Tyler_Distefano_REU_Conference_Poster
1
The Development of a New Small-Bore Taylor-Impact Launcher Tyler DiStefano 1 | The Cooper Union for the Advancement of Science and Art Dr. Daniel Eakins 2 | Institute of Shock Physics at Imperial College London IREU: Georgia Institute of Technology School of Materials Science and Engineering INTRODUCTION AND BACKGROUND Light Gas Guns (LGGs) are used to launch metallic-plated sabots at high velocities towards parallel metal alloy plates. The resulting collision between the sabot and the metal plate generates shock waves that longitudinally propagate through the material of interest. Analysis of the wave propagation reveals material properties and can result in an experimental thermodynamic equation of state through the Rankine- Hugoniot equations. 1 The Institute of Shock Physics has a newly built meso-scaled LGG that launches 12.95-mm small-bore sabots. The impacting sabot velocity is critical information for the use of the Rankine-Hugoniot relations. System analysis and optimization is necessary to obtain predictable impact velocities of the sabots. The analysis is focused on the time response and optimization of the piston located within the breech of the small-bore LGG. EXPERIMENTAL METHODS Experimental analysis of the current system was performed using the LineVISAR system and HetV tools to observe the impact velocity of the Al-1060 plate and 3.98-g sabot, respectively. The sabot projectile had a Copper flyer plate that was lapped to ensure flatness and to eliminate any effects of tilt within the collision. The LineVISAR system was set up using a combination of optical mirrors and lenses with a 2.2-W laser. Furthermore, the streak camera captured a shifted interference pattern that indicates an impact velocity of the parallel metal alloy at the end of the barrel. The HetV tool was installed by a system of probes at the end of the barrel, which uses Doppler-shifted light to calculate the velocity of the sabot as it travels along the barrel from the instant of firing. The HetV tool was also used to track the velocity of the piston along the breech without the presence of a sabot and target plate, where the front-loading chamber was set to 35-bar and the evacuating reservoir was initially set to 40- bar. The experimental results were then compared to a series of 3D simulations run through ANSYS Workbench/Mechanical, which modeled the time response of the piston. Pneumatic modeling of the breech’s internal ballistics provided a representative time constant of the system, including realistic conditions such as friction and system jitter. 2 The simulations ran through a succession of decreased time constants, which reflected numerous prototypes of the current system that included design changes. ANSYS Mechanical also simulated a novel three-chamber alternative design for the breech and was then compared to the current results. RESULTS AND DISCUSSION Analysis of the current ballistics provided motivation for a redesign of the breech with different initial conditions than the current ones used to launch the sabot. The HetV data indicated that the piston currently displaces 5-mm backwards. This displacement does not clear the entire pressurized valve and shows that the sabot does attain its full potential velocity with the previously used initial conditions. The solutions from the simulations provided insight to fill the dual-pressure system proportional to the effective surface area corresponding to the force in the sliding direction. The proportion between the front-loading chamber and the evacuating reservoir is a 1.8x differential. Furthermore, this change ensures that there is a faster time response after firing the gas gun because the operating pressures are now near equilibrium conditions of the piston. As the simulations were sampled across lower time constants, it reflected design changes to the physical system. It was determined from analytical pneumatic modeling that increasing the valve diameters from 6-mm to 10-mm increases gas flow rate by 2.7x, thereby decreasing the previous time constant by that amount. Moreover, the three-pressure system was deemed to have a considerably lower time constant (τ=2-ms) than that of the dual-pressure system, where the front-loading and reservoir chambers are pressurized to 4-bar and () = 4^-t/τ, until P(t) reaches 1-bar, respectively. As shown in Figure 4, the lower time constant results in a faster displacement response of the piston and consequently a more predictable sabot velocity. SUMMARY AND CONCLUSION A mathematical analysis and optimization of the breech’s internal ballistics was performed using the 3-D Explicit Dynamics suite from ANSYS Mechanical/ AUTODYN. Following numerous experimental and simulated tests, it was determined to redesign the breech of the meso-scaled gas gun from a two- pressure system to a three-pressure system, in which the driving pressure of the sabot is separate from the pressurized chambers that launch the piston backwards. This change optimizes the current performance of the gas gun such that initial pressure conditions can yield controlled collision velocities. Future work includes the physical fabrication of the breech’s new design and implementation into the meso-scaled LGG. The new installment will involve an extra gas valve in the laboratory because of the switch from two-pressure chambers to three-pressure chambers. Moreover, it is critical to calibrate the internal ballistics of the breech’s new design to corresponding impact velocities of the sabot in order to ensure experimental control. ACKNOWLEDGEMENTS A very special thank you to Dr. Daniel Eakins and the Institute of Shock Physics for their continued advisement throughout the duration of this summer project, and their warm welcome to Imperial College London. Furthermore, thank you Dr. Naresh Thadhani and Dr. Valeria Milam for their substantial support, and to the NSF for the organization and funding of the SURF/IREP program. REFERENCES [1] Winter, Ron. AWE. Key Concepts of Shock Hydrodynamics. 2011. [2] Hong, Ing. Tessmann, Richard. The Dynamic Analysis of Pneumatic Systems using HyPneu. 1998. Figure 4—Piston time response within the new three-pressure breech design across varying time constants of the system. Figure 2—Section view of the previous dual pressure system. Figure 3—Section view of the new three pressure breech Rankine-Hugoniot Relations Figure 1—Experimental shock response from previously existing LGG design.
