The electrical resistance of copper foil under multiple shock compression to a pressure of 40 GPa is studied experimentally in several explosive systems: in a reflected shock wave, under compression in a rigid shell, and in a layered system generating a sequence of waves of increasing amplitude. An improved design of the measuring cell is proposed, which significantly reduces the influence of parasitic eddy currents on the recorded voltage. Under shock compression, the electrical resistance of copper increases monotonically, but the growth rate depends on the loading history. Under compression by a sequence of shock waves, the electrical resistance of the metal is lower than under compression by a single shock wave (at the same incident shock pressure in the dielectric shell). In this case, the main change in the electrical resistance of copper occurs in the first shock wave. In subsequent waves, the electrical resistance also increases, but the final value is lower than in a single shock wave. The crystal structure defect concentration in a copper sample under complex loading is estimated. Under multiple compression, the defect concentration is lower than in the case of single compression (at the same wave pressure or deformation). This implies that during complex shock loading, defects are mostly generated in the early stages of compression, and subsequently there is only a relatively small increase in the number of defects. Qualitatively, the defect concentration during complex shock loading is determined by the deformation in the first shock wave.
The interaction of a shock wave with a near-wall gas bubble (transverse cylinder) filled with a hydrogen–oxygen mixture with added xenon is numerically investigated in a two-dimensional plane formulation using the Euler equations. Gas combustion is modeled using a detailed kinetic mechanism involving 19 reversible reactions. A high-order WENO finite difference method is applied. Shock wave refraction and reflection, as well as the focusing of secondary shock waves, are described. Various detonation initiation modes in the bubble are detected: direct initiation, initiation with shock refraction and reflection from the wall, and initiation with shock wave focusing on the symmetry plane near the wall. Based on a series of calculations, the dependence of ignition regimes and threshold Mach numbers of the incident shock wave on the bubble shape is determined. It is shown that the combination of shock focusing on the bubble and reflection from the wall leads to a significant decrease in threshold Mach numbers compared to both a plane layer of combustible gas in front of the wall and a free bubble without a wall.
This paper presents the most important gas-dynamic and kinetic parameters of combustion, explosion, and detonation for ammonia/oxygen combustible systems. Stoichiometric, lean, and rich compositions are considered with the addition of molecular nitrogen, which corresponds to the transition from fuel–oxygen mixtures to fuel–air mixtures. The same parameters are also reported for fuel-air mixtures across a range of concentrations from the lower to the upper flammability limit and as a function of initial pressure. From the perspective of explosion safety, the most critical data concern the critical initiation energy, which enables analysis of the relative hazard of different mixtures. Critical energy E_* is defined as the minimum initiator energy required to sustain the propagation of combustion and detonation waves in the mixture under study: the lower this energy, the more hazardous the mixture. Additionally, data on the detonation cell size are presented; this length scale is used to determine characteristic parameters of combustion chambers.
A coupled combustion model is used to study unsteady combustion of a metallized composite solid propellant with a harmonic pressure change above the propellant surface. The propellant combustion model includes chemical reactions in the condensed and gas phases. Above the propellant surface, the convection and diffusion of gas mixture components, the two-phase nature of the flow, the velocity and thermal nonequilibrium of phases, and aluminum particle combustion are taken into account. The boundary conditions of equality of mass and energy fluxes are specified on the propellant surface. The results of a theoretical computational study of the dependence of the propellant burning rate on the amplitude and frequency of pressure oscillations are presented. The study is carried out for two values of the gas-phase reaction order. The influence of the frequency of pressure oscillations on the amplitude of change in the propellant burning rate is determined.
We have studied the effect of preliminary mechanical activation (MA) of carbon black powder on the properties, densification, and combustion behavior of equiatomic Ti + C mixtures. MA has been shown to cause breakdown of the arched structure and disintegration of agglomerates of carbon black, leading to an increase in its bulk density by more than three times. During densification, carbon black powder behaves as a solid nonplastic material with a high elastic recovery value (up to 14
