alexandra woldman –undergraduate researcher dr...
TRANSCRIPT
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Alexandra Woldman – Undergraduate ResearcherDr. Gangbing Song – Faculty Mentor
Dr. Haichang Gu – Postdoctoral Mentor
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� Certain materials, when placed in an electric field will align the dipoles of their ions
� When the electric field is removed, some of the alignment remains
http://www.physikinstrumente.com/tutorial/4_15.html
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� When a strain is applied to the material, changing the alignment of the poles, a voltage is produced
� Conversely, when voltage is applied to the relaxed material, the poles realign, inducing a strain
Direct Effect
Converse Effect
http://www.bostonpiezooptics.com/?D=6
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� Sensors◦ Output a voltage when strained
� Actuators◦ Change shape when voltage is applied to them
First Experiment
Second Experiment
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� Measures charge and converts to voltage
� More accurate than direct measurement
� Could provide accurate strain data for piezoceramic embedded in concrete
www.kistler.com
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� Used aluminum beam with piezoceramic sensor mounted on one side and strain gauge on other side
� Strain gauge and piezo sensor experience equal and opposite strain and beam is flexed◦ Piezoceramic wired to charge amplifier
◦ Strain gauge connected to signal conditioner
◦ Both devices produce voltage
Clamped EndStrain Gauge
(opposite side, piezo patch)
Aluminum Beam
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� Use the readings from both devices to create a transformation from Voltagestrain gauge to Voltagecharge amp
� For strain gauge voltage1 mV = 1 mircostrain
� Thereby, the voltage from the charge amplifier, can be converted to strain
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The voltage produced by a piezosensor is proportional to the strain, therefore linear relationship can be developed from the strain gauge output voltage to the piezosensor output voltage
Vstain gauge=1.577341*Vcharge amp + 0.132023 - V0,charge amp
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� Piezoceramic patch embedded in concrete
� Try to apply same transformation and compare to theoretical results for static loads
� Drift – increase or decrease in signal without load application
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� “The signal drift is probably caused by low insulation resistance which is characteristic of ceramic piezo elements.” -Leon P. Fialkowski
� Increase insulation:◦ Water insulation
◦ Liquid electric tape
◦ Combination
� Drift still too large for static loads to register
� For further testing with the charge amplifier, better sensors are necessary
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� Used for:◦ Determination of strength
◦ Detection of cracks and void
� Send signal through material◦ Velocity of signal related to strength
◦ Cracks and voids reflect signal
◦ Changes the signal gathered by receiver
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� Loaded concrete cylinders under compression
� Two cylinders, each with two piezoceramic patches embedded inside
Actuator
ActuatorSensor
Sensor
12”
1”
Load Load
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� Test Procedures◦ Take first measurement at zero load
◦ Take reading every 4-5 kips increase in load
� Each reading◦ Sends signal from piezoceramic actuator
◦ Collects voltage data at sensor for 10 sec
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� To get an understanding for the change in wave propagation as the load increases, calculate the energy for each reading
Energy = [x] * [x] T
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0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
x 104
50
60
70
80
90
100
110
120
130
Load Applied (lbs)
Energy
Act-Top 1
Act-Top 2
Act-Top 3
Sen-Top 1
Sen-Top 2
Sen-Top 3
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0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
x 104
10
15
20
25
30
35
40
45
50
55
60
Load Applied (lbs)
Energy
Act-Top 1
Act-Top 2
Act-Top 3
Sen-Top 1
Sen-Top 2
Sen-Top 3
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� Test conducted until cylinder failed under compression
� Failure occurred at 129 kips
� Primary crack between sensor and actuator 0 2 4 6 8 10 12 14
x 104
100
120
140
160
180
200
220
Load Applied (lbs)
Energy
Local Max
Broken
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� Close up scatter plot of voltage data collected by sensor indicates that small fractures had developed in the cylinders
� “Noise” in data close ultimate load
40 kips
126 kips
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� The highest energy is at zero load◦ Boundary condition different from any non-zero load
◦ Top end free can vibrate freely, so no suppression of vibration
� As soon as any load is applied, energy drops
� After first 10% of ultimate load is applied, the energy remains relatively level
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� The tests with the sensor on top always showed higher energy readings
� Slight energy drops as cylinder comes close to failing
� Tremendous drop in energy once cylinder fails
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� For future tests with wave propagation:
◦ Calibrate tests under loading, for accurate results under loading
◦ Above 10% of the load, the energy of the wave does not change much, so safe to adjust loading up and down without compromising tests results
◦ Always take note of where the sensors are placed in the specimen and consider how that will affect results
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� Piezoelectric materials are the future of structural monitoring
� A better understanding of these materials will allow for large savings in repairs in structures◦ Notice damage earlier
◦ Repair before damage it is catastrophic
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Special thanks to:
Dr. Song, Dr. Mo
Dr. Gu, Claudio