Structural Health Evaluation of Composite Materials using Lamb Wave Methods

Transcription

1 Structural Health Evaluation of Composite Materials using Lamb Wave Methods NRO Midterm Review Meeting Contract #: NRO-2-C-625 January 14 th, 23 Technology Laboratory for Advanced Composites Department of Aeronautics and Astronautics Massachusetts Institute of Technology Mechanical Design Composites Engineering SHM

2 BAA Team Members Metis Design Corporation Seth S. Kessler, Ph.D. President, Principal Investigator Kristin Jugenheimer Chief Engineer Chris T. Dunn, Ph.D. Research Engineer Massachusetts Institute of Technology Kim B. Blair, Ph.D. Principal Researcher S. Mark Spearing, Ph.D. Associate Professor Abel Hastings Master s Student NRO BAA 22 MidTerm 2

3 Outline Motivations Work plan overall plan results from materials and configuration testing preliminary results from simple coupon tests planned built-up testing test matrix for program Schedule Budget Summary Future research ideas NRO BAA 22 MidTerm 3

4 Program Goals Motivations for SHM within NRO OSL hidden damage possible during manufacture and handling detect and interpret damage in composite primary spacecraft structure lack of access to make quantitative measurements SHM systems requirements for space launch detect/map extent of damage before and/or on the launch pad facilitate launch/no-launch decisions low cost, weight and power, automated, simple to interpret Three areas of research sensor/actuator development (MIT led) testing (joint venture) analysis and system design (MDC led) NRO BAA 22 MidTerm 4

5 Lamb Wave Methods Form of elastic perturbation that propagates in a solid medium actuation parameters determined from governing equations excite A o wave for long travel distances and to minimize clutter Damage can be identified in several ways group velocity approximately (E/ρ) 1/2, damage slows down waves reflected wave from damage can be used to determine locations Research uses piezoelectric sensors to detect energy present in transmitted waves, and reflections using self-sensing actuators NRO BAA 22 MidTerm 5

6 Thin Laminate Results: Finite Element Analysis Figure on left shows FEA results for coupon without damage Figure on right shows FEA results for coupon with 25 mm disbond Movie files show z-displacement at 1 microsecond intervals Can use to measure time-of-flight and observe reflections NRO BAA 22 MidTerm 6

7 Stiffened Plate FEA Results Figure on left shows FEA results for stiffened plate without damage Figure on right shows FEA results for rib with 25 mm disbond Movie files show z-displacement at 1 microsecond intervals Disbond yields fringe pattern in both reflected and transmitted wave NRO BAA 22 MidTerm 7

8 Blind-Test Beam Results Wavelet coefficient plot for beam blind test compares energy content for 5 khz Three control specimens with high density Al core, one has an unknown delamination Controls compared to a specimen with a known delamination Top two clearly have more energy present, and are the controls Bottom two with little energy present are debonded specimens Indicates viability of wavelet method for use in at least simple structures NRO BAA 22 MidTerm 8

9 Work Plan Two phases of research goals design of test configuration and sensor/actuator materials testing of complex sandwich structure specimens Sensors/actuator initiative (work completed in 22) increase reliable, robustness, signal strength of sensor/actuator more efficient sensing schemes (architecture) damage evaluation algorithms in MATLAB large set of simple test results to compare, confirm, and tune (this work is near completion, will be concluded in January) Sandwich structure initiative (work taking place in 23) test sensors/algorithms on more complex geometries observe effects of various core densities and thickness observe effects of disbonds, delams and gaps continue to update algorithms, FEA NRO BAA 22 MidTerm 9

10 Specimen Selection Determination of exact inspection requirements from NRO vehicles of interest expendable launch vehicles material systems graphite/epoxy of greatest concern, both unidirectional and woven layers, most are sandwich construction characteristic flaw type delaminations and disbonds are primary damage, cracks are also important Specimen specifications AS4/351-6 quasi-isotropic laminates [/±45/9] s (unidirectional plies) 3 specimen types: undamaged, Teflon delam, fatigue cracks sandwich structures with quasi-isotropic facesheets and Al core 3 specimen types: undamaged, Teflon delam, Teflon disbonds NRO BAA 22 MidTerm 1

