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NDT in aircraft

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  • This brings me to the topic of my today’s talk which is “Latest trends in nondestructive testing with reference to PAF”. I am SqnLdrFarrukhMazhar from Aerospace Engineering Dept, College of Aeronautical Engineering PAF Academy Risalpur.
  • The sequence that I will be following is as flashed (hold for 10s)
  • The structure inspection of an aircraft require thatSafety and airworthiness have to be ensured throughout the complete aircraft’s lifetimeAny initial manufacturing damage as well as any service-induced damage must not affect the safe operation of the aircraft by timely detecting themTo achieve this goal, a structure inspection program has been developed for PAF fleet
  • As discussed in the beginning Corrosion, Fatigue (cyclic loading), Fabrication defects, Operation and Maintenance induced defects and Unforeseen loading (overloads) causes structure to deteriorate which could lead to failure or fracture
  • Typically, there are three Inspection Levels are in use in PAF:General Visual Inspection (GVI)A visual examination, performed in frame of the zonal inspection e.g. this is performed During pre, tru or post flight inspDetailed Visual Inspection (DET)An intensive visual examination of a specified detail or assembly searching for evidence of irregularity e.g. during periodic inspectionsSpecial Detailed Inspection (SDET)An intensive examination of a specific location similar to the detailed Inspection but requiring special techniques, mostly NDT e.g. NDT of selected parts during periodic inspections
  • NDT can be defined as Technique that allows a component to be inspected for serviceability, without impairing its usefulness, in which noninvasive techniques are used to determine the integrity of a material, component or structure i.e. Inspect or measure without doing harm
  • A typical case of NDT failure is the crash of United Flight 232, in Sioux City, Iowa, July 19, 1989.A defect that went undetected in an engine disk was responsible for the disk failureInvestigation attributed the cause of the accident to a failure of maintenance processes to detect an existing fatigue crack. Post-crash analysis of the crack surfaces showed the presence of a penetrating fluorescent dye used to detect cracks during maintenance. The presence of the dye indicated that the crack was present and should have been detected at prior inspection.
  • Now where should we focus, the focus of all inspections should be the critical area let us first define what is periodic inspPeriodic inspection should be a systematic and complete examination of the entire structure with particular attention given to the critical locations”
  • Out of these six most common NDT techniques which are used in PAF are Visual, Liquid Penetrant , Magnetic , Ultrasonic, Eddy Current, and X-ray
  • The visual inspection can be classified in to Direct Visual Testing, Remote Visual Testing. Here I’ll be focusing on a relatively modern technique called remote visual inspection We generally use fiberscope, borescope, portable remote video inspection units for performing remote visual inspections
  • A flexible borescope includes a bundle of optical fibers which divide the image into pixels. It is also known as a fiberscope and can be used to access cavities which are around a bend, such as air inlets, combustion chamber, compressor, turbine blades, seals and inaccessible aircraft parts. So as to view the condition of the part without disassembling .
  • A video borescope or "inspection camera" is similar to the flexible borescope but uses a miniature video camera at the end of the flexible tube. A display shows the camera view. As the complex optical waveguide is replaced with an inexpensive electrical cable, video borescopes are much less costly and has potentially better resolution, depending on the specifications of the camera. Digital models often have an integrated recorder and can save images / videos in common digital formats.
  • Now I will be discussing the modern techniques of non destructive testing
  • Almost all modern non destructive techniques are sensor based in which excitation source produces signal through a transducer which is captured by a measurement transducer. The signal or image processing techniques are used to improve the result quality. The input and output are analyzed in a computer and results are displayed on a screen.
  • The modern NDT techniques available today are as shown in this slide.
  • The few more techniques are;In subsequent slides I ll be discussing the modern techniques in relevance to potential application in PAF
  • Wire rope NDT is used extensively in the routine inspection of hoist ropes throughout the world. It is also used for inspecting wire ropes installed in crane ropes, mining eqpt,mountain installations, cable cars and ski lifts etc. This effective technology depends on the magnetic properties of the steel wire rope.The principles of operation for electromagnetic wire rope NDT systems employ: measurements of EM fields near the surface of the rope to detect local defects such as broken wires, corrosion pitting, and local wear. measurements of changes in magnetic flux passing through a short length of rope to quantify changes in metallic cross section of the rope
  • The readings obtained during inspection of a wire rope are compared with a “signature” trace taken when the rope was first installed, and then subsequent traces, to assess more accurately any degradation which has developed in the rope.Regular NDT inspections provide a powerful tool in monitoring the rate of degradation of a rope. Under consistent conditions a rope in perfect conditions will show a trace that is a reproducible “signature” determined by its complex helical structure. The quality of a trace is improved by avoiding vibration and maintaining a steady speed.LMA (loss of metalic cross sectional area)
  • Acoustic Emission (AE) is a naturally occurring phenomenon whereby external stimuli, such as mechanical loading, generate sources of elastic waves due to small surface displacement of the materialThis occurs due to stress waves generated when there is a rapid release of energy inside a material, or on its surface. The wave generated by the AE is used in inspection, process monitoring ,quality control, system feedback,etc
  • AE is related to an irreversible release of energy, and can be generated from sources not involving material failure including friction, cavitations and impact. Acoustic emissions can be detected in frequency ranges under 1 kHz, and can be detected to frequencies upto 100 MHz.Which is due to Rapid stress-releasing events generating a spectrum of stress waves starting at 0 Hz and typically ranging upto several MHz.
