J. C. Gois

Influence of glass microballoons size on the detonation of nitromethane based mixtures

Detonation velocities and critical diameters of nitromethane (NM) based explosive mixtures sensitized by glass microballoons (GMBs) were measured. The control parameters of this experimental study were the nature and diameter of the confinement, the GMB size and their mass fraction.As GMB mass fraction is increased, the diameter effect curves (detonation velocity versus reciprocal charge diameter) become less and less dependent upon the confinement nature and size. Furthermore the shape of these curves, which for low concentration of GMBs is concave downward like that of heterogeneous explosive, tends to be straight like that of homogeneous explosives for larger GMB mass fractions.The critical diameter is found to be strongly dependent on GMB size and mass fraction. The mechanism of NM sensitization by GMBs is qualitatively analyzed and estimations of the effect of GMB concentration and size on the critical diameter of the mixtures agree with the experimental results.

Extinction and initiation of detonation of NM-PMMA-GMB mixtures

The influence of the addition of a small amount of glass microballoons (GMB) on the extinction and initiation of NM-PMMA mixtures is investigated. Numerical simulation using DYNA 3D code shows the collapse of small GMB, under NM detonation. GMB of a mean particle diameter of 45 μm were added into NM-PMMA explosive mixture. Polymethylmetacrylate (PMMA) was added to nitromethane (NM) to avoid buoyancy movements of GMB, increasing the viscosity of the original NM. Different failure tests were done initially proving the low values of critical extinction diameter and thickness. Accurate failure thickness experiments were performed using a prismatic configuration with a small opening angle of 2.9°. A double resistive wire technique and an aluminium witness bar were used to determine its critical thickness, as a function of GMB mass concentration. This double resistive wire technique shows, in real time, the induction time and distance of initiation. The failure thickness was correlated with those previously obt...

Thermal decomposition of energetic materials

The studies of thermal decomposition to identify mechanisms and quantify kinetic parameters are complex and its extrapolation to real scale could be not acceptable. Using an intermediate scale setup, three typical explosives, AN, PETN and RDX, with an inert material (silica sand) are submitted to fast heating rate. The experimental apparatus is based in a propane/air burner, a combustion chamber and a glass tube. Through the fuel/air ratio and the distance between the combustion chamber and the sample container is set different temperatures of the combustion gases. Mass loss and the temperatures evolution are measured simultaneously. The experimental results, obtained for samples with 500 mg weight, are compared with its obtained using DSC. The theoretical approach is based in the model of Zinn & Mader. The kinetic parameters, the ignition temperature and time are determined as a function of heating rate (HR) and particle size of inert and energetic materials. Except for AN, the theoretical results are ge...

New equation of state for the detonation products of explosives

A new equation of state (EoS), named HL, supported by a Boltzmann EoS type and based on physical intermolecular potential of gas components, is presented. This EoS, used in THOR code, takes α=13.5 to the exponent of the intermolecular potential and θ=1.4 to the adimensional temperature. It allows the calculation of thermodynamical properties and final compositions of gas and solid species, at adiabatic isobar and isochor combustion conditions (deflagration) and at Chapman-Jouguet detonation regimes, as a function of the initial composition of energetic system. Its validation has been done, initially, correlating the calculations of detonation of gaseous mixtures to experimental results. Predictions of detonation properties of condensed energetic materials give results in good correlation with experimental values. Deviation is more important in nitroaromatic compounds than in nitramines. Predicted values of detonation velocity show similar results independently of H/NO2 and H(CH2)/NO2 ratios of energetic m...

Effect of GMB on Failure and Reaction Regime of NM/PMMA‐GMB Mixtures

The effect of the addition of small amounts of glass microballoons (GMB) on heterogeneous explosives has been investigated with the aim of understanding mechanisms that lead to the strong reduction of its critical diameter. However, there is no clear identification of the changes on detonation wave propagation and its structural features. To obtain a better understanding of the contribution of GMB as a particular heterogeneity, the detonation failure and the re‐initiation of NM/PMMA‐GMB mixtures is studied. Corner turning configuration was performed in order to determine the influence of the GMB concentration and size on failure phenomena by observing the trajectories of the divergent shock waves around the corner. The shape of the printed traces on a copper witness plate, coupled with detonation velocity and front curvature measurements, was used to evaluate the evolution of the detonation reaction regime and its cellular structure. The obtained results of printed flow lines show significant changes of t...

