Group 14 Derek BurneyBarnabas FeketeJason HoodFred Nguyenloc

Project Sponsor Dr. Joel House

Taylor Impact Test Velocity Measurement System

4

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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

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 apartSame 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 2007 http://kurzzeit.com/e_bmc17.htm

“Eddie Current Velocity Measurement.” Sensorland.com. 31 September 2007 <www.sensorland.com/AppPage048.html>

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

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

V V V VIM PACT t M EASURED FR ICTION DRAG

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

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

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.

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

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 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

Velocity Measurement Phase IMeasured the velocity of 40 samples with the optical barrier system

Velocity Measured from the gun = 37.3+2.3m/s

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

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

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 1/30th 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 $14.85.

Replace the Helium-Neon Lasers. They have an average life span of two years. Current lasers are twenty years old.

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. (

Questions?