HYBRIDIZED THERMOPLASTIC ARAMIDS: ENABLING MATERIAL TECHNOLOGY FOR FUTURE FORCE HEADGEAR S.M. Walsh*, B.R. Scott, D.M. Spagnuolo, and J.P. Wolbert U.S. Army Research Laboratory Weapons & Materials Research Directorate Aberdeen Proving Ground, Maryland, 21005-5069 ABSTRACT uses improved strength (Riewald et al., 1991; Yang, 1993) aramid fibers (Kevlar K129, KM2 and Twaron are U.S. Army ballistic helmet manufacturing has not all higher performance para aramids), but still uses changed significantly in nearly 30 years. Advances in thermoset phenolic matrix materials and molding U.S. helmet technology have been largely in shell design, processes that are more than 60 years old. improved aramid fibers, and helmet liner and suspension systems. The Army is currently replacing its first There are new helmet efforts on the horizon, as well as composite ballistic helmet, Personnel Armor System opportunities to introduce materials and process Ground Troops (PASGT), with the Advanced Combat improvements to the current ACH helmet. The Future Helmet (ACH). ACH has undergone ballistic testing and Force Warrior (FFW) Program, for example, demands a system analysis with improvements to weapons and body helmet that is lighter than the current ACH helmet system. armor interfacing issues. Still, ACH uses some of the FFW is the precursor to the Ground Soldier System same materials (butyl rubber toughened phenolic resin (GSS). FFW weight reduction requirements are driven with aramid fabric reinforcements) and the same process largely by the desire to accommodate head-borne technology as its 30 year old PASGT predecessor. The electronic devices without exceeding a total headgear current research effort has focused on identifying and weight of about 5.5 lbs. The challenge is delivering resolving technology barriers that limit a new and increased capability and supporting the weight of the new improved generation of ballistic materials from being hardware without sacrificing the ballistic protection and considered for use in future helmet systems. Both integrity of the helmet shell. Figure 1 illustrates some of historical and contemporary perspectives of ballistic the past, current, and future U.S. helmet technologies. helmet technology are provided as rationale for the development of alternative helmet materials and their There are several challenges in developing a new set of associated processes. The primary technology barriers are materials for use in future U.S. Army systems. The four-fold: structural durability (static and dynamic primary technical barrier is to deliver a safe, durable, deformation), contiguous preform construction (less robust helmet system at lighter weight. Another concern cutting of the reinforcement without wrinkling), is the ability to introduce these materials effectively by hybridization of dissimilar fibers and resins, and low cost offering a process to the current manufacturing manufacturing (rapid heating, consolidation, and cooling infrastructure to optimally manufacture the helmet shells of tools and parts). Flat plates and full helmet shells en masse. Finally, there are economic and affordability were molded to quantify the performance and benefits of issues that will influence domestic U.S. helmet hybridized materials to meet current and future demands manufacturers. Replacing traditional – and largely for increased ballistic mass efficiency. effective – helmet manufacturing equipment is a serious capitalization and investment decision. 1. INTRODUCTION 2. BACKGROUND The introduction of the PASGT helmet (McManus et al., 1976) in the late 1970s revolutionized head-borne ballistic The PASGT helmet has been in service for nearly 30 protection for the individual soldier. From World War I years. Its design has been adopted or imitated by military, until the conclusion of the Vietnam war, Hadfield steel police and other agencies both in the United States and was the outer shell ballistic material in the standard issue abroad. The fact that it has enjoyed such long and US military helmets. The commercialization of the para- successful utility poses interesting questions for future aramid polymer, Kevlar, enabled a helmet that had an helmet programs. Evolving U.S. helmet technology will average of 30% more ballistic protection at the same total likely benefit from smaller, more frequent changes in weight of the two-part steel-based helmet it replaced. helmet design and materials. Helmet variants produced Only recently has the Army begun replacing the PASGT by these endeavors allows for technology assessment – helmet with the Advanced Combat Helmet (ACH), which Form Approved Report Documentation Page OMB No. 0704-0188 Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. 1. REPORT DATE 2. REPORT TYPE 3. DATES COVERED 01 NOV 2006 N/A - 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER Hybridized Thermoplastic Aramids: Enabling Material Technology For 5b. GRANT NUMBER Future Force Headgear 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. 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THIS PAGE UU 30 unclassified unclassified unclassified Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18 WWI WWII/Korea/Vietnam PASGT MICH/ACH FFW Design Material Rolled steel Hadfield Steel Kevlar 29/PVB Phenolic Kevlar 129/PVB phenolic Thermoplastic aramid Twaron/PVB phenolic Spectra/Dyneema Hybrids Areal Density (psf) 2.3-2.4 2.3-2.4 2.3-2.4 2.0-2.1 1.5-1.8 Threat Shrapnel Fragmentation Fragmentation Fragmentation Fragmentation 9mm bullet 9mm bullet 9mm bullet Fig. 1. Past, current, and future U.S. Army helmet systems and migration. An excellent example of technology It is important to consider the impact of performance migration is the development and production of the ACH. specs as they directly influence – if not enable – the The ACH is a helmet currently being fielded to the introduction of more mass efficient ballistic material and general Army but it had its origins in MICH (Modular improved manufacturing processes. The MICH helmet Integrated Communications Helmet). The MICH was used an improved toughness Kevlar, increased the developed for the Special Forces engaged in missions reinforcement content, changed to foam pad suspension where hearing is crucial, as is the ability to communicate and a new geometric design that removed nearly 10% of information stealthily and efficiently. the surface coverage of the helmet. The latter was done to improve helmet interfacing with both weapons and body It is instructive to consider the forces that ultimately led to armor, as well as improved hearing, communication, and the ACH helmet, primarily because it provides a potential situational awareness capability. The total weight of the path for introducing a new generation of materials and helmet was reduced. The subsequent success of the processes, as well as modifications to the design and MICH ballistic shell and suspension system led to the configuration of the helmet system. Furthermore, development of the Advanced Combat Helmet. The ACH changes in the Army’s procurement specifications have and Future Force Warrior both provide opportunities to allowed domestic manufacturers more freedom to develop introduce improvements in helmet materials and systems. innovative approaches that had been more difficult to Introduction of these improvements are largely enabled pursue under traditional military specification (“MIL by performance based specifications. Spec”) doctrines. 2.2 Historic Perspective of Helmet Materials 2.1 Military vs. Performance Specifications It has been demonstrated with historical evidence as early The traditional approach in helmet development was for as 1915 (Dean, 1920) that considerable thought had been the U.S. government to explicitly define not only given to the design of a "modern" combat helmet shell. performance parameters for a helmet, but the types of The German designs were particularly advanced and materials and processes that may be considered. In demonstrated a more sophisticated assessment of threats. essence, the MIL Standards provided a step-by-step Advances in metallurgy provided