Instruction
- Total number of questions : 20
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Aerospace Structures [ Question No: 1 To 20 ] :
A test programme uses \( 2000 \) coupons, \( 200 \) elements, \( 20 \) sub-components and \( 1 \) full-scale article. This pyramid illustrates
Compression after impact testing is used to establish
Taken together, the methods in this topic answer which question?
Assertion (A): An occasional tensile overload can lengthen the life of a cracked component.
Reason (R): The overload leaves a plastic zone that closes in compression on unloading.
Select the correct answer from the options below.
Which statement about combining stresses is INCORRECT?
Consider the following statements about analysing a wing section:
1. Section properties depend on the idealisation chosen.
2. Shear flows depend on the direct stress distribution.
3. The deflection must be computed before the stresses.
Which of the statements given above is or are correct?
The shear flow applied to a fuselage frame by the surrounding skin is
Consider the following statements about imperfections in columns:
1. An initial bow grows rapidly as the load approaches the critical value.
2. Real columns therefore fail below the Euler load.
3. The Southwell plot requires the column to be loaded to collapse.
Which of the statements given above is or are correct?
Local buckling of a stiffened panel refers to
The overall lesson of this topic for a stress engineer is that
Post-buckled skin is described as being in a diagonal tension field when
All of the following are legitimate reasons to idealise a structure EXCEPT
Consider the following statements about global-local modelling:
1. The coarse model supplies displacements or forces to a refined submodel.
2. It gives detailed stresses without meshing the whole structure finely.
3. The submodel must be coarser than the global model.
Which of the statements given above is or are correct?
Which statement about a two-cell box under torque is TRUE?
Assertion (A): A buckled compression panel is treated as only partly effective in bending.
Reason (R): After buckling, the middle of the panel sheds load while material near the stiffeners keeps carrying it.
Select the correct answer from the options below.
In unsymmetric bending, the neutral axis is
Which statement about gust loads is TRUE?
Assertion (A): The gust alleviation factor is always less than one.
Reason (R): A real gust builds up over a distance, and the aircraft starts to respond during that build-up.
Select the correct answer from the options below.
Four stringers of \( 300 \) mm\( ^2 \) each sit at the corners of a box \( 0.5 \) m deep. Ignoring the skin, the second moment of area about the neutral axis is
Tear straps bonded or riveted to a pressurised fuselage skin serve to
Total number of questions : 20
Number of answered questions : 0
Number of unanswered questions : 20
Aerospace Structures [ Question No: 1 To 20 ] :
A test programme uses \( 2000 \) coupons, \( 200 \) elements, \( 20 \) sub-components and \( 1 \) full-scale article. This pyramid illustrates
Your Answer : (Not Answered)
Correct Answer : C
Numbers fall and complexity rises as the pyramid is climbed, so that confidence built cheaply at coupon level supports the few expensive tests at the top. Composite certification relies on it far more heavily than metallic certification does.
Compression after impact testing is used to establish
Your Answer : (Not Answered)
Correct Answer : A
A panel is struck with a defined energy and then loaded in compression to failure. The result gives the design allowable for a structure assumed to contain barely visible damage, and it typically governs the sizing of a composite compression panel.
Taken together, the methods in this topic answer which question?
Your Answer : (Not Answered)
Correct Answer : D
Static strength answers the first of the alternatives; fatigue and damage tolerance answer the question of endurance over tens of thousands of flights. The two together, and only together, establish that a structure is fit for service.
Assertion (A): An occasional tensile overload can lengthen the life of a cracked component.
Reason (R): The overload leaves a plastic zone that closes in compression on unloading.
Select the correct answer from the options below.
Your Answer : (Not Answered)
Correct Answer : A
Both statements are true and the second is the reason for the first. The retardation is real but it makes test spectra containing frequent overloads unconservative, so spectrum development takes care over how such cycles are represented.
Which statement about combining stresses is INCORRECT?
Your Answer : (Not Answered)
Correct Answer : A
Correct answer: Direct and shear stresses may be added arithmetically
This is the incorrect statement. Direct and shear stresses act on different planes and cannot simply be summed; they must be combined through the principal stresses or through a failure criterion. Von Mises gives \( \sqrt{\sigma^2 + 3\tau^2} \), the factor of three reflecting that shear is the more damaging of the two, and Tresca works on the maximum shear stress. The other three statements are all correct.
Consider the following statements about analysing a wing section:
1. Section properties depend on the idealisation chosen.
2. Shear flows depend on the direct stress distribution.
3. The deflection must be computed before the stresses.
Which of the statements given above is or are correct?
Your Answer : (Not Answered)
Correct Answer : B
Correct answer: 1 and 2 only
Statements 1 and 2 are correct: the idealisation determines what area is credited to each boom and therefore the section properties, and the shear flows follow from the direct stress distribution through the shear flow equation. Statement 3 reverses the order - deflection is obtained by integrating the curvature, which requires the stresses and the section properties to be known first.
The shear flow applied to a fuselage frame by the surrounding skin is
Your Answer : (Not Answered)
Correct Answer : A
The frame does not act alone: the skin feeds shear into it all the way round, and that distributed reaction is what balances the concentrated load applied to it. Ignoring it and treating the frame as a free ring badly overstates the bending moments.