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Transcript of Tyler_Distefano_REU_Conference_Poster
The Development of a New Small-Bore Taylor-Impact Launcher Tyler DiStefano1 | The Cooper Union for the Advancement of Science and Art
Dr. Daniel Eakins2 | Institute of Shock Physics at Imperial College London IREU: Georgia Institute of Technology School of Materials Science and Engineering
INTRODUCTION AND BACKGROUND Light Gas Guns (LGGs) are used to launch metallic-plated sabots at high velocities towards parallel metal alloy plates. The resulting collision between the sabot and the metal plate generates shock waves that longitudinally propagate through the material of interest. Analysis of the wave propagation reveals material properties and can result in an experimental thermodynamic equation of state through the Rankine- Hugoniot equations.1 The Institute of Shock Physics has a newly built meso-scaled LGG that launches 12.95-mm small-bore sabots. The impacting sabot velocity is critical information for the use of the Rankine-Hugoniot relations. System analysis and optimization is necessary to obtain predictable impact velocities of the sabots. The analysis is focused on the time response and optimization of the piston located within the breech of the small-bore LGG.
EXPERIMENTAL METHODS Experimental analysis of the current system was performed using the LineVISAR system and HetV tools to observe the impact velocity of the Al-1060 plate and 3.98-g sabot, respectively. The sabot projectile had a Copper flyer plate that was lapped to ensure flatness and to eliminate any effects of tilt within the collision. The LineVISAR system was set up using a combination of optical mirrors and lenses with a 2.2-W laser. Furthermore, the streak camera captured a shifted interference pattern that indicates an impact velocity of the parallel metal alloy at the end of the barrel. The HetV tool was installed by a system of probes at the end of the barrel, which uses Doppler-shifted light to calculate the velocity of the sabot as it travels along the barrel from the instant of firing. The HetV tool was also used to track the velocity of the piston along the breech without the presence of a sabot and target plate, where the front-loading chamber was set to 35-bar and the evacuating reservoir was initially set to 40- bar. The experimental results were then compared to a series of 3D simulations run through ANSYS Workbench/Mechanical, which modeled the time response of the piston. Pneumatic modeling of the breech’s internal ballistics provided a representative time constant of the system, including realistic conditions such as friction and system jitter.2 The simulations ran through a succession of decreased time constants, which reflected numerous prototypes of the current system that included design changes. ANSYS Mechanical also simulated a novel three-chamber alternative design for the breech and was then compared to the current results.
RESULTS AND DISCUSSION Analysis of the current ballistics provided motivation for a redesign of the breech with different initial conditions than the current ones used to launch the sabot. The HetV data indicated that the piston currently displaces 5-mm backwards. This displacement does not clear the entire pressurized valve and shows that the sabot does attain its full potential velocity with the previously used initial conditions. The solutions from the simulations provided insight to fill the dual-pressure system proportional to the effective surface area corresponding to the force in the sliding direction. The proportion between the front-loading chamber and the evacuating reservoir is a 1.8x differential. Furthermore, this change ensures that there is a faster time response after firing the gas gun because the operating pressures are now near equilibrium conditions of the piston. As the simulations were sampled across lower time constants, it reflected design changes to the physical system. It was determined from analytical pneumatic modeling that increasing the valve diameters from 6-mm to 10-mm increases gas flow rate by 2.7x, thereby decreasing the previous time constant by that amount. Moreover, the three-pressure system was deemed to have a considerably lower time constant (τ=2-ms) than that of the dual-pressure system, where the front-loading and reservoir chambers are pressurized to 4-bar and 𝑃 (𝑡) = 4𝑒^-t/τ, until P(t) reaches 1-bar, respectively. As shown in Figure 4, the lower time constant results in a faster displacement response of the piston and consequently a more predictable sabot velocity.
SUMMARY AND CONCLUSION A mathematical analysis and optimization of the breech’s internal ballistics was performed using the 3-D Explicit Dynamics suite from ANSYS Mechanical/AUTODYN. Following numerous experimental and simulated tests, it was determined to redesign the breech of the meso-scaled gas gun from a two-pressure system to a three-pressure system, in which the driving pressure of the sabot is separate from the pressurized chambers that launch the piston backwards. This change optimizes the current performance of the gas gun such that initial pressure conditions can yield controlled collision velocities. Future work includes the physical fabrication of the breech’s new design and implementation into the meso-scaled LGG. The new installment will involve an extra gas valve in the laboratory because of the switch from two-pressure chambers to three-pressure chambers. Moreover, it is critical to calibrate the internal ballistics of the breech’s new design to corresponding impact velocities of the sabot in order to ensure experimental control.
ACKNOWLEDGEMENTS A very special thank you to Dr. Daniel Eakins and the Institute of Shock Physics for their continued advisement throughout the duration of this summer project, and their warm welcome to Imperial College London. Furthermore, thank you Dr. Naresh Thadhani and Dr. Valeria Milam for their substantial support, and to the NSF for the organization and funding of the SURF/IREP program.
REFERENCES [1] Winter, Ron. AWE. Key Concepts of Shock Hydrodynamics. 2011. [2] Hong, Ing. Tessmann, Richard. The Dynamic Analysis of Pneumatic Systems using HyPneu. 1998.
Figure 4—Piston time response within the new three-pressure breech design across varying time constants of the system.
Figure 2—Section view of the previous dual pressure system.
Figure 3—Section view of the new three pressure breech
Rankine-Hugoniot Relations
Figure 1—Experimental shock response from previously existing LGG design.
