The behavior of a material subjected to dynamic loading conditions should include sufficient information about the major hydrodynamic variables (pressure, volume, and particle velocity) to properly describe an equation of state. Shock speed, a phase component of particle velocity and the easiest characteristic to measure, does not provide sufficient information to serve as the universal experimental diagnostic. Pressure and particle velocity, parameters which yield to relatively accurate experimental measurements, provide direct ties to theoretical studies, as well as to determining tables of coefficients for an equation of state. At the Lawrence Livermore National Laboratory, pressure and particle velocity gauge measurements in both reactive and nonreactive materials are conducted at our large-bore gun facility, where projectiles of up to 1.5 kg reach speeds as high as 2.2 mm/μs. Described here are in-situ foil gauges for both pressure and particle velocity measurements. In addition, the optical Fabry-Perot interferometer for observing particle and free surface velocities in transparent media is discussed. Although these techniques are not new, they have been continuously improved and upgraded at our facility to yield greater accuracy, reliability, and state-of-the-art performance. The emphasis in this paper is on the operational features of the measuring techniques, but examples of experimental results are also included.

Pressure and particle velocity measurements in solids subjected to dynamic loading

Hugoniot and Mie–Grüneisen equation of state of unreacted 2,4-dinitroanisole (DNAN)

VISAR instrumentation has been used to examine how compressive waves grow towards detonation in granular explosives. In the experiments, a variety of initial waveforms have been generated in explosive samples using planar impact techniques and carefully designed projectile and target assemblies. Despite limitations due to window interfaces, VISAR measurements have provided important insights into initiation processes, and have contributed to a useful data base for the evaluation of predictive models.

Velocity Interferometer System For Any Reflector (VISAR): Studies Of Wave Growth In Granular Explosives

Amorçage en détonation des explosifs hétérogènes de type coulé-fondu : établissement de corrélations entre microstructure et réactivité / par Vincent Chuzeville

In situ measurements of pressure and particle velocity have always been crucial in the development of theoretical models and formulation of equations of state for both inert and reactive materials. Formerly, measurements were made with separate gauge stations placed between layers of investigated material stacked in the direction of shock propagation. This arrangement not only generates a disturbance in the flow field but also causes interruption in the chemical reaction process being monitored. The introduction of multiple gauge packages placed on an inclined surface has eliminated most of the problems encountered with separate in line gauge stations. Such multiple gauges provide the capability of measuring changes in pressure and particle velocity at depth intervals much smaller than those between separate gauge stations. In addition each consecutive gauge element is not engulfed in the flow wake of the preceding one. The multiple element gauges described here are ideal for monitoring rapid changes in pressure and particle velocity in processes such as transition to detonation or phase transformation. With this arrangement in a single experiment one can have as many as twelve signal traces from within a very thin depth in a sample. 20 refs., 9 figs.

Multiple gauges for in situ measurements of pressure and particle velocity in condensed materials

Manganin stress gages have been fabricated and used successfully to study initiation and detonation of high explosives. These four-terminal, low-impedance gages have been specially designed and encapsulated to minimize the effects of various gage failure mechanisms. Several candidate dielectric encapsulation materials have been tested in the reactive environment, and of these polytetrafluoroethylene has been chosen. Gage stations are formed by thermally bonding the manganin foil between layers of this dielectric. Gages manufactured in this way have been used to provide stress profiles throughout the region of build-up to detonation in PBX-9404 and TATB.

Manganin stress gages in reacting high explosive environment (5. Experimental methods and techniques). [PBX-9404 and TATB]

Data from stress gages embedded in shocked high-explosives can be used to estimate chemical energy release rates in the region of the gages and to test the validity of numerical hydrodynamic simulations of shock initiation experiments No commercially available stress gages were suitable for this use Techniques developed for fabricating and encapsulating maganin stress gages which can be used in a reacting high-explosive environment are described (LCL)

Fabrication of manganin stress gauges for use in detonating high explosives

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Manganin stress gages in reacting high explosive environment (5. Experimental methods and techniques). [PBX-9404 and TATB]

Fabrication of manganin stress gauges for use in detonating high explosives