Consider the following statements about imperfections in columns:
1. An initial bow grows rapidly as the load approaches the critical value.
2. Real columns therefore fail below the Euler load.
3. The Southwell plot requires the column to be loaded to collapse.
Which of the statements given above is or are correct?
Your Answer : (Not Answered)
Correct Answer : D
Correct answer: 1 and 2 only
Statements 1 and 2 describe imperfection sensitivity correctly: an initial bow amplifies without limit as the load approaches the critical value, so a real column never reaches the theoretical figure. Statement 3 is the reverse of the Southwell plot’s purpose - it extrapolates from readings well below the critical load precisely so that collapse is not required.
Local buckling of a stiffened panel refers to
Your Answer : (Not Answered)
Correct 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.
The overall lesson of this topic for a stress engineer is that
Your Answer : (Not Answered)
Correct Answer : D
Correct answer: Every model embeds assumptions
Whether it is a boom and panel idealisation or a million-element finite element model, someone has decided what carries what, what may be neglected and how the structure is supported. The engineer’s task is to know what those assumptions are and where they cease to hold. Software does not remove that judgement; the finest model is not automatically the right one; and hand methods survive precisely because they make the assumptions visible.
Post-buckled skin is described as being in a diagonal tension field when
Your Answer : (Not Answered)
Correct Answer : C
The panel gives up its shear stiffness on buckling but continues to carry load as a series of inclined straps. The uprights and flanges must then be sized for the inward pull those straps produce, which is a load case that would not exist otherwise.
All of the following are legitimate reasons to idealise a structure EXCEPT
Your Answer : (Not Answered)
Correct Answer : C
Correct answer: To beat the real structure for accuracy
An idealisation is a deliberate simplification and can never be more accurate than the structure it represents - that is not what it is for. The three legitimate purposes are all present in the other options: making the load path explicit so that the analyst must decide what carries what, reducing an intractable geometry to something that can be analysed, and allowing options to be compared quickly while the design is still moving.
Consider the following statements about global-local modelling:
1. The coarse model supplies displacements or forces to a refined submodel.
2. It gives detailed stresses without meshing the whole structure finely.
3. The submodel must be coarser than the global model.
Which of the statements given above is or are correct?
Your Answer : (Not Answered)
Correct Answer : C
Correct answer: 1 and 2 only
Statements 1 and 2 describe the method and its purpose. Statement 3 inverts the arrangement - the submodel must be very much finer than the global model, typically by a factor of ten or twenty, since detail in the critical region is the whole object. The coarse model supplies the displacements on the submodel’s cut boundaries, which must be placed well away from the region of interest.
Which statement about a two-cell box under torque is TRUE?
Your Answer : (Not Answered)
Correct Answer : A
Correct answer: Both cells must twist at the same rate
The two cells share a web and belong to one structure, so compatibility requires them to have the same rate of twist. That condition, together with equilibrium of the total torque, is what determines how the shear flow divides between them. The flows are generally unequal, and the shared web carries their difference, not their sum.
Assertion (A): A buckled compression panel is treated as only partly effective in bending.
Reason (R): After buckling, the middle of the panel sheds load while material near the stiffeners keeps carrying it.
Select the correct answer from the options below.
Your Answer : (Not Answered)
Correct Answer : C
Both are true and the second explains the first. Counting an effective width attached to each stiffener reproduces the load the panel really carries. Treating the panel as fully effective would overstate the section's bending capacity.
In unsymmetric bending, the neutral axis is
Your Answer : (Not Answered)
Correct Answer : A
Only when bending occurs about a principal axis does the neutral axis lie perpendicular to the moment. With a non-zero product of inertia the section prefers to bend about a different direction, so the neutral axis rotates away and a moment applied in one plane produces deflection in another.
Which statement about gust loads is TRUE?
Your Answer : (Not Answered)
Correct Answer : D
The gust increment is inversely proportional to wing loading, so the same gust produces a larger load factor on a light aircraft. It follows that the gust envelope must be checked at light weight as well as heavy, since the critical case is not always the heaviest.
Assertion (A): The gust alleviation factor is always less than one.
Reason (R): A real gust builds up over a distance, and the aircraft starts to respond during that build-up.
Select the correct answer from the options below.
Your Answer : (Not Answered)
Correct Answer : B
Both statements are true and the second is the reason for the first. Because the aircraft begins accelerating upward before it is fully immersed, the angle-of-attack change it experiences is less than the sharp-edged idealisation predicts, so the factor reduces the computed load.
Four stringers of \( 300 \) mm\( ^2 \) each sit at the corners of a box \( 0.5 \) m deep. Ignoring the skin, the second moment of area about the neutral axis is
Your Answer : (Not Answered)
Correct Answer : C
Each of the four areas lies \( 0.25 \) m from the axis, so \( I = 4 \times 300 \times 10^{-6} \times 0.25^2 = 4 \times 3 \times 10^{-4} \times 0.0625 = 7.5 \times 10^{-5} \) m\( ^4 \). Booming off the stringers like this is the standard idealisation for a stiffened box.
Tear straps bonded or riveted to a pressurised fuselage skin serve to
Your Answer : (Not Answered)
Correct Answer : D
By providing a local increase in fracture toughness and load path, a tear strap turns a crack that would run for many frames into one that stops at a bay boundary. The result is a controlled decompression rather than a catastrophic failure, which is the central idea of damage tolerance.
Marks
Total number of questions : 20
Number of answered questions : 0
Number of unanswered questions : 20