Structural Health Monitoring (SHM) Jaap Heida Aerospace Vehicles Division NANDTB, NDT Expert Day 18 November 2009 Nationaal Lucht- en Ruimtevaartlaboratorium National Aerospace Laboratory NLR
National Aerospace Laboratory NLR Staff of 700 Turnover ~ 80 MEuro/yr 2
NDI expertise at NLR Evaluation of NDI techniques Investigation of NDI reliability - POD, false calls NDI of hybrid/composite materials - Glare, CFRP, RTM Full scale tear-down and inspection - EPAF TDI of RNLAF F-16A aircraft J-239 - LHS wing TDI of Lockheed P-3C Orion - Airbus A380 Megaliner Barrel TDI Structural health monitoring (SHM) Level III assistance, training and examination of NDI personnel Modelling of NDI (CIVA nde ) 3
Contents Structural health monitoring (SHM) Principle and objectives of SHM NLR experience with SHM SHM techniques/sensors Applicability of SHM 4
Structural health monitoring (SHM) Long-term and in-service monitoring of the condition and damage state of vehicle systems in operation using advanced sensors that are permanently attached to the structure Main objectives: - Introduce condition-based structural maintenance (replacing scheduled maintenance) - Reduce the cost of ownership (inspection and maintenance) - Improve the system operational availability while maintaining current safety levels Additional objectives: Solve problems of poor accessibility and remove the human factor of inspector fatigue 5
Conventional scheduled maintenance Shearography Manual UT NH-90 tail fatigue test UT C-scan Pulsed thermography 6
Structural health monitoring (SHM) Kumar, Acellent Technologies 7
SHM features Part of on-board systems (centralised or distributed) with lowprofile sensors that are permanently attached to the structure Operation on-line during the flight (vehicle in operation) or off-line on the ground Static system that interrogate the structure at predetermined intervals (active measurement), or dynamic system that require continuous, reliable monitoring (passive measurement) Global inspection of large surface areas, or local inspection of highly critical areas (hot spots) 8
NLR experience with SHM EU projects MONITOR (Monitoring On-line Integrated Technologies for Operational Reliability) AHMOS I + II (Active Health Monitoring System) CESAR (Cost Effective Small Aircraft) FP7? NIVR SRP projects SHM system for composites based on optical FBG sensors (embedded and surface mounted) Dutch Space project SHM applications for hot metallic structures RNLAF project Optical FBG sensors for strain measurement on metallic structure 9
Active Health Monitoring System Prototype demonstration of modular structural health monitoring system for military platforms NLR participation: - Instrumented NLR test bench - Central computer for data acquisition - Eddy current array inspection - Evaluation of AHMOS project AHMOS ACTIVE HEALTH MONITORING SYSTEM 10
AHMOS-II flight test Hawk MK1A jet with flight test pod 2 metallic test specimens 11
AHMOS data presentation, level 1 12
AHMOS data presentation, level 2 13
AHMOS data presentation, level 3 14
SHM techniques Piezoelectric sensor Fibre optic sensor Eddy current sensor Comparative vacuum monitoring (CVM) Other sensors Corrosion sensor, strain gauge, accelerometer, temperature sensor, heat flux sensor, leak detection, MEMS, etc. 15
Piezoelectric sensor Dynamic system (passive mode) System that requires continuous, reliable monitoring - Acoustic emission Static system (active mode) System that interrogates the structure at predetermined intervals - Phased array - Lamb wave - SMART layer 16
Acoustic emission PE sensors in the passive mode Real time and on-line detection of defect initiation and defect growth Global monitoring of large specimens (Localisation of defects may be difficult) 17
Acoustic emission Monitoring of superalloy specimens with TBC during creep CM186 SX specimen at 950 C and 160 MPa 18
UT phased array inspection 19
UT phased array (SWISS sensor) 20
Lamb wave inspection Combination of transverse and longitudinal waves in plate-like structures. Propagation over long distances Transmission measurements with sensors in pitch- catch configuration Localisation and sizing of damage is difficult AHMOS pod Disbond detection in an Al stringer assembly a) undamaged structure and b) disbond 21
