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Encapsulated Air Energy Absorbing Flooring


OBJECTIVE: The majority of blast event casualties experience injuries to the lower leg. The current flooring systems are not designed to minimize occupant injuries. Little investment has been made in mitigating the blast impulse from the vehicle"s underbody structure to the occupant through the use of energy absorbing flooring systems. Underbody kits have been integrated into the survivability solution but most have a negative weight and mobility impact on the vehicle. Add-on blast mats are the only integrated and fielded solution in energy absorbing flooring solutions. There are opportunities to evaluate many other technologies to mitigate energy to reduce injury and improve weight/mobility characteristics. The objective is to develop an encapsulated air energy mitigating flooring system to mitigate energy from mine blast to reduce occupant injury. This effort addresses high priority Army demonstration programs and Army vehicle acquisition programs. DESCRIPTION: Technology objective is to safeguard vehicle occupants and mitigate various levels of energy generated by underbody mine blast. The developed flooring system should mitigate energy so the force and acceleration seen by the occupant is below the published injury criteria for tibia, foot/ankle, and femur. Encapsulated air in a flooring system shall be utilized to mitigate energy. Currently, there is little information on the performance of encapsulated air as it relates to occupant protection and survivability from underbelly blast threats. Understanding the potential performance characteristics of an energy mitigating flooring system that uses encapsulated air could lead to lighter vehicles, enhanced mobility, improved occupant protection, reductions in logistics/sustainment costs, and rapid manufacturing. The areas of concern that the encapsulated air energy mitigating flooring system should address are the following objectives: 1. Provide the ability to create simplified floor systems allowing geometric blast mitigation capabilities that cannot be achieved with metallic structures. 2. Provide variable material / system properties that can be tailored to address areas of high concern or areas of low concern. 3. Realize weight reduction when compared to a comparable metallic solution. 4. Address the concern with excessive dynamic deflection of flooring systems when subjected to blast loads. 5. Provide integration flexibility that will potentially reduce logistics/sustainment costs. 6. Enhance manufacturing efficiency with low cost tooling and accelerated part production. 7. Allow efficient use of system space claim available to absorb the underbody blast impulse. PHASE I: Develop an initial encapsulated air flooring system concept to show performance of the design in respect to reduction of occupant injury, energy transferred to the occupant, and dynamic deflection of the flooring system. The system shall reduce measured tibia compressive force below the tibia force measured on a bare floor during the same floor acceleration from a simulated blast event. The tibia axial force shall not exceed 9074N @ 0ms, 7562 @ 10ms; foot/ankle 5355N, and femur axial force 9070 @ 0ms, 7560 @ 10ms. The system shall be attached in a manner which secures the system to a generic vehicle structure and maintains integrity when subjected to an impulse of 350G peak for a period of 5ms. The concept shall show a weight savings compared to current state of the art metallic or composite energy mitigating flooring system solutions. Utilize blast (high strain rate) Modeling and Simulation (M & S) to model key elements of an encapsulated air energy mitigating flooring system concept for tactical and combat vehicles. The M & S shall show the encapsulated air flooring system concept can react to the energy from the blast within the quick blast timeline. The M & S should also show the interaction of the flooring system and the occupant seated in a vehicle with their feet on the flooring system. Provide background rationale leading to the final concept down selection (such as research completed, design iteration process, etc). For down selection of concepts use the following guidelines: performance 60%, weight 30%, cost 10%. Finite Element Analysis should be conducted on the encapsulated air flooring system to ensure its ability to withstand normal military vehicle structural loads and user wear and tear with no degradation of physical properties. Conduct proof of principle experiments supporting the concept and provide evidence of the integration feasibility and manufacturability of the approach. The proof of principle experiments should support information gathered during modeling and simulation. Outputs from this phase are the CAD system model, the M & S analysis and final report which contains a summary of the Phase I effort (to include performance evaluation against the injury criteria) and includes rationale to move to Phase II. PHASE II: Based on modeling completed in Phase I, develop, build, and validate through system level evaluation two prototype encapsulated air energy mitigating flooring systems meeting the requirements provided in the description of this SBIR and other requirements provided by the Army. Validation can be accomplished through live fire testing or impulse loading evaluation to the parameters listed under Phase I. The published injury criteria for Revised Tibia Index (RTI) should be used as the metric. RTI, or the Revised Tibia Index, is an injury calculation that takes into account both the compression (Fz) and bending moments (Mx and My) of the tibia. ARL calculates RTI in both the upper and lower tibia. RTI is calculated as: RTI = (Fz/Fc) + (My/Mc), where Fz is the measured axial force, Fc is the critical compression value, My is the measured bending moment, and Mc is the critical bending value. The revised index states that appropriate critical values for the 50th percentile male are 12 kN for compression and 240 Nm for bending. Results over the 0.75 threshold correlate to an AIS2+ fracture. Manufacturing process is refined and preproduction validation samples are manufactured for System - Vehicle level testing (Certification Lot). Any and all system level tuning / manufacturing improvements / retesting is conducted at this phase. At this phase the proposed system is ready to be tested and validated at the PEO level. Outputs from this phase are the system level evaluation report, summary of the Phase II effort, and rationale to move to Phase III. PHASE III: The proposed system created from this investment can be applied to commercial automotive, truck, marine and air craft. In addition the proposed system can be applied in Tactical Wheeled Vehicles, Tracked Vehicles, Amphibious Vehicles, Air Craft or any other type of vehicle (Construction Equipment, ATV, Fork Lifts, etc). As applicable in Ground Systems Survivability the investment in any and all Safety Systems results in a reduction of Soldiers wounded and killed in action. REFERENCES: John J. Wang, Roy Bird, Bob Swinton and Alexander Krsticnter, Protection of Lower Limbs against Floor Impact in Army Vehicles Experiencing Landmine Explosion, Journal of Battlefield Technology, Volume 4 Number 3, November 2001 Ripple, Gary R.; Mundie Thomas G., Medical Evaluation of Non fragment Injury Effects in Armored Vehicle Live Fire Tests; AD-A233 058; Walter Reed Army Institute of Research (WRAIR), Washington D.C., USA, 1989 FR/GE/UK/US International Test Operations Procedure (ITOP) 4-2-508 Vehicle Vulnerability Tests Using Mines, US Army Aberdeen Test Center, 14 April 2005 ALLIED ENGINEERING PUBLICATION AEP-55, Volume 2 (Edition 1), PROCEDURES FOR EVALUATING THE PROTECTION LEVEL OF LOGISTIC AND LIGHT ARMOURED VEHICLES VOLUME 2 for MINE THREAT, September 2006
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