Inspec'on Fundamentals Chapter 8 Inspec'ons •  To insure airworthiness, a mechanic must always be inspec'ng •  Follow the manufacturer’s recommended procedures •  Required inspec'ons: Preflight/Post flight   Annual/100-­‐hour   Progressive   Con'nuous 
Nondestruc've Inspec'on •  Evaluate the proper'es of a material, component or system without causing damage •  Radiographic Inspec'on Examina'on with X-­‐rays or Gamma-­‐rays   Very specialized equipment and test environment   Can test components without taking them out   Can see damage inside a component   Can see corrosion inside a component 
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Radiographic Factors Material thickness and density Shape and size of the object Type of defect to be detected Characteris'cs of X-­‐ray machine used The exposure distance The exposure angle Film characteris'cs Type of intensifying screen, if one is used Penetrant Inspec'on •  Used to find faults on the surface of a component 
Nonporous •  Dye-­‐penetrant – a penetrant dye is applied to a component, washed off and then a developer is applied to pull the penetrant out of the fault so you can see it •  Fluorescent penetrant – a form of penetrant dye that glows ultraviolet light (black light) Penetrant Inspec'on Steps •  Completely clean the component’s surface Don’t use an abrasive cleaning or blas'ng, it may hide a small fault   Use a vola'le petroleum-­‐base solvent 
•  Apply penetrant Soak in a vat of penetrant for a period   Penetrant can also be sprayed on. The penetrant must be given a specific period of 'me to “soak” in   The size and shape of the fault being looked for determine the soak 'me (dwell 'me)   Small faults may require longer soak 'me 
Penetrant Inspec'on Steps •  Remove the penetrant with cleaner or emulsifier Removes penetrant from the surface not the fault   Bad cleaning job will give fuzzy results 
•  Dry component •  Apply developer or powder Draws penetrant from fault up to the surface   Developer may react with penetrant to create a bright color 
•  Inspect 
May require the use of a black light •  Video 1 •  Video 2 Penetrant Inspec'on Magne'c Field Magne'c Field Magne'c Par'cle Inspec'on •  Detects flaws in ferromagne'c material on the surface or subsurface faults near the surface •  A flaw causes a disrup'on in the magne'c field that is visible •  Good for detec'ng fa'gue cracks in highly stressed area Magne'c Par'cle Inspec'on Magne'c Par'cle Inspec'on Magne'c Par'cle Inspec'on •  Process: Magne'ze the component   Spray on iron oxide par'cles suspended in a fluid 
•  Can be done with just dry iron oxide •  Iron oxide has high permeability (magne'c conduc'vity) and low reten'vity (the ability to retain magne'sm) 
Visually inspect •  Oaen done with a black (ultraviolet) light Magne'c Par'cle Inspec'on •  Two methods: 
Con'nuous •  Magne'c field is lea on •  Produces the strongest fields and is generally used for large parts •  Most common method 
Residual •  The component is removed from the magne'c field •  Component must have high reten'vity 
Reten'vity -­‐ the ability to retain magne'sm Magne'c Par'cle Inspec'on •  Faults are best seen if they are 90° (perpendicular) to the magne'c field 
Difficult to see beyond 45° Magne'c Par'cle Inspec'on Longitudinal magne'za'on produces a magne'c field that extends lengthwise through the part. North and south poles form along the part, and the oxide par'cles show up faults that extend across the part.
Magne'c Par'cle Inspec'on •  Circular magne'za'on Used to detect lengthwise flaws (along the length of the part)   The magne'c filed is generated by passing current through the material while it is held between the heads of the machine 
Circular Magne'za'on Circular magne'za'on is put into a small object, such as a wrist pin, by passing the current through a rod inserted through the hollow pin. The rod is clamped firmly between the heads of the machine.
Circular Magne'za'on Circular magne'za'on produces a magne'c field encircling the part. North and south poles are formed across a fault, and the oxide par'cles show up faults that extend along the length of the part.
Magne'c Par'cle Inspec'on •  Longitudinal magne'za'on Used to detect cracks that extend across the material   The magne'c field is generated by placing a magne'c coil around the component 
Longitudinal Magne'za'on Longitudinal magne'za'on is put into a part by passing the magne'zing current through a coil which surrounds it. The part becomes the core of an electromagnet, and the lines of flux extend lengthwise through the part.
Longitudinal Magne'za'on Large parts, such as steel propeller blades, can be longitudinally magne'zed by passing the magne'zing current through a heavy insulated copper cable wrapped around the blade.
Longitudinal Magne'za'on Longitudinal magne'za'on produces a magne'c field that extends lengthwise through the part. North and south poles form along the part, and the oxide par'cles show up faults that extend across the part.
Magne'c Par'cle Inspec'on •  Cracks that are oriented at 45° to the material can be detected by either circular or longitudinal magne'za'on •  A complete inspec'on includes both circular and longitudinal inspec'on •  Aaer a part has been inspected, it must be thoroughly demagne'zed 
Done with a magne'c field that con'nually reverses its polarity and decreases its strength (or is slowly move away from field) Magne'c Par'cle Inspec'on •  Video 1 •  Video 2 Eddy Current Inspec'on •  Checks for faults inside a metal that change the metals conduc'vity •  Can see below the surface 
Good method for detec'ng intergranular corrosion •  May also be used to separate metals or alloys and their heat-­‐treat condi'ons •  Electromagne'c field induced into the metal causes an eddy current •  Changes in the eddy current are evaluated •  Doesn’t require any special prepara'on Ultrasonic Inspec'on •  A transducer is used to send very high frequency sound wave into a component •  The reflec'on of the sound wave are measured •  Can be used on metals, plas'cs, and ceramics. •  Can see below the surface Ultrasonic Inspec'on Vibra'ons from the transducer pass through the test specimen and reflect off of the back surface. This produces two pips on the CRT screen, one for the front surface and one for the back surface.
Ultrasonic Inspec'on A fault within the material being inspected by the ultrasonic method will reflect enough energy to form a pip between the front and back surface pips.
Ultrasonic Inspec'on Composite Inspec'on •  Most common test is the metallic ring test Detects delamina'on (separa'on of the layers)   A good component will make a “ringing” sound when tapped with a coin   A bad component will make a “thud” 
•  Ultrasonic inspec'on is more accurate •  Radiograpic inspec'on is also used 
Only way to detect water in a composite component Welding Bead Bead Bead Bead Too rapid
Too hot
Oxidized flame
Too cold
Rough edges
Too much
acetylene
Inconsistent
Too cold