2016 Insensitive Munitions & Energetic Materials Technology Symposium Nashville, TN, United States, September 12-15, 2016 MITIGATION DEVICE FOR NEXT GENERATION MEDIUM CALIBER AMMUNITION Nicolas Bruno 1 , Dr. Roy Kelly 2 & Nausheen Al-Shehab 3 1 Nostromo S.R.L., Argentina 2 Nostromo L.L.C., United States 3 U.S. Army ARDEC, United States 1 DISTRIBUTION STATEMENT A: APPROVED FOR PUBLIC RELEASE, DISTRIBUTION IS UNLIMITED.
OUTLINE 1. INTRODUCTION 2. MEMORY ALLOY RING 3. MITIGATION DEVICE FOR 30X113MM CARTRIDGE CASES 4. STRUCTURAL ANALYSIS 5. EXPERIMENTAL TESTING 6. CONCLUSIONS 2 DISTRIBUTION STATEMENT A: APPROVED FOR PUBLIC RELEASE, DISTRIBUTION IS UNLIMITED.
1. INTRODUCTION • Compared to other segments of ordnance, medium caliber ammunition has lagged in modernization and incorporation of insensitive munition (IM) technologies. While some attempts have been made, the effort to incorporate IM mitigating solutions into medium caliber ammunition has in many cases been hampered because of the difficulty of finding and qualifying less sensitive propellants with sufficient energy to replace nitrocellulose and nitroglycerine powders. The USMC was able to vent their 40mm MK281 family of cartridges, demonstrating the value of venting techniques in achieving IM solutions. • In support of ARDEC, Nostromo has conducted 6.2 development of medium caliber propulsion venting systems using memory alloy rings to create large venting areas. • In 2014 and 2015, with ARDEC support, Nostromo developed and demonstrated actuation of a mitigation device for 30x113mm cartridge cases that uses a heat- shrinkable memory alloy ring to allow rapid venting when subjected to elevated temperatures associated with slow and fast cook-off conditions, while maintaining their ability to function as expected under normal operating conditions. 3 DISTRIBUTION STATEMENT A: APPROVED FOR PUBLIC RELEASE, DISTRIBUTION IS UNLIMITED.
2. MEMORY ALLOY RING Specifications and Characterization • For this study it was decided to use an existing memory alloy ring from the supplier Intrinsic Devices Inc., with a size and memory alloy that was suitable for the mitigation device for 30x113mm cartridge cases. • Two samples of the selected memory alloy ring were tested in order to characterize the thermal behavior. As Supplied As Shrunk Dimension (Low Temperature) (High Temperature) Inside Diameter (D) 12.82 mm 12.25 mm Thickness (T) 1.70 mm - Length (L) 3.45 mm - Nickel/Titanium Alloy (wt% Ti 38, Ni 48, Nb 14) 4 DISTRIBUTION STATEMENT A: APPROVED FOR PUBLIC RELEASE, DISTRIBUTION IS UNLIMITED.
3. MITIGATION DEVICE FOR 30X113MM CARTRIDGE CASES Requirements: • Give proper structural integrity and sealing for a burst pressure of 335 MPa at normal operation. • Activate at a burst pressure level lower than 11 Mpa (equivalent to 8000N bullet pull strength) when auto-ignition is produced at stored emergency conditions. Open a vent area greater than 127 mm 2 when activated. • 5 DISTRIBUTION STATEMENT A: APPROVED FOR PUBLIC RELEASE, DISTRIBUTION IS UNLIMITED.
3. MITIGATION DEVICE FOR 30X113MM CARTRIDGE CASES Operation: • Normal Operation: • The memory alloy ring works as a lock at temperatures below 60 ° C. • Stored Emergency Condition: • The memory alloy ring begins decreasing its diameter when the temperature rises above the trigger value of 60 ° C and reaches a maximum shrinkage at 120 ° C. At this point the memory alloy ring releases the cartridge case central part and it can be extracted by a small pressure, preventing the projectile blast and the separation of the bullet. Memory Alloy Ring 6 DISTRIBUTION STATEMENT A: APPROVED FOR PUBLIC RELEASE, DISTRIBUTION IS UNLIMITED.
4. STRUCTURAL ANALYSIS Finite Element Model: • The finite element model components and definitions of contacts, constraints and loads are shown below. Memory Alloy Ring Finite Element Model Components Contact Definitions Constraint Definitions Load Definitions 7 DISTRIBUTION STATEMENT A: APPROVED FOR PUBLIC RELEASE, DISTRIBUTION IS UNLIMITED.
