mitigation device for next generation medium caliber...

1

MITIGATION DEVICE FOR NEXT GENERATIONMEDIUM CALIBER AMMUNITION

DISTRIBUTION STATEMENT A: APPROVED FOR PUBLIC RELEASE, DISTRIBUTION IS UNLIMITED.

2016 Insensitive Munitions & Energetic Materials Technology SymposiumNashville, TN, United States, September 12-15, 2016

Nicolas Bruno1, Dr. Roy Kelly2 & Nausheen Al-Shehab3

1 Nostromo S.R.L., Argentina2 Nostromo L.L.C., United States

3 U.S. Army ARDEC, United States

2

OUTLINE

1. INTRODUCTION

2. MEMORY ALLOY RING

3. MITIGATION DEVICE FOR 30X113MM CARTRIDGE CASES

4. STRUCTURAL ANALYSIS

5. EXPERIMENTAL TESTING

6. CONCLUSIONS


3

1. INTRODUCTION

• Compared to other segments of ordnance, medium caliber ammunition has lagged inmodernization and incorporation of insensitive munition (IM) technologies. While someattempts have been made, the effort to incorporate IM mitigating solutions intomedium caliber ammunition has in many cases been hampered because of the difficultyof finding and qualifying less sensitive propellants with sufficient energy to replacenitrocellulose and nitroglycerine powders. The USMC was able to vent their 40mmMK281 family of cartridges, demonstrating the value of venting techniques in achievingIM solutions.

• In support of ARDEC, Nostromo has conducted 6.2 development of medium caliberpropulsion venting systems using memory alloy rings to create large venting areas.

• In 2014 and 2015, with ARDEC support, Nostromo developed and demonstratedactuation of a mitigation device for 30x113mm cartridge cases that uses a heat-shrinkable memory alloy ring to allow rapid venting when subjected to elevatedtemperatures associated with slow and fast cook-off conditions, while maintaining theirability to function as expected under normal operating conditions.


4

2. MEMORY ALLOY RING


DimensionAs Supplied

(Low Temperature)As Shrunk

(High Temperature)Inside Diameter (D) 12.82 mm 12.25 mm

Thickness (T) 1.70 mm -Length (L) 3.45 mm -

Specifications and Characterization

• For this study it was decided to use an existing memory alloy ring from the supplierIntrinsic Devices Inc., with a size and memory alloy that was suitable for the mitigationdevice for 30x113mm cartridge cases.

• Two samples of the selected memory alloy ring were tested in order to characterize thethermal behavior.

Nickel/Titanium Alloy(wt% Ti 38, Ni 48, Nb 14)

5



Requirements:

• Give proper structural integrity and sealing for a burst pressure of 335 MPa at normaloperation.

• Activate at a burst pressure level lower than 11 Mpa (equivalent to 8000N bullet pullstrength) when auto-ignition is produced at stored emergency conditions.

• Open a vent area greater than 127 mm2 when activated.

6



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. Atthis point the memory alloy ring releases the cartridge case central part and it canbe extracted by a small pressure, preventing the projectile blast and theseparation of the bullet.

Memory Alloy

Ring

7



Finite Element Model:

• The finite element model components and definitions of contacts, constraints and loadsare shown below.

Finite Element Model Components Contact Definitions

Constraint Definitions Load Definitions

Memory Alloy

Ring

8



Stored Emergency Condition:

• In stored emergency condition, the ammunition is subject to a high temperaturesituation, the heat-shrinkable memory alloy ring activates and unlocks the cartridgecase central part. The only force retaining the cartridge case central part from beingreleased is the interference/friction with the cartridge case external part. This situationwas simulated taking into account the memory alloy ring shrinkage and a variablemanufacturing tolerance for the interference/friction.

9



Normal Operation:

• In normal operation the support for the cartridge case central part is mostly providedby the cannon. Not being the most important mean of support, the memory alloy ringnow 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 atthe right bottom corner of the memory alloy ring. Such a high contact pressurecontributes positively to the sealing of the propellant chamber.

10



Testing Device & Test Setup:

• A testing device was designed in order to simplify the experimental testing. The testingdevice was equivalent to the mitigation device for 30x113mm cartridge cases.

• A heated shrunk memory alloy ring was used in stored emergency condition test and anoriginal not shrunk memory alloy ring was used in normal operation test.

• A manual hydraulic press (test machine) was used to generate the force needed toperform all the tests. Using the test machine force was gradually applied on theexperimental testing device, recording displacement and pressure.

11



Stored Emergency Condition Test:

• According to the manufacturing report, the interference/penetration between theassembled parts was 0.00375 mm and the corresponding force level required to extractthe cartridge case central part is 148 kg according to structural analysis results.

• Superficial change in roughness and corresponding brightness were observed in testedparts, but no further damage.

ForceMeasured [kg]

Equivalent Pressure [MPa]

Event

89 4.2 -104 4.9 -

118 5.6 0.3 mm displacement133 6.3 Cartridge case central part ejected

12



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.

ForceMeasured [tons]

Equivalent Pressure [MPa]

Event

1.0 47.1 -2.0 94.2 -3.0 141.3 -4.0 188.4 -5.0 235.6 0.15 mm displacement6.0 282.7 0.40 mm displacement7.0 329.8 0.65 mm displacement

13

6. CONCLUSIONS


• A mitigation device for 30x113mm cartridge cases based on a heat-shrinkable memoryalloy ring was developed and validated by simulation and experimental testing.

• Structural analysis was performed for stored emergency condition and normaloperation. For the stored emergency condition, the results demonstrated thedependence of the pressure required to extract the cartridge case central part with themanufacturing tolerances. For normal operation the results shown that plastic strainscould be expected at very small localized regions without affecting the ammunitionoperation.

• Experimental testing was performed and the results shown that, in principle, memoryalloy technology can be used to allow rapid venting in 30x113mm cartridge casessubjected to elevated temperatures associated with slow and fast cook-off conditions,while maintaining their ability to function as expected under normal operatingconditions.

• The current study was restricted to off-the-shelf availability of memory alloyformulations and ring sizes from the selected supplier. The starting point of future workshould be to define a customized NiTi alloy formulation and ring size that moreaccurately reflects the temperature range at which modern single and double basedpropellants ignite in slow and fast cook-off conditions.

mitigation device for next generation medium caliber...

Documents