Ceramic Gun Barrel Technologies Larry Burton Jeff Swab Rob Carter Ryan Emerson U.S. Army Research Laboratory Weapons & Materials Research Directorate

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1 Contact info Larry Burton U.S. Army Research Laboratory

2 Ceramic Gun Barrel Technologies Larry Burton Jeff Swab Rob Carter Ryan Emerson U.S. Army Research Laboratory Weapons & Materials Research Directorate

3 Ceramic Materials Material Vendor Vendor Code ARL Code Density (g/cm3) Al2O3 CoorsTek AD995 ALOX 3.8 ZrO2 CoorsTek Ce-TZP ZRO2 6.1 SiC Saint-Gobain Enhanced Hexoloy SA SCEH 3.1 SiC Saint-Gobain LPS Hexoloy SA SCLH 3.1 SiC Ceradyne 146-5S SC Si3N4 Ceradyne N SN Si3N4 Kyocera SN235P SN5P 3.2 SiAlON Kennametal TK4 STK4 3.4 Eight candidate materials were chosen from commercial vendors All materials are off-the-shelf technologies No material development was planned for this ATO Extensive test matrix developed to characterize the mechanical and thermal properties of each material

4 Erosion and Damage Tests Different simulators used to test the erosion resistance of ceramics Blow-out Gun ARL Extreme condition erosion test Closed Bomb Test ARL Examine propellant gas-ceramic chemical interactions Vented Erosion Simulator (VES) Test Benet Laboratories Simulates the IB conditions seen in a 12mm system Pulsed Laser Heating Test Benet Laboratories Blow-Out Gun (a) Vented Erosion Simulator Combustion Chamber Gas Outlet Gas Inlet High P, T, & h Capable of inducing thermal shock damage similar to that created during an IB event Sample Insert Coating Surface (b) Sample Insert Burst Disk

5 VENTED EROSION SIMULATOR Simulates erosive environment of a Large Caliber tank gun SN5P scheduled to be exposed to 1 rounds Mass loss determined after every 1 rounds Terminated after 44 and 94 rounds due to potential damage to the VES fixtures NOT because of damage to the ceramic.7 Unsupported edge of sample chipped off after 28th shot Mass Loss (g/1 shots).6 Sample 1 Sample Unsupported edge of sample chipped off after 35th shot Exhaust End # of VEST shots 8 1

6 Erosion Summary Si3N4 and SiAlON performed well in all tests Lower mass loss per shot than gun steels Exhibited some fracturing Not unexpected since all fixtures were originally designed for steel samples with no modifications made for the ceramic samples Damaged VES samples did not exhibit an accelerating erosion rate SiC and Al2O3 showed significant mass loss due to fracture ZrO2 exhibited extensive damage & accelerating mass loss Low erosion rates make ceramics attractive as gun barrel materials However, ceramics are hindered by brittle facture, low fracture toughness, and highly variable tensile strength Need new modeling and failure prediction approaches to design a ceramic lined barrel. Require methods for imparting high compressive prestress

7 Modeling Brittle Failure Ceramics can support tensile load, but are subject to large scatter in the observed strength Brittle material design requires a change from the deterministic methods used in metals to a probabilistic approach: Failure initiated at random flaw sites scattered throughout the material Failure strength for each sample determined by the stress exceeding the strength at a critical flaw Weibull statistics are used incorporate this information into design parameters Pf = 1 e σ σo m dv Pf = Weibull Probability of Failure σ = Applied Stress σo = Characteristic Strength m = Weibull Modulus Inherent flaws are undetectable and potential failure sites 12% 1% Probability of Failure 8% 6% Metal m=3 m=1 m=5 4% 2% % 4% 6% 8% 1% 12% 14% Percent of Failure Strength 16%

8 Internal Pressure Testing Experimental Data and Model Predictions Ceramic tubes tested by internal pressurization Model predictions based on measurements for the strength of different flaw populations Uniaxial tension to determine the volumetric flaws C-ring tests the outer surface flaws A lack of data on the inner surface flaws - they are presumed to be identical to the outer surface flaws This leads to two different predictions for the following plots High - the predicted strength for volumetric flaws only Low - the predicted strength for volumetric and surface flaws

9 Model Predictions SN47 Unsheathed SN47 + Composite Sheath 1% 1% Low 5% Pf Experimental 75% High 25% Pf Pf 75% 5% 25% Pf SN47 Experimental % % Pressure (ksi) Internal Pressure (MPa) Calculated failure pressure ranges bracket the experimental values The model predicts ranges for both unsheathed and sheathed tubes 4

10 Failure Surface Plots Experimental data supports model predictions The next step is to apply the model to search for successful Ceramic Failure designs for different gun/cannon tubes - Sheath Failure - Ceramic Failure - Successful Design 1 All Ceramic 75 Failure surface plots illustrate the effects of varying ceramic thickness and pre-stress level for a pressurized tube Successful Design 5 Percent Ceramic Sheath Failure Provides quick approach for visualizing 1, different design concepts Interference -.45 Increasing Pre-Stress All Steel

11 Probabilistic Modeling Summary 1% Validated probabilistic modeling capability for predicting the strength of ceramic lined gun tubes has been coupled with FEA models to assess: Pf 75% 5% 25% % 1 Transient thermal behavior Thermal shock on the bore surface Dynamic thermo-mechanical loading Rifling/engraving Projectile/barrel interactions Pressure (ksi) 75 5 Percent Ceramic 25 1% 1 mil fillet 1 mil Smooth Interference PF % 5% 25% % Pressure (MPa) 25 3

12 High-Tension Winding

13 High-Tension Winding Results Hoop Strain in Alum. Mandrel 5 Final strains after cure and cool to RT -365 µε -5 Hoop Strain -1 (µε ) deg, 45 N, Continuous Cure 82 deg, 18 N, Continuous Cure 82 deg, 54 N, Continuous Cure 82 deg, 67 N, Continuous Cure 82 deg, 67 N, Progressive Cure 82 deg, 286 N, Continuous Cure sheath thickness =.1 inch Number of Layers 15 µε (9.1 MPa)

14 Multiaxial Sheathing Sheath Ceramic Tapered sleeves for press-fit Barrel Strain (µε) OD Hoop Strains During Assembly 3 Gage # 1 25 Gage # 2 Gage # Demonstrated sheathing pressure in excess of 2MPa Time (sec) 4 5 6

15 Ballistic Test Fixture Ceramic tu b e Graphite Sheath

16 Ballistic Specimens

17 Firing History & Plans Four Si3N4 tubes with high-tension wind Maximum pressure achieved ~45 ksi Ceramic tubes crack but failure is not catastrophic Two SiAlON tubes with high-tension wind Maximum pressure achieved ~25ksi Issues with tube concentricity and the firing fixture have limited the achievable pressure Test of multi-axial confinement schemes planned by year end

18 Conclusions Identified commercially available ceramics for ceramic-lined gun barrel application Developed a probabilistic design approach to account for ceramic failure behavior Investigated robust sheathing schemes to provide the required level of compressive pre-stress Have conducted preliminary firing tests with 25-mm tubes achieving 45 ksi (in line with predicted limits of sheathing)

19 Future Challenges Imparting rifling without degrading the performance of the ceramic liner Manufacturing of longer, straighter, more concentric tubes held to tight tolerances