NDT in aircraft

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NDT in aircraft

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  3. 3. 3 LATEST TRENDS IN NONDESTRUCTIVE TESTING WITH REFERENCE TO PAFSqn Ldr Farrukh MazharDepartment of Aerospace EngineeringCollege of Aeronautical EngineeringPAF Academy, Risalpur
  4. 4. 4 SequenceAircraft structure inspectionsNDT – DefinitionNeed for NDTNDT applicationNDT in PAFModern NDT techniquesConclusion
  5. 5. 5 Structure Inspection - AimEnsure safety and airworthinessDetecting manufacturing or service- induced damageTo achieve this goal, a structure inspection program has been developed for PAF fleet
  6. 6. 6 Structural DeteriorationCorrosionFatigue (cyclic loading)Fabrication defectsOperation and MaintenanceUnforeseen loading (overloads)Result into Failure or Fracture
  7. 7. 7 Inspection LevelsGeneral Visual Inspection (GVI)  During pre, tru or post flightDetailed Visual Inspection (DET)  During periodic inspectionSpecial Detailed Inspection (SDET)  NDT of selected parts during periodic inspections
  8. 8. 8 Definition of NDTTechnique that allows acomponent to beinspected forserviceability, withoutimpairing its usefulnessi.e. Inspect or measurewithout doing harm
  9. 9. 9 Uses of NDT MethodsFlaw detection and evaluationLeak detectionLocation determinationDimensional measurements
  10. 10. 10 Uses of NDT MethodsStructure and microstructure characterizationMaterial sorting and chemical composition determinationMechanical and physical properties estimationStress (strain) and dynamic response measurements
  11. 11. 11 Aircraft Inspection• During manufacturing of aircraft• To detects damage during operation of the aircraft• A fatigue crack that started at the site of a lightning strike is shown below
  12. 12. 12 Jet Engine Inspection• During engine overhaul• Completely disassembly, cleaning, ins pection and reassembly• Fluorescent penetrant inspection is shown to check engine parts
  13. 13. 13 Crash of United Flight 232A defect that wentundetected in an enginedisk was responsible forthe crash of United Flight232
  14. 14. 14 Critical Areas – Where to look “Periodic inspection should be asystematic and complete examination of the entire structure with particular attention given to the critical locations”
  15. 15. Airframe Loading : Critical LocationsNon-destructive testing (NDT) is needed in order to ensure the integrity ofthe airframe.
  16. 16. 16 Methods of NDTVisual
  17. 17. 17Six Common NDT Methods in PAF Visual Liquid Penetrant Magnetic Ultrasonic Eddy Current Radiography
  18. 18. 18 Visual Inspection - Types Direct Visual Testing Remote Visual Testing Tools for remote inspection include fiberscope & borescope Portable video inspection unit with zoom allows inspection of large tanks and vessels
  19. 19. 19 Remote Visual Testing – BorescopesFlexible Borescopes Contains a bundle of optical fibers Also known as a fiberscope Used for inaccessible cavities Such as air inlets, combustion chamber, compressor, turbine blades, seals and other inaccessible aircraft parts Good Image quality is required
  20. 20. 20 Remote Visual Testing – BorescopesVideo borescopesSimilar to the flexible borescope but uses a miniature video cameraA display shows the camera viewMuch less costly and have potentially better resolutionDigital models have an integrated recorder and images / video can be saved
  21. 21. 21MODERN NDTTECHNIQUES
  22. 22. 22 Sensor Based Inspections : Principle Excitation Source Signal / Image Display Recognition Result Input transducerMeasurement Signal / Imagetransducer Processing
  23. 23. 23 Modern NDT Techniques Acoustic emission testing (AE or AT) Electromagnetic testing (ET)  Alternating current field measurement (ACFM)  Alternating current potential drop measurement (ACPD)  Direct current potential drop measurement (DCPD)  Magnetic flux leakage testing (MFL)  Remote field testing (RFT) Ellipsometry Guided wave testing (GWT) Impulse excitation technique (IET) Infrared and thermal testing (IR)
  24. 24. 24 Modern NDT Techniques Laser testing  Profilometry  Shearography Optical microscopy Radiographic testing (RT)  Computed radiography  Digital radiography (real-time) Ultrasonic testing (UT)  Electro Magnetic Acoustic Transducer (EMAT)  Laser ultrasonics (LUT)  Phased array ultrasonics  Time of flight diffraction ultrasonics (TOFD)