  • For non-destructive testing of materials AE normally uses the ultrasonic regime, typically between 100 kHz and 1 MHz.Unlike conventional ultrasonic testing, AE sensorsare passive devices which are designed for monitoring acoustic emissions produced within the material and then collecting them after they have traveled through the material, rather than actively transmitting wavesThe technique is used, to study the formation of cracks during the welding process, a material under active stress as in case of an airplane during flight, transducers mounted in an area can detect the formation of a crack at the moment it begins propagating.A group of transducers can be used to record signals then locate the precise area of their origin by measuring the time for the sound to reach different transducers.In addition to non-destructive testing, acoustic emission monitoring has application in process or condition monitoring.
  • Phased Array (PA) ultrasonics is an advanced method of ultrasonic testing that has applications in industrial nondestructive testing and medicine.the PA image shows defects hidden inside a structure or weld.
  • The PA probe consists of many small elements, each of which can be pulsed separately. In the figure the element on the right is pulsed first, and emits a pressure wave that spreads out like a ripple on a pond.The second to right element is pulsed next, and emits a ripple that is slightly smaller than the first because it was started later. The process continues down the line until all the elements have been pulsed. The multiple waves add up to one single wave front travelling at a set angle. In other words, the beam angle can be set just by programming the pulse timings. The beam can be steered electronically. The beam is swept like a search-light through the object being examined, and the data from multiple beams are put together to make a visual image showing a slice through the object.In TOP fig: The phased array probe emits a series of beams to flood the weld with sound.In BOTTOM fig: The flaw in the weld appears as a red indication on the instrument screen.
  • Multiple probe elements produce a steerable, tightly focused, high-resolution beam.Produces an image that shows a slice through the object.Compared to conventional, single-element ultrasonic inspection systems, PA instruments and probes are more complex and expensive.In industry, PA technicians require more experience and training than conventional technicians.
  • Shows the phased array scan of a metallic part
  • Modern type of ultrasonic inspection is Ultrasonic Imaging this tech is similar to one used in medicineIn this technique High resolution images can be produced by plotting signal strength or time-of-flight using a computer-controlled scanning systemAs shown in figure complete 3d inside picture of the object can be obtained
  • Another modern Technique is Infrared or Thermal testingThe Principle is that All objects emit electromagnetic radiation of a wavelength dependent on the object’s temperature. The frequency of the radiation is inversely proportional to the temperature. Thermographic inspection refers to the nondestructive testing of parts, materials or systems through the imaging of the thermal patterns at the object's surfacethermography refers to all thermographic inspection techniques used to monitor the thermal changes. Infrared thermography is a nondestructive, nonintrusive, noncontact mapping of thermal patterns or "thermograms", on the surface of objects through the use of some kind of infrared detector.An infrared thermographic scanning system can measure and view temperature patterns based upon temperature differences as small as a few hundredths of a degree Celsius. In infrared thermography, the radiation is detected and measured with infrared imagers The imagers contain an infrared detector that converts the emitting radiation into electrical signals that are displayed on a color or monochrome computer display monitor.
  • An infrared thermographic scanning system measures surface temperatures only. But the surface temperatures are dependent upon the subsurface conditions.The subsurface configuration effects are based upon the theory that energy cannot be stopped from flowing from warmer to cooler areas, it can only be slowed down by the insulating effects of the material through which it is flowing.It can also be used to detect hidden thermal insulation faults and subsurface targets such as hot air leaks.After the thermal data is processed, it can be displayed on a monitor in multiple shades of gray scale or color. The colors displayed on the thermogram are arbitrarily set by the Thermographer to best illustrate the infrared data being analyzed.