11 Electrical Connections Goals provide easily accessible location to attach ground wire provide an electrical path to the underside of the piezoelectric wafers Desirable attributes should minimize in-plane stiffness, E*t, to maximize actuation metal desirable so that wires can be soldered needs to be thick enough so that it will not tears easily reasonable through-thickness conductivity (resistance less than 1Ω) Bottom electrode brass Alloy 26, 1 mil. thick chosen for conductor 81% less stiff than copper shim used previously Wires co-axial twisted cable for connections, small gauge for flexibility Pb solder with flux NRO BAA 22 MidTerm 11

12 Adhesive Connections Goals adhere bottom electrode to the structure provides electrical path between conductor piezoelectric wafers Desirable Attributes must be removable without damaging structure low application temperature to prevent depoling of piezoelectric wafers uniform thickness to reduce variability in surface mounting high electrical conductivity must minimize G/t to maximum actuation 3M 973 electrically conductive double-sided tape chosen used for both adhesive applications, non-conductive version available 2 mil. thick chosen for adhesive smoother and more repeatable than Ag epoxy NRO BAA 22 MidTerm 12

13 Piezoelectric Wafer Dimensions and Waveforms Actuator and sensor lengths chosen to be.5 based upon equations for 15 khz actuation could be either length or diameter Actuator and sensor configuration concentric disk/ring chosen for sensor/actuator, common ground experiments demonstrated highest amplitudes with this setup yields less electrical noise than self-sensing concepts Optimal actuation waveform 15kHz chosen based on previous work 3.5 sine waves w/hanning window, will also collect data for 5.5 waves Sent Signal NRO BAA 22 MidTerm 13

14 Sensors Material Analysis Use 3-1 piezoelectric coupling properties to output an open circuit voltage in response to strain wave Desirable attributes 2 k31 2 maximize d31( 1 k31) where d 31 is the 3-1 piezoelectric strain coefficient and k 31 is the 3-1 coupling coefficient minimum stiffness to maximize strain of wave passing though it length of (1 + n / 2)*λ where λ is the wavelength and n =,1,2,3, capacitance such that 1 MΩ (oscilloscope impedance) appears as an open circuit to the sensor NRO BAA 22 MidTerm 14

15 Sensors Material Comparison Material k 31 d 31 g 31 Y 11 D (k 31 ) 2 /(d 31 (1 - (k 31 ) 2 ) (-) (p m / V) (mv m / N) (GPa) V / (mm µε) PZT-7A EBL# EBL# EBL# EBL# PZT PZT EBL# PZT-7D PZT-5R EBL# PZT-5B PZT-5A EBL# PZT-5J EBL# PZT-5H EBL# PZT-5M EBL# PZT-5K PT2/PC Chart compares figure of merit for available PZT Separate analysis performed for PVDF Candidate materials which were selected to test broad range EBL#5 EBL#1 EBL#2 EBL#23 EBL#3 NRO BAA 22 MidTerm 15

16 Actuator Material Analysis Uses 3-1 piezoelectric coupling properties to output a strain wave in response to voltage Desirable attributes maximize the strain per volt induced in the structure, P=2πfCV 2 e 31 ( ) ( ) s P P P maximize c where e P 11 + c12 h P + Q11 + Q12 h is the planar piezoelectric stress coefficient, h P and Q are the thickness and stiffness of the actuator, and h S and c P are the thickness and stiffness of the structure minimize the power delivered by the function generator by minimzing the admittance P P 2 ( ) ( ) ( ) P 1 2c11 k ε33 + P P hp c11 + c12 hp + Q11 + Q12 hs where k P is the planar coupling coefficient and ε P the planar permittivity resonant actuators also considered, but low frequencies required large dimensions (3-4 for 25 khz) and had narrow range (25 Hz PZT-5A) NRO BAA 22 MidTerm 16

17 Actuator Material Comparison Material k P s 11 E s 12 E σ P ε33 P e 31 P (-) (p m 2 / N) (p m 2 / N) (-) (nf/m) (N / m V) EBL# PZT-5K PZT-5M EBL# PZT-5H PZT-5J PZT-5B EBL# EBL# EBL# PZT-5R EBL# PZT-5A EBL# PZT EBL# PZT-7D EBL# PZT EBL# PZT-7A BT Chart compares figure of merit for available PZT Separate analysis performed for resonant actuators Candidate materials which were selected to test broad range EBL#23 (disk) EBL#3 EBL#2 EBL#1 (disk) EBL#5 NRO BAA 22 MidTerm 17