UT SMART layer 22
UT SMART layer Detection of crack growth and disbond growth of a bonded repair on F-16 aircraft structure Stanford University, CA 23
UT SMART layer Detection of crack growth and disbond growth of a bonded repair on F-16 aircraft structure 24
Fibre optic sensor (FOS) technology Main applications: Structural damage detection - environmental, accidental Strain/temperature/vibration monitoring Process monitoring of composite materials - state of cure during fabrication - internal strain after fabrication Best prospect for SHM exploitation of FOS technology: Fibre Bragg Gratings (FBG) 25
Fibre optic Bragg grating sensor λ B λ B = 2n.Λ 26
Fibre optic Bragg grating sensor CASA composite inter-tank demonstrator with embedded and surface mounted optical fibres (McKenzie, ESA, 2005) 27
Fibre optic Bragg grating sensor Advantages: Small diameter, light weight, flexible, non-electrical and EMI immunity, low signal loss High sensitivity (~ 1 pm/με) Multiplexing of multiple FBG s per fibre Possibility of embedded sensors in composites Limitations Vulnerability of the sensor system Sensor/connector integration into the structure 28
Eddy current inspection 29
Eddy current array sensor - AHMOS project - Local detection of cracks, monitoring of limited number of critical areas ( hot spots ) in metallic aircraft structure High-frequency (800 khz), flexible, absolute sensor Low-frequency (1-20 khz), ring-shaped, reflection sensor 30
Eddy current array sensor Evaluation of EC sensors using specimens with artificial defects and real fatigue cracks. TRL4 demonstrated High-frequency absolute sensor for detection of surface cracks. Flexible sensor, reliable signals for radii down to 7 mm Low-frequence reflection sensor for detection of sub-surface cracks in fastener holes. Practical detection depth in Al about 4 mm 31
Comparative vacuum monitoring (CVM) Vacuum technique developed by SMS Ltd. (Australia) cross-section dwarsdoorsnede top bovenaanzicht view sensor vliegtuigcomponent to naar SIM8 oppervlaktescheur surface crack polymer sensor 32
Comparative vacuum monitoring (CVM) CVM portable version CVM lab kit CVM recording 33
CVM measurements on FSW panels 25000 CVM CVM reading delta P [Pa] 20000 15000 10000 5000 0 11:36:00 11:37:26 11:38:53 11:40:19 11:41:46 11:43:12 11:44:38 11:46:05 11:47:31 Time [hrs:min:sec] 34
Accelerometer Impact detection system (IDS) for WLE of NASA Space Shuttle (result of Columbia crash, 2003) On aft surface of each WLE spar: - 66 accelerometers - 22 temperature sensors (Studor, NASA, 2007) 35
Multifunction sensor (Hunter, NASA GRC, 2005) (Wrbanek, NASA GRC, 2001) 36
Applicability of SHM techniques - hot metallic structures - SHM technique Defect type Impact event Fatigue crack Fastener damage Seal leakage Bondline failure PE passive (AE) ++ + 0 - + PE active - Phased array - Lamb wave - SMART Layer - - + ++ + + - ++ + Optical FBG + - - + + Strain gauge 0 - - - - Accelerometer ++ - - - - Temp. sensor - - - ++ - Heat flux sensor - - - + - Leak detection - - - + - ++ primary method, + secondary method, 0 method applicable but not practical or with limitation, - method not applicable - - - + + + 37
SHM application Slow transition from laboratory to field application Optimised sensor layout (small-scale damage to be detected in large-scale structures) Self-diagnostics (damage to the structure or damage to the sensor itself) Environmental compensation Probability of detection Damage quantification Robustness and redundancy of the SHM system (Beard and Farrar, 2007) 38
Near-term and far-term application of SHM Near-term application Retrofitting existing air vehicles with SHM systems to detect well-defined damage in known hot spots Far-term application Additional maturation of current SHM technologies that will be designed-in to the structure. Result: continuous, autonomous, real-time, inservice monitoring of the entire vehicle structure (Derriso, AFRL, WP AFB, 2007) 39
AFRL SHM Vision Sensors for: - strain - temperature - corrosion 40
Structural health monitoring (SHM) Kumar, Acellent Technologies 41
End of presentation Questions? 42