Modeling of shock-wave compaction of powder ceramics using a ballistic testing unit

Abstract

The problem of creation of high-density compacts from raw material in ultradispersed ceramic powder is considered. In many cases, preliminary treatment of powders of refractory compounds by pulsed pressure substantially facilitates further formation of compact products by the methods of powder metallurgy [1, 2]. On the one hand, shock-wave compression of nanocrystallite submicron ceramics leads to a qualitative change in the morphology and to fragmentation of the powder particles: the bulk density increases, and additional saturation of the particles by defects of the crystalline structure is observed. The accumulated strain energy increases in the powder and polymorphous conversions occur. On the other hand, the possibility arises of obtaining, immediately in the shock wave, large agglomerates or one-piece compacts of particles, with a density close to that of a monolith. In both cases, it is necessary to know the optimal regimes of shock-wave treatment, because it is known that, for example, the degree of defectiveness and the area of the particle surface are the functions of pressure. As the intensity of the shock wave increases, bonding of the crystalline powder goes through a maximum, and under very strong loadings monolithic compacts are difficult to obtain because of dislocation breakdown of the lattice.The physicomechanical and chemical properties of new modifications of nanocrystallite ceramics depend not only on the amplitude of shock compression, but also on many other factors, including the load rate and duration and pressure gradients in unloading waves. It can be expected that, having constructed an optimal stress-time diagram, one can obtain the required modifications of submicron ultradispersed powders at various structural levels and form sufficiently dense homogeneous compacts with an acceptable concentration of defects in the powder. However, selection of optimal regimes of shock-wave compaction is by no means easy, because the pulsed compaction of powders is often multidimensional and nonstationary, and the set of kinematic and dynamic parameters of it is difficult to record experimentally over a wide time interval. The pressure amplitude at the wall of a conservation ampoule is, as a rule, an estimate that is accessible to determination and sufficiently reliable.One of the methods of finding the optimal parameters of shock-wave compression is to obtain quantitative information on the evolution of the stress-strain state on the basis of simulation of the dynamics of powder compaction with an appropriate experimental testing for model adequacy at the reference points of the initial and final compaction stages.In the present paper, we present the results of an experimental-theoretical investigation of shock-wave compaction of the powder of ultradispersed tetragonal zirconium dioxide using a ballistic test unit. Pulsed loading of the powder using a ballistic test unit is of interest, because the stress-time diagram can be varied widely in time, with variation in the impact velocity, mass, length,...

Hydrodynamic and Thermodynamic Nonequilibrium Effects around Shock Waves: Based on a Discrete Boltzmann Method

“…Shock waves are widespread in many fields of physics and engineering [ 1 , 2 , 3 , 4 ], and their frequent occurrence is based on the fact that matter is more or less compressible [ 5 ]. The shock wave is a kind of disturbance waves that carries abundant energy and propagates at supersonic speed in the medium [ 6 ].…”