Insensitive munition
Insensitive munitions are munitions that are chemically stable enough to withstand mechanical shocks, fire and impact by shrapnel, but that are still able to explode as intended in order to destroy their targets.
Description
Insensitive munitions (IM) will only burn (rather than explode) when subjected to fast or slow heating, bullets, shrapnel, shaped charges or the detonation of another nearby munition. The term refers to warheads, bombs, rocket motors, although different countries' armed forces may have their own definitions.
Due to “accidents, and the subsequent loss of human life, cost of repair and replacement of materiel, and the toll taken on operational readiness and capability, Insensitive Munitions (IM) improvements are mandated by law in the U.S..[1]
Three approaches are taken when designing insensitive munitions: Firstly, the high energy device can be protected and transported with an external protection of some kind. Some munition shipping containers are designed to provide a degree of protection and thermal insulation. Secondly, the chemistry of the high energy fill is chosen to provide a higher degree of stability, for example by using plastic bonded explosives. Lastly, the casings of high energy devices can be designed in such a way as to allow venting or some other form of pressure relief in a fire.
In addition to the three approaches above, other threats are required to be addressed when designing IM, e.g., slow and fast cook-off, sympathetic detonation, bullet and fragment impact, and shaped charge jet impact. Extensive testing requirements for potential IM candidates to address these threats are extremely costly. Modeling programs are being designed to simulate the threat of bullet and fragment impact in an effort to reduce testing costs. One of the most promising techniques that engineers and scientists within the U.S. Department of Defense (DoD) are employing to help to achieve IM performance enhancement is the application of advanced multiphysics modeling programs.[1] In addition, another effort is underway developing 2-D numerical code that will simulate the threat of slow and fast cook-off.[2]
Insensitive high explosives
Insensitive munitions are almost always filled with fire resistant, shock resistant insensitive high explosives (IHE) such as triaminotrinitrobenze (TATB) or various insensitive explosive mixtures or polymer or plastic bonded explosives. TATB particularly will not detonate if impacted by typical fragments or burned in a fire.
A new IHE called Insensitive Munitions Explosive (IMX-101), has been qualified and approved by the U.S. Army to replace trinitrotoluene (TNT). IMX-101 is said to have the “same lethality as traditional TNT, but is far less likely to explode if dropped, shot at or hit by a roadside bomb during transport”.[3] This IHE has been tested and proven to be a safer alternative within large-caliber projectiles currently utilized by the Army and Marine Corps.
Another, experimental, IHE is FOX-7.
IHEs often combine amino groups and nitro groups in the same molecule.
Origin
Following the 1966 Palomares B-52 crash and the 1968 Thule Air Base B-52 crash, concerns were raised by accident investigators about the high explosive used in the nuclear devices, which had detonated on impact. Efforts were started to find an explosive that was stable enough to withstand the forces involved in an aircraft accident.[4] The Lawrence Livermore National Laboratory developed the "Susan Test" — a standard test designed to simulate an aircraft accident by squeezing and nipping explosive material between metal surfaces of a test projectile. Following experimentation with this device, the Los Alamos National Laboratory developed a new safer type of explosive, called insensitive high explosive (IHE), for use in U.S. nuclear weapons.[5]
IHE explosives can withstand impacts up to 1,500 feet per second (460 m/s), as opposed to conventional HE, which will detonate at only 100 feet per second (30 m/s).[6]
Use in nuclear weapons
Insensitive high explosive has been available to the United States military for use in its nuclear weapons since 1979—by 1991, 25% of the country's nuclear stockpile was using IHE.[7] Most modern American nuclear weapons, and at least those of the United Kingdom, are manufactured using insensitive munition designs. These are almost exclusively TATB plastic bonded explosive (LX-17-0 and PBX-9502). Conventional high explosives are still used in missiles and artillery shells where weight and volume is a factor (IHE by weight contains only two-thirds the energy of HE, so more is required to achieve the same effect).[7]
References
- ^ a b DeFisher,S., Pfau, D, & Dyka,C., (2010. Insensitive Munitions Modeling Improvement Efforts, Retrieved from http://www.imemg.org/res/IMEMTS%202010/papers/DeFisher-10536_Insensitive%20Munitions%20Modeling%20Improvement%20Efforts_IMEMTS2010-Paper.pdf
- ^ Aydemir, E., Ulas, A. (2011). A numerical study on the thermal initiation of a confined explosive in 2-D geometry (Feb 2011, Journal of Hazardous Materials, 186(1), 396-400.) Retrieved from Academic Search Premier Database.
- ^ Picatinny Public Affairs (2010) Army approves safer explosive to replace TNT. Retrieved from http://www.army.mil/-news/2010/08/11/43553-army-approves-safer-explosive-to-replace-tnt/
- ^ Jonas A. Zukas, William P. Walters (2002). Explosive Effects and Applications. Springer. pp. 305–307. ISBN 0387955585.
- ^ Nathan E. Busch (2004). No end in sight. University Press of Kentucky. pp. 50–51. ISBN 0813123232.
- ^ Sidney David Drell (2007). Nuclear weapons, scientists, and the post-Cold War challenge. World Scientific. pp. 147–150. ISBN 9812568964.
- ^ a b "How Safe is Safe?". Bulletin of Atomic Scientists: pp. 34–40. 1991.
{{cite journal}}:|pages=has extra text (help); Unknown parameter|month=ignored (help)