  25. 25. 25 Wire Rope InspectionElectromagnetic devicesand visual inspectionsare used to find brokenwires and other damageto the wire rope
  26. 26. 26 Wire Rope NDT Technology Uses the magnetic properties of the steel wire rope The principle of operation employs:  Measurements of EM fields near the surface to detect local defects  Measurements of changes in magnetic flux passing through the rope to evaluate cross section
  27. 27. 27 Wire Rope NDT Readings compared with new wire “signature” Monitoring the rate of degradation of a rope A good rope will show a reproducible “signature” trace
  28. 28. 28 Acoustic Emission (AE)External stimuli, like mechanical loading, generate elastic waves in the materialAs stress waves are generated when there is a rapid release of energy in a material, or on its surfaceUsed for part inspection, process monitoring etc
  29. 29. 29 Acoustic Emission PhenomenaRelated to an irreversible release of energyCan be generated from friction, cavitations and impactRanges from 1kHz, up to 100 MHz frequencies
  30. 30. 30 Use in Non-destructive TestingAE uses ultrasonic regime ( 100kHz and 1MHz)Uses passive sensor which monitors acoustic emissions producedUsed to study the formation of cracksGroup of transducers record signals and locate area of defect originApplications in process monitoring
  31. 31. 31 Phased Array (PA) UltrasonicsPhased Array (PA) ultrasonics has applications in industrial nondestructive testingThe PA image shows the defects hidden inside a structure or weld
  32. 32. 32 Phased Array (PA) Ultrasonics PA probe consists of many small elements pulsed separately Ultrasonic ripple are send as multiple waves to make a single wave front travelling at a set angle Weld examination by phased array
  33. 33. 33 Features of Phased ArrayProduce a steerable, tightly focused, high- resolution beamProduces an inside image of the objectPA instruments and probes are more complex and expensiveMore experience and training than conventional technicians
  34. 34. 34Phased Array Scan
  35. 35. 35 Ultrasonic Imaging  High resolution images can be produced by plotting signal strength or time-of-flight using a computer-controlled scanning systemGray scale image produced using the Gray scale image produced using thesound reflected from the front surface sound reflected from the back surface ofof the coin the coin (inspected from “head’s” side)
  36. 36. 36 Infrared and Thermal Testing Principle electromagnetic radiation emission as a function the temperature Thermographic inspection NDT of parts through the surface imaging of the thermal patterns Used for monitoring thermal changes Infrared Thermography mapping of thermal patterns, on the surface of objects using infrared Resolution few hundredths of a degree Celsius Radiation is detected, processed and displayed on a computer display
  37. 37. 37 Thermographic TestingMeasures surface temperatures onlyBut surface temperatures are dependent upon the subsurface conditionsEnergy flows can be slowed down by the insulating effectsDetect hidden thermal insulation faults and subsurface targets such as hot air leaks
  38. 38. 38 Thermographic TestingTwo methods are used :  Passive, in which the features of interest are naturally at a higher or lower temperature than the background  Active, in which an energy source is required to produce a thermal contrast
  39. 39. 39Active Thermography Excitations
  40. 40. 40 Thermographic Testing Energy sources induces a thermal contrast between defective and non-defective zones Energy cannot pass through a flaw External excitation  photographic flashes (for heat pulsed stimulation) or  halogen lamps (for periodic heating) Internal excitation  Mechanical oscillations, with a sonic or ultrasonic transducer  Burst and amplitude modulated stimulations
  41. 41. 41 Thermographic Testing : FeaturesThermographic inspection is safe, nonintrusive and noncontact, allowing the detection of relatively shallow subsurface defectsLarge area can be inspectedFast and time savingFriction in moving parts like control links, cables, surfaces hinges etc.Hidden hydraulic, hot /cold air, fuel leak can be detected
  42. 42. 42 Thermographic Testing : FeaturesLooks for “hot spots” in electrical equipment, showing high resistance areasInspecting composite or honeycomb aircraft structural componentsThis method is reliable and cost effective This thermogram shows a fault with an industrial electrical fuse block.
