Group 14 Derek Burney Barnabas Fekete Jason Hood Fred Nguyenloc Project Sponsor Dr. Joel House Taylor Impact Test Velocity Measurement System 4 _______________________________________________________________ Fall 2007 Final Design ________________________________________________________________

Outline Taylor Impact Test Problem Statement Project Scope Design Ideas  Decision Matrix  Initial and final designs Spring semester Progress  Bracket design

Taylor Impact Test Used to study strain rate properties of materials during high velocity collisions. High speed camera captures the collision between the specimen and the anvil. The average test speed is 200m/s.

Taylor Impact Test Currently two methods are used to measure the velocity of the test specimen. 1.Optical Barrier – 2 lasers spaced apart a certain distance. When the beam breaks, it allows us to know the time frame. 2. Pressure Transducer – pair of transducers recording pressure at a certain distance apart Same concept as lasers

Problem Statement Recently the laser detectors have been producing erroneous velocities.  Signal from second optical barrier has a delayed response.  The measured velocity is lower compared to the pressure transducers and the expected velocity calculated from the propellant load.

Project Scope Update laser velocity measurement system such that it: Provides accurate velocity measurement of projectiles with average speed of 200m/s using non- contact methods. Must be accommodating of test samples with diameters of.21’’ to.50’’. New equipment must easily integrate into the existing system.

Initial Design Ideas Four Ideas to Fix Problem  Sound Detectors  Eddy Current Detector  Chronograph  Lasers “Optical Chronograph.” 01 October “Eddie Current Velocity Measurement.” Sensorland.com. 31 September

Decision Matrix Design Criteria Material Limitations Strobe Interference System Compatibility DurabilityCostSafetyTotal ** Weight Factors RateWF * RateWF * RateWF*RateWF * RateWF * RateWF * Detector Types Laser Infrared Eddy Current Sound * WF = Rate x Weight Factor** Total is sum of WF

Edmund Optics® photodiode receiver modules (3) 5.6mm laser diodes Custom brackets Initial Design Ideas From Decision matrix, the laser barrier method proved to be the best option. Improve the Reliability of the system by adding 3 optical barriers Helium Neon lasers replaced with laser diodes

Problems Encountered with Initial Design Edmund Optics receivers were too large to integrate three into the design. Purchasing laser diodes and receivers would set us 30% over our budget.

Final Design Incorporates currently used lasers so we do not exceed budget. Two Edmund Optics® photodiode receiver modules with power supply

Final Design

Bracket Design

Design Consideration Is the measured velocity a representation of the impact velocity. Point 1 – Force of the propellant and Friction in the tube Point 2 – Friction from contact and Drag Point 3 – Drag

Velocity Between 2 and 3 Acceleration due to propellant equals 0 at point 2 1.

Low Velocity Test Measure the velocity of a Nerf Dart using two methods and compare the results.  Method One – Measured the distance the dart traveled horizontally from a fixed vertical distance and apply Newton’s Law to projectile motion  Method Two – Measure the velocity with the opticla barrier system

Method One – Projectile Motion The Gun was fired horizontally from a fixed position 40 times The Level was set with a pendulum The x-distance was measured

Method One – Projectile Motion Because of the darts low mass (0.21kg) Drag could not be assumed negligible.

Method One – Projectile Motion The drag deceleration is a function of the projectile velocity which changed over the x- distance Initial Velocity = m/s

Method II - Optical Barriers The optical barrier uses interruption to measure time to travel a set x-distance The time was measured using a computer based oscilloscope

Method II - Optical Barriers TheoreticalActual The initial run of the demonstrated that the detectors functioned opposite of expected and that they where flooded by ambient light. 680nm specific filters were ordered and the test resumed

Velocity Measurement Phase I Measured the velocity of 40 samples with the optical barrier system Velocity Measured from the gun = m/s

Method II - Optical Barriers Results V PROJ = m/s V BAR = m/s The projectile method had the higher accuracy due to the interpretation of the time from the graphs. The system used on site was expected to prevent the excess error

Velocity Measurement Phase I Performed Projectile Velocity Test to Determine Average Nerf Dart Velocity Compared the Detector Velocities to the Projectile Tests Average System Reading = 23.5 m/s m/s Average Nerf Dart = 24.6 m/s m/s

High Velocity Test Install new detectors at Eglin site The 200m/s projectile passed through the barriers before the detectors could change in voltage

High Velocity Test The diodes in the detectors had a time to peak voltage of 300μs. The optical barrier is only blocked for 10μs with a 200m/s test specimen The diode only rose approximately 1/30 th of the peak voltage The group initially determined the high voltage gain of the detector circuit would compensate for the slower rise time.

Corrective Recommendations After review of the technical manual for the current in use detectors:  Replace the detector photodiodes. A suitable replacement with a 1530 ns peak time is available for $  Replace the Helium-Neon Lasers. They have an average life span of two years. Current lasers are twenty years old.

Proposed Solution 1.Complete Package Unit 2.Rated for Projectiles of 5000 m/s with 1% accuracy 3.Estimated Cost ₤8000. (

Questions?