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University of California, San Diego
Mechanical and Aerospace Engineering
MAE 156B: Senior Design Project
Final Assembled Prototype
Background
Background
Shock testing is performed to see how items respond to shock vibrations caused by a sudden impact. This is useful for obtaining experimental results to compare with shock analysis results. A motivation for shock testing and analysis is to test small electronics on satellites and spacecraft that may break from shocks during launch experience.
One way to perform shock testing is with a shock testing table. A firing mechanism shoots a projectile with a specific momentum at a tuner attached to the bottom of a resonant beam. This tuner and beam are tuned to particular frequencies, so the impact from the projectile produces a specific shock that acts on the test article. The test item is fitted with sensors to record the loads the item experiences. These recorded loads can be compared to analytical results to determine how the test item will react to shocks when the item is in use.
Project Objective
Project Objective
The objective is to create the firing mechanism that will be used for the shock testing table. This firing mechanism will be pneumatically operated and will shoot a projectile of different masses into a testbed at different velocities. The range of the projectile masses is 1-3 kg, and the range of the projectile impact velocities is 6-13 m/s. There will also be different safety measures such as remote venting and firing.
Final Design Overview
Final Design Overview
Below is a diagram of the final product. Based on the specific mass and velocity requirements for each test, a certain amount of compressed air will be let into the air tank pictured below. This air tank will have a passive and active relief valve to meet safety requirements, as well as a pressure transducer to measure the pressure in the tank.
To quickly release air into the barrel, a solenoid valve is used. The air moves through the tubing and enters the barrel, where it acts as a pressure force on the slug. This pushes the slug upwards through the barrel until it hits the testbed at the desired impact velocity. This impact velocity is measured with a velocity sensor, which will be right under the impact table. A venting valve is then opened to prevent any back pressure behind the slug, which prevents unwanted repeated impacts.
Final Narrated Video
Performance Summary
Performance Summary
For initial testing with the 1 kg test slug, low-pressure readings were used. Filling the tank with 3 psi was enough to get the slug to hit the impact table and slide down the barrel. Using a high-speed camera and velocity analysis, the impact velocity is found to be around 3 m/s, matching theoretical results. By incrementally increasing the pressure, a linear pressure vs impact velocity relationship can be found.
Surprisingly, back pressure inside the barrel proved to be an issue with pressures higher than 3 PSI. To mitigate this, a venting valve was added to the nozzle in the final design. This valve was programmed to open at a set delay time after the firing valve was opened. The air behind the slug can then be released through this venting valve, and prevent unwanted repeated impacts from back pressure.
With this final design, a similar pressure vs impact relationship can be determined using the same methods as before. In this linear relationship, the impact velocity increases by about 0.5 m/s as the pressure increases by 1 PSI.
6.9 PSI acting on 1 Kg Slug, taken with High Speed Camera. Impact velocity is 9 m/s
Final Pressure Vs. Velocity Relationship
PDR Presentation.pptxEdited Final Poster.pdfPage updated
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