A theoretical model is formulated to describe a complex
interplay of mechanical, thermal, chemical processes
associated with intense shear in mixed powders. The model is
an outgrowth of a recent numerical study of chemical
reactions in Nb-Si and Ni-Al mixtures. In the analytical
model, mass mixing of constituents is represented
effectively by a mixing characteristic time, which is
assumed to be a function of strain rate. The overall
governing equations resemble a theory of continuously
stirred chemical reactors. Using a dimensionless system of
equations, we show a variety of flow regimes in terms of the
mixing time, whcih is found to be equivalent to residence
time in the reactor theory. Solutions include oscillatory as
well as discontious behavior. The conditions of spontaneous
ignition and extinction are evaluated in terms of
dimensionnless groups that are functions of process
parameters such as surface heat transfer coefficient, heat
of reaction, and the width of shear bands. The ignition
conditions are also examined in the context of shock-wave
processing.
[R4.02] Shock Induced Reaction to Refractory Metal Di-Silicides from MA Precursor
Tatsuhiko Aizawa (Department of metallurgy, University of Tokyo), Ken-ichi Ichige (Department of Metallurgy,University of Tokyo), Yasuhiko Syono (Institute of materials Research, Tohoku Univerisity), Silicide Collaboration
In general, when using the elemental powder mixes, little or
no reactions occurred; since full reactivity can be realized
when starting from the MA precursors or the pretretaed
element constituent mixes by mechanical miling, variation of
shock loading conditions leads to direct investigation of
shock reaction mechanism in terms of post-shock analyses. In
this paper, Mo-Si and Ti-Si systems are employed to discuss
the fundamental shock induced reaction process intrinsic to
each system. The feature common to these systems is that the
shock induced reaction should be composed of two or more
steps. In Mo-2Si system, the amorphous phase might be first
synthesized during shock loading and followed by the
regularization process into MoSi2. Through microstructure
observation of post-shock samples, volume fraction of
amorphous phase, with the local chemical compositions
varying from Mo60Si40 to Mo40Si60, increases with decreasing
the shock pressure. On the other hand, no intermediate phase
can be seen in the microstructure in Ti-Si system;
regularization process into TiSi2 in the same shock loading
condition is activated by increasing the milling time. Local
fine mixture of Ti and Si or solid-solution-like phase can
be seen through precise microstructure observation. TEM
analysis is further performed to describe these
pre-regularization processes and to discuss the effect of
shock loading condition on the transient reaction path to
synthesize the refractory metal di-silides with
consideration on the role of Si.
[R4.03] An Analysis of Shock-Compression in Mo-Si Powder Mixtures Using Recovery and Time-Resolved Measurements
Kevin S. Vandersall, Naresh N. Thadhani (Georgia Institute of Technology)
The densification and reaction characteristics in the Mo-Si
system were investigated utilizing recovery experiments as
well as time resolved measurements with in-situ stress
gages. The starting sample in all cases consisted of
statically pressed Mo + 2 Si powder mixtures (\sim55% TMD). The
recovery experiments were performed using the Sandia Momma
Bear and Momma Bear A fixtures with baratol and composition
B explosives respectively. The instrumented experiments were
performed in a capsule design similar to that of the Momma
Bear, but modified to incorporate poly-vinyl di-flouride
(PVDF) stress gages at the front and rear surfaces of the
powder. These experiments were performed using a single
stage gas gun in the velocity range of 500 m/s to 1 km/s.
The instrumented experiments allow the crush strength,
densification history, and reaction threshold to be mapped
at increasing pressure to correlate with reaction observed
in the recovery experiments.
[R4.04] Possibility of making polycrystalline diamond using high-temperature shock consolidation technique
Kazuyuki Hokamoto, Masahiro Fujita (Dept. of Mech. Eng. amp; Mater. Sci.,Kumamoto University, Japan), Sei-ichiro Tanaka (Kumamoto Prefectural College of Technology, Japan), Makoto Ayabe (Graduate Student, Kumamoto University), Shigeru Itoh (Dept. of Mech. Eng. amp; Mater. Sci., Kumamoto University, Japan)
The making of polycrystalline diamond using shock compaction
technique has been pursued by many researchers, but the
difficulty is due to cracking by the propagation of strong
shock wave and the lack of interparticle bonding through an
intensive surface deformation. The authors tried to develop
high-temperature shock compression apparatus using
converging underwater shock wave. Some of the samples are
successfully recovered up to 1373 K though the samples are
cracked. One of the polycrystalline diamond recovered shows
high Vickers hardness above 90 GPa, which corresponds with
the value of natural diamond, based on the strong
interparticle bonding between particles by the help of
heating. High fracture toughness is measured for the sample
which depends on the isotropic property.
