Alexandra Woldman Undergraduate Researcher Dr. Gangbing Song Faculty Mentor Dr. Haichang Gu Postdoctoral Mentor

Alexandra Woldman Undergraduate Researcher Dr. Gangbing Song Faculty Mentor Dr. Haichang Gu Postdoctoral Mentor

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

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

Sensors Output a voltage when strained First Experiment Actuators Change shape when voltage is applied to them Second Experiment

Measures charge and converts to voltage More accurate than direct measurement Could provide accurate strain data for piezoceramic embedded in concrete www.kistler.com

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 Aluminum Beam Clamped End Strain Gauge (opposite side, piezo patch)

Use the readings from both devices to create a transformation from Voltage strain gauge to Voltage charge amp For strain gauge voltage 1 mv = 1 mircostrain Thereby, the voltage from the charge amplifier, can be converted to strain

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 V stain gauge =1.577341*V charge amp + 0.132023 - V 0,charge amp

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

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

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

Loaded concrete cylinders under compression Load Actuator Load Sensor 1 Two cylinders, each with two piezoceramic patches embedded inside 12 Sensor Actuator

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

To get an understanding for the change in wave propagation as the load increases, calculate the energy for each reading Energy = [x] * [x] T

130 120 110 Act-Top 1 Act-Top 2 Act-Top 3 Sen-Top 1 Sen-Top 2 Sen-Top 3 100 Energy 90 80 70 60 50 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 Load Applied (lbs) x 10 4

60 55 50 Act-Top 1 Act-Top 2 Act-Top 3 Sen-Top 1 Sen-Top 2 Sen-Top 3 45 40 Energy 35 30 25 20 15 10 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 Load Applied (lbs) x 10 4

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 Energy 220 200 180 160 140 120 Broken Local Max 100 Load Applied (lbs) x 10 4

Close up scatter plot of voltage data collected by sensor indicates that small fractures had developed in the cylinders 40 kips 126 kips Noise in data close ultimate load

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

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

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

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

Special thanks to: Dr. Song, Dr. Mo Dr. Gu, Claudio