18 Sensors/Actuator Material Testing Sensors bonded to circular Al plate EBL#5 (PZT-7A) -.5x.25x.1", 1.x.25x.1" EBL#23 (PZT-5K) -.5x.25x.1" EBL#3 (PZT-5H) -.5x.25x.1",.5x.5x.1" EBL#2 (PZT-5A) -.5x.25x.1",.5x.25x.2" EBL#1 (PZT-4) -.5x.25x.1 DT2-52K/L PVDF SDT1-28K PVDF Actuator disk in center EBL#23 (PZT-5K).5"(diameter)x.1" EBL#1 (PZT-4).5"(diameter)x.1" Tests performed actuated from 1 khz to 25 khz 2 V peak to peak duplicates tested for each on separate plates tests also performed in reverse NRO BAA 22 MidTerm 18

19 Sensors Material Results 7 6 Amplitude of sensed signal (mv) Max Avg Min PZT4 PZT5A PZT5A thick PZT5H PZT5H wide PZT5J PZT7A PZT5K DT2-52K/L SDT1-28K PZT-5A, PZT-5H, PZT-5J, PZT-5K all comparable maximums PZT-5A and PZT-5J have highest means and minimums PZT-5A selected because of bandwidths of maximum peaks NRO BAA 22 MidTerm 19

20 Actuator Material Results 4 35 Amplitude of sensed signal (mv) Max Avg Min PZT4 PZT5A PZT5A thick PZT5H PZT5H wide PZT5J PZT7A PZT5K DT2-52K/L SDT1-28K PZT-5H and PZT-5K have highest amplitudes, PZT-5A close Overall averages were lower due to poor center sensor PZT-5A selected due to better actuation temperature stability NRO BAA 22 MidTerm 2

21 Temperature Stability PZT-5A has the best temperature stability of PZT materials PZT-5H has worst stability of PZT materials PZT-5K has comparable thermal properties to PZT-5H NRO BAA 22 MidTerm 21

22 Actuator/Sensor Schematic Sensor Actuator Electrically conductive tape Brass shim stock Electrically conductive tape Complete sensor/actuator NRO BAA 22 MidTerm 22

23 Data Collection Setup Actuation from LABVIEW VI file on Dell Inspiron Laptop NI DaqPad data acquisition board HP oscilloscope used to capture data Will be integrated into one VI file for next series of tests NRO BAA 22 MidTerm 23

24 Data Reduction Goals Analysis of data gathered during previous research to develop set of algorithms and procedure for comparison presence and severity of damage location of damage differentiation between damage types Perform/refine procedure for newly collected data Automated algorithm to identify damage information NRO BAA 22 MidTerm 24

25 Data Reduction Old Procedure Method determined from previous research focused on db3 wavelet decomposition and voltage signal comparison Subjective results, lots of noise and drift Only can decipher presence of damage, maybe severity NRO BAA 22 MidTerm 25

26 Data Reduction New Procedure Procedure developed within Matlab to reduce data bandpass filter designed to remove low frequency drift and high frequency electrical noise without affecting signal shape perform wavelet decomposition using Morlet mother wavelet to breakdown signal energy distribution between khz plot integrated voltage over time yielding total received energy to determine presence and severity of damage plot normalized wavelet energy at driving frequency of 15 khz to determine time of arrival thus damage location plot normalized energy received for across wavelet spectrum to determine type of damage need 4 sets of plots: transmitted & reflected for 2 locations Need more consistent signals from new experiments to refine algorithms for automatic determination of damage NRO BAA 22 MidTerm 26

27 Data Reduction Outputs Control vs Fatigue Crack Control vs Teflon Delam New method yields sets of three plots to compare the measured signal with the control signal Fatigue cracks reduce energy level, lag, spread spectrum Controlled delam has energy dissipation, lag in arrival time NRO BAA 22 MidTerm 27

28 Work Plan Testing for 22 Sensor/actuator test series #1: piezopatch verification 1-D linear wave scans on 25cm square plate specimens AS4/351-6 quasi-isotropic laminates [/±45/9] s 3 of each type: undamaged, Teflon delam, fatigue cracks measure transmission and reflection from each end Sensor/actuator test series #2: complex testing make any necessary adjustments to piezopatches test multiple damage: plate with delam+cracks, plate with 2 delams blind test: plate with randomly placed 1 Teflon strips on plate Slightly behind schedule due to lead time in receiving PZT NRO BAA 22 MidTerm 28

