Air Bearing Upgrade for Split-Hopkinson
Pressure Bar (SHPB) Experiment
Donald Hayes II, Joseph Chason, Sarah Napier, Zachary Johnson
Department of Mechanical Engineering
Sponsor
Dr. Joel House
Eglin Air Force Base Research Laboratory
Advisor
Erica Cosmutto
FAMU/FSU College of Engineering
April 12, 2012
Overview











Introduction
Concept Generation & Selection
Final Concept
Components
Functional Diagram
Results & Discussion
Project Budget
Safety Concerns
Conclusion
Acknowledgements
Questions
2
Introduction: SHPB Basics
Initial Strain Pulse
Striker
Mechanism
Incident Bar / Strain Gauges
/ Bushings
Reflected Pulse
Material
Sample
Transmitter Bar / Strain
Gauges / Bushings
Momentum
Trap
Transmitted Pulse
3
Introduction: SHPB Basics
Striker
Mechanism
Strain Gauges
Material
Sample
Strain Gauges
Momentum
Trap
Data
Data Acquisition
System
4
Introduction: Needs Assessment
 Research air bearings for existing 5/8 inch
diameter journal bearing system
 Develop:
 Bar alignment method
 System upgrade from journal bearings to air bearings
 Determine efficiency of air bearings over journal
bearings
5
Introduction: Objectives
 Analyze SHPB design based on use of air bearings
 Analyze:




Hardware cost
Interface requirements
Installation procedures
Impact on bar geometry
 Assess strain gauge technology
 Develop procedure to align bars
 Design a working prototype to show knowledge of
system
 Remain within $2500 budget
6
Generating Concepts: Methodology





Break system into base components
Treat components as individual systems
Generate multiple solutions per system
Determine most suitable components
Combine and implement into design
7
Generating Concepts: Components
& Concerns
 SHPB Components







Base Structure
Striker Mechanism
Incident & Transmission Bars
Strain Gauges
Air Bushings
Momentum Trap
Air Supply System
 Concerns
 Bar Alignment Method
 Data Acquisition
8
Generating Concepts: Criteria





Cost
Weight
Size
Simplicity
Durability





Portability
Scalability
Accuracy
Data Quality
Ease of Use
9
Selecting Concepts
10
Selecting Concepts
11
Selecting Concepts
Mass
Cost
Portability
Data Quality
Simplicity
Scalability
Ease of use
Size
Durability
Accuracy
Score
12
Final Concept
Component
Final Selection
Base Structure
T-Slotted Framing
Striker Mechanism
Electric Solenoid
Incident, Transmission & Striker Bars
0.75” dia. 1566 Steel
Strain Gauges
Foil Type (Vishay Co.)
Air Bushings
0.75” ID (New Way Air Bearing Co.)
Momentum Trap
Custom
Gas Supply
Compressed Argon
Data Acquisition
NI Hardware & Software (LabView)
Bushing Alignment Method
Laser Insert
13
Components: Striker Mechanism
Solenoid
Striker bar
Striker bar
tube
McMaster Carr
336 ozf.
14
Components: Air Bushings
Air line
Bushing block
housing
Air bushing
New Way Air Bearings
0.75” Inner Diameter
30 lb. Radial Load
15
Components: Strain Gauges and
Material Sample
Strain gauges
16
Components: Strain Gauges and
Material Sample
Vishay Micromeasurements
Gauge factor ≈ 2
Resistance = 120 Ω
Located 6” from sample
Strain gauges
17
Components: Strain Gauges and
Material Sample
Copper specimen
~ 0.3” diameter
~ 0.3” thick
18
Components: Momentum Trap
(bar stopper)
19
Final Concept
Incident bar
Length = 8 ft.
Width = 7 in.
Height = 3.5 in.
Copper specimen
Striker bar
mechanism
Momentum trap
Air bushing
Strain gauges
Transmitter bar
20
Functional Diagram
120 Volts
AC
DC
Power
Supply
Wheatstone
Bridges
Data
Acquisition
System
Data
Recording &
Storage
Activation
Switch
Striker
Mechanism
Data
Power
Gas
Incident Bar / Strain
Gauges / Bushings
Material
Sample
Transmitter Bar / Strain
Gauges / Bushings
Momentum
Trap
Gas Supply
21
Visualizing
Sample
Strain Pulse:the
Visualization
Copper
Sample
Steel
Incident
Bar
Steel
Transmitter
Bar
22
Reduced Sample Area
Strain Pulse:
Visualization
Increases
Applied
Stress
Dsteel
0.75 in
DCopper
0.31 in
23
Visualizing the Strain Pulse
Surface: Von Mises Stress
Yield Stress
σy Copper
½ σy Steel
24
Analyzing Data
 LabView hardware & software
 250 kHz Sampling rate
 Measured Voltage
Calculated Strain
 Strain Waves
Strain Energy
 Geometric Definitions + Boundary Conditions
Material Description
25
Data Acquired
26
Incident Wave Equal to Consequent Waves
27
Elastic Impulse Wave Area
∫dε*dt (s)
Incident
Reflected
Transmitted
Strain-Seconds
1.15 x 10-8
4.47 x 10-9
5.46 x 10-9
% of Initial Pulse
100 %
38.7 %
47.3 %
"Absorbed"
14 %
Low sampling rate error
28
Discussion
 Potential improvements in system
 Use of stainless steel bars
 Potential improvements in testing
 Annealed copper specimen
 Higher data rates
 Used 250 kHz
 Recommend  1 MHz
 Implement friction imitation method to evaluate
efficiencies between air bushings and journal
bearings
29
Project Budget
 Within budget
 Total budget
 $2,500
 Total expenditures
 $2117
 Percentage under budget
 15%
30
Allocation of Expenditures
Striker
2.8%
Support Systems
3.0%
Frame
3.1%
Bars
11.9%
Budget Savings
15.3%
Bearings
64.0%
31
Safety Concerns

