Retrofiting survivability of military vehicles
- Los Alamos National Laboratory
In Iraq the terrain was such that vehicles could be distributed horizontally, which reduced the effectiveness of mines. In the mountainous terrain of Pakistan and Afghanistan vehicles are forced to use the few, passable roads, which are dirt and easily seeded with plentiful, cheap, intelligent mines. It is desirable to reduce the losses to such mines, preferably by retrofit means that do not greatly increase weight or cost or reduce maneuverability. V-bottom vehicles - A known approach to reducing vulnerability is the Buffalo, a large vehicle developed by South Africa to address mine warfare. It has large tires, high axles, and a reinforced, v-shaped bottom that deflects the blast from explosions below. It is developed and tested in combat, but is expensive and has reduced off-road mobility. The domestic MRAP has similar cost and mobility issue. The addition of v-shaped blast deflectors to vehicles such as Humvees could act much as the deflector on a Buffalo, but a Humvee is closer to the ground, so the explosive's expansion would be reduced. The deflector would also reduce a Humvee's clearance for rough terrain, and a deflector of adequate thickness to address the blast by itself could further increase cost and reduce mobility. Reactive armor is developed and has proven effective against shaped and explosive charges from side or top attack. It detects their approach, detonates, and defeats them by interfering with jet formation. If the threat was a shaped charge from below, they would be a logical choice. But the bulk of the damage to Humvees appears to be from the blast from high explosive mines for which the colliding shock from reactive armor could increase that from the explosive. Porous materials such as sand can strongly attenuate the kinetic energy and pressure of a strong shock. Figure 1 shows the kinetic energy (KE), momentum (Mu), velocity (u), and mass (M) of a spherically expanding shock as functions of radius for a material with a porosity of 0.5. Over the range from 0.5 to 4.5 cm the shock KE is attenuated by a factor of {approx}70, while its momentum is changed little. The shock and particle velocity falls by a factor of 200 while the mass increases by a factor of 730. In the limit of very porous media u {approx} 1/M, so KE {approx} 1/M, which falls by a factor of {approx}600, while momentum Mu does not change at all. Figure 2 shows the KE, Mu, u, and M for a material with a porosity of 1.05, for which the KE changes little. In the limit of media of very low porosity, u {approx} 1/{radical}M, so KE is constant while Mu {approx} {radical}M, which increases by a factor of 15. Thus, if the goal is to reduce the peak pressure from strong explosions below, very porous materials, which strongly reduce pressure but do not increase momentum, are preferred to non-porous materials, which amplify momentum but do not decrease pressure. These predictions are in qualitative accord with the results of experiments at Los Alamos in which projectiles from high velocity, large caliber cannons were stopped by one to two sandbags. The studies were performed primarily to determine the effectiveness of sand in stopping fragments of various sizes, but could be extended to study sand's effectiveness in attenuating blast pressure. It would also be useful to test the above predictions on the effectiveness of media with higher porosity. Water barriers have been discussed but not deployed in previous retrofit survivability studies for overseas embassies. They would detect the flash from the mine detonation below, trigger a thin layer of explosive above a layer of water, and drive water droplets into the approaching blast wave. The blast loses energy in evaporating the droplets and loses momentum in slowing them. Under favorable conditions that could attenuate the pressure in the blast enough to prevent the penetration or disruption of the vehicle. However, such barriers would depend on prompt and reliable detonation detection and water droplet dispersal, which have not been tested. There is a large literature on the theoretical effectiveness of such barriers, but little careful experimentation. An exception is the set of experiments performed by the Australian government DoD. They measured pressures at 1, 2, and 3 m distances from 500 g PBX charges, using commercial fire sprinklers to produce the spray of droplets between the charge and the pressure gauges. The experiments showed some attenuation, but were performed only at a few atmosphere over pressure, so they did not test the effect of the principal posited vaporization mechanism. Preliminary experiments at Los Alamos showed some reduction, but used sheets of water, so they could only test the effect of momentum coupling.
- Research Organization:
- Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC52-06NA25396
- OSTI ID:
- 991262
- Report Number(s):
- LA-UR-09-04820; LA-UR-09-4820; TRN: US201021%%140
- Resource Relation:
- Conference: Army Science Board ; July 31, 2009 ; Washington, DC
- Country of Publication:
- United States
- Language:
- English
Similar Records
The concept of explosives malfunctioning in rock blasting
Nuclear Test Scenarios for Discussion of On-Site Inspection Technologies