The tangent modulus theory of inelastic buckling replaces Young's modulus with
Answer: C
Above the proportional limit the material's effective stiffness falls, and the tangent modulus captures that. It gives a lower critical load than the elastic formula and agrees well with test results for real aluminium struts.
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A plate's critical buckling stress is proportional to
Answer: D
The plate formula carries the square of t over b, so halving the panel width for the same thickness quadruples its buckling stress. This is precisely why stringers are added to a skin: they shorten the panel and raise its buckling stress sharply.
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The buckling coefficient in the plate formula depends on
Answer: A
The coefficient encapsulates the geometry and boundary conditions, taking a value near four for a long simply supported plate in compression and rising considerably for clamped edges. It is read from standard charts rather than computed each time.
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For a long, simply supported plate in uniaxial compression, the buckling coefficient is close to
Answer: B
The coefficient dips to a minimum of four and then oscillates gently about it as the aspect ratio increases, because the plate buckles into a number of roughly square half-waves. Long panels are therefore treated with a value of four regardless of length.
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A long plate in compression buckles into half-waves that are
Answer: C
The plate finds the cheapest mode, which turns out to make each half-wave about as long as the panel is wide. This is why the buckling coefficient becomes insensitive to length once the plate is more than a few widths long.
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Clamping the unloaded edges of a plate rather than simply supporting them
Answer: D
Restraining the rotation at the edges makes the buckled shape more expensive in strain energy, so the critical stress rises, roughly by a factor of one and three quarters for a long plate. Real riveted edges fall somewhere between the two ideals.
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Unlike a column, a plate that has buckled
Answer: A
Membrane action lets the plate redistribute load towards its supported edges and go on carrying more, which is the whole basis of effective width design. A column, by contrast, has no such reserve and its buckling load is essentially its failure load.
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Local buckling of a stiffened panel refers to
Answer: B
Local instability affects individual elements while the panel as a whole remains straight. Overall or global buckling, in which the stiffener and its attached skin buckle together as a column, is the separate mode that must also be checked.
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An efficient stiffened compression panel is usually designed so that
Answer: C
Correct answer: Local and overall buckling occur at similar loads
Whichever mode arrives first ends the panel’s useful capacity, so material invested in making the other mode stronger is wasted. The efficient design balances the two, sizing the skin, the stringer pitch and the stringer section so that local and overall buckling arrive together.
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Inter-rivet buckling is the buckling of
Answer: D
Treated as a short strip fixed at each fastener, the skin can buckle between rivets if the pitch is too coarse. It is prevented by choosing a pitch small enough that the inter-rivet buckling stress exceeds the stress the skin is expected to reach.
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