Zukunft der Faserverbundwerkstoffe in der österreichischen Luftfahrtindustrie und -forschung Montag, 1. Dezember 2008, TU Wien

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1 Structural Health Monitoring Potential for smart composite aircraft structures M. Scheerer, ARC Zukunft der Faserverbundwerkstoffe in der österreichischen Luftfahrtindustrie und -forschung Montag, 1. Dezember 2008, TU Wien

2 Definition Structural Health Monitoring (SHM): Implementation of a NDE-System (Non- Destructive Examination) in a component or structure for a continuous monitoring of the structural status (health) of the component / structure in operation. Imitation of the nervous system of the human body (Speckmann) Determination of remaining life Algorithm for damage analyses Failure mechanism of materials NDT Methods for Online Inspection 2

3 Certification Issues 100% 90% 60% 50% 33% -10% -30% -10% Hachenber D. 2002, The role of Advanced Numerical Methods in the Design and Certification of Future Composite Aircraft Structures 5th world congress on Computational Mechanics WCCM V, Vienna, Austria, July 7-12, 2002 Motivation for SHM Failure strain level (Mean) Scattering (B-value) Stress intensity (impact & notch Sensitivity) Environment (hot/wet) Ultimate Design Strain ( Ultimate Load j=1.5) Required Safety Factor 1.5 Limit design Strain Max. load spectrum ( Limit Load j=1.0) Potential for SHM by impact & delamination detection Individual Maintenance / Repair Strategies From Time Based Maintenance to Condition Based Maintenance Control of difficult / impossible to inspect parts Optimized Design To date: uncertainties in integrity of their manufacture susceptibility to barely visible impact damage (BVID) Design load: 33% of failure load compared to 60% in metals 3

4 Types of Monitoring System 4

5 Type of Sensors Sensor Technologies Smart Materialies Fibreoptics MEMS Piezos SMA s CNT s FBG s EFPI BOTDR Electr. Mechan Therm Mechan Elektr. Mechan Displacement / strain Optical properties 5

6 Type of Methods SHM - Methods Acoustic Methods Electrical Methods Stat. / dyn. strain CVM Acoustic Emission Guided Waves Phased Array Impedance Eddy current strain vibration Defects creates acoustic signal Acoustic signal modified by defect Acoustic beam modified by signal Impedance from piezo modified by defect EM field modified by defect Local strain modified by defect Global vibration modified by defect Pressure exchange by defect 6

7 Comparison of the SHM Methods 100 Modal Analyses (E) Optical Fibre (S) size of damage [mm] Sensor coverage: entire plate (E) Half Plate (H) Sensor Area (S) size of damage [mm AE (H) Optical Fibre (S) Strain Gauge (S) Eddy Current (S) Strain Gauge (S) Modal Analyses (E) Lamb Wave (E) Sensor coverage: entire plate (E) Half Plate (H) Sensor Area (S) Lamb Wave (E) Acoustic Emission (H) Eddy Current (S) power required by sensor [W] size of sensor [mm] 7

8 Research Activities at ARC Fatigue Damage Quantification by On-line Acoustic Emission and FBG strain analyses (Funded within the Austrian Aeronautics Research K-Net and the EU FP6-Project SMIST) Impact Damage Quantification by On-line Acoustic Emission Analyses (Funded within the EU FP6-project Cost Efficient Small AiRcraft) Project ASHMOSD - Austrian Structural Health Monitoring System Demonstrator (Funded within the Take Off Program) 8

9 Fatigue Damage Quantification by On-line Acoustic Emission and FBG strain analyses Test set-up: 4-point bending tests with AE and FBG sensors Test campaign: 4-point bending tests at different load levels and frequencies in deflection and load control 9

10 Fatigue Damage Quantification by On-line Acoustic Emission and FBG strain analyses av. hit rate [s-1] bl-55: 1.36% strain control (stress: 795 MPa) Test01-85%: 755 MPa stress control (strain: 1.3%) 8-bl-55: rel. hit rate Test01-85%: rel hit rate cycles Rel. stiffness vs. average hit rate relative stiffness [%] relative stiffness Rel. stiffness and average hit rate vs. cycles large scatter band average hit rate [s-1] 8-bl-55 Test01-85% 10