29 Experimental Results Controls I signals (V) total energy (ms) energy arrival peak freq (khz) Highly reproducible signal between same set of actuators and sensors tested several times NRO BAA 22 MidTerm 29

30 Experimental Results Controls II signals (V) total energy (ms) energy arrival peak freq (khz) Signal shape remains unchanged when propagating in reverse direction, other metrics remain similar NRO BAA 22 MidTerm 3

31 Experimental Results Controls III signals (V) total energy (ms) energy arrival peak freq (khz) Similar response across several different pairs of equally spaced actuators/sensors on same plate NRO BAA 22 MidTerm 31

32 Experimental Results Controls IV signals (V) total energy (ms) energy arrival peak freq (khz) Similar response between pairs of actuators/sensors located on several undamaged plates NRO BAA 22 MidTerm 32

33 Experimental Results Delamination signals (V) total energy (ms) energy arrival peak freq (khz) Delaminated signal is time-lagged, and has slightly lower energy content. Frequency bandwidth remains similar NRO BAA 22 MidTerm 33

34 Experimental Results Microcracks signals (V) total energy (ms) energy arrival peak freq (khz) Some matrix cracking caused a slight time delay, less tail energy and a small shift to a higher frequency bandwidth NRO BAA 22 MidTerm 34

35 Experimental Results - Conclusions Overall setup has increased signal strength nearly a factor of 4 over the previous configuration New decomposition algorithm appears to work well with new data for transmitted wave Undamaged response is very reliable/reproducible Controlled damage does not have significant effect on most parameters, however voltage signal is lagged Reflected signal not yielding much information thus far need to perform further analysis, maybe look at other frequencies could affect ability to pinpoint damage location Will continue to collect more data and try alternate configurations over the next month while manufacturing NRO BAA 22 MidTerm 35

36 Work Plan Testing for 23 Sandwich structure test series #3: core testing uniform sandwich plates with laminated face sheets several cores varying E and t: sheet Al, solid Al, high and low density Al honeycombs, Nomex, Rohacell one plate of each w/disbond and undamaged Sandwich structure test series #4: facesheet testing vary facesheets of high density Al sandwich plates outer ply of, 9, and 45, still quasi-isotropic one plate of each w/disbond and undamaged Sandwich structure test series #5: complex testing non-uniform sandwich plates with and without disbond: half solid half honeycomb and solid between two pieces of honeycomb gap between two pieces of high density Al honeycomb damage in facesheet on high density Al honeycomb sandwich plate NRO BAA 22 MidTerm 36

37 Work Plan Testing for 23 High density Al honeycomb Low density Al honeycomb Nomex core Rohacell core High density Al honeycomb and solid Al core High density Al honeycomb surrounding solid Al core High density Al honeycomb with small gap NRO BAA 22 MidTerm 37

38 Test Matrix Control Delam Crack Disbond Blind Test #1 Thin laminate 3 (3) 3 (3) 3 (3) Test #2 Thin laminate 1 (3) 1(3) 1 (12) Test #3 Sheet Al 1 (3) 1 (3) Bar stock Al 1 (3) 1 (3) HD Al core 1 (3) 1 (3) LD Al core 1 (3) 1 (3) Nomex 1 (3) 1 (3) Rohacell 1 (3) 1 (3) Test #4 9 ply on top 1 (3) 1 (3) 45 ply on top 1 (3) 1 (3) Test #5 Core/Bar 1 (3) 1 (3) Core/Bar/Core 1 (3) 1 (3) Core/Gap/Core 1 (3) 1 (3) HD Al core 1 (3) 1 (3) NRO BAA 22 MidTerm 38

39 Work Plan Analysis for 23 Application and refinement of MATLAB algorithms in support of the sandwich structure tests to interpret results and significance of each variable Finite element modeling of each of the specimen using plane strain elements for detection concepts More robust automation software, try to integrate with data acquisition system New system configurations to be considered (elliptical method) NRO BAA 22 MidTerm 39

