Projectile Impact Tester

Transcription

1 Projectile Impact Tester Design Team Neil Cameron, Laura Paradis, Tristan Whiting Betsy Huse, James Leithauser Design Advisor Prof. Mohammad Taslim Abstract The purpose of this project was to design a setup for conducting high-speed impact of small metal projectiles. To accomplish this goal, an apparatus was designed, analyzed and built that fires projectiles of 1-2 millimeters in diameter at a target that is approximately 0.5 meters away. There are four adjustable variables: speed of the projectile, impact angle, material of the projectile and the target surface material. The most important requirement is that the projectile must be fired at a speeds ranging from m/s. The apparatus designed meets these specifications, is safe and easy to use. Rotating Impact Surface Door Latch and Sensor Chronograph Chronograph Output Sabot Platform Solenoid Scissor Jack Capacitor Bank For additional information, please contact Prof. Taslim at m.taslim@neu.edu.

2 The Need for Project To test the effects of projectiles traveling at high speeds colliding with various impact surfaces for cold spray and high energy Solenoid Sabot & Projectile impact characteristics. Scissor Jack Final Solenoid and Projectile Loading Mechanism Setup The purpose of this project was to design a setup to perform research in the area of particle impact. Graduate students at Northeastern University in the Department of Mechanical Engineering will use the apparatus to research the effects and properties of cold spray and other material collision characteristics. The current apparatus used is a pneumatic system, which fires projectiles at a top speed of 80 m/s. The department is looking for an apparatus that will launch projectiles at faster speeds than their current system. The team has designed a system that uses a solenoid to generate a magnetic field, which will propel projectiles at an adjustable speed of m/s. The solenoid system was chosen because the speed of the projectiles can be easily controlled by adjusting the current that is passed through the solenoid. Because the magnetic field is entirely surrounding the projectile, it will not produce spin that the compressed gas caused as it propelled the projectile forward. Since the setup requires high voltage circuitry, a safety system has been integrated to protect the operator. The Design Project Objectives and Requirements The project objective is to accelerate projectiles in excess of 200 m/s in a straight line in order to test the effects of collisions between various projectiles and impact surface materials. Chronograph Used For Recording Speed of Projectile Design Objectives The critical design goal is to predictably propel the projectile at high speeds. The projectiles will then collide with various impact surfaces, and the user can study the effects of the collision on both the projectile and the surface. The group was advised to design a system utilizing magnetic propulsion in order to achieve the desired speeds. The voltage and current needed to meet the system goals with an electromagnetic system can be very dangerous, so safety is another important design objective. The circuitry involved must be proven reliable and electronic switches must be used to ensure a safe and functional apparatus. Design Requirements The apparatus must accelerate 1-2 mm projectiles at an adjustable speed of m/s. The projectiles must be individually loaded into the apparatus so that different materials can be used for testing. The apparatus utilizes a magnetic field to fire the projectiles, but the projectiles are non-ferrous metals, such as aluminum, copper, brass, and stainless steel. A ferromagnetic sabot, or carrier shell, must be

3 Design Concepts considered designed and used to carry the projectile through the barrel (solenoid) and across a maximum distance of 0.6 meters. The impact surface must be removable, to allow for testing of different materials. The impact surface must have the capability to rotate, so that the user can also investigate the effects of the projectile impacting at specified angles. Alternate design concepts considered a rail gun based design, the use of different capacitor bank setups and varied sabot designs. Rail Gun Design During the initial research stage, a rail gun setup was considered. The rail gun would have worked similarly to the solenoid design, except two rails would carry the current rather than a coil. The rail gun design was ruled out because there is inherent wear to the system, and the rails would have had to be replaced after several uses. After performing several calculations, the group also concluded that the current would move through the system too quickly for the projectile, and there would be a higher likelihood for the system to misfire or short. Capacitor Bank Alternatives Several capacitor bank alternatives were considered and tested thoroughly. The system works by charging up several capacitors, and then switching the system from the charging stage to the firing stage. The group conducted calculations using commercially available Capacitors in Series/Parallel capacitors in order to optimize the circuitry before ordering and physically testing the design. These calculations can be found in the Projectile Sabot report. After weeks of testing and calculating, the optimal circuit was created. Sabot Alternatives Since the projectiles are non-ferrous, and therefore not affected by a magnetic field, an alternative method had to be designed to carry the projectiles through the barrel. One solution used a guide rail system, which would carry the sabot to the end of the barrel but stop it from accelerating into the impact surface with the projectile. This would be achieved with a break-away sabot which would ride on rails that curved outwards at the end of the barrel. A crash plate design was also considered, which would stop the sabot at the end of the barrel by crashing into a hard surface and releasing the projectile. Pictured are two options that were considered based on potential suction problems Sabot Alternative Designs between the sabot and projectile and available machining capabilities.

