No abstract

The Modified Steven test geometry has been used with several different target designs to investigate the mechanical loading behavior of PBX9501 to a low velocity impact. A 2 kg. mild steel spigot projectile is launched via a new powder driven gun design, from-20 to 105 m/s, at lightly confmed, steel targets. Brief descriptions of the gun design and operation are given. The threshold velocity to reaction for various target designs, different PBX 9501 lots, and different high explosive (HE) thicknesses are reported and compared. Various diagnostics have been employed to evaluate the pressure profile and timing, and target strain behavior relative to projectile impact. The violence of reaction, as measured by both passive and active techniques, is reported relative to a steady state detonation in PBX 9501. Experimental results suggest slightly different ignition mechanisms dominate based on (HE) thickness, resulting in delayed reactions from-0.2-to 2.8ms after impact. Post-test analyses of the PBX 9501 are briefly summarized.

No abstract

Laser irradiation can be utilized to remove (i.e., ablate) material in a controlled manner by a hydrodynamic process, referred to as front sudace spallation. In this process, a thin layer next to a free surface is heated to a level (below vaporization) so rapidly that it cannot undergo thermal expansion during laser heating. This generates a stress pulse, which propagates both inward and toward the free surface, with an initial amplitude that can be calculated using the GrUneisen CXMficient. As the pulse reflects from the free surface, a tensilo tail can devebp of sufficient amplitude, exceeding the material strength, that a layer will be spalled olt, taking much of the laser-deposited energy with it. To achieve spallation amctitbns, the laser wavelength, pulsele~h and fluence must be tailored to the absorption depth, GrUneisen coefficient, and spalt strength. Hydrodynamic calculations and analytical modeling are presented to explain lhe process and illustrate conditions under which it should be expected to occur. Utier some conditions, front surface spallation can have advantages over ablation by thermal vaporization, where residual temperatures are generally higher,

We considered the coupling of momentum to near-Earth objects (NEOs) for the purposes of collision avoidance or collision damage mitigation through trajectory modification. The momentum sources considered were pulsed lasers, kinetic energy impactors, and nuclear (or conventional) explosives, detonated above or below the surface of the NEO by the nonnuclear and nuclear momentum sources listed above. We did not address the system tradeoffs or the environmental implications of momentum source delivery.