  • There are two approaches used in thermographic inspection: 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 between the feature of interest and the background, for The figure shows the thermogram of an aircraft panel the dark color shows the greater material thickness
  • This slide shows the principle of operations and various excitation sources for active Thermography
  • A wide variety of energy sources can be used to induce a thermal contrast between defective and non-defectiveif the energy is delivered to the surface it propagates through the material until it encounters a flaw; which can be detected in the thermogramTypically, external excitation is performed with optical devices such as photographic flashes (for heat pulsed stimulation) or halogen lamps (for periodic heating), whereas internal excitation can be achieved by means of mechanical oscillations, microwave etc with a sonic or ultrasonic transducer for both burst and amplitude modulated stimulation.
  • Thermographic inspection is safe, nonintrusive and noncontact, allowing the detection of relatively shallow subsurface defects (a few millimeters in depth) under large surfaces (typically 30x30 cm2 at once, although inspection of larger surfaces is possible) and in a fast manner (from a fraction of a second to a few minutes depending in the configuration)Friction in moving parts like control links, cables, surfaces hinges etc.Hidden hydraulic, hot /cold air, fuel leak can be detected by their thermal signature
  • A typical application for regularly available IR Thermographic equipment is looking for “hot spots” (40 °C to 150 °C ) in electrical equipment, which illustrates high resistance areas in electrical circuits. Widely used for inspecting composite or honeycomb aircraft structural componentsThis method is reliable and cost effective. This thermogram shows a fault with an industrial electrical fuse block
  • Fuselage inspection of a Boeing 737 aircraft using thermography shows the skin lap joints, stringers, doublers, and rivets. This image shows no defects part. The frame station and the frame of the window appear in a darker color, an indication that they are made out of thicker material.The bottom picture shows the thermograph of 737 hull and debonding defect in composite
  • Digital Radiography is essentially filmless x-ray imaging, where digital X-ray sensors are used instead of traditional photographic film. Advantages include time efficiency through bypassing chemical processing and the ability to digitally transfer and enhance images. Also less radiation can be used to produce an image of similar contrast to conventional radiography.The advantages of DR over film include immediate image preview and availability, a wider dynamic range which makes it more forgiving for over- and under-exposure as well as the ability to apply special image processing techniques that enhance overall display of the image. Typically there are two variants of digital image capture devices. Flat Panel detectors (FPDs), and High Density Line Scan Solid State detectors.
  • This slide shows the Radiographic Setup and image results for a typical Flat Panel Xraydetectors (FPDs)
  • Conventional eddy current inspection techniques use sinusoidal alternating electrical current of a particular frequency to excite the probe. The pulsed eddy current technique uses a step function voltage to excite the probe. A step function voltage contains a continuum of frequencies. As a result, the electromagnetic response to several different frequencies can be measured with just a single step. Since the depth of penetration is dependent on the frequency of excitation, information from a range of depths can also be obtained. Since, the measurements are made in the time domain, indications produced by flaws or other features near the inspection coil will be seen first and more distant features will be seen later in time.
  • To improve the strength and ease of interpretation of the signal, a reference signal is usually collected, to which all other signals are compared this is similar to nulling the probe in conventional eddy current inspectionFlaws, conductivity, and dimensional changes produce a change in the measured signal. The difference between the reference signal and the measurement signal is displayed on the screenThe distance of the flaw and other features relative to the probe will cause the signal to shift in time. Therefore, time gating techniques like in ultrasonic inspection can be used to gain information about the depth of a feature of interest.
  • This slide shows a typical pulsed eddy current equipment and driving voltage and the coil current
  • Shearography is an optical nondestructive testing method that provides information about the inside quality of different materials. Shearography is extensively used in production and development within aerospace, space, wind rotor blades, automotive and materials research areas. Main advantages of shearography are the large area testing capabilities (up to 1 m² per minute), non-contact characteristics and good performance on composites and honey-comb materials, which is a big challenge for traditional NDT methods.
  • In this technique the images of a test specimen's surface is taken with a special Shearography camera. The camera acquires an interferometric image of the surface and stores it in a computer. This image can be thought of as a unique footprint of this surface, including surface roughness and shape. The material is then stressed with a small amount of load (thermal). The material tries to expand when heated up, and if it has weak spots it will expand more. At the loaded state one more interferometric image is taken.
  • Using an appropriate software, a shearogram is created. By subtracting the two images. The defects will be seen as fringe patterns resembling a pair of “hills” or a pair of "bulls-eyes" superimposed on the surface's image. The size of the defects (in plane) can be quantified by measuring how large this fringe pattern is.
  • This slide A primitive shearography setup; Two physical points on test object will be projected on to one point on the CCD chip to record a interferometric footprint. The tested surface is illuminated with a monochromatic light, typical 650 nm.The primitive shearography principle. A shearography image is recorded at unloaded state and one image is recorded in the loaded state. Thereafter they are subtracted and in the result defects can be detected.
