James D. Kershner

Three-dimensional modeling of inert metal-loaded explosives

Abstract The reactive three-dimensional hydrodynamic code 3DE has been used to investigate the reactive hydrodynamics of a matrix of tungsten particles in HMX. A propagating detonation proceeding through the matrix of tungsten particles gives calculated detonation velocities and pressures that are much higher than observed. If the heterogeneous shock initiation Forest Fire rate for HMX is used to describe the reactive kinetics, some of the individual detonation wavelets between the tungsten particles fail. The shocked explosive continues to decompose and release energy after shock passage. Equations of state are described for a tungsten and a leadloaded explosive that reproduce the observed performance of these nonideal explosives. The calibrated equations of state use a partial energy release suggested by the three-dimensional model. Evidence is presented that the explosives have a flat top Taylor wave characteristic of weak detonations.

Three-dimensional modeling of shock initiation of heterogeneous explosives

The basic processes in the shock initiation of heterogeneous explosives have been investigated theoretically using a model of a cube of nitromethane containing 91 cubic air holes. The interaction of a shock wave with the density discontinuities, the resulting hot spot formation and interaction, and the buildup to propagating detonation were computed using three-dimensional numerical Eulerian hydrodynamics with Arrhenius chemical reaction and accurate equations of state. The basic process in the desensitization of a heterogeneous explosive by preshocking witha shock pressure too low to cause propagating detonation was numerically modeled.

Three-dimensional modeling of explosive desensitization by preshocking by

Abstract The reactive three-dimensional hydrodynamic Code 3DE has been used to investigate the reactive hydrodynamics of desensitization of heterogeneous explosives by shocks too weak to initiate propagating detonation in the geometries studied. The preshock desensitizes the heterogeneous explosive by closing the voids and making it more homogeneous. A higher pressure second shock has a lower temperature in the multiple shocked explosive than in single shocked explosive. The multiple shock temperature may be low enough to cause a detonation wave to fail to propagate through the preshocked explosive.

On the Role of Crack Orientation in Brittle Failure

Many materials contain a large number of microcracks that can propagate under sufficiently high stress, but their stability is sensitive to crack orientation. We have explored this sensitivity using classical fracture mechanics with the added feature that interfacial friction is accounted for in the behavior of compression cracks. Our analysis shows that four types of unstable crack growth are possible for a penny‐shaped crack under a general state of stress, depending on crack orientation: opening without shear, mixed opening and shear, pure shear without friction, and shear with interfacial friction. In addition, interfacial friction prevents crack growth at all stress intensities in a certain range of compressive stress. It will be shown that these analytic results are captured by the SCRAM brittle‐failure algorithm, and that friction strongly affects the orientation of the most unstable shear crack as well as the range of unstable orientations. A second study examines the variations in material response as a function of the number of orientations represented. This is done by computing the dynamic response of an axisymmetric thick ring to internal pressure. With the traditional 9 crack orientations the fluctuation in porosity is about 28%, while with 480 orientations the fluctuation drops to just over 2%.

Numerical modeling of the effect of temperature and particle size on shock initiation properties of HMX and TATB

Abstract The three-dimensional Eulerian reactive hydrodynamic code 3DE has been used to investigate the effects of particle size (and the remaining void or hole size) and of initial temperature on the shock initiation of heterogeneous explosive charges of HMX and TATB. Shocks interacting with HMX and TATB containing various hole sizes have been modeled. The void fraction was held at 0.5% while the spherical hole sizes were varied from 5.0- to 0.00005 mm radius. The shock pressure was also varied. As the hole size in TATB was varied from 5.0 to 0.5 mm, the explosive became more sensitive to shock. Decreasing the hole size to 0.0005 mm resulted in failure of the shock wave to build toward a propagating detonation. This is similar to the results previously reported for TNT. HMX became more sensitive to shock as the hole size was varied from 0.5 to 0.005 mm. The hole size had to be decreased to 0.0005 mm before the explosive became less shock sensitive. Smaller hole sizes (0.00005 mm) resulted in failure of t...

Numerical modeling of the reaction zone in heterogeneous explosives

Abstract The calculated reaction zone of PBX-9404 using solid HMX Arrhenius kinetics is stable to perturbations. The calculated reaction zone Von Neumann spike pressure agrees with the experimental observations within experimental uncertainty associated with different experimental techniques. The calculated homogeneous explosive reaction zone thickness is larger than observed for the heterogeneous explosive. The effect of two volume percent air holes on the reaction zone was modeled using the three-dimensional Eulerian reactive hydrodynamic code, 3DE. The air holes perturb the reaction zone. A complicated, time-dependent, multi-dimensional reaction region proceeds through the heterogeneous explosive. The experimentally observed reaction zone characteristic of heterogeneous explosives are mean values of an irregular, three-dimensional reaction region.