I. V. Yakovlev

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.

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.

Thermocouple Method for Studying Pressure Fields in Metals under Dynamic Loading

Thermoelectric effects in a bimetal plate loaded by a gliding detonation wave are explored. The electric–potential distribution is measured on the surface of such a thermocouple which is nonuniformly heated as a result of high–rate deformation. Experimental results are used to determine the stress state of the metal and are compared to calculations performed within the framework of the Mie—Grüneisen model.

Variation of the Magnetic Field in a Powder Metallic Medium upon Explosive Compaction

The propagation of a plane shock wave of constant intensity over a powder metallic medium in the presence of a magnetic field is considered. The compression of the magnetic field by a shock–induced conducting wave in the medium is studied in detail. It is assumed that the magnitude of the macroscopic electric conduction increases monotonically from zero to its maximum and is constant behind the shock–wave front. The problem of determining the magnetic field is solved under the assumption that the characteristic time of field variation is much greater than the time required for convection and diffusion through the front. The dependence of the magnetic field on the coordinate and the time inside the shock–wave front is established.

Morphology of craters at hypervelocity impact in isotropic composites with inclusions

Results of a study of hypervelocity impact in model disperse-reinforced composites with an epoxy or aluminum matrix with metallic (Al and Pb) or ceramic (SiO2) inclusions are reported. The goal of the present study is to find materials that possess a higher resistance to penetration of a high-velocity projectile compared with materials of separate components. This resistance is characterized by the ratio of the depth of a crater in a sufficiently thick target to the diameter of a spherical projectile. For two composites studied, we show that in impact of a steel particle with a velocity ranging from3 to11km/sec, the crater depth is approximately one projectile diameter smaller than that for lead or aluminum targets.