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This paper reports results from experimental studies of the strength of ethanol under impulsive tension due to interaction of a triangular compression pulse with the free surface. The experiments were performed in the range of strain rates 4 · 10 4 -4 · 10 5 sec −1 . It is established that the failure of ethanol is a two-stage process. In the first stage at a negative pressure of about 14 MPa, pore formation begins, which proceeds at a rather low rate and is manifested as an inflection on the free-surface velocity profile. In the second stage, the porosity growth rate increases, resulting in formation of a spalling pulse. The possibility of using the model of homogeneous nucleation to interpret experimental data is discussed.According to theoretical concepts, liquids can endure high tensile stresses of up to 0.1-1 GPa [1][2][3]. It is assumed that discontinuity of the material results from pore formation by a homogeneous nucleation mechanism. At the same time, considerably smaller values are observed [4] in practice under static test conditions, which is explained by the presence of heterogeneous centers in real liquids, at which pore growth is initiated.Conditions of liquid fracture during homogeneous nucleation can be obtained using dynamic tension. In the present study, this is done by analyzing the spalling phenomena involved in the reflection of compression pulses from the free surface of the examined material [5]. An advantage of this method is that at a pulse duration of order of 1 µsec, the fracture is volume (with no effect of the boundaries) and occurs in a thin layer of the material, which considerably reduces the number of heterogeneous centers capable of influencing the fracture of the liquid. In addition, one might expect that precompression in a shock wave leads to partial pore collapse, which also enhances the role of homogeneous nucleation.Impulsive tension under shock-wave loading has been used previously to study the cavitation of liquids (glycerol [6-9], water [10-13], ethylene glycol [11], ethanol [12], hexane [9] and mercury [14]). It has been shown, in particular, that the kinetics of pore formation and, as a consequence, the nature of the dependence of strength on strain rate are largely determined by the physicochemical properties of the liquids. To elucidate the general features of cavitation, it is of interest to compare the fracture patterns of liquids of various structures. The present paper considers the results of experiments on determining the spall strength of ethanol, which has not been studied previously, and discusses the possibility of using the homogeneous nucleation model to interpret the results obtained. Dremin et al. [12] obtained an estimate P s ≈ 48 MPa for the spall strength of ethanol, but the employed method did not allow regularities of the fracture kinetics to be established. This is one of the objectives of the present study.Diagram and Results of Experiments. A diagram of the experiments on impulsive tension of liquids is presented in Fig. 1. Shock waves were pr...
Detonation in mixtures of nitromethane with methanol as an inert (nonexplosive) diluent is studied. Ignition experiments with mixtures in steel tubes of various diameters provided information on the effect of the degree of dilution on detonability.Mass velocity profiles with a chemical spike characteristic of detonation waves were recorded at the unsteady detonation front in all mixtures studied. This made it possible to distinguish the Chapman-Jouguet state and obtain a fairly complete set of detonation parameters. The dependence of the pressure in the detonation products on the methanol concentration is determined, which is required, in particular, to find the true (absolute) limit of detonation propagation for the concentration of diluted liquid explosives using the method proposed and validated by A. N. Dremin. Some results were found to be inconsistent with one-dimensional detonation theory.
Experimental studies of the reaction zone structure in hexanitrohexaazaisowurtzitane (CL-20) at different initial densities with a multichannel VISAR laser interferometer have been carried out. It is shown that the flow in the reaction zone corresponds to the Zeldovich-von Neumann-Döring theory with a characteristic reaction time of 50 ns. The dependence of the detonation velocity on the initial density is well approximated by a similar line for HMX with a charge diameter of 20 mm. With a decrease in diam-eter to 4 mm, a sharp drop in the detonation parameters of CL-20 has been recorded. The initiation of detonation under shockwave action is investigated, and the comparison of data for CL-20 and PETN has shown that their shockwave sensitivity is quite close. The experiments on the acceleration of thin steel plates by detonating CL-20 charges have been performed, and it is found that its accelerating ability is higher than that of HMX and retarded RDX.
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