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The wing spar ABD of a light plane is made from 2014-T6 aluminum and has a cross

ID: 1719073 • Letter: T

Question

The wing spar ABD of a light plane is made from 2014-T6 aluminum and has a cross-sectional area of 800 mm2, a height of 76 mm. and a moment of inertia about its neutral axis of 1.21(10^-6) m^4. Assume A, B and C are pins. The neutral axis passes through the cross-section at half of its height. Connection is made along the central longitudinal axis of the spar. The anticipated loading is to be as shown. Part A Determine the absolute maximum bending stress in the spar. Express your answer to three significant figures and include the appropriate units.

Explanation / Answer

Drawing Free Body Diagram (FBD) of the span,

Writing equilibrium equation in vertical direction,

R1 + R2 = -19.44

Writing moment equation about point A,

R2 = -19.44

R1 = 0

Maximum bending stress will be at the support point A.

Maximum bending moment = 19.44 x 0.8 = 15.552 kN-m.

Maximum bending stress = Mc/I = 15.552 x 0.038 / 1.21 x 10-6 m4

= 488.409 MPa