L. M. Erickson

Hysteresis‐corrected calibration of manganin under shock loading

The coefficient of electrical resistance of manganin was measured under shock loading and ramp unloading. We made 64 measurements of loading stress in the 1.3–40.5‐GPa range and 22 measurements of unloading stress in the 1.9–23.2‐GPa range. The average loading coefficient was 14% larger than the average unloading coefficient—a clear measure of resistance hysteresis. The source of the hysteresis is attributed to an irreversible resistance change in manganin caused by shock damage. We present techniques to correct for the effects of this irreversible resistance change. With this correction, both loading and unloading levels showed the same average coefficient of resistance 0.0221±0.004 per GPa. Our unified calibration procedure can be very useful for analyzing complex stress signals that are produced, for example, by reactive shock waves.

Precision stress measurements in severe shock‐wave environments with low‐impedance manganin gauges

We describe new techniques that permit the use of low‐impedance manganin stress gauges in chemically reacting shock waves in the 1.0–40.0 GPa range. The rugged, small, and fast response gauge has reproducibility better than 2% when used in conjunction with a pulsed bridge circuit and adjustable, current‐regulated power supplies. Techniques are presented for fabricating the transducer package, calibrating the bridge circuit and oscilloscopes, designing the drive system, and reducing the data. Data are presented for planar impact experiments performed with a 102‐mm gas gun on high‐explosive samples. In particular, we directly measured the Chapman‐Jouquet pressure in the explosive RX03‐BB [92.5% triaminotrinitrobenzene (TATB)/7.5% polychlorotrifluoroethylene (Kel‐F binder)] as 28.2±0.6 GPa. These new developments open the possibility of applying low‐impedance manganin gauges in chemically reactive hydrodynamic flows such as the evolution of a shock wave into a detonation wave.

Reactive flow modeling of recent embedded gauge and metal acceleration experiments on detonating PBX-9404 and LX-17

Abstract The ignition and growth model of the reactive flow during shock initiation and detonation wave propagation in the heterogeneous solid explosives PBX-9404 and LX-17 is compared to recent embedded particle velocity and stress gauge measurements in detonating PBX-9404 and Fabry-Perot free surface velocity measurements of thin metal plates accelerated by detonating PBX-9404 and LX-17. The overall agreement between the numerical calculations and the various experimental records, which have time resolutions in the nanosecond regime, is very good. The regions of disagreement emphasize some of the processes involved in reactive flow and metal acceleration that are not fully understood and directions for future experimental and modeling work. These new experimental and calculational results are also compared to some previously reported back surface particle velocity gauge and free surface velocity measurements for detonating PBX-9404. The experimental records and the numerical results clearly demonstrate ...

Pressure and particle velocity measurements in solids subjected to dynamic loading

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.

SHOCK INITIATION, DETONATION WAVE PROPAGATION AND METAL ACCELERATION MEASUREMENTS AND CALCULATIONS FOR RX-26-AF

Embedded pressure and particle velocity gauge records of shock initiation and detonation wave propagation in the heterogeneous solid explosive mixture RX-26-AF are shown to be accurately calculated by an ignition and growth reactive flow model that separates the growth reaction rates into those of the individual explosives HMX and TATB. Fabry-Perot measurements of the free surface velocity histories of tantalum plates driven by detonating RX-26-AF are also compared to model predictions.

Reactive flow lagrange analysis in plastic bonded explosives

Abstract A description of Lagrange gauge measurements in PBX-9404 and RX-26-AF is given. The data are used to study the progress of reaction in these explosives. The results are discussed along with the underlying theortetical assumptions. Emphasis is given to the practical problems of constructing a description of the chemical reaction from gauge data.

A comparison of stress and velocity measurements in PBX-9404 explosive

We measure the stress and particle velocity histories of Lagrangian points in a plane initiation wave in PBX-9404 explosive. Stress histories calculated from velocity histories agree well with experiment and indicate that both types of gauges record faithfully in reactive flow. The inverse calculation is more difficult since errors accumulate in the computation. We describe and compare two computational methods: pathline and direct analysis. Our results show that a complete gauge analysis should use multiple bare velocity gauges, companion experiments with single insulated stress gauges and pathline analysis.

Improvements in the Signal Fidelity of the Manganin Stress Gauge

The manganin stress gauge has been and still is the primary diagnostic tool for measuring longitudinal stresses in materials shocked from 10 to 400 kb in one‐dimensional (1D) uniaxial strain experiments [1]. Its simple and robust design allows this gauge to survive in harsh environments. The manganin gauge has several limitations. For example, in the eventual failure mode, the manganin gauge has a reputation of being a noise generator to the remaining functioning manganin gauges at different lagrangian positions in the experiment. The manganin gauge also demonstrates undesirable signal effects when the front edge of the incoming shock first makes contact. These two limitations and the experiments for the mediation of these effects on shock experiments will be presented in this paper. Our ultimate goal is to provide practical manganin gauging that has true fast rise time and little or no noise generation on failure in explosive detonation waves. A device was found that mitigates the noise generation withou...

REACTIVE FLOW LAGRANGE ANALYSIS IN RX-26-AF

A series of Lagrange gauge records, taken in RX-26-AF are analyzed. The explosive is initiated at 27 Kb sustained shock pressure. The resulting reaction runs through approximately 1.5 cm of the PBX, while pressure and velocity measurements are taken at various Lagrange coordinates. Using the equation of state for reactant, and product gases, in the J.W.L. form, a reactive flow Lagrange analysis (RFLA) is used to calculate the reaction progress coordinate. The results show an interesting two-stage reaction possibly associated with the different reaction rates of HMX and TATB. Problems with consistency and error are discussed.

Free‐surface velocity measurements of plates driven by reacting and detonating RX−03−BB and PBX−9404

Copper plates 80 mm in diameter, of thickness 0.25 mm and 0.5 mm, were accelerated by adjacent 17 mm thick, 90 mm diameter cylinders of RX−03−BB or PBX−9404−03. The explosive was initiated by impact of a thick flyer from the LLNL 102 mm gun, providing either a reactive or fully detonating wave, by approprite choice of flyer velocities up to 1.30 mm/μs. The free‐surface velocity of the plates was measured with a Fabry‐Perot velocimeter. We have obtained excellent experimental free‐surface velocity histories. Our calculations of this history employing beta‐burn and nucleation and growth high explosives models are in good agreement with fully detonating experiments. For reacting RX−03−BB, adjustments in the parameters are needed. We have an experimental technique that gives records whose agreement with calculation is sensitive to the model and is therefore a good way of testing new high explosive models. Also, this method allows us to infer information about the reaction zone length.