11 Fatigue Damage Quantification by On-line Acoustic Emission and FBG strain analyses Input: Transient AE Signals (as function of time) Model (FEM) Model of structure with defects Signal processing Time - Frequency Analyse Max. Amplitude (for each time window), Frequency at max. Amplitude Location Processor Location of located Event (LE), Clustering (Number of LE in a defined region) Filtering of LE (Noise from other sources than defects) Frequency Range, Amplitude Range, Position (position of pressure and support roles) Weighting of filtered LE based on FEM Effect of position of local damage on the global stiffness reduction Normalization of the weighted, filtered LE by results from static tests Optimization loops rel. stiffness FPF (20 x 20 mm²) SPF (20 x 20 mm²) Correl. Fact.: relative localized weighted hit rate Filtered, localized and FEM based weighted relative hit rate Correlation between filtered, localized and FEM based weighted relative hit rate and global stiffness change Correlation between filtered, localized and FEM based weighted relative hit rate and location, (type) and severity of damage rel. local stiffness rel. local hit rate / (cycle x area) [1/s cm²] 11

12 rel. local hit rate / cycle area [1/s cm²].. Fatigue Damage Quantification by On-line Acoustic Emission and FBG strain analyses FPF SPF TPF rel hits/cycle calculated rel stiffness position [mm] rel. local stiffness rel. local stiffness rel. local hit rate / (cycle x area) [1/s cm²] 12

13 Impact Damage Quantification by On-line Acoustic Emission Analyses Impact Damage Introduction: 0 / 5 J / 10 J / 15 J / 20 J Damage quantification by conventional US C-san Bending tests with AE Monitoring : 33% of maximum strain / 100 cycles 13

14 Impact Damage Quantification of GFRP Plates by On-line Acoustic Emission Analyses US C-scan AE-Monitoring Results 10 J 20 J 14

15 AE based Damage assessment of structures / components Coupon Reference AE measurment on coupon with defined load before damage Component Reference AE measurment on component with defined load before damage Introduce different amounts of damage Verify amount of damage with conventional NDT AE Measurment of coupon with defined load for different amounts of damage Calculate correlation function between relative AE feature and amont of damage Databasis Usage of component AE Measurment of structure with defined load after usage Evaluation of relative AE feature Comparrison with the databasis Damage status of the structure 15

16 ASHMOSD Austrian Structural Health Monitoring System Demonstrator Goal Development of an Austrian SHM system for on-line monitoring of aeronautic structures Research Partners: ARC, IMA, Joanneum, ÖAW, Profactor; SCCH Industrial Partners Bernard Ing, FACC, Siemens Cooperation: EADS-IW, EADS-M, Airbus Projekt-Data Coordination: ARC Volumen: 3.6 M Duration: 3 years / Start: Oct

17 8.00E E E E E E E E E E E E E E -04 right left back Austrian Research Centers GmbH - ARC SHM at ARC: Overall Goal Adaptive Structures Off- & Online Diagnostic Prognostic Remaining Life 7B-L-55, 10 cycles 1000 cycles cycles relative stiffness relative max hit rate Conventional NDT & mechanical Testing 17

18 Conclusion SHM: Reduced Maintenance Cost via Condition Based Maintainance (CBM) and Optimized Aircraft Design Potential for Composite Structure Design as Smart Structure by implementing a SHM system Still a lot of technology challenges Accurate Material Models incorporating damage evolution and fatigue Validation of diagnostic systems for damage size and location identification Techniques for sensor embedding & connection (including wiring) Power & Data Handling Validation of SHM under aircraft service condition including repair & replacement procedures 18

19 Future Aspects for SHM SHM Prognosis Diagnosis Prognosis Residual Life & Performance Prediction Smart Sensing Technologies Material Characterization Structural & Damage Modeling M. Scott et al., Structural Health Monitoring The Future of Advanced Composite Structures, 5th Int. Workshop on SHM, Stanford CA, Sept Through Life Monitoring including Process Monitoring 19