4 Recommended Design Concept The projectile impact tester incorporates the use of capacitors to provide a strong but temporary magnetic field to accelerate a single projectile. There are several safety devices incorporated in the design. Scissor Jack Used to Load Projectile Into the Solenoid Rotating Impact Surface Velocity vs. Voltage Experimental Data Plot Design Description The final design uses eight capacitors of equal voltage and capacitance. The capacitors are configured in two parallel sets of four capacitors wired in series. The capacitors function on two separate circuits, which are activated by electronic switches. Once the capacitors finish charging, the user flips a switch that disconnects the power supply and connects the discharging circuit. The spike in current through the discharging circuit creates a strong but temporary magnetic field, which accelerates the sabot carrying the projectile through the solenoid at high and adjustable speeds, based on the supply voltage. The sabot collides with a rubber stopper located at the end of the barrel to keep it from colliding with the impact surface. The entire apparatus is contained in a Lexan enclosure with a door which can be opened for loading the projectiles. There are two safety switches, an emergency switch and a door switch, that if tripped will discharge the energy stored in the capacitors through high powered resistors. This is in place because there is very high current flowing through the system when it is on, and it would be dangerous for someone to stick their hands into the enclosure while the electronics are live. There are two ways with which to monitor the speed of the projectile: there is a radar chronograph inside the enclosure with an external readout, and a high-speed camera set up outside of the enclosure to track the motion of the projectile. The camera can be used both for determining speed and angles of impact incidence and reflection. Analytical Investigations Several calculations were performed before testing capacitor setups. The group tested on a small scale with inexpensive low energy capacitors before designing for the high speeds desired. Energy calculations were performed in order to find commercially available capacitors that would provide a high enough current spike in the solenoid to accelerate the projectiles. Calculations were also done to determine the optimal mass of the sabot in order to get the optimal efficiency out of the system. All equations can be found in both the Magnetic Propulsion section and the Final Design section of the report.

5 Experimental Investigations After performing extensive calculations, testing was performed on capacitors of low voltage and capacitance to verify the results. The testing consisted of a setup similar to the final design on a smaller scale. Testing evolved from using a disposable camera circuit to a capacitor bank circuit built on a breadboard. The calculations were verified with extensive data collection, and trends were recorded. It was determined that a capacitor bank capable of high voltage and Disposable Camera Circuit medium capacitance was crucial to creating a large magnetic field in the solenoid. Using this information, a final decision on capacitor requirements was made and implemented in the final design. Key Advantages of Recommended Concept The advantages to the system described are that it is a reliable device capable of the speeds needed by the department. The system only requires a standard electrical outlet, as it incorporates two power supplies to get the high voltages needed by the system. The apparatus is fully enclosed and can be transported using a standard cart. There is very little inherent wear in the design, as the sabot and projectile never come in contact with the solenoid. There are various safety Circuit Diagram precautions taken, which make the system safe to use. Financial Issues This product is intended for The apparatus described would only be useful for research research facilities only. The cost facilities interested in the effects of projectiles colliding with various of the prototype is approximately surfaces. The total cost of this prototype is around $600. Many of the $600. parts had to be custom made, including the loading mechanism and the Lexan enclosure. Implementation costs depend on the facility using this apparatus. The department had two power supplies and a high-speed camera that the group was able to utilize. Recommended Improvements More testing should be conducted To improve the design, more testing would need to be using a variable power supply, conducted. There were talks of eliminating the use of a capacitor bank which could potentially replace and instead using a variable pulse power supply to fire the projectile. the capacitor bank setup. There was not enough time to investigate this possibility in a safe and efficient manner. This change would decrease the cost and the complexity of the circuitry in the design and could potentially increase launch speed if more energy could be pushed into the existing system.