Durability and Survivability of Piezoelectric Wafer Active Sensors Mounted on Aluminum Structures for Aerospace Vehicle Health Monitoring Victor Giurgiutiu, Bin Lin, James Doane University of South Carolina AEROMAT-2005 Integrated Systems Health Monitoring Session 6-9 June 2005, Orlando, FL Acknowledgments: Air Force Office of Scientific Research grant # FA9550-04-0085, Capt. Clark Allred, PhD, program manager Air Force Research Laboratory contract through Universal Technologies, Inc. Dr. Blackshire, Dr. Nagy
Outline Introduction to piezoelectric wafer active sensors () SHM E/M Impedance Durability and survivability of Temperature cycling Outdoor exposure Submersion exposure Large strains and fatigue loads Conclusions 2
Piezoelectric Wafer Active Sensors () Conventional ultrasonic transducer 7 mm PIEZO ELEMENT Rivet head ~ V(t) t t Lamb wave 3 P-wave λ/2
Passive Sensors Monitor the health of the structure over time Sensor can listen to the structure but can not interact with the structure SHM Technology Active Sensors Interact with the structure by sending a signal and then listen to the structure s response 4
Impedance-based Structural Health Monitoring New Structural Health Monitoring (SHM) method. Real-time structural damage assessment. The electrical impedance of the PZT material can be directly related to the mechanical impedance of a host structural component. The change in the structure s impedance is attributed to the change in integrity of the structure due to damage. The real part of electric impedance is more reactive to damage or changes in the structure s integrity than the imaginary part Electromechanical Impedance is Quality Control Method 0 Re Z, Ohms 40 30 20 -mm Crack Rivet head Piezoelectric active sensors #1 #2 #3 #4 200 0 1800 2600 Frequency, khz Sensor 1 Sensor 2 Sensor 3 Sensor 4 5 From Dr. Giurgiutiu and Dr. Zagrai s paper
Objective Explore the durability and survivability issues on associated with various environmental conditions and fatigue Improve properties, layer deteriorates in time under environmental attacks (temperature, humidity, etc.). Improve properties, layer deteriorates in time under fatigue attacks Bond layer, 0.2-mm thick Substrate structure, 1-mm thick -structure bond layer 6
Durability under Thermal Cyclic Temperature (F) 200 190 180 170 160 150 140 130 120 1 0 50 150 200 250 Time (min) y 00 01 (FREE) Initial measurement Oven after 1 cycles Oven after 500 cycles Oven after 0 cycles Oven after 1500 cycles 00 02 (Bonded) Bonded Oven after 1 cycles Oven after 500 cycles Oven after 0 cycles Oven after 1500 cycles Oven after 1600 cycles Oven after 1700 cycles Re(Z) (Ohms) 0 Oven after 1700 cycles Re(Z) (Ohms) 0 7 1 300 500 700 900 20 30 40
Development of suitable damage metrics and damage identification algorithms The damage index is a scalar quantity that serves as a metric of the damage present in the structure. RMSD Damage Index Re(Z) (Ohms) 00 0 0.8 0.7 02 (Bonded) 20 30 40 Bonded Oven after 1 cycles Oven after 500 cycles Oven after 0 cycles Oven after 1500 cycles Oven after 1600 cycles Oven after 1700 cycles RMSD = N 0 Re( Zi) Re( Zi ) N 0 Re( Zi ) 2 2 RMSD 0.6 0.5 0.4 0.3 0.2 0.1 8 0 0 500 0 1500 2000 Cycles
Acoustic Microscope Imaging 00 E/M Impedance 02 Bonded Oven after 1700 cycles Adhesive/ Bad 02 Re(Z) (Ohms) 0 00 20 30 40 (Bonded) Good Re(Z) 0 9 20 30 40 Scanning Area: mm x mm Collaboration with Prof. Nagy
