Sensitivity comparison of PVDF and nanocomposite PVDF-TrFE/ZnO by Pitch Catch measurement

Development and characterization of PVDF nanocomposite for structural health monitoring PVDF poly(vinyledene difluoride)-TrFE(Trifluoroethylene)/ZnO Zinc Oxide

nanocomposite piezo sensor is developed in solvent cast method. PVDF-TrFE-3g ZnO in two different concentration 10&60wt%1. PVDF-TrFE pellets dissolved in DMF(dimethyl Formamide) for 30minutes2. Zinc oxide dispersion in DMF under sonication for 4hours3. Same zinc oxide solution is then mix with PVDF-TrFE solution4. Continuous stirring for 10minutes.5. Cast the prepared solution on a glass mould keep it in furnce at

120degC for 2hours.

Characterization of PVDF-TrFE/ZnO nanocomposite film

X-ray diffraction for structural study Dielectric study Sensitivity : pitch catch measurement

X-ray diffraction

Here, peak positions of reflections corresponding to PVDF(110) and ZnO(101) are marked in the pattern which is matching with the

literature value

Dielectric study

For PVDF permittivity is 16.2

@10kHz, for PVDF-TrFE/ZnO

at 10wt% of ZnO Permittivity

is 11.22 & for PVDF-TrFE/ZnO

at 60wt% of ZnO Permittivity

is 5.665.

Piezoelectric coefficient

Sensor Freq

(Hz)  

(Hz)

d33(pC/

N)

Permittivity(

ε)

g33(Vm/N)

(g=d/ε)

(Vm/N)

PVDF 100 22 16.2 1.35

10wt%

of ZnO100 10

11.20.89

60wt%

of ZnO100 15

5.6652.64

Further, the poled PVDF-TrFE/ZnO nano-composite samples were evaluated for piezoelectric properties.

5 7 9 11 13 15 170

0.5

1

1.5

2

2.5

3

1.35

0.89

2.64

Permittivity

g, V

olta

ge C

oeffi

cien

t(mV

m/N

)

Above graph says as the g33, sensitivity depends on the permittivity, it says sensitivity is

more for the 60wt% ZnO dopant to the PVDF-TrFE, i.e2.64mVm/N at 5.665 permittivity

Pitch catch measurement

i) For the test, in Fig. 1, one aluminum cantilever beam

is used. On the beam one actuator (PZT) and one

sensor (PVDF) is bonded using structural epoxy.

ii) The actuator is connected to one channel of function

generator and also to one channel of CRO. Thus,

input to actuator can be seen on the CRO screen.

iii)The sensor is connected to one channel of CRO. This

channel is selected as a trigger.Frequency 100-400Hz

Amplitude 10Vpp

Frequency response

The specimens were excited using two square 13 mm PZT wafers which were temporary adhered with araldite to the base of the specimen and actuated out of phase by an 10 Vpp which was sent to the Piezos through a function generator to drive them between 100 Hz and 15MHz in first trial. Finally, how the piezos will responds for higher frequency range has been observed. i.e., from 15Hz,15Kz and 15Mhz

Keeping amplitude constant and varying the frequency from 100 Hz to 400 Hz, variation in voltage output is observed.

As the frequency increases voltage of nanocomposite sensor starts deteriorating from 7 to 5V and PVDF from 3to2V.

Frequency response of PVDF and Nanocomposite sensor from Hz to Mega Hertz(MHz) range:

As the frequency

increases from 15 Hz to

15MHz range amplitude

starts decreasing and

voltage peak to peak

reduces 9V to 1 V for

nanocomposite and 4V

to 736mV.

PVDF Piezoelectric Film for monitoring linearity, repeatability

& directionality for Structural health monitoring

What is Structural Health Monitoring (SHM)

“The process of implementing a damage detection and characterization strategy for aerospace, mechanical

and civil engineering structures”

Not a new concept• Has been around for several decades• Advances in electronics made it easier

to implement.

Several non-destructive evaluation (NDE) tools available for monitoring.

Health monitoring Operational EvaluationData Feature Extraction Statistical Models Development

1. Strain gages2. Inclinometers3. Displacement transducers4. Accelerometers5. Temperature gages

6. Pressure transducers 7. Acoustic sensors8. Piezometers9. Laser optical devices

Instrumentation used:

SHM Involves:

• Most of these sensors can be wirelessly connected.• Technology using solar energy is very common in instrumentation.• Latest technology even has self powered systems, i.e. no external power

required.