Pinching/crushing fingers

Flying Fragments

Electrocution
32
Review
 Analyzed:
 SHPB design based on use of air bushings
 Interface requirements
 Installation procedures
 Designed alignment tool
 Impact on bar geometry
33
Review
 Assessed strain gauge technology
 Foil gauges sufficient
 Semiconductor gauges if high accuracy required
 Designed a working prototype that shows
knowledge of system
 Remained within $2500 budget
 Total expenditures ≈ $2100
34
Conclusion
 Accomplished major requirements!
 Critical Factors




Segmented design
Ease of manufacture
Team cooperation
Excellent support
35
Acknowledgements
We would like to thank the following people for their help and support
which made this project a success…
Dr. House – Eglin AFRL
Dr. Shih – FAMU/FSU COE
Dr. Kosaraju – FAMU/FSU COE, CAPS
Dr. Dalban-Canassy – FAMU/FSU COE, ASC
Dr. Hovsapian - CAPS
Mr. Bob Walsh - NHMFL
Mr. Dustin McRae – FAMU/FSU COE, NHMFL
Dr. Solomon – FAMU/FSU COE
Mr. Ryan Jantzen – FAMU/FSU COE, HPMI
Mr. Bill Starch - ASC
Dr. Hellstrom – FAMU/FSU COE, ASC
THANK YOU!
36
Questions?
Comments?
Detailed Budget
Solenoid
T-slot Framing 1 1/2 inch (96 inch length)
Incident & Transmission Bar: 1566 Steel Bar 0.75 inch (36inch
length)
Quantity Unit Cost Total Cost
1
69.94
$69.94
2
48.15
$96.30
2
29.42
$58.84
T-slot Framing 1 1/2 inch (4 foot length for 6 inch braces)
Air Manifold (72 inches)
Striker Bar: 1566 Steel Bar 0.75 inch (6inch length)
Right Angle Fastener
Fasteners (Packs of 4)
Strain Gauges (Pack of 10)
Air Bushings 0.75 inch
Bushing Block 0.75 ID
0.25”x3”x72” Aluminum Sheet
1
1
2
16
16
3
4
4
1
25.15
16.34
5.17
4.06
2.71
20
265
135
40.35
$25.15
$16.34
$10.34
$64.96
$43.36
$60.00
$1,060.00
$540.00
$40.35
0.75” Diameter x 12” Long High Tolerance Aluminum Bar
12” Aluminum U-Channel
0.75” diameter x 6” Long High Tolerance Steel Bar
Total
1
1
1
12.1
14.19
5.26
$12.10
$14.19
$5.26
$2,117.13
38
Velocity Calculations
T he velocity of the striker bar is needed
T he only r equiremen t is that th e specimen plasticaly deform
while the incident and transmitter bars are only loaded elasticaly
T he following equatio ns show t he process
y c   7 0MP a
Y ield s tres s of c opper
2
.4
2
A reac      i n  0 .12 6i
 n
2 
Area of t he copper
F   y c A reac  5 .67 5k
 N
Forc e Required t o reac h Y ield
N ex t the mass of t he s t eel bar is c omputed
   7 .85
gm
D ensit y of st eel
3
cm
2
0 .75 2
3
v     
i n  6i n  2 .65 1i
 n

