Y. Horie

Constitutive model of shock‐induced chemical reactions in inorganic powder mixtures

An improved hydrodynamic model has been developed for analysis and interpretation of shock‐induced chemical reactions in inorganic powder mixtures. Attention is focused on the interaction of hydrodynamic flow with the thermodynamic changes associated with chemical reactions such as specific volume, specific internal energy, and material properties. Predictive capabilities of the model have been illustrated using experimental shock wave profile data involving Ni‐Al and Al‐Fe2O3 mixtures.

A numerical study of shock-induced particle velocity dispersion in solid mixtures

Shock-induced particle velocity dispersion in solid mixtures was numerically investigated using two approaches: discrete element simulation and continuum mixture calculation. Results show (i) a trend-wise agreement between the two models, (ii) nonequilibrium distributions of particle velocity dispersion, and (iii) particle velocity dispersions of 20–100 m/s for a 10 GPa shock wave in Ni/Al mixtures and 5–70 m/s for a 5 GPa shock wave in Ti/Teflon mixtures. Particle velocity dispersions of this magnitude are thought to be the driving mechanism for initiation of chemical reactions in reactive solid mixtures.

Discrete meso-dynamic simulation of thermal explosion in shear bands

A two-dimensional discrete element code (DM2), was used to model a complex interplay of deformation and chemical reaction in a region of localized shear at the particle level. Two exothermic mixtures of Nb–Si and Ni–Al particles having dimensions of 5 μm×25 μm were considered. Computational experiments showed that the mixtures exhibit a classical phenomenon of thermal explosion under high rates of shearing. The threshold shear rates were found to be approximately 1.2×108/s and 8.0×107/s for the Nb–Si and Ni–Al mixtures, respectively. The ignition conditions were sensitive to the thermal boundary conditions and the computationally observed values are considered to be the upper limits. The thermal explosion results from the interaction of mechanical mass mixing and heating that were primarily caused by thinning (plastic deformation) and fragmentation. The modeling showed an interesting result: that there is a ratio of fracture strengths that maximizes the mass mixing.

Unique fine microstructures of iron caused by intense shearing under shock compression

Sample assemblies consisting of an iron rod and a concentric 2024-aluminum alloy cylinder were shock-treated by impaction of an iron flyer plate. Since the shock wave velocity of the rod is slower than that of the cylinder, oblique shock waves from the cylinder interact with the plane shock waves in the iron rod and form a conical region of plane loading in the front one-third of the rod. An ellipsoidal region, due to Mach effect, might even be formed in the next one-third. Outside of the conical region, intense shearing is anticipated. Microstructures of a longitudinal cross section of the recovered rod and Vickers hardness were axis-symmetric. The ellipsoidal region could not be seen in the cross section. However, outside of the region, fine microstructures were observed. These fine structures might be formed during the intense shearing in the high-pressure e phase of iron and subsequent reverse transition to the normal α phase.

Classification of steady‐profile shocks in liquids

The stability and classification of steady‐profile plane shocks in liquids are studied by hydrodynamic equations which include the relaxational properties of momentum and heat fluxes. The thermodynamic behavior during shock deformation is shown to be equivalent to the dissipative motion of a particle described by a generalized Lienard equation. The stability condition produces relations for the relaxation times for momentum and heat fluxes. These relations are in agreement with acoustic data and other theoretical calculations which produce the relaxation times of 10−13−10−14 sec.

Numerical Integration of Plane Elastic‐Relaxing Plastic Shock Waves by a Two‐Step Method

Hyperbolic equations with a differential constitutive relation of dynamic yielding are numerically integrated without the pseudoviscosity. The scheme is shown to be stable and the resulting shock profiles are smooth. The example of iron shows a good agreement with those of the viscosity method and suggests that a stable profile will emerge as mesh sizes decrease.

Adiabatic Theory of Plane Steady Shock Profiles in Solids

Duvall, Manvi, and Lowell have shown a close relationship between a continuum theory of shock structures in solids and that of one‐dimensional lattices. In this paper, extending their results, we have shown that the thermodynamical behaviors of shock structures are equivalent to those of the dissipative autonomous system described by a generalized Lienard equation. The theory assumes adiabatic conditions and the relaxational transformation of instantaneous work into equilibrium internal energy.

Analysis of plane shock structures in 606‐T6 aluminum

The steady profile of plane shocks in 6061‐T6 aluminum by Johnson and Barker is compared with the unsteady ones obtained by a finite‐difference integration of the Lagrangian dynamic equations. The results purport the conclusions similar to theirs but are not conclusive as they claim. It is also found that strain‐rate functions proposed by Johnson and Barker are double valued at high stresses for fixed strains and need to be further clarified in future experiments.

Microstructures of single‐crystal copper rods shock‐treated by a rod‐in‐cylinder technique

Two single‐crystal copper rods were shock‐treated with a rod‐in‐cylinder technique. One rod was treated in a polycrystal copper cylinder. Strong contrast areas due to shock waves interactions were not observed with an optical microscope. Another rod was shock‐treated in a 2024‐aluminum cylinder. An area compresed by plane shock waves and an ellipsoidal area compressed by a Mach‐wave were distinguishable with an optical microscope. Complex microstructures were found in the ellipsoidal area. We believe that such microstructures were caused by the heterogeneity of particle velocity, shearing stress, pressure and temperature in the shock‐treated specimen.

Local rapid quenching in a powder mixture and its utilization to synthesize novel compounds in the B‐C‐N system

A selective surface heating of particle and local mixing are known as a typical microscopic effect on shock compression of powder. In the case, the thermal conductivity of powder particle is sufficiently high, like diamond, shock compression technique can be used as a means of local heating and rapid quenching of particle surface. Shock compression of powder in a metal capsule causes steep distribution of pressure and temperature by shock waves interaction. A rod‐in‐cylinder type recovery assembly composed of steel rod having sample cavity and aluminum alloy cylinder is used in this study. After shock‐treatment, particle surfaces in the powder mixture of diamond and boron nitride were observed with a high resolution transmission electron microscope. It is demonstrated that this method has a high potential as a tool of new material exploration.