  43. 43. 43Fuselage inspection of Boeing 737
  44. 44. 44 Digital Radiography Digital X-ray sensors are used instead of traditional photographic film Time efficient due to through bypassing chemical processing Digital processing and transferable enhance images Also less radiation required Typically there are two variants of digital image capture devices  Flat Panel detectors (FPDs)  High Density Line Scan Solid State detectors
  45. 45. 45Digital Radiography
  46. 46. 46 Pulsed Eddy Current InspectionStep function voltage is used to excite the probe instead of sinusoidal AC currentA step function voltage contains a continuum of frequenciesThe electromagnetic response to different frequencies can be measuredDepth information can be obtained
  47. 47. 47 Pulsed Eddy Current InspectionReceived and reference signals are comparedFlaws, conductivity, and dimensional changes can be measuredDepth of a part can be measured
  48. 48. 48Pulsed Eddy Current Inspection
  49. 49. 49 ShearographyShearography is an optical nondestructive testing methodUses include aerospace, space, wind rotor blades, automotive and materialsAdvantages include the large area testing capabilities, non-contact properties and its good performance on composites and honey-comb materials
  50. 50. 50 Principle of OperationAn interferometric image of the surface is taken and stored it in a computerImage is a unique footprint of the surfaceThe material is then stressed with a small amount of thermal loadThe material tries to expand when heated up, and weak spots will expand moreSecond interferometric image is taken
  51. 51. 51 Principle of Operation By subtracting the two images a shearogram is created The defects will be seen as fringe patterns resembling a pair of “hills” or a pair of "bulls- eyes" The size of the defects can be quantified by measuring how large this fringe pattern is
  52. 52. 52 Shearography A primitive shearography setup; Two The primitive shearography principle. physical points on test object will be A shearography image is recorded at projected on to one point on the CCD unloaded state and one image ischip to record a interferometric footprint. recorded in the loaded state.The tested surface is illuminated with a Thereafter they are subtracted and in monochromatic light, typical 650 nm. the result defects can be detected.
  53. 53. 53Structural Health Monitoring
  54. 54. 54 What is SHMContinuous monitoring of structures using integrated or applied sensorsAimed at assuring structural integrity of the aircraft, by detecting damages resulting from fatigue, corrosion, excessive loads, impact ...This does not imply knowing the status of the structure in real-time
  55. 55. 55 What is SHMAfter normal or exceptional events, maintenance can be planned at next appropriate inspectionSystems are available for aircraft condition monitoring - mostly for loads (accelerations, flight parameters, etc.) and enable decisions to be made based on actual flight load levels
  56. 56. 56 SHM Advantage In terms of life cycle cost, a US DoD study attributed that  27% of the total cost of an aircraft being maintenance related with structural inspection being a significant driver of this cost suggesting  SHM could save up to 44% of current inspection time on modern fighter aircraft SHM will improve reliability since structures are monitored directly, measuring the effect of damage
  57. 57. 57 SHM AdvantageSHM has many advantages:  No access to the inspection area necessary  Safe inspection of hazardous areas  Eliminating time consuming setup  Sensors used in the inspection are integral to the structure  Automated process - no human factors influence on inspection POD  Interrogating many locations or wide field at once - significant time saving
  58. 58. 58 Structural Health MonitoringWith SHM new possibilities exist which can beused to ensure the structure integrity: Damages Loads/Strains Flight parameters and conditions Environmental conditions Production parameters
  59. 59. 59 Possibilities for NDT Visual Inspection (VI) • More than 95% of all NDI inspection are done visually Non-Destructive Testing (NDT) • Performed where VI is not sensitive enough or damages are not visible on the surface Structural Health Monitoring/Management • Sensor permanently attached / embedded in the structure • Information on structural events or states to arbitrary times available • Automated assessment and prognostic of the health of aircraft structuresThe optimum solution for structural inspections should be chosenout of these 3 options
  60. 60. 60 NDT in PAFFrom visual inspections to more detailed technique based on penetrant inspection, eddy currents, ultrasonics, x-rays, etc…Inspection intervals are generally OEM specified or self experience basedThese Inspections result in downtime and significant effortMonitoring activity comes at a considerable cost and accounts a large maintenance man-hours for commercial aircraft
  61. 61. 61 ConclusionsNDT plays key role in safe operation and especially in damage tolerant design / operations of aircraft structuresFurthermore NDT is “enabler” for reliable introduction of new materials, technologies and design conceptsWe have to realize that adopting new NDT techniques and more focus on training can improve flight safety
  62. 62. 62 Conclusions Enhanced training On job expertise Developing NDT trade or screening NDT trained specialists Developing and managing NDT pool through sub NDT classifications Acquiring latest and modern equipment Education everyone about NDT Advantages and Hazards
  63. 63. 63 Conclusions Including introductory NDT course in PPT curriculum Thorough scrutiny of inspection procedures from NDT Perspective Ensuring availability of personnel protecting equipment especially in RT and PT Making a PAF level certifying, training and regulation body
  64. 64. 64Questions?

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