A physical model of low-velocity detonation in plasticized HMX is considered. In this model, a low-velocity detonation wave is a combination of a weak leading shock wave and a subsequent compression wave. This combination is formed by the simultaneous effects of energy release and spreading of the reacting medium. The main features of low-velocity detonation observed in experiments are reproduced in two-dimensional calculations.

A model for the electronic thermal conductivity of shock-compressed TATB is developed using experimental data on the growth kinetics of its electrical conductivity. It is shown that electronic thermal conduction can be the main mechanism of energy transfer from hot spots in detonating explosives.It is well known that during shock-induced detonations of heterogeneous condensed explosives (HEs), chemical reactions start at so-called hot spots -combustion microcenters which arise from a local temperature rise during shock-wave propagation through heterogeneities in the HE. The volume fraction of the microcenters is small; therefore, most of the HE reacts during combustion-wave propagation from the microcenters and the wave velocity determines the macrokinetics of HE decomposition and energy release (see, for example, [1]).At the macrolevel, the time of chemical-energy release in a detonating heterogeneous HE can be estimated as ∆τ ≈ δ/D, where D is the velocity of combustion-wave propagation from hot spots, δ is the average distance between the hot spots (on the order of the HE microcrystal size). For the characteristic values δ ≈ 10 µm and ∆τ ≈ 0.1-1 µsec, the velocity of combustion-wave propagation from the hot spots is estimated as D ≈ 10-100 m/sec. However, in shock-compressed and heated triaminotrinitrobenzene (TATB), the calculated combustion-wave velocity turned out to be smaller -D ≈ 0.1-1 m/sec [2], indicating the need for a more detailed analysis of the physical processes determining the velocity of combustionwave propagation in shock-compressed HEs.In this connection, it should be noted that the parameters of the calculation model of [2] were chosen so as to describe the measured ignition times of HEs at rather low temperatures at the boundary (up to 700 K) and low pressures (up to 1.5 GPa). The adequacy of this model for the range of much higher pressures and temperatures (10-20 GPa and 2000-3000 K), characteristic of the shock initiation of TATB, is questionable because the chemical-reaction kinetics is known to depend greatly on temperature and pressure.Another possible source of errors in calculations of the combustion of compressed-shock HEs is the great uncertainty in modeling heat transfer from hot spots to the crystalline HE. Experimental data on the thermal conductivity of shock-compressed HEs are not available. Moreover, the thermal conductivity mechanism in this case is not understood. The model of [2] considers only the lattice (phonon) thermal conductivity of HEs. However, phonon thermal conduction is a rather slow process characterized by a relaxation time of about 100 psec (see, for example, [3]). Thus, it is possible that the phonon mechanism of energy transfer from hot spots is ineffective at times of the picosecond scale characteristic of the reaction of HEs in combustion waves [4].The present paper gives calculation results for combustion-wave propagation from hot spots obtained under the assumption [4-6] that energy transfer from hot spots occurs by electronic thermal conduction.

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A physical model for the macrokinetics of shock-wave initiation of detonation in plastic-bounded TATB-based explosive is proposed that is based on the assumption of electronic energy transfer from hot spots. Results of numerical modeling of experiments on shock-wave initiation of detonation of LX-17 are presented.

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].