  • This bring me to a slightly newer concept in aviation maintenance called Structural Health Monitoring. This methodology is analogous to real time monitoring of pain receptors in humans replaced by on board sensors monitoring aircraft structural health
  • 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 aircraftSHM will improve reliability since structures are monitored directly, measuring the effect of damage
  • Compared to conventional NDT based maintenance, SHM has many advantages:No access to the inspection area necessary – fewer access panels & component removal requirementsNo physical operation in the area - safe inspection of hazardous areasNo use of scanners necessary – eliminating time consuming setupSensors used in the inspection are integral to the structureAutomated process - no human factors influence on inspection ProbabilityOf DetectionInterrogating many locations or wide field at once - significant time saving
  • Additional to conventional NDI with SHM new possibilities exist which can be used to ensure the structure integrity:Damages Loads/StrainsFlight parameters and conditionsEnvironmental conditionsProduction parameters
  • SHM has verey large potential for NDTVisual Inspection (VI)More than 95% of all NDI inspection are done visuallyNon-Destructive Testing (NDT)Performed where VI is not sensitive enough or damages are not visible on the surfaceStructural Health Monitoring/ManagementSensor permanently attached / embedded in the structureInformation on structural events or states to arbitrary times availableAutomated assessment and prognostic of the health of aircraft structures
  • NDT plays key role in safe operation and especially in damage tolerant design / operations of aircraft structuresFurthermore NDT is “enabler” for reliable introduction of new materials, technologies and design conceptsWe have to realize that adopting new NDT techniques and more focus on training we improve flight safetyHowever we need to emphasize more on NDT
  • As NDT is highly skill based inspection we have to accord due importance to it byMore trainingOn job experienceDeveloping NDT trade or screening NDT trained specialistsDeveloping and managing NDT pool through sub NDT classificationsAcquiring latest and modern equipmentEducation everyone about NDT advantages and Hazards
  • Including introductory NDT course PPT curriculum for young engineering officers Thorough scrutiny of inspection procedures from NDT PerspectiveEnsuring availability of personnel protecting eqpt especially in RT and PTMaking a PAF level certifying, training and regulation body monitoring all NDT related activities in PAF
  • Transcript

    • 1. 1
    • 2. 2
    • 3. 3 LATEST TRENDS IN NONDESTRUCTIVE TESTING WITH REFERENCE TO PAFSqn Ldr Farrukh MazharDepartment of Aerospace EngineeringCollege of Aeronautical EngineeringPAF Academy, Risalpur
    • 4. 4 SequenceAircraft structure inspectionsNDT – DefinitionNeed for NDTNDT applicationNDT in PAFModern NDT techniquesConclusion
    • 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 Structural DeteriorationCorrosionFatigue (cyclic loading)Fabrication defectsOperation and MaintenanceUnforeseen loading (overloads)Result into Failure or Fracture
    • 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 Definition of NDTTechnique that allows acomponent to beinspected forserviceability, withoutimpairing its usefulnessi.e. Inspect or measurewithout doing harm
    • 9. 9 Uses of NDT MethodsFlaw detection and evaluationLeak detectionLocation determinationDimensional measurements
    • 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 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 Jet Engine Inspection• During engine overhaul• Completely disassembly, cleaning, ins pection and reassembly• Fluorescent penetrant inspection is shown to check engine parts
    • 13. 13 Crash of United Flight 232A defect that wentundetected in an enginedisk was responsible forthe crash of United Flight232
    • 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. Airframe Loading : Critical LocationsNon-destructive testing (NDT) is needed in order to ensure the integrity ofthe airframe.
    • 16. 16 Methods of NDTVisual
    • 17. 17Six Common NDT Methods in PAF Visual Liquid Penetrant Magnetic Ultrasonic Eddy Current Radiography
    • 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 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 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. 21MODERN NDTTECHNIQUES
    • 22. 22 Sensor Based Inspections : Principle Excitation Source Signal / Image Display Recognition Result Input transducerMeasurement Signal / Imagetransducer Processing
    • 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 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 Wire Rope InspectionElectromagnetic devicesand visual inspectionsare used to find brokenwires and other damageto the wire rope
    • 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 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 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 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 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 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 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 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. 34Phased Array Scan
    • 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 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 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 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. 39Active Thermography Excitations
    • 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 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 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. 43Fuselage inspection of Boeing 737
    • 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. 45Digital Radiography
    • 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 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. 48Pulsed Eddy Current Inspection
    • 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 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 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 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. 53Structural Health Monitoring
    • 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 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 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 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 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 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 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 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 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 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. 64Questions?