Composite Aerospace Structures Questions and Answers

Answer: A

The first two describe the approach. The third inverts its justification: the pyramid exists precisely because composite failure modes are less amenable to prediction from first principles, so confidence must be built empirically.

Answer: B

Correct answer: A-2, B-1, C-4, D-3

Four elements with four distinct roles. The fibre carries load along its own direction. The matrix transfers load between fibres, supports them against buckling in compression, and protects them. The ply interface, having no fibre crossing it, is the weakest plane and the site of delamination. And a conductive mesh in the outer surface gives the lightning current a path, which carbon fibre alone cannot adequately provide.

Answer: C

Correct answer: A-2, B-3, C-4, D-1

Two of these are material properties and two are consequences of stacking. Longitudinal modulus follows the direct rule of mixtures and is fibre-dominated; transverse modulus follows the inverse rule and is matrix-dominated. Extension-bending coupling is the B matrix, removed by making the laminate symmetric, and extension-shear coupling is removed by making it balanced.

Answer: D

The modes appear roughly in order of severity and of how readily they are detected. Fibre breakage is generally terminal, while matrix cracking may be tolerated, and it is the undetectable middle case that drives the design allowables.

Answer: A

Correct answer: A-2, B-1, C-4, D-3

Four stages, each with its own characteristic. Prepreg comes with its resin content fixed in advance, which is what gives the control, and needs cold storage in return. The autoclave applies heat and pressure together, which is what gives the low void content. Automated fibre placement supplies rate and repeatability. And a scarf repair tapers the joint through the thickness so the load path is restored ply by ply.

Answer: B

Correct answer: A-2, B-1, C-4, D-3

Each problem has its standard remedy. A glass fibre interleaf or sealant breaks the electrical path that would otherwise corrode the aluminium. A conductive mesh in the outer surface conducts lightning current away. A symmetric stacking sequence makes the B matrix vanish and removes extension-bending coupling. And the hot-wet strength reduction is handled by applying a knock-down to the allowable.

Answer: C

Correct answer: Easier inspection and repair

Inspection and repair are harder with composites, not easier: damage may be internal and invisible, ultrasonic or thermographic methods are needed to find it, and a repair means a scarfed and re-cured patch rather than a riveted doubler. The other three are genuine advantages - tailorable properties, freedom from corrosion of the laminate itself, and higher specific stiffness along the fibres.

Answer: D

Correct answer: Its properties match in every direction

Quasi-isotropic means isotropic in the plane only. Through the thickness the laminate remains very weak, since no fibres cross the ply interfaces, and that difference is the source of delamination and of the impact sensitivity. The other three statements are all correct descriptions of such a layup.

Answer: A

Immunity overstates a real advantage into an error. Matrix cracking, delamination growth and the growth of impact damage under compression are all genuine mechanisms, even though tensile fatigue is far less troublesome than in aluminium.

Answer: B

A higher fibre fraction raises the fibre-dominated properties rather than lowering them, up to the point where the resin can no longer wet the fibres. The other three are all knock-downs applied in arriving at a design value.