Gerrit Sutherland

Tensile failure of water due to shock wave interactions

A series of low stress shock impact experiments were performed on water to examine the dynamic response under tension and establish a lower bound for water rupture or cavitation threshold. The experimental cell configuration permitted particle velocity measurements at the water-air free surface separated by a 5-μm-thick aluminized Mylar diaphragm. Water samples were triply distilled, de-ionized, and degassed prior to experiments. The average tensile strength for shock-induced cavitation in the water was found to be 8.7±0.2MPa. Experiments are compared with hydrocode simulations using a simple fracture criterion and published experimental data.

Shock equation of state of multi-constituent epoxy-metal particulate composites

The shock properties of epoxy-based particulate composites have been extensively studied in the literature. Generally, these materials only have a single particulate phase; typically alumina. This paper presents equation of state experiments conducted on five epoxy-based particulate composites. The shock stress and shock velocity states were measured for five different composites: two epoxy-aluminum two-phase composites, with various amounts of aluminum, and three epoxy-aluminum-(metal) composites, where the metal constituent was either copper, nickel, or tungsten. The impact velocities ranged from 300 to 960 m/s. Numerical simulations of the experiments of epoxy-Al are compared with mesoscale simulations of epoxy-Al2O3 composites to investigate the effect of the soft versus hard particulate; additionally, an epoxy-Al–W simulation was conducted to investigate the material properties of the second phase on shock response of these materials. In these epoxy-based particulate composites, the slope of the shoc...

Shock equation of state of a multi-phase epoxy-based composite (Al–MnO2-epoxy)

There are several studies in the literature regarding the equation of state of alumina-epoxy composites. Although these single component systems interact in a complex manner with shock waves, the addition of a second metal or ceramic particulate can result in even more complex interactions. This paper presents the shock equation of state results on a multi-phase composite Al–MnO2-epoxy. Equation of state experiments were conducted using three different loading techniques—single stage light gas gun, two stage light gas gun, and explosive loading—with multiple diagnostic techniques. The Us−up relationship is shown to be linear, with deviations from linearity at low, and possibly high, pressures due to the behavior of the epoxy binder. The experimental equation of state data is compared to volume averaged and mesoscale mixture models.

SHOCK EQUATION OF STATE OF SINGLE CONSTITUENT AND MULTI‐CONSTITUENT EPOXY‐BASED PARTICULATE COMPOSITES

There are several studies in the literature regarding the equation of state of alumina‐epoxy composites. Although this single component system interacts in a complex manner with shock waves, the addition of a second metal or ceramic particulate can result in even more complex interactions. This paper presents a review of shock loading studies on epoxy‐based particulate composites. The relationship between equation of state parameters and particulate concentration is investigated. The measured shock properties are compared with a mixture model for two and three phases.

A new gun facility dedicated to performing shock physics and terminal ballistics experiments

A new building has been constructed to house various powder and single-stage and two-stage gas guns at the Naval Surface Warfare Center, Indian Head Division. Guns previously located at the Naval Research Laboratory and the former White Oak Site of the Naval Surface Warfare Center have been relocated here. Most of the guns are mounted on moveable pedestals to allow them to be shot into various chambers. The facility includes a concrete blast chamber, a target chamber/catch tank for flyer plate experiments, and a target chamber outfitted for terminal ballistics measurements. This paper will discuss the capabilities of this new facility.

MODELING OF LARGE SCALE AND EXPANDED LARGE SCALE GAP TESTS USING THE CTH HYDROCODE

CTH calculations for the shock and particle velocities in the PMMA gap of large scale (LSGT) and expanded large scale (ELSGT) gap tests were performed to determine which PMMA and Pentolite material models available in CTH best replicate measured calibration data. This effort was in support of simulations for the reactive response of the test explosive. The best match to the LSGT calibration was with a Mie‐Gruneisen EOS and a geological strength model. However, the simulation results were not within experimental error for gaps over 50 mm. For the ELSGT, all models predicted larger than observed shock velocities at times greater than 10 μs. Further work is suggested to enable better predictions and to determine why the LSGT and ELSGT do not dimensionally scale. This work includes additional gap test calibration experiments and PMMA model development.

