group 14 derek burney barnabas fekete jason hood fred nguyenloc project sponsor dr. joel house...
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Group 14 Derek BurneyBarnabas FeketeJason HoodFred Nguyenloc
Project Sponsor Dr. Joel House
Taylor Impact Test Velocity Measurement System
4
_______________________________________________________________
Fall 2007 Final Design
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Outline
Taylor Impact Test Problem Statement Project Scope Design Ideas
Decision Matrix Initial and final designs
Spring semester Progress Bracket design
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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.
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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 apartSame concept as lasers
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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.
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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.
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Initial Design Ideas
Four Ideas to Fix Problem Sound Detectors Eddy Current Detector Chronograph Lasers
“Optical Chronograph.” 01 October 2007 http://kurzzeit.com/e_bmc17.htm
“Eddie Current Velocity Measurement.” Sensorland.com. 31 September 2007 <www.sensorland.com/AppPage048.html>
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Decision MatrixDesign Criteria
Material Limitations
Strobe Interference
System Compatibility
Durability Cost Safety Total **
Weight Factors
0.236 0.208 0.180 0.152 0.125 0.097 0.998
Rate WF*
Rate WF*
Rate WF* Rate WF*
Rate WF*
Rate WF*
Detector T
ypes
Laser 4.95 1.16 4.50 0.94 4.16 0.74 5.00 0.76 0.67 0.08 4.5 0.44 4.12
Infrared 4.95 1.16 3.50 0.73 4.16 0.74 5.00 0.76 0.67 0.08 5.0 0.48 3.95
Eddy Current
4.00 0.94 5.00 1.04 0.52 0.09 0.50 0.08 1.33 0.16 4.0 0.39 2.70
Sound 5.00 1.18 5.00 1.04 2.60 0.46 0.75 0.11 2.50 0.31 5.0 0.48 3.58
* WF = Rate x Weight Factor ** Total is sum of WF
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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
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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.
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Final Design Incorporates currently used lasers so we do not exceed
budget. Two Edmund Optics® photodiode receiver modules with power
supply
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Final Design
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Bracket Design
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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
V V V VIM PACT t M EASURED FR ICTION DRAG
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Velocity Between 2 and 3
F mg
a g
v a x
Fric tion
loss
2
adrag
Cd As v2
2 mspecimen
Acceleration due to propellant equals 0 at point 2
1.http://www.fas.org/man/dod-101/navy/docs/es310/ballstic/Ballstic.htm
vdrag 2 adrag x
V VIM PACT MEASURED
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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
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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
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Method One – Projectile Motion
y y g t
x x v t a t
o
o x d
1
21
2
2
2
FC D v
Dd 2 2
8
aF
md
dart
Because of the darts low mass (0.21kg) Drag could not be assumed negligible.
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Method One – Projectile Motion
The drag deceleration is a function of the projectile velocity which changed over the x-distance
Initial Velocity = 36+0.8 m/s
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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
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Method II - Optical BarriersDetector One .50 cal 200m/s Test
0 100 200 300 400 500 600 700
Time (us)
Vo
ltag
e (V
)
Theoretical Actual
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
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Velocity Measurement Phase IMeasured the velocity of 40 samples with the optical barrier system
Velocity Measured from the gun = 37.3+2.3m/s
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Method II - Optical Barriers
Results VPROJ = 36.0 + 0.75m/s
VBAR = 37.3 + 2.3m/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
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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 + 0.95 m/s
Average Nerf Dart = 24.6 m/s + 1.7 m/s
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High Velocity Test
Install new detectors at Eglin site
The 200m/s projectile passed through the barriers before the detectors could change in voltage
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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 1/30th of the peak voltage
The group initially determined the high voltage gain of the detector circuit would compensate for the slower rise time.
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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 $14.85.
Replace the Helium-Neon Lasers. They have an average life span of two years. Current lasers are twenty years old.
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Proposed Solution
http://www.compulink.co.uk/~msinstruments/pdf/858_optical_detector.pdf
1. Complete Package Unit
2. Rated for Projectiles of 5000 m/s with 1% accuracy
3. Estimated Cost ₤8000. (
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Questions?