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Slide 1: 

What's Eating You? Corrosion, Fatique, Loading, …….. 1

Slide 2: 

Non Destructive Testing Solution 2


LATEST TRENDS IN NONDESTRUCTIVE TESTINGWITH REFERENCE TO PAF Department of Aerospace Engineering College of Aeronautical EngineeringPAF Academy, Risalpur Sqn Ldr Farrukh Mazhar 3

Sequence : 

Sequence Aircraft structure inspections NDT – Definition Need for NDT NDT application NDT in PAF Modern NDT techniques Conclusion 4

Structure Inspection - Aim : 

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 5

Structural Deterioration : 

Structural Deterioration Corrosion Fatigue (cyclic loading) Fabrication defects Operation and Maintenance Unforeseen loading (overloads) Result into Failure or Fracture 6

Inspection Levels : 

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 7

Slide 8: 

8 Technique that allows a component to be inspected for serviceability, without impairing its usefulness i.e. Inspect or measure without doing harm Definition of NDT

Uses of NDT Methods : 

Uses of NDT Methods Flaw detection and evaluation Leak detection Location determination Dimensional measurements 9

Uses of NDT Methods : 

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 10

Aircraft Inspection : 

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 11

Slide 12: 

Jet Engine Inspection During engine overhaul Completely disassembly, cleaning, inspection and reassembly Fluorescent penetrant inspection is shown to check engine parts 12

Crash of United Flight 232 : 

13 A defect that went undetected in an engine disk was responsible for the crash of United Flight 232 Crash of United Flight 232

Slide 14: 

“Periodic inspection should be a systematic and complete examination of the entire structure with particular attention given to the critical locations” Critical Areas – Where to look 14

Airframe Loading : Critical Locations : 

Airframe Loading : Critical Locations Non-destructive testing (NDT) is needed in order to ensure the integrity of the airframe.

Methods of NDT : 

Methods of NDT Visual Liquid Penetrant Magnetic Particle Eddy Current Ultrasonic X-ray Microwave Acoustic Emission Thermography Laser Interferometry Replication Flux Leakage Acoustic Microscopy Magnetic Measurements Tap Testing 16

Six Common NDT Methods in PAF : 

Six Common NDT Methods in PAF Visual Liquid Penetrant Magnetic Ultrasonic Eddy Current Radiography 17

Visual Inspection - Types : 

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

Remote Visual Testing – Borescopes : 

19 Remote Visual Testing – Borescopes Flexible 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

Remote Visual Testing – Borescopes : 

Remote Visual Testing – Borescopes Video 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 20

Slide 21: 


Sensor Based Inspections : Principle : 

22 Sensor Based Inspections : Principle Excitation Source Signal / Image Processing Signal / Image Recognition Display Result Input transducer Measurement transducer

Modern NDT Techniques : 

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) 23

Modern NDT Techniques : 

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) 24

Slide 25: 

Wire Rope Inspection Electromagnetic devices and visual inspections are used to find broken wires and other damage to the wire rope 25

Wire Rope NDT Technology : 

Wire Rope NDT Technology Uses the magnetic properties of the steel wire rope The principle of operation employs: 26 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

Wire Rope NDT : 

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 27

Acoustic Emission (AE) : 

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 28

Acoustic Emission Phenomena : 

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 29

Use in Non-destructive Testing : 

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 30

Phased Array (PA) Ultrasonics : 

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 31

Phased Array (PA) Ultrasonics : 

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 32

Features of Phased Array : 

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 33

Phased Array Scan : 

34 Phased Array Scan

Ultrasonic Imaging : 

35 Ultrasonic Imaging Gray scale image produced using the sound reflected from the front surface of the coin Gray scale image produced using the sound reflected from the back surface of the coin (inspected from “head’s” side) High resolution images can be produced by plotting signal strength or time-of-flight using a computer-controlled scanning system

Infrared and Thermal Testing : 

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 36

Thermographic Testing : 

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 37

Thermographic Testing : 

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 38

Active Thermography Excitations : 

39 Active Thermography Excitations

Thermographic Testing : 

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 40

Thermographic Testing : Features : 

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 41

Thermographic Testing : Features : 

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. 42

Fuselage inspection of Boeing 737 : 

43 Fuselage inspection of Boeing 737 43

Digital Radiography : 

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 44

Digital Radiography : 

45 Digital Radiography

Pulsed Eddy Current Inspection : 

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 46

Pulsed Eddy Current Inspection : 

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 47

Pulsed Eddy Current Inspection : 

Pulsed Eddy Current Inspection 48

Shearography : 

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 49

Principle of Operation : 

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 50

Principle of Operation : 

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 51

Shearography : 

Shearography 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. 52

Structural Health Monitoring : 

Structural Health Monitoring 53

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 What is SHM 54

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 What is SHM 55

SHM Advantage : 

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 56

SHM Advantage : 

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 57

Structural Health Monitoring : 

58 Structural Health Monitoring With SHM new possibilities exist which can be used to ensure the structure integrity: Damages Loads/Strains Flight parameters and conditions Environmental conditions Production parameters

Possibilities for NDT : 

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 structures The optimum solution for structural inspections should be chosenout of these 3 options

NDT in PAF : 

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 60

Conclusions : 

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 61

Conclusions : 

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 62

Conclusions : 

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 63

Questions? : 

Questions? 64

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