Detonation Meso‐Scale Tests for Energetic Materials

The objective of the present study is to characterize, on the meso‐scale level, the detonation behaviour of PBX based on HMX , based in the minimisation of the test samples of energetic materials up to 10 mg. The development of a non‐intrusive, high resolution, optical metrology procedures, using multi‐fibber strip, allows the testing of PBX micro‐samples, formed by few crystals surrounded by binder, with the simultaneous registration of parameters as local detonation velocity and pressure, geometrical shape of detonation front and the structure of the shock‐to‐detonation transition zone. The enhanced information allows a better understanding of the processes of formation and propagation of detonation wave. This procedure can be applied to the study of new advanced energetic materials.

Interaction of double corner turning effect in PBX

The corner turning effect in PBX has been studied. The setup built with Cu or PMMA plates, has a channel with a square cross section of 5×5 mm and 10×10 mm, corresponding respectively to 1.33 and 2.67 of PBX failure diameter. A thin optical fibre (250 μm) strip, connected to a fast electronic streak camera, and the printed erosion figure on an witness plate (base plate and internal walls of setup) allows clear quantification of the detonation wave turning phenomena and the printed current lines of the products of detonation. The optical probes allow in real time, an original, direct front observations of multiple zones, by the registration of the interacting waves. Even in the cases of Cu-confinement, the corner turning effect shows the existence of non-detonated PBX (“dark zone”). The correlation between the non-monotonic (x-t) diagrams and light pulsations, recorded during the propagation of detonation wave inside the channels and after the corner section, proves the existence of pulse behaviour and cel...

Failure and re-initiation detonation phenomena in NM/PMMA-GMB mixtures

The addition of a small amount of glass microballoons (GMB) on nitromethane/polymethylmethacrylate (NM/PMMA) mixture reduces strongly the failure thickness and increases the detonation sensitivity. Based in an explosive mixture of NM/PMMA (96/4 by weight) with 1% of GMB (QCel 520 FPS, mean particle diameter of 45 μm), the failure and re-initiation phenomena are investigated experimentally using the corner turning experiments. The printed erosion figure on a polished copper plate, is used as a witness surface. This witness plate not only shows the shock oblique waves but also, around the corner, the re-initiation points and curves. In the dark zone two re-initiation fronts are observed. Two detonation curve fronts can be observed, corresponding to behaviours of homogeneous and heterogeneous explosives. In order to evaluate the influence of shear and normal stress waves, the original set-up has been modified, fixing a thin sheet of a kapton barrier (50 μm thickness) at different angles from the corner. It h...

Coarse Explosive Particles of PBX as a Dominant Factor of Detonation Instability

In this paper we have studied the phenomenon of local instabilities of DW in PBX compositions 82%HMX/18%GAP that are distinguished by the HMX grains sizes. A multi‐channel high‐resolution optical method based on application of 64‐optical fiber strips has been applied for the 3D‐registration of DW flow in PBX and the Us field in optical stack monitor. Scale of spatial/temporal fluctuations of detonation flow in PBX is characterized as a function of mean grain sizes d50 and mean values of the front curvature. We have found that for high dense PBX, coarse HMX particles play the dominant role in mechanism of cluster/cell formation in detonation flow. Local fluctuations occur as a result of delay of shock reaction inside the coarse HMX crystals, followed by the ejecta phenomenon.

Process of shock attenuation inside a hollow glass microsphere/polymeric composite media

The shock wave (SW) structure and its attenuation process, in the pressure range of 0.1 to 5 GPa inside a composite material (CM), is presented. The CM is based in a thermoset resin (TR) of polyester having, as inert filler, hollow glass micro-spheres (HGM) enclosing an inert gas. This kind of CM, known as syntactic foam, presents very interesting properties for shock absorption applications. The used HGM have density of 256 kg/m3, a wall thickness of 1 μm and a mean gas cavity diameter of 78 μm. They are dispersed inside the TR, in three different mass ratios (5/100, 10/100 and 25/100). An explosive plane wave generator has been used for sample shock loading. A thin multifibre optical strip, connected to an electronic streak camera, allowed the measurement of the SW velocity, with spatial resolution less than 250 μm and the observation, in real time, with a nanosecond temporal resolution, of the shock front irregularities. The results allow the establishment of the pressure-shock velocity evolutions and the evaluation of the shock attenuation, as a function of the HGM/TR mass ratio.