Structural health monitoring

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Structural Health Monitoring using Naocomposite PVDF-TrFE/ZnO thin film

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  • XRD measurements were carried out in order to study the crystal structure of Zno thin films.
  • The permittivity is a measure of how much the molecules oppose the external E-field
  • Resistive strain guage
  • Structural health monitoring

    1. 1. Sensitivity comparison of PVDF and nanocomposite PVDF- TrFE/ZnO by Pitch Catch measurement
    2. 2. 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 30minutes 2. Zinc oxide dispersion in DMF under sonication for 4hours 3. Same zinc oxide solution is then mix with PVDF-TrFE solution 4. Continuous stirring for 10minutes. 5. Cast the prepared solution on a glass mould keep it in furnce at 120degC for 2hours.
    3. 3. Characterization of PVDF-TrFE/ZnO nanocomposite film  X-ray diffraction for structural study  Dielectric study  Sensitivity : pitch catch measurement
    4. 4. 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
    5. 5. 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.
    6. 6. 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 ZnO 100 10 11.2 0.89 60wt% of ZnO 100 15 5.665 2.64 Further, the poled PVDF-TrFE/ZnO nano-composite samples were evaluated for piezoelectric properties. 1.35 0.89 2.64 0 0.5 1 1.5 2 2.5 3 5 7 9 11 13 15 17 g,VoltageCoefficient(mVm/N) Permittivity 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
    7. 7. 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
    8. 8. 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
    9. 9. 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.
    10. 10. 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.
    11. 11. 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.
    12. 12.  Health monitoring Operational Evaluation Data Feature Extraction Statistical Models Development 1. Strain gages 2. Inclinometers 3. Displacement transducers 4. Accelerometers 5. Temperature gages 6. Pressure transducers 7. Acoustic sensors 8. Piezometers 9. 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.
    13. 13. Monitoring Metrics Measure:  Acceleration  Strain  Climatic Conditions  Curvature  Displacements  Load Identify:  Corrosion  Cracking  Strength  Tension  Location of rebar /delaminations
    14. 14. 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.
    15. 15. Methodology:  Impact of known energy will be made on composite structure at known location  Strain developed in structure will be observed with PVDF sensor  These will be compared with conventional strain gages  Pattern and profile for strains developed under various energies of impact will be taken  These profiles will be used to conversely predict the impact energy and location based on damage occurred
    16. 16. 1. Static Analysis
    17. 17. 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
    18. 18. 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
    19. 19. 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
    20. 20. O b s e r v a t i o n Angle Trial 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 -2.13295 0 1.004034 -1.41232 1.119668 -1.48516 1.70534 -2.60267 10 1.179591 -1.90361 1.221367 -1.77897 1.20738 -1.7414 20 1.100083 -1.9348 1.256186 -1.66937 1.495461 -2.21248 30 1.182704 -1.80934 0.940167 -1.25182 1.087983 -1.60236 40 1.061459 -1.55429 1.000197 -1.32096 1.112323 -1.43387 50 1.097387 -1.33743 1.032448 -1.23148 1.679943 -2.08662 60 0.942713 -1.33263 0.859171 -1.37734 1.579155 -2.07065 70 1.113512 -1.62083 1.085304 -1.7484 1.681362 -2.69384 80 1.007912 -1.62993 1.141654 -1.74292 1.079625 -1.88151 90 1.92805 -1.6861 1.391464 -1.54187 1.299706 -1.64393
    21. 21. Impact energy : 1J
    22. 22. Impact energy 2J
    23. 23. Results: fit Trial1 1J Trial 2 1J Trial 2J +ve 1.257 1.119 1.469 -ve 1.685 1.68 1.947 max 1.697 1.46 1.959 Further Approach: Dynamic (time-domain) analysis of PVDF sensor
    24. 24. 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
    25. 25. 2. Dynamic Analysis
    26. 26. 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
    27. 27. 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.
    28. 28. 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 26.7 25 128.4 50 64.24 100 32.12
    29. 29. Observations:
    30. 30. Shown below are responses of PVDF sensors and corresponding strain gauges for impact at centre of composite plate (245,170).
    31. 31. Shown below are responses of PVDF sensors and corresponding strain gauges for impact near to sensor1on composite plate (370,230).
    32. 32. Shown below are responses of PVDF sensors and corresponding strain gauges for impact near to sensor2 on composite plate (125,230).
    33. 33. Shown below are responses of PVDF sensors and corresponding strain gauges for impact near to sensor3 on composite plate (370,105).
    34. 34. Shown below are responses of PVDF sensors and corresponding strain gauges for impact near to sensor4 on composite plate (125,105)
    35. 35. 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).
    36. 36.  Shown here, is the response of RSG1 and PVDF sensror1 for impact at location 1 (75,175)
    37. 37.  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:
    38. 38. Frequency Response Analysis
    39. 39.  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 of strain gauge and FBG sensor with PVDF sensor t b l Composite Cantilever  Cantilever 2 (for FBG and PVDF) ◦ 25cm x 4cm x 0.1cm ◦ Tip distance 4cm
    40. 40. 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.
    41. 41. Results:  Shown here are the responses for PVDF sensor and strain gauge along with and their respective frequency spectra for first trial.
    42. 42. Results:  Shown here are the responses PVDF sensor and FBG along with their respective frequency spectra for first trial.
    43. 43. Observations: PVDF & FBG FBG PVDF Trial1 18.43 18.33 37.22 50 117.8 135.6 Trial2 18.45 18.24 37.06 50 117.6 135.9 PVDF & RSG RSG PVDF Trial1 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
    44. 44. Conclusions:  A good agreement was found in frequency spectra of PVDF sensor and RSGs as well as FBGs for free vibration of composite cantilever.
    45. 45. Conclusion fit Trial1 1J Trial 2 1J Trial 2J +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 ZnO Dielectric 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 =23msec Rise time PVDF=17msec RSG=61msec Settling time PVDF=12.36msec RSG=33.08msec PVDF & FBG FBG PVDF Trial1 18.43 18.33 37.22 50 117.8 135.6 Trial2 18.45 18.24 37.06 50 117.6 135.9 PVDF & RSG RSG PVDF Trial1 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:
    46. 46. Thank You

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