4. STRUCTURAL ANALYSIS Stored Emergency Condition: • In stored emergency condition, the ammunition is subject to a high temperature situation, the heat-shrinkable memory alloy ring activates and unlocks the cartridge case central part. The only force retaining the cartridge case central part from being released is the interference/friction with the cartridge case external part. This situation was simulated taking into account the memory alloy ring shrinkage and a variable manufacturing tolerance for the interference/friction. 8 DISTRIBUTION STATEMENT A: APPROVED FOR PUBLIC RELEASE, DISTRIBUTION IS UNLIMITED.
4. STRUCTURAL ANALYSIS Normal Operation: • In normal operation the support for the cartridge case central part is mostly provided by the cannon. Not being the most important mean of support, the memory alloy ring now takes relevance in the sealing of combustion gases from the propellant chamber. Plastic strains at normal operation could be expected at very small localized regions at the right bottom corner of the memory alloy ring. Such a high contact pressure contributes positively to the sealing of the propellant chamber. 9 DISTRIBUTION STATEMENT A: APPROVED FOR PUBLIC RELEASE, DISTRIBUTION IS UNLIMITED.
5. EXPERIMENTAL TESTING Testing Device & Test Setup: • A testing device was designed in order to simplify the experimental testing. The testing device was equivalent to the mitigation device for 30x113mm cartridge cases. • A heated shrunk memory alloy ring was used in stored emergency condition test and an original not shrunk memory alloy ring was used in normal operation test. • A manual hydraulic press (test machine) was used to generate the force needed to perform all the tests. Using the test machine force was gradually applied on the experimental testing device, recording displacement and pressure. 10 DISTRIBUTION STATEMENT A: APPROVED FOR PUBLIC RELEASE, DISTRIBUTION IS UNLIMITED.
5. EXPERIMENTAL TESTING Stored Emergency Condition Test: • According to the manufacturing report, the interference/penetration between the assembled parts was 0.00375 mm and the corresponding force level required to extract the cartridge case central part is 148 kg according to structural analysis results. • Superficial change in roughness and corresponding brightness were observed in tested parts, but no further damage. Force Equivalent Pressure Event Measured [kg] [MPa] 89 4.2 - 104 4.9 - 118 5.6 0.3 mm displacement 133 6.3 Cartridge case central part ejected 11 DISTRIBUTION STATEMENT A: APPROVED FOR PUBLIC RELEASE, DISTRIBUTION IS UNLIMITED.
5. EXPERIMENTAL TESTING Normal Operation Test: • Displacement was measured starting at 5 tons, probably due to plastic deformation. • The memory alloy ring did not show any signs of deterioration or marks after the test. • The lower part of the cartridge case central part got constrained inside the cartridge case external part after the test due to plastic deformation and could not be extracted. • The bottom surface of the experimental testing device was characterized by plastic deformation in a similar manner to real ammunition in normal gun firing mode. Force Equivalent Pressure Event Measured [tons] [MPa] 1.0 47.1 - 2.0 94.2 - 3.0 141.3 - 4.0 188.4 - 5.0 235.6 0.15 mm displacement 6.0 282.7 0.40 mm displacement 7.0 329.8 0.65 mm displacement 12 DISTRIBUTION STATEMENT A: APPROVED FOR PUBLIC RELEASE, DISTRIBUTION IS UNLIMITED.
6. CONCLUSIONS • A mitigation device for 30x113mm cartridge cases based on a heat-shrinkable memory alloy ring was developed and validated by simulation and experimental testing. • Structural analysis was performed for stored emergency condition and normal operation. For the stored emergency condition, the results demonstrated the dependence of the pressure required to extract the cartridge case central part with the manufacturing tolerances. For normal operation the results shown that plastic strains could be expected at very small localized regions without affecting the ammunition operation. • Experimental testing was performed and the results shown that, in principle, memory alloy technology can be used to allow rapid venting in 30x113mm cartridge cases subjected to elevated temperatures associated with slow and fast cook-off conditions, while maintaining their ability to function as expected under normal operating conditions. • The current study was restricted to off-the-shelf availability of memory alloy formulations and ring sizes from the selected supplier. The starting point of future work should be to define a customized NiTi alloy formulation and ring size that more accurately reflects the temperature range at which modern single and double based propellants ignite in slow and fast cook-off conditions. 13 DISTRIBUTION STATEMENT A: APPROVED FOR PUBLIC RELEASE, DISTRIBUTION IS UNLIMITED.
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