Monitoring Metrics

Measure:AccelerationStrainClimatic ConditionsCurvatureDisplacementsLoad

Identify: Corrosion Cracking Strength Tension Location of rebar

/delaminations

Damage Detection and Impact Prediction:

Damage detection is a problem of prime interest in aircraft structures

Aim of current study is to analyze damage detection caused due to impact on structure and use those observation for prediction of impact location and energy

This study will be helpful in real-time impact detection in aircraft structures.

Real-time detection will be better than damage detection after failure. This will save lot of time and also reduce failures caused because of damages occurred in structures.

Methodology: Impact of known energy will be made on composite structure at

known location Strain developed in structure will be observed with PVDF sensorThese will be compared with conventional strain gagesPattern and profile for strains developed under various energies

of impact will be takenThese profiles will be used to conversely predict the impact

energy and location based on damage occurred

Experimental1. Static Analysis

Proportionality of Response :

PVDF sensor was fixed on composite plate

Impact was made at a fixed distance from the sensor with different energies

Corresponding voltage values were recorded

Impact Position

PVDF Sensor

Results:Energy(J) +ve peak -ve peak Max. of abs

1 1.04188 -1.14113 1.14113

2 1.549449 -1.36849 1.549449

3 2.06722 -1.90539 2.06722

Voltage increased proportionally with increase in impact energy

Proportionality factor from obtained values is 0.463V/J

Direction Dependence and Repeatability:

Impacts were made around PVDF sensor in a circular path

With same energy, impacts were made with step of 10°

2trials for 1J energy and one trial for 2J were conducted

Observation

AngleTrial 1_1J Trial 2_1J Trial 1_2J

+ve peak -ve peak +ve peak -ve peak +ve peak -ve peak-90 1.091693 -1.56037 1.132474 -1.52887 1.507252 -2.33628-80 1.150267 -1.6023 1.041477 -1.34567 2.033199 -2.38395-70 1.140076 -1.55194 1.029984 -1.75659 1.343843 -2.02198-60 1.270749 -1.50136 1.027031 -1.09734 1.433522 -1.30784-50 1.553907 -2.00647 1.020616 -0.86894 1.353675 -1.25856-40 1.495541 -1.91412 1.385657 -1.58436 1.377144 -1.63372-30 1.743303 -2.33434 0.771667 -0.83048 1.532751 -2.08906-20 1.362303 -1.45809 1.344471 -1.47443 1.687561 -1.86865-10 1.475035 -1.86387 1.460196 -1.95776 1.721271 -2.132950 1.004034 -1.41232 1.119668 -1.48516 1.70534 -2.60267

10 1.179591 -1.90361 1.221367 -1.77897 1.20738 -1.741420 1.100083 -1.9348 1.256186 -1.66937 1.495461 -2.2124830 1.182704 -1.80934 0.940167 -1.25182 1.087983 -1.6023640 1.061459 -1.55429 1.000197 -1.32096 1.112323 -1.4338750 1.097387 -1.33743 1.032448 -1.23148 1.679943 -2.0866260 0.942713 -1.33263 0.859171 -1.37734 1.579155 -2.0706570 1.113512 -1.62083 1.085304 -1.7484 1.681362 -2.6938480 1.007912 -1.62993 1.141654 -1.74292 1.079625 -1.8815190 1.92805 -1.6861 1.391464 -1.54187 1.299706 -1.64393

Impact energy : 1J

Impact energy 2J

Results: fit Trial11J

Trial 2 1J

Trial2J

+ve 1.257 1.119 1.469-ve 1.685 1.68 1.947

max 1.697 1.46 1.959Further Approach:

Dynamic (time-domain) analysis of PVDF sensor

PVDF Piezoelectric Film for monitoring the impact

loading of the structures

Previously-:PVDF sensor was tested for SHM application• Static analysis was performed for impacts of known energies• Repeatability and proportionality was verified for PVDF sensor• Directional dependence of sensor to impacts was analysed

Further Approach:Dynamic (time-domain) analysis of PVDF sensor

Experimental2. Dynamic Analysis

Test Set-Up The composite plate was fixed with 4 sensors as

shown in schematic figure 4 strain gauge were also placed at same position

for direct comparison with sensor Impacts were made at various location with same

energy

is dielectric constant of material

Working Formulae: The voltage generated by a piezo-sensor is given by:

where, C is capacitance of material given by:

Sensitivity of material to strain is defined as,

Conversely, strain to the sensor can be calculated as,

‘Y’ is Young’s Modulus of elasticity

l , b , t represent the length, breadth & thickness of

sensor resp.

Pre-Calculations: 4 PVDF sensors of thickness 120µm, 25µm, 50µm and100µm

were taken and applied at respective positions on the test composite plate.