Outdoor Exposure of Temperature 90 80 70 60 50 40 30 20 0 MAX MIN AVE /25/2004 11/25/2003 12/25/2003 1/25/2004 2/25/2004 3/25/2004 4/25/2004 5/25/2004 6/25/2004 7/25/2004 8/25/2004 9/25/2004 (F) 11/25/2004 12/25/2004 1/25/2005 2/25/2005 3/25/2005 4/25/2005 5/25/2005 Rainfall 3.5 3 2.5 2 1.5 1 0.5 0 11/ 25/ 2003 1/ 25/ 2004 3/ 25/ 2004 5/ 25/ 2004 7/ 25/ 2004 9/ 25/ 2004 (inch) 11/ 25/ 2004 1/ 25/ 2005 3/ 25/ 2005 5/ 25/ 2005 Adhesive M-Bond 200- cyanoacrylat e adhesive with catalyst M-Bond AE- 2-part % epoxy system adhesive No coating -22-33 M-Coat A- Polyurethane -23-34 M-Coat C-Silicon -27-35 M-Coat D-Acrylic -28-36 Protective coating
Free Impedance Spectrum under Outdoor Exposure Settling in effect. 00 0 Impedance spectrum (Free 43 ) Baseline 1 week week 20 week 30 week 40 week 50 week 60 week 70 week No significant change Re(Z) Damage index shows the impedance spectrum remains constant. RMSD 1 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 300 500 700 900 Damage index (Free 43) 0 20 40 60 80 Weeks 11
Bonded Impedance Spectrum under Outdoor Exposure Settling in effect. Significant change has been recorded. 12 Damage index shows the impedance changes. 1 0.9 Damage Index ( 22) RMSD 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 20 30 40 50 60 70 80 Cycles
Displacement Field Imaging 00 (Bonded) 60 week 0 Re(Z) 20 30 40 00 02 Bonded 0 Re(Z) 20 30 40 13 Collaboration with Dr. Blackshire
submersion tests Distilled water Saline solution Hydraulic fluid MIL-PRF- 83282 Synthetic hydrocarbon Hydraulic fluid MIL-PRF- 87257 Synthetic hydrocarbon Hydraulic fluid MIL-PRF- 5606 Mineral Aircraft lube oil MIL-PRF-7808L Grade 3 Turbine engine synthetic Aviation kerosene 14 RESULTS: 60 weeks without failure except in saline solution which failed after 15 weeks
Impedance Spectrum under Submersion Exposure A little impedance changes in distilled water 00 0 00 - Distilled Water Baseline 8 week 13 week 28 week 54 week The submerged in saline solution survived only a little over 85days due to the detachment of the soldered connection Re(Z) 1 300 400 500 600 700 800 The corrosive effect of the saline solution. 00 0 01 - Saline Water 1week 3 week 8 week 13 week Re(Z) (Ohms) 15 1 300 400 500 600 700 800
Large Strain and Fatigue Testing Specimen MTS Testing Machine Data Acquisition PC Large strain specimen Fatigue specimen 1-mm diameter hole 7-mm Wheatstone bridge Impedance Analyzer 16
Large-Strain Testing Minimal changes up to 4000 µε (0.84Y) Failure at 7300 µε (1.13Y) 200 150 Re(z) (Ohms) 50 0 17 Failed @ 7300 µε -50 1 120 130 140 150 160 170 180 190 200 3000 microstrain 4000 microstrain 5000 microstrain 6000 microstrain
Fatigue Survivability Tests F1 F2 F3 F4 F5 Max load 24 N 1560 N 1335 N 1156 N 67 N Min load 2 N 156 N 134 N 116 N 7 N Mean load 1157 N 858 N 734 N 636 N 587 N Cycles to failure 178 kc 670 kc 1.3 Mc 6.25 Mc 12.2 Mc 200 180 Stress concentration Maximum Stress, MPa 160 140 120 80 60 40 20 0 18 1.E+04 1.E+05 1.E+06 1.E+07 Cycles to failure, N
Conclusions Piezoelectric wafer active sensors () are a promising technology for active structural health monitoring Durability and survivability of Temperature cycling Outdoor exposure Submersion exposure Large strains and fatigue loads Further work needs to be performed to better understand and gain confidence in this emerging technology 19
20 Thank you!