Hot Surfaces in Heterogeneous Explosives Initiated by a Shock Wave

Abstract

A model for the macrokinetics of chemical reactions in detonating heterogeneous explosives is proposed based on the assumption that not only point but also surface microcenters (hot surfaces) are formed under the action of an initiating shock wave. The occurrence of surface hotspots can be cause by a local rise in temperature near microcracks and on grain boundaries. The model is tested by measuring pressure profiles during detonation initiation in a TATB based explosive composition.At present, the hotspot mechanism of shock-wave initiation of detonation in heterogeneous condensed explosives is generally accepted. It assumes that the passage of a head shock wave through heterogeneities in an explosive leads to the formation of microscopic reaction centers -hotspots -and burnout of most of the explosive mass proceeds in spherical waves of layer-by-layer combustion which propagate from the hotspots [1].Specific energy release during combustion of the microcenters (ΔE) should increase with time in proportion to the relative mass of the material at the hotspots in an elementary volume of the reactive heterogeneous explosive mixture and explosion products (EPs). As usual (see, for example, [1]), the macrokinetics of heterogeneous reactions in a detonating explosive is considered with reference to volume elements whose sizes are small compared to the characteristic sizes of the sample in the experiment but much larger than the average distance between the microcenters.In the initial stage where the microcenters are not overlapped, ΔE ∼ (Dt) 3 [2], where D is the velocity of propagation of the combustion wave. The increase in pressure (Δp) due to energy release in the explosive also depends on time as Δp ∼ ΔE ∼ t 3 . However, in experiments with detonation initiation, a linear rather than cubic time dependence of the pressure is observed [3].

Hot spot formation and chemical reaction initiation in shocked HMX crystals with nanovoids: a large-scale reactive molecular dynamics study

“…Only a few studies on the effects of crystal surface properties on hot spots in shocked HEs have been reported to the best of our knowledge. Varfolomeev et al 41 considered that surface microcenters (hot surfaces) play a determining role in the formation of pressure profiles in the initial stage of the process, where the degree of decomposition of the explosive is insignificant. However, one must be cautious to ensure that the continuum-scale model description and numerical implementation accurately capture the physics of the material and processes on the spatial-temporal scales being studied.…”

X‐ray Phase Contrast Imaging of the Impact of Multiple HMX Particles in a Polymeric Matrix

“…Again, two different types of multi‐particle samples were used in this study: multi‐particle and two single crystals. These multi‐particle samples are of interest as stress concentration and frictional heating at the interfaces are considered possible sources of hot spot formation . It should be noted that X‐ray PCI differs from a conventional X‐ray image in that the measurement is a change in the X‐ray phase due to the refractive index of the material, not attenuation of the X‐ray .…”

“…These HE particles would be a production-grade, thus polycrystalline containing possible defects and voids. These defects and voids are prime locations for the formation of hot spots and increase the sensitivity of PBX [21][22][23][24][25].…”

X‐Ray Phase Contrast Imaging of the Impact of a Single HMX Particle in a Polymeric Matrix

“…Such fracture behavior in energetic crystals has not been well documented previously. Since cracks are a possible source for hot spot formation [21,23], it is important to understand the formation of new cracks in the particle under dynamic loading. The images that were taken after the last image (Figure 9) show the particle being pushed flat against the sample holder.…”

“…Production HE particles are polycrystalline and inherently possess intraparticle defects, mostly in the form of voids and cracks ( Figure 1) making them candidates for the observation of hot spot dynamics [19,20]. Defects in the form of voids, grain boundaries, or cracks are considered to be nucleation sites for hot spots and therefore increase the sensitivity of energetic samples [21][22][23].…”