Using the working formulae the strain developed per unit voltage generated for the sensors was found to be:

Sensor thickness(µm) ε/V (µstrains)120 26.725 128.450 64.24100 32.12

Observations:

Shown below are responses of PVDF sensors and corresponding strain gauges for impact at centre of composite plate (245,170).

Shown below are responses of PVDF sensors and corresponding strain gauges for impact near to sensor1on composite plate (370,230).

Shown below are responses of PVDF sensors and corresponding strain gauges for impact near to sensor2 on composite plate (125,230).

Shown below are responses of PVDF sensors and corresponding strain gauges for impact near to sensor3 on composite plate (370,105).

Shown below are responses of PVDF sensors and corresponding strain gauges for impact near to sensor4 on composite plate (125,105)

Dynamic Analysis: Two important features in dynamic response of sensor are response time and

relaxation time. Since, throughout the experiment responses of sensors were recorded for a single

impact which causes strain to develop in the composite and reduces gradually afterwards.

The rise time and settling time for strain caused due to impact as measured by strain gauge and PVDF sensor will be compared here forth.

Rise time: time taken for sensor output to increase from zero/offset to maximum, corresponding to strain developed in structure.

Relaxation time: time taken for settling of sensor output from max. back to zero/offset (or 0.7of maximum).

Shown here, is the response of RSG1 and PVDF sensror1 for impact at location 1 (75,175)

Response time TrRSG –TrPVDF =0.023sec Rise time

PVDF=17msec RSG=61msec

Settling time PVDF=12.36msec RSG=33.08msec

*Above values are for PVDF sensor1 and RSG1 at centre impact. Similar results were obtained in other trials as well for all sensors.

Results:

Frequency Response Analysis

Cantilever 1 (for RSG and PVDF) 50cm x 1.8cm x 0.4cm Tip distance 4.5cm

Free Vibrations

Schematic of the setup made for comparison of frequency response ofstrain gauge and FBG sensor with PVDF sensor

t

bl

Composite Cantilever

Cantilever 2 (for FBG and PVDF)◦ 25cm x 4cm x 0.1cm◦ Tip distance 4cm

The experiment:

PVDF sensor and RSG were fixed on a cantilever beam of composite material.

The cantilever was forced to free vibrations and responses from RSG and sensor was recorded.

The frequency spectra of the two sensors was obtained and compared.

On another composite cantilever, PVDF sensor and FBG sensor were fixed.

Same procedure was followed for this cantilever as well, for comparison of FBG and PVDF sensor.

Results:

Shown here are the responses for PVDF sensor and strain gauge along with and their respective frequency spectra for first trial.

Results:

Shown here are the responses PVDF sensor and FBG along with their respective frequency spectra for first trial.

Observations:PVDF & FBG

FBG PVDFTrial1 18.43 18.33 37.22 50 117.8 135.6Trial2 18.45 18.24 37.06 50 117.6 135.9

PVDF & RSG RSG PVDFTrial1 13.25 82.65 13 83 240 Trial2 13.64 81.82 13 82 239 Trial3 26.76 170.4 26 170 478 Trial4 26.79 26 170 478 Trial5 25 25 170 480 Trial6 25.44 26.67 51.67 168.3 478.3

Conclusions:

A good agreement was found in frequency spectra of PVDF sensor and RSGs as well as FBGs for free vibration of composite cantilever.

Conclusion

fit Trial11J

Trial 2 1J

Trial2J

+ve 1.257 1.119 1.469

-ve 1.685 1.68 1.947

max 1.697 1.46 1.959

Part 1: X-ray diffraction shows at(110) reflection highest peak is 20.--- and (101) reflection highest peak is 36.----for ZnODielectric as the dielectric constant increases sensitivity decreases as shown in the graph no----Piezo coefficient though piezo coefficient is less for nanocomposites its sensitivity is high Frequency response as the frequency increases PVDF is comes in mV and nano will be in V.

Response time TrRSG –TrPVDF =23msecRise time

PVDF=17msecRSG=61msec

Settling timePVDF=12.36msecRSG=33.08msec

PVDF & FBG FBG PVDF

Trial1 18.43 18.33 37.22 50 117.8 135.6Trial2 18.45 18.24 37.06 50 117.6 135.9

PVDF & RSG RSG PVDFTrial1 13.25 82.65 13 83 240 Trial2 13.64 81.82 13 82 239 Trial3 26.76 170.4 26 170 478 Trial4 26.79 26 170 478 Trial5 25 25 170 480 Trial6 25.44 26.67 51.67 168.3 478.3

Part 2:

Part 3:

Thank You