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PBXIH-135

The navy's insensitive munitions advanced development program for high explosives (IMAD/HE) has developed a new insensitive, cast-cured pbx called PBXIH-135. PBXIH-135 has enhanced internal blast performance and improved vulnerability and penetration survivability characteristics compared to PBXN-109. PBXIH-135 was subjected to insensitive detonating substance (EIDS) testing to include cap, gap, external Fire, slow cookoff, and friability.

The Navy began developing thermobaric explosives in the late 1980's and resumed research and development in the mid 1990's, responding to the need for internal blast explosives to defeat hard and deeply buried structures as evidenced during Operation Desert Storm. NSWC Indian Head scientists developed the PBXIH-135 thermobaric explosive, which not only offers effective blast and thermal effects, but also is extremely insensitive to factors that may cause accidental detonation during transit or storage. The secret to PBXIH-135 is the addition of a precise mixture of aluminum powder, which burns in the hot gases. Long after the initial shock wave, the burning aluminum sends heat and pressure bounding through corridors.

In response to the Sept. 11, 2001 terrorist attacks on the United States, the Defense Threat Reduction Agency (DTRA) organized a 60-day joint project with NSWC Indian Head, the Air Force and Department of Energy to identify, test and integrate a solution to deliver a new capability for tunnel defeat. NSWC Indian Head was responsible for the payload and booster design, as well as loading of the new bombs.

After static and flight tests at full-scale tunnel facilities at the Department of Energy's Nevada test site, the program culminated in December with a successful flight test of a laser-guided weapon, containing Indian Head's PBXIH-135 thermobaric explosive, launched from an F-15E Strike Eagle. NSWC Indian Head, along with DTRA and the Air Force, engaged in a three-year advanced Concept Technical Demonstration of another thermobaric weapon. Indian Head is developing the new payload, which would have superior performance to that of PBXIH-135.

Two different energetic composite formulations can be used in hard target penetrator warheads: PBXN-109 and AFX-757. Four explosive formulations have been evaluated for the Mk-83 warhead. The four candidate formulations: AFX-777, AFX-757, PBXN-111 and PBXW-129 were tested against the Mk-83 baseline fill, PBXN-109.

Two test series involving the static detonation of a new design Hellfire missile warhead, now designated as a type N thermobaric warhead, were conducted in 2002 to determine fragment spatial, mass, and velocity distributions. The data from the type N tests are compared with the performance of a hellfire type M blast-frag warhead (BFWH) loaded with the conventional explosive PBXN-109. Of particular interest in the tests was the assessment of thermobaric phenomena with regard to warhead effectiveness.

The cookoff of energetic materials involves the combined effects of several physical and chemical processes. These processes include heat transfer, chemical decomposition, and mechanical response. The interaction and coupling between these processes influence both the time-to-event and the violence of reaction. The prediction of the behavior of explosives during cookoff, particularly with respect to reaction violence, is a challenging task. To this end, a joint DoD/DOE program has been initiated to develop models for cookoff, and to perform experiments to validate those models. In this paper, a series of cookoff analyses are presented and compared with data from a number of experiments for the aluminized, RDX-based, Navy explosive PBXN-109.

Computational tools were developed to predict the response of Navy ordnance to abnormal thermal (cookoff) events. The Naval Air Warfare Center (NAWC) and Naval Surface Warfare Center (NSWC) performed cookoff experiments to help validate DOE computer codes and associated thermal, chemical, and mechanical models. Initial work at the NAWC was focused on the cookoff of an aluminized, RDX-based explosive, PBXN-109 that is initially confined in a tube with sealed ends. The tube is slowly heated until ignition occurs. The response is characterized using thermocouples, strain gauges, and high-speed cameras. A modified version of this system was developed at the NSWC. The designs of these cookoff systems are relatively simple to facilitate initial model development. An effort was made to achieve a wide range of results for reaction violence.

Lawrence Livermore National Laboratories (LLNL) and Sandia National Laboratories (SNL) developed computer codes and materials models to simulate cookoff for ordnance safety evaluations. The computer program ALE3D from LLNL was used to simulate the coupled thermal transport, chemical reactions, and mechanical response during heating and explosion. SNL employed multiple computer codes in a parallel effort.