, coincided with the calculated inert gas mole fraction contour that corresponds to a sharp increase in the ZND induction zone length, e.g., 70% argon dilution for a stoichiometric hydrogen-oxygen predetonator mixture.     

All Eulerian method of computing elastic response of explosively pressurised metal tube

We present an all Eulerian approach to simulate the elastic response of a metal tube loaded explosively by a gaseous detonation. The high strain rate deformation of the metal tube subjected to high explosive detonation is mathematically described by hyperbolic processes where the characteristics of existing wave motions were correlated with the local particle velocities through the speed of sound in the metal. This is a favourable case for the hydrocode which is based on a compressible gas dynamics solver and for simulating a high strain rate and dominantly plastic response of a material subject to an explosive loading. The hydrocodes fall substantially short of predicting elastic motion without the plastic flow of the confining material, for relatively minor pressure loadings due to a gaseous explosion as opposed to a high explosive detonation of a charged tube. The corresponding loading pressure due to gaseous explosion is a few orders of magnitude lower than those resulting from high explosive loadings. Utilising a hydrocode designed to handle the reactive process leading to a plastic flow of the confining materials is of great interest and a significant challenge. The new technique, based on the Eulerian framework, preserves the feature of a Lagrangian code while utilising all the benefits of an Eulerian solver that uses fixed grids with the level-sets for defining the multi-material interfaces. The hybrid particle level-set algorithm is combined with a hydrodynamic solver that adds an elasticity correction when handling the structural response while the overall scheme remained hyperbolic during the entire reactive flow. Several unseen dynamics of detonation flow associated with the elastically loaded tube of finite thickness are reported by using the present method for analysing the highly pressurised vessel.