 2 
Volume of t he 3/ 4 inc h diameter, 6 inc h
s triker bar
mass   v    0 .34 1k g
Mas s of the s triker bar
39
Velocity Calculations
N ex t the amount of time t he st rik er bar will impact t he inc ident bar
m
c   6 10 0
s
Speed of wav e propogation in s teel
Lengt h of St rik er bar
L   6i n
t   2
L
c
5
 4 .99 7 1 0
t  4 9.9 67s

s
Pres sure wav e propogat ing down the
s trikerbar and returning
= 2 x lengt h/ speed
D urat ion of impact
Finaly the minimum v eloc ity of t he s t rik er bar needed t o plas tic aly def orm t he s pecim en
V
F
m
 t  0 .83 2
mass
s
V  1 .86
mi
hr
Minimum v elocit y of st rik er bar
needed to plast icaly def orm the
c opper specimen
40
Velocity Calculations
A cc  
1 30o zf
m
 1 05 .99 3
mass
2
s
Lso l   1i n
D
Ac celerat ion av ailable f rom t he
c hosen solenoid
Lengt h of pist on with giv en f orce
Do  Vo  t  .5A  t
2
Generic dy namic pos ition equat ion
.5
 Lso l 
t imeso l   
  0 .02 2s
0
.5

A
cc


D eriv ed t ime, f rom prev ious equation
mi
Vst kr   A cc t imeso l  5 .19 1
hr
C alc ulated v eloc ity f rom giv en s olenoid
41
Plastic Energy Derivation
• Stress
σ = F/A
• Strain
ε = (Li – Lo) / Lo
• Gauge Factor GF = [ (Ri - Ro) / Ro] / ε
• Data Strain
ε (Ri) = [ (Ri - Ro) / Ro] / GF
42
Plastic Energy Derivation
• Strain in Specimen:
dεavg / dt = ( cb / Ls ) * (εI – εR – εT)
• Integration:
εs = (Cb / Ls) * ∫0t [(εI – εR – εT) *dt]
Strain through the specimen
43
Plastic Energy Derivation
• Strain energy for each wave
Kinetic energy = 0.5 * m * v2
• Initial
EI = 0.5* AB * CB * EB * T *εI2
• Reflected
Er = 0.5* AB * CB * EB * T *εR2
• Transmitted
Et = 0.5* AB * CB * EB * T *εT2
44
Plastic Energy Derivation
• Strain energy
δSE = EI – ER – ET
• Plastic Energy absorbed by specimen
Es = 2 * δSE
45
Solenoid Optimization
Unacceptable Region
2000
Applied Force (oz F)
1500
Acceptable Region
1000
500
Unacceptable Region
0
0
10
20
30
40
50
60
70
80
90
100
Cost ($)
46
Weak Formulation for FEA
 A 
d
2
dt
2
T
d 
 d u   f ( x t)
E

A

  
d x
 d x 
0







2
d
d 

d 
w   A  d t2 T  w d xE A   d xu   w f ( x t) d ( x t) 0






(  A )   d w    d T   w f ( x t) d ( x t)  w  A    d T  0


 

 
d
t
d
t


 

d t 
47
Weak Formulation for FEA
48