Buckling of Plates and Columns Questions and Answers

Answer: A

Skin buckling is delayed by increasing internal pressure.

Fuselage skin buckles under compression or shear from bending and torsion of the fuselage. Cabin pressurisation puts the skin into tension in both the hoop and longitudinal directions, which offsets part of the compressive stress and also stiffens the curved panel, so a higher load is needed before it buckles.

Placing stiffeners farther apart increases the unsupported panel size, and the buckling stress of a panel falls with the square of its width. Reducing skin thickness lowers it with the square of thickness. The last option combines two changes that both promote buckling.

Answer: B

Both [a] and [r] are true, but [r] is not the correct reason for [a].

[a] is true: ribs support the stringers at intervals along the span, so each stringer buckles as a column only over the shorter length between ribs, and the column buckling load rises as the inverse square of that length.

[r] is also true: ribs transfer concentrated loads, such as those from engines, undercarriage and control surfaces, into the skin and spars, and redistribute stresses around cut-outs. But that is a different function. The increase in buckling strength comes from shortening the effective column length, not from load distribution, so [r] does not explain [a].