phase4 - AIRCRAFT STRUCTURES PROJECT PHASE IV EAS 4200C...

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AIRCRAFT STRUCTURES PROJECT PHASE IV EAS 4200C Roberto Barraza IFID 0087-1745 12/15/2010

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1. A 1.5 in long through thickness crack has been discovered on the bottom surface of the wing close to the fuselage as shown in the figure below. The crack makes a 45 angle with the y-axis of the wing (along the span). Determine the stress intensity factor KI for Mode I loading. If the fracture toughness of the alloy used is IC K = 24 MPa m , would you recommend grounding the airplane? From phase III of the project, we know that the shear stress at the root for both cases is: AVG AVG q t   1248.5 psi, ( ) yy AVG -15729 psi ell ell q t   1846.9 psi, ( ) yy ell -17620 psi 0 0 1( ) ( ) sin(45 ) cos(45 ) AVG AVG yy AVG 0 0 1( ) ( ) sin(45 ) cos(45 ) ell ell yy ell Thus, we can calculate the stress intensity factor as follows: ( ) 1( ) I AVG AVG K a -15717.2 psi in ( ) 1( ) I ell ell K a -17120.2 psi in Converting the fracture toughness to English units, we get IC K 21841.1 psi in . Thus both cases (average and elliptical) are within safe limits and the airplane is safe to flight.
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