Final Design

     In order to support the barrel of the firing system as well as the resonant plate, a table is needed which can withstand the 279 kN force induced due to impact. As both the table structure and connections are affected by the load, the material chosen for the table as well as the fastener strength for the connections needs to withstand at least 2 times the impact force. 

     Aluminum extrusion was chosen for the final design mainly due to its modular design which allows for adaptations in the overall table design. To assemble the aluminum extrusion sections steel brackets designed by ATA, both flat corner and 90 degree, for use with the specified aluminum extrusion were used along with 5/16" black-oxide button head hex drive alloy steel screws. The aluminum extrusion has a max tensional load of 748.8 kN while the resultant tensile capacity of the bolts is 846.31 kN and the shear capacity is 564.21 kN, all significantly greater than the max impact force. 

Assembled Aluminum Extrusion Table

     The resonant plate serves as the impact surface for the slug and produces a specific SRS response depending how the plate is sized and tuned. The test articles are placed directly on top of the resonant plate where high frequency shock vibrations are directly induced into the part. While the material and dimensions for the resonant plate is determined by ATA, 25’’ X 18’’ X 2’’ ATP-5 aluminum, a mounting method is needed to secure the plate to the table by integrating with the aluminum extrusion used for the shock table construction and allow for plate changes using basic hand tools. Similar to the table beams and fasteners, to ensure safety during impact, the mounting method needs to withstand more than 279 kN. 

     After researching both indirect and direct clamping methods, the decision was made to use a direct clamping mechanism with the through hole design. The resonant plate was drilled with a series of 28 clearance holes meant to accommodate 5/16" black-oxide alloy steel screws which can withstand a max tension load of 899.20 kN (SF = 3.5).  To prevent direct contact with metal on metal and to absorb the high frequency vibrations between the resonant plate and aluminum extrusion support beams,  a ⅛’’ thick 50A neoprene rubber strip was added. 

Mounted ATP-5 Aluminum Resonant Plate

     The pneumatic firing device’s function is to fire a 1 kg slug at impact velocities of up to 13 m/s via pressurized air. The firing device consists of four main components, the air tank, the solenoid valve, the nozzle block and the barrel. The air tank was selected for its high operating pressure (200 PSI) and having more than 4 ports (7 ports). It functions by taking air from an air compressor and holding it before it is transferred to the barrel. The air tank was fitted with a ball valve, which acts as the inlet for the pressure into the tank, a pressure transducer which takes pressure measurements in the air tank, a passive relief valve and a muffler to reduce noise. One of the air tank ports has an attached hose which connects to the solenoid. The solenoid that was selected is a 1” NPT US Solids Solenoid Valve,  selected due to its high mass flow rate and remote actuation. To interface with the barrel, the previous group developed a nozzle block by combining a bolt-on pipe flange with a snap ring that fixes it to the barrel. The final element of the existing firing mechanism was the barrel. A honed steel tubing was chosen due to its low friction and tight tolerance, optimizing the slug’s motion up the barrel to the resonant plate. 

     An issue experienced by the previous team was multiple impact of the slug on the resonant plate due to back pressure buildup in the nozzle. After considering manufacturing feasibility and venting efficiency, it was decided to drill a series of 8 0.5'' venting holes directly into the barrel. Through numeric simulation of the post impact pressure, it was determined these holes would reduce the pressure to 0.564 psi after the 42 millisecond venting window, well below the maximum 0.702 psi threshold. 

Position, velocity and pressure simulation graphs for post impact dynamics. Based on a system with 8 0.5” diameter holes