[R4.05] Shock and impact initiation of a porous incendiary material
Jeffery Davis (Naval Air Warfare Center, China Lake CA 93555), Phil Miller, Diana Woody
A series of gas gun tests has been performed on an energetic composition containing KClO4 and Al/Mg. These materials are currently being developed for an initiation system in medium caliber bullets. Initiation begins upon impact of the bullet with the target through the interaction of the compaction wave with an incendiary charge. In order to better understand the deformation - initiation process, experiments have been performed in which the incendiary charge was impact tested via gas gun at velocities ranging from 0.33 - 0.98 mm/ms at two densities: 84 and 70
[R4.06] Attempts to initiate detonations in metal-sulfur mixtures
Samuel Goroshin, Junping Jiang, John H.S. Lee, Massimiliano Romano (McGill University, Canada)
Deflagration waves, which convert solid reactants into solid products, have been observed in certain inorganic mixtures. The possibility of self-sustained "gasless" detonation waves has yet to be experimentally demonstrated. The present study attempts to initiate detonation in metal-sulfur mixtures. Specifically, manganese-sulfur mixtures are used because they are extremely energetic with flame temperature as high as 4000 K and all their detonation products exist in a condensed phase. The charges were 50 mm in diameter and 250 mm long, and were confined with a heavy walled steel pipe. At one end, a short length of bare Mn-S charge was wrapped with sheet explosive. Upon initiation of the sheet explosive, a strong Mach disk was driven into the Mn-S charge. Contact gauges and ion probes were used to monitor the shock and reaction front in the charge. The results indicate that the speed of the reaction front in the part of the charge surrounded by explosive was 6-7 km/sec, but quickly decelerated to below 2.5 km/s as it propagated into steel-confined charge. The results indicate that self-sustained "gasless" detonation is not observed even using an overdriven Mach disk for initiation. Rapid reactions can be initiated by shock wave, but the shock wave apparently cannot be maintained without significant volume expansion in the products.
[R4.07] Three-dimensional modeling of impact of capsule with Ti-C powder mixture on target
Vassili A. Gorelski, Vadim V. Kim, Aleksei Yu. Smolin (Tomsk Branch of the Institute of Structural Macrokinetics and Materials Science RAS)
A problem of oblique high-velocity interaction of a steel
capsule containing stoichiometric porous mixture of titanium
and carbon with a rigid wall is considered. The angle of
impact is 15^\circ, the impact velocity is varied in the
range of 500--1200~m/s. The diameter of the capsule is
7.62~mm, the height is 26~mm. Three values of the initial
porosity of the mixture are used: 0%, 50% and 70%. The
set of equations describing adiabatic motion of a
compressible chemically active medium consists of the
equations of continuity, motion, energy, chemical kinetics
and the equation describing generation and growth of the
specific volume of pores. The finite-element method is used
for solving the problem. The time-dependencies for specific
volume of pores, pressure and interaction force as well as
configurations of the capsule at different times are
analyzed. The influence of initial velocity and porosity on
chemical reaction is revealed. The results of simulation
allows to subdivide the process into three stages: 1)~when
only compaction process occurs, 2)~the chemical reaction of
synthesis takes place in porousless mixture near the contact
surface, 3)~the chemical reaction takes place in mixture at
the upper side of the capsule.
[R4.08] Investigation of Role of Cocentration Ingomogeneity of Powder Mixture in the Initiation of "Shock-Induced" Chemical Reaction
V.N. Leitsin, V.A. Skripnyak (Tomsk State University, Russia)
The main aim of the work is development of thermo-mechanical initiation model of chemical reactions under deformation of powders mixtures as Ti-Al. Computer simulation of processes, occurring in reacting laier at shock compression showed: 1. The rection of synthesis of intermetallic compounds in systems Ti-Al can be "self-assisted"; 2. The speed of propagation of front of chemical transformations is defined by a degree and papameters of spatial concentration inhomogeneity of powders mixture; 3. Necessery conditions for initiation of "shock-induced" chemical reactions includes the presence of non-zero porosity and certain initial temperature of a mixture. It is essential, that reduction of porosity and degree of concentration ingomogeneity of powder mixture can lead to changing of a mode of reaction and down to complete its prohibition.