The Role of Shear in Shock Initiation of Explosives

This describes an experiment to test the hypothesis that the energy dissipated due to shear driven plastic deformation provides the hot spots needed for shock initiation of explosives. To develop controlled shear, sinusoidal shock wave fronts were generated and used to initiate PBXN‐110 explosive charges. A threshold level was found for nearly flat shock wave fronts that did not initiate the explosive charges yet sinusoidal shock waves of lower amplitude caused initiation in the regions of maximum shear and not in the regions of minimum shear in identical explosive charges. As predicted, initiation occurred as long rows centered over the regions of maximum slope — maximum shear of the corrugated sinusoidal surface. These experiments will be discussed in detail.

Simulations of disk acceleration experiments

Hydrocode simulations demonstrated that experimental and sample features can affect detonation pressure measurements obtained from a disk acceleration experiment. Experimental features include a layer of material (e.g, air or mineral oil) between the sample and disk. Sample features include a binder-rich or porous surface which would be in contact with the disk. The meso-scale features of the explosive can cause pressure and velocity fluctuations that would result in variations in the initial disk velocity histories. The simulations showed that a thin layer of either air or a porous polyurethane as well as a thick layer polyurethane would affect the detonation pressure measurements. Additionally, two-dimensional quasi-meso-scale simulations showed the meso-scopic features lead to variability in the initial disk velocities and inferred detonation pressures.Hydrocode simulations demonstrated that experimental and sample features can affect detonation pressure measurements obtained from a disk acceleration experiment. Experimental features include a layer of material (e.g, air or mineral oil) between the sample and disk. Sample features include a binder-rich or porous surface which would be in contact with the disk. The meso-scale features of the explosive can cause pressure and velocity fluctuations that would result in variations in the initial disk velocity histories. The simulations showed that a thin layer of either air or a porous polyurethane as well as a thick layer polyurethane would affect the detonation pressure measurements. Additionally, two-dimensional quasi-meso-scale simulations showed the meso-scopic features lead to variability in the initial disk velocities and inferred detonation pressures.

Alternate methodologies to experimentally investigate shock initiation properties of explosives

Reactive flow models are desired for new explosive formulations early in the development stage. Traditionally, these models are parameterized by carefully-controlled 1-D shock experiments, including gas-gun testing with embedded gauges and wedge testing with explosive plane wave lenses (PWL). These experiments are easy to interpret due to their 1-D nature, but are expensive to perform and cannot be performed at all explosive test facilities. This work investigates alternative methods to probe shock-initiation behavior of new explosives using widely-available pentolite gap test donors and simple time-of-arrival type diagnostics. These experiments can be performed at a low cost at most explosives testing facilities. This allows experimental data to parameterize reactive flow models to be collected much earlier in the development of an explosive formulation. However, the fundamentally 2-D nature of these tests may increase the modeling burden in parameterizing these models and reduce general applicability. S...

Simulations of the modified gap experiment

Modified gap experiment (test) hydrocode simulations predict the trends seen in experimental excess free surface velocity versus input pressure curves for explosives with both large and modest failure diameters. Simulations were conducted for explosive ”A”, an explosive with a large failure diameter, and for cast TNT, which has a modest failure diameter. Using the best available reactive rate models, the simulations predicted sustained ignition thresholds similar to experiment. This is a threshold where detonation is likely given a long enough run distance. For input pressures greater than the sustained ignition threshold pressure, the simulations predicted too little velocity for explosive ”A” and too much velocity for TNT. It was found that a better comparison of experiment and simulation requires additional experimental data for both explosives. It was observed that the choice of reactive rate model for cast TNT can lead to large differences in the predicted modified gap experiment result. The cause of...