The primary presentation is a color graphics display

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The primary presentation is a color graphics display, which has two separate screens. The main screen depicts the top and side views of the fighter bomber (Fig. 2). Superimposed upon each of these views are the locatable acoustic emission events, colored according to severity, as well as transducer locations shown as small black dots. Acoustic emission locations are displayed essentially in real time — that is, they appear on the color display within a second of being detected on the aircraft. All acoustic emission test results were located to ±0.15 m (6 in.) on a scaled diagram of the aircraft. The instrument’s second color screen is a numerical listing of the attributes of each locatable acoustic emission event, with each line colored green, yellow or red according to severity. This display aids the operator in determining how many events occurred at a particular spot because on the aircraft display acoustic emission events can superimpose, yellow taking priority over green and red taking priority over yellow and green. The 361 Aerospace Applications of Acoustic Emission Testing F IGURE 2. Diagrams of F-111 jet fighter, showing locations of acoustic emission indications: (a) side view; (b) top view. Wing pivot support Crack in forward tunnel truss Cover bolt of wing carry-through box Cover bolt of wing carry-through box Crack in forward tunnel truss (a) (b)
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numerical listing shows the fuselage station, water line and butt line position (in inches) for each locatable acoustic emission event, as well as the load (in percent of limit) at which each event occurred. Another use for the numerical display is in determining the exact severity of the acoustic emission event, instead of relying on the green, yellow and red color coding. Of particular interest in Fig. 2 are the cluster of acoustic emission events in the tunnel truss area, the event on the starboard wing and a critical event in the left front corner of the wing carry-through box. The events in the tunnel truss area were caused by the formation of a crack in the forward tunnel truss during cold proof testing. This truss is an arch shaped piece of aluminum; its aft counterpart is shown in Fig. 1. The events on the starboard wing (two acoustic emission events at the same site) are believed to be caused by the formation of a disbond in the wing skin to wing pivot support assembly joint. One critical event is caused by the failure of a large bolt that helps attach the cover of the wing carry-through box, which also serves as a fuel tank. The failure of the bolt could not be verified immediately because fuel tank sealant held it firmly in position. However, ultrasonic testing of bolt lengths revealed that one bolt was shorter than its installed length. Similar bolts on the rear left edge of the wing carry-through box may be seen in Fig. 1.
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  • Fall '19
  • Fighter aircraft, Nondestructive testing, Acoustic Emission, Acoustic Emission Testing

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