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Self-fragmenting Structural Reactive Materials (SF-SRM) for High Combustion Efficiency

Description:

TECHNOLOGY AREA(S): Weapons

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), which controls the export and import of defense-related material and services. Offerors must disclose any proposed use of foreign nationals, their country of origin, and what tasks each would accomplish in the statement of work in accordance with section 5.4.c.(8) of the solicitation.

OBJECTIVE: Develop, test and evaluate a scalable metal-based reactive structural material that will self-fragment to micron or sub-micron scale fuel particles when subjected to explosive shock loading, resulting in significantly enhanced metal combustion efficiency.

DESCRIPTION: The Defense Threat Reduction Agency (DTRA) desires to enhance the effectiveness of conventional high-explosive munitions across a broad range of ordinance platforms, for use against an array of potential targets ranging from chemical and biological threat materials to WMD targets in deeply buried/hardened tunnels and multi-chamber bunkers. While new explosive materials may yield improved blast loading, much more significantly enhanced blast effects are potentially achievable by taking advantage of reactive structure used as the ordinance casing. The shock from a detonation yields high stresses, pressures, and temperatures to the casing materials, which causes rapid fragmentation of the case to occur. If the case is made of a combustible structural material such as Aluminum, sufficiently rapid combustion of these fragments can significantly enhance the blast. The high combustion enthalpy of metal fuel casing materials can substantially contribute to the work being done behind the initial blast wave, yielding sustained overpressure and improved thermal loadings.[1] It has been shown that various metal fuels and reactive material compositions can have a substantial effect on the delivered blast loading [2]. However, if the initial shock does not break the bulk of the casing material into sufficiently small fragments, or the metal particles are cooled quickly in the surrounding air, the metal oxidation efficiency will be low, which will result in lower delivered performance. The overall efficacy of these enhanced blast casing materials is largely dependent upon providing sufficiently short metal combustion residence times. While casing geometry can play a role in enhanced case fragmentation, the objective of this study is to develop a new material that inherently “self-fragments” into the required small metal particle size distribution, rather than developing a new ordinance design technology or platform.

This STTR seeks the development, testing and evaluation of innovative reactive structural casing materials that will, upon exposure to explosive shock loading, induce the in situ formation of micron-scale or submicron-scale metal fuel particles/droplets from the bulk of the casing, which particles will then combust extremely rapidly to significantly enhance blast effects. The research must demonstrate a feasible method of rapid fine-particle-fragmentation of the bulk casing material’s metallic component(s) and show its delivered performance in controlled enhanced blast experiments. The casing material may be multicomponent in nature (i.e., composite), but must be at least 70 weight percent metallic (typically Aluminum, but not required to be Aluminum). Additionally, the casing material must be such that it can be used to fabricate typical DoD munition cases using state-of-art fabrication processes, for example, such that cases can be formed through pressing from a powdered state, with nominal starting particle size no smaller than 1 micron and no larger than 80 microns. The proposed casing material(s) must also show feasible scalability, and acceptable sensitivity and ageing properties, for future DTRA adoption across a broad range of ordinance platforms.

PHASE I: Develop by analysis a list of candidate Self-fragmenting Structural Reactive Materials (SF-SRM). Perform initial characterization for one candidate metal-based SF-SRM (e.g., using powders) for use as an ordinance casing material. The consolidated material must be shown to be safe to handle, including low sensitivity to electrostatic shock, friction, and drop weight impact. In the final configuration the material. Perform initial combustion characterization of this SF-SRM, at high heating rates relevant to the intended use in munition applications, using laboratory techniques (e.g. via. laser heating). Perform initial evaluation of the ability of this candidate SF-SRM for rapid self-fragmentation and dispersion of fine fragments. Phase I deliverable is a final report documenting the effort and results, and should include a recommendation for casing material(s) to be further investigated and developed in Phase II. It is understood that the analytical and experimental efforts will be conducted in full partnership between a small business and a university or other eligible collaborator, with details of the work breakdown at the discretion of the partners.

PHASE II: From the list of candidate SF-SRM developed in Phase I, down-select to one to two (depending on resource availability) candidate casing materials for further development and evaluation. For these materials, demonstrate that the consolidated materials are sufficiently resistant to oxidation by exposure to air and moisture (to provide long shelf-life). Demonstrate the proposed casing material(s) in small scale explosive shock experiments. For the purposes of intended application of this work, these experiments must have a minimum high explosive charge of 10 grams and a case-mass-to-fill-mass-ratio ratio of 3:1, i.e., relevant to current DoD penetrating munitions. The experiments must be able to quantify initial blast loadings, sustained overpressure, and delivered casing combustion efficiency. The spatial and spectral breakout characteristics of the casing material(s) must also be investigated. All experiments must be compared to a baseline aluminum casing of the same geometry. The scalability of the highest performing casing material must also be shown in respect to starting material manufacturing and application. As part of this process, a larger explosive shock experiment must be performed and analyzed with a minimum explosive charge of 100 grams and at the same case-mass-to-fill-mass-ratio ratio. Final scale-up feasibility shall be to manufacture and deliver to DTRA three test cases of sufficient size and mass for testing at the DTRA Chestnut test range (detailed drawings for these test cases will be provided to performer by DTRA; rough size of these test items is 5.5 inch inner-diameter cylinder, wall thickness determined by material density, case weight approximately 12 pounds mass, length approximately 9 inches.) Phase II deliverables include the 3 test cases and a detailed final report describing the testing implementation and results, and scale-up observations. The report must also contain detailed procedures for casing material synthesis/fabrication and scaling.

PHASE III DUAL USE APPLICATIONS: A successful Phase II demonstration will motivate several commercial applications, including the development of new explosive devices for mining and drilling operations. Additional commercial applications for these materials may be as metallized fuels in solid rocket propellants (e.g., satellite booster motors) and pyrotechnics.
A successful Phase II demonstration will motivate encourage DTRA and Department of Defense adoption of the technology use across a wide range of weapon platforms that house conventional explosive ordinance packages to improve weapon performance and utility. Again, these materials may also be used as metallized fuels in future solid rocket propellants (e.g., tactical missiles) and pyrotechnics.

REFERENCES:

    • Dearden, P., New blast weapons. J R Army Med Corps, 2001. 147(1): p. 80-6.

 

  • Clemenson, M.D., et al., Explosive Initiation of Various Forms of Ti/2B Reactive Materials. Propellants, Explosives, Pyrotechnics, 2014. 39(3): p. 454-462.

KEYWORDS: enhanced blast, thermobaric, reactive material, energetic material, ordinance, explosive, casing

  • TPOC-1: William H. Wilson
  • Phone: 703-767-4216
  • Email: william.h.wilson6.civ@mail.mil
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