3Overview Goal Approach Technical Barriers Development of a baseline thermo-mechanical model for a 5.56 mm cartridge inside a M16A2 barrel.ApproachCreation and validation of a model for the M855 brass cartridge.Utilize FEA to assess the feasibility of lightweight polymers in cartridge case applications.Technical BarriersMaterial functionality is required over the full spectrum of environmental conditions.Strength required to meet all operational functionspropellant gas pressure, primer strike, feed, extraction
4Polymer Cartridge Payoff Polymers have the potentialto reduce the manufacturing costBy reducing the number of steps through injection moldingreduce logistical loadimprove accuracyInjection mold the bullet in placeMaintain the centerline alignmentCurrent Basic Issue7 Magazines M85510 Magazines withPolymer Case CartridgesEquivalent Weight
6Brass Cartridge Characteristics Current brass systems require numerous manufacturing steps to produce the final microstructure and hardness gradientHardness and microstructure gradient required toaccurately model M855 response
7Brass Cartridge Model 2D Static Model Models a 5.56mm brass cartridge in a M16A2 barrel with barrel extension.Incorporates the effect of the hardness gradient along the cartridge length.Material models include plasticity.Primer is assumed have the same structural characteristics as the cartridge.Contact pair between the cartridge and chamber wall and the cartridge and primer.Pressure gradient is applied to the inside of the cartridge.Thermo-mechanical model.M855 Pressure Profile
9Brass Cartridge Model Applied Boundary Conditions Axisymmetric along y axisSymmetric BC on primer wall along the axis.Zero displacement BC in all directions applied to the head of the cartridge.Assumes continuous intimate contact between the bolt and the cartridge.Does not account for rearward motion during firing.Zero displacement BC in all directions applied to the barrel extension.Total of 31,000 elements.
10Thermal FEA Modeling 2D Axisymmetric Sequential Model Meshed with 8 node thermal elementsID contains surface effect element6000 elementsCalculated from interior ballisticsThermal loads are applied in a tabular format to the ID
13Brass Model SummaryGoal has been to benchmark the M855 brass cartridge with a FEA model.The current model incorporates the strength changes in the cartridge due to the variations in the hardness and microstructure.The model yields a stress state within the brass that demonstrates 2.0 ultimate factor of safety.Measurements from expended cartridges show good correlation with the predicted plastic deformation.
14Polymer Cartridge Model 2D Axisymmetric ModelCartridge is entirely polymerNylon 612Internal pressure is loaded in smaller increments
15Polymer Cartridge FEA Results Subjected to an Internal Pressure of 5 ksiFailure CriteriaNylon 612sult tensile = 7 ksieult tensile = 0.4
17Polymer Model SummaryThe polymer cartridge model is currently a work in progress.Due to the mechanical properties of the polymer, modifications to the case design will be required.Investigations continue into optimizing the model includingParametric assessment of increased wall thickness on survivability of polymer cartridgeThe effect of the cartridge head design on the survivability of the polymer cartridge.Alternate materialsDifferent polymer systems or filled composite systems
18Conclusions &Future Direction The FEA modeling of the brass M855 cartridge provides a solid foundation to evaluate alternative cartridge materials.Future efforts will focus onApplying the thermal capability to determine in-bore heating profile.Allows for investigation of cook-off and thermal softening.Use existing model to examine stress state due toPrimer strike, extraction and feed.