40 Design Initiative Requirements Calculations Sensors Initiative Sensors Actuators Backing Self-sensing Wiring Testing Initiative Manufacture #1 Series #1 Series #2 Manufacture #2 Series #3 Series #4 Series #5 Analysis Initiative Old data New data Automation Kick-off Gantt Chart Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun NRO BAA 22 MidTerm 4 z Mid-term Final review

41 Budget Contract #: NRO-2-C-625 $35, $3, $25, Dollars $2, $15, $1, NRO Payments Predicted Burn Rate Actual Expenditures Anticipated Burn Rate $5, $ June July August September October November December January February March April May June Month NRO BAA 22 MidTerm 41

42 Testing configuration Summary this task has been very successful, important to future research selection of backing materials and adhesives with best properties selection of PZT material for best actuation and sensing new architecture of concentric disk/ring yields better signal Analytical work slightly behind schedule due to compressed experimental schedule MATLAB algorithms produce clearer ways to compare signals provides path towards automation, will continue to work in Q3 Experimental work basically on schedule now, past month has been intense manufacturing/testing to start in late Jan. for sandwich specimens SPIE conference and SHM workshop presentations 3 rd Quarter review over phone in late March 23 NRO BAA 22 MidTerm 42

43 M.E.T.I-System Suite of Damage Detection Systems M.E.T.I.-NDE portable quick and accurate non-destructive evaluation device for composite structures based on Lamb wave methods M.E.T.I.-Strip capable of detecting damage present between any pair of narrow strips ideal for cylindrical structures M.E.T.I.-Patch patches to be mounted in critical regions by a thermoplastic backing yields a detailed damage report for the area located below its surface M.E.T.I-Chip small chips will be designed to scan large area (~2m) detect presence and location of both surface and subsurface damage NRO BAA 22 MidTerm 43

44 SHM System Components Architecture: integration of system components for efficiency, redundancy and reliability real-time VS discontinuous monitoring Damage characterization: identification of damage types for target application quantification of damage signature and effect on structural integrity Sensors: strain, vibration, acoustic emission, impedance, magnetic field, etc. active VS passive sampling methods Communication: both between neighboring sensor cells and global network wired VS wireless Computation: locally control sensing systems and acquire data process and combine local and global data Algorithms: interpretation of damage location, severity, likelihood of failure Power: supply electricity to each component Intervention: actively mitigate damage, repair damage Honeywell MEMS sensor Rockwell RF receiver NRO BAA 22 MidTerm 44

45 M.E.T.I.-Patch Schematic Wireless communication chip Acoustic emission sensor Rechargeable polymer battery Lamb wave sensor Modal analysis sensor Data acquisition, storage device Inductive Power loops NRO BAA 22 MidTerm 45

46 Proposed Research Comparison of behavior and reliability of SHM viable NDE methods different materials (metals, CFRP, GFRP) manufacturing processes (uni-tape, woven fabric, filament wound) Attenuation study compare sensor density and power requirements for composite varying thickness, stiffness, density, core material and curvature Patterned electrode formations for actuator beam steering would enable a sonar-like imaging capability for detecting damage using either Lamb wave or acoustic emission Development of a wireless SHM capabilities data acquisition and actuator function generating system matching size, power and speed specifications for an SHM system NRO BAA 22 MidTerm 46

47 Proposed Research Development of a thin-film polymer rechargeable battery wireless inductive-loop recharging system matching size and power specifications for an SHM system Study of packaging techniques for all of the SHM components isolate from harsh natural, mechanical,and electrical environments Testing of the developed sensor patch on large built-up structures in noisy operating environments (natural, mechanical and electrical) Economic study of SHM system implementation strategies provide justification for the use of these systems optimal strategy for their introduction into military and civil applications NRO BAA 22 MidTerm 47

48 M.E.T.I-System Team Metis Design Corporation (Dr. Kessler) team lead, system architecture, system integration, algorithms MIT Department of Aeronautics/Astronautics (Dr. Spearing) sensor optimization, structure interface, manufacturing, packaging MIT Department of Materials Engineering (Dr. Sadoway) polymer battery, wireless recharging system University of Michigan Aerospace Department (Dr. Cesnik) actuator optimization, environmental/dynamic testing MicroStrain (Townsend) wireless data acquisition, wireless actuation, data storage Boeing (White)? customer voice, interface requirements, weight/cost limits, testing NRO BAA 22 MidTerm 48