Shock-wave compression of brittle solids

A fourth-power law relating the stress jump through a steady structured shock wave and the maximum strain rate within the shock wave has received recognition as a unifying relation over a sensibly wide range of materials and shock compression amplitudes. Less widely recognized is the complementary applicability of the invariance of the product of the energy dissipated and the time over which this energy is dissipated through a structure shock wave—a property with the dimensions of action. While the latter invariance implies the fourth-power behavior for steady shock waves, this invariance also has an apparent application to unsteady structured waves under certain conditions. A brief history of the origin of the fourth-power law is provided. Some commentary is offered on the physical principles of solid viscosity in the shock wave and the underlying invariance of the energy-time product in the shock wave event. The results for steady structured waves in porous and composite solids, which do not in general exhibit fourth-power behavior, are examined. Observations of systematic behaviors with component cell size and impedance disparities suggest acoustic scattering may contribute to wave structuring in selected materials.

Structured shock waves and the fourth-power law

Metastable Si-B-C-N ceramics and their matrix composites developed by inorganic route based on mechanical alloying: Fabrication, microstructures, properties and their relevant basic scientific issues

We succeeded in synthesizing a bulk crystal of wurtzite-type boron nitride (w-BN) by the direct conversion method. The synthesized crystal was approximately 2 mm wide and 350 µm thick, and highly oriented to the c-axis. We performed nanoindentation measurements on the c-plane of the w-BN crystal at room temperature to evaluate the mechanical properties of w-BN. The hardness and Young's modulus of w-BN from the obtained curves were simultaneously determined to be 54 ± 2 and 860 ± 40 GPa, respectively. The underlying physical mechanism that dominates the mechanical properties of group-III nitride semiconductors is also examined.

http://iopscience.iop.org/article/10.7567/JJAP.56.030301/pdf

Nanoindentation measurements of a highly oriented wurtzite-type boron nitride bulk crystal

Formation of diamond-like BN phases under shock compression of graphite-like BN with different degree of structural ordering

Phase composition, structure, and properties of polycrystalline BNsph sintered in shock waves

Treatment of powders of superhard materials by a shock wave for the purpose of obtaining a compact specimen with the necessary service characteristics in subsequent sintering is finding ever wider use in high pressure technology [i]. Many of the properties of polycrystalline materials obtained in such a manner depend significantly upon the structural condition of the material after treatment. However, data on the fine structural condition of polycrystalline materials produced by sintering directly in shock waves is lacking.

The substructure of BNsph formed in sintering in a shock wave

Mass transfer in metals caused by a convergent cylindrical shock wave

Phase and structural transformation in sintering wurtzite boron nitride in shock waves

1.

A study was made of the effect of pressure on the friction, wear, and surface microhardness of some transition metals of Groups V, VI, and VIII sliding under dry friction conditions in a vacuum.




2.

The existence is demonstrated of certain “threshold” pressures at which the frictional force and wear sharply increase. The microhardness of sliding surfaces at first rises and then falls.




3.

The increase in frictional force is attributable to the fact that, with rise in pressure, the type of linkage between the atoms in the sliding surfaces in contact changes. The wear becomes more intense when the zone with a critical dislocation density moves away from the surface with rise in pressure.

V. I. Kovtun

Papers

Phase composition, structure, and properties of polycrystalline BNsph sintered in shock waves

The substructure of BNsph formed in sintering in a shock wave

Mass transfer in metals caused by a convergent cylindrical shock wave

Phase and structural transformation in sintering wurtzite boron nitride in shock waves

Effect of pressure on the friction, wear, and surface properties of the transition metals