V. V. Pai

An investigation of ceramic/aluminium composites as shields for hypervelocity impacts

Summary The protection efficiency of single-shield bumpers made of composites based on the aluminum matrix containing the disperse ceramic inclusions of SiO2 or Al2O3 is considered for a Whipple-type shield. The aim of the paper is to compare the protection efficiency of the first bumpers made of the metal composites with that for the duralumin shield by impact of spherical steel projectile with the velocity of 5.5 and 7.5 km/s. Mass fraction of the ceramic inclusions accounts for 15 and 30 percent of the total composite. A thick backwall plate was used, and the maximum depth of fragment craters on the witness plate is taken as a protection characteristic of shields made of different materials: reference aluminum alloy, composites under study, and loosely-packed metal powder bumpers. The bumpers made of the metal composites, Al-matrix plus embedded ceramic inclusions, are shown to have the poorer protection efficiency than those made of the duralumin alloy when used with steel impactors. It is shown that by impact of the hypervelocity steel projectile the shield material strength, if it is rather low but not zero, may essentially affect the damage pattern of the backwall in spite of the high level of realized impact pressures.

Explosive compaction of aluminum powder and the structure of compacts

Macrodefects of the structure of samples produced by explosive compaction of an aluminum powder were examined. The areas of the new contact particle surfaces produced by high-rate deformation were measured by stereological methods. The eddy current method was used to measure the macroscopic electric conductivity of the compacts. From these data, the mean sizes and number of macrodefects per unit volume of a compact were calculated. The techniques employed can be useful for an analysis of the structure of composite materials produced by various methods.

Protective properties of shields of ceramic/aluminum composite for hypervelocity impact

The protective effect of thin shields of metal-composites based on a matrix of aluminum with dispersed inclusions of SiO2 and Al2O3 for hypervelocity impact of spherical steel particles are examined in a one-layer protection scheme. The protective effect of shields of these materials are found to be inferior to shields of homogeneous aluminum alloy.

INVESTIGATION OF SHOCK COMPRESSION OF COMPOSITE POROUS MEDIA BY A NONDISTURBING ELECTROMAGNETIC TECHNIQUE

A remote-control electromagnetic technique is developed to determine the mass velocity behind a shock wave(SW) in porous, fibrous, and other heterogeneous media. As an application of the technique a shock adiabat ofAl2O3 powder of bulk density was constructed in the region of low pressures.

Approximate evaluation of loading parameters in composite materials with strong shock waves

A simple and sufficiently accurate method is proposed for estimating the parameters of shockwave loading of porous materials under conditions of complete compaction of the material to the density of a monolith.

Temperature measurements of a shock-compressed emulsion matrix

The temperature of a shock-compressed invert emulsion based on an aqueous solution of ammonium and sodium nitrates was measured using two experimental techniques: using planar thermocouples at pressures of 3.4–12.0 GPa and optical pyrometry at pressures of 9–22 GPa. The experimental data obtained using the thermocouple method are consistent with the calculated values. The optical measurement results are significantly higher than the calculated data and indicate the presence of a spatially inhomogeneous temperature field behind the shock front in the emulsion due to the structural inhomogeneity of the medium.

Thermal processes in explosive welding

New computational and experimental methods for studying the thermal processes occurring during metal explosive welding are developed based on the use of natural and local thermocouples and allowing one to reliably construct temperature fields in the heat-affected zone and thermal welding cycles. The basic regularities of thermal processes in the heat-affected zone during explosive welding are revealed. It is theoretically shown and experimentally confirmed that, in this zone, the heat released during detonation of the explosive can significantly increase the temperature of the contacting metal layers and lead to melting of the latter.

Effect of the Strength of the Material of a Plate Accelerated by Low-Rate High Explosives

Plate acceleration by a gliding detonation wave is studied experimentally for detonation rates of ≈ 950–2000 m/sec. It is found that regular elastic waves occur at the surface of the projectile plate made of a rather strong material, which disappear upon attainment of the upper limit of the detonation rate.

Electromagnetic processes in thermocouples under dynamic loading

Electromagnetic processes in flat thermocouples made of metals with varying conductivity under conditions of dynamic loading with a traveling load are studied. The distribution of the electric potential over the thermocouple surface is shown to carry information on the velocity field and the strained state of the thermocouple materials. An experimental procedure for validating various theoretical models of continua under high-velocity deformation is proposed. As an illustration, results of numerical simulations for flow of an ideal incompressible fluid are presented.

Wave Formation in Symmetric Collision of Metal Plates

Collision of metal plates is treated in the frames of model of a viscous incompressible liquid. In such terms a wave formation process corresponds to an initial stage of occurrence of turbulence in accordance to L.D.Landau’s scenario. To verify conformity between the theoretic description and the real process, a series of experiments on symmetric collision of aluminum plates is carried out with identical collision angles and different velocities of a collision point. It is established that with great magnitudes of the Reynolds number R and consequently, with the big velocities of a collision point, excitation of wave formation has soft type, with smaller magnitudes of R there is an area of metastability where the mode of excitation has rigid type, and with even smaller magnitudes of R any influence does not lead to wave formation in conformity with Landau’s theory.