Delamination is a failure mode in which
Answer: C
The interface is matrix-dominated and has no reinforcement across it, so it is the weakest direction in the material. Delamination often results from impact or from interlaminar stresses at a free edge, and it severely reduces compressive capability.
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Barely visible impact damage is a concern because
Answer: D
A tool dropped on a panel can delaminate a substantial area while leaving little surface mark. Since the reduction in compression strength can be forty per cent or more, design allowables are set assuming such damage is present and undetected.
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Compression after impact testing is used to establish
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.
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Composite laminates are notably weaker in which loading direction?
Answer: B
No reinforcement crosses the ply interfaces, so through-thickness strength is a matrix property and very low. Designs therefore avoid out-of-plane loads wherever possible, and features such as curved sections and joints receive special attention.
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Bolted joints in composites differ from those in metals in that composites
Answer: C
A metal redistributes load plastically around a hole, sharing it more evenly between fasteners. A composite is essentially elastic to failure, so the peak stays where the elastic analysis puts it and joints must be designed with that in mind.
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Bonded joints in composite structure are attractive because they
Answer: D
Drilling cuts the very fibres that carry the load, so a bonded joint that transfers load through shear over an area is inherently more efficient. The difficulty is that a weak bond is hard to detect, which is why critical bonded joints often carry fasteners as well.
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The hot-wet condition is used for composite design allowables because
Answer: A
Epoxy absorbs moisture over time, and the combination with high temperature lowers the glass transition and reduces matrix-dominated properties. Allowables are therefore quoted for the hot-wet case, which can be twenty per cent or more below the room-temperature dry value.
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Carbon fibre composite in contact with aluminium presents a risk of
Answer: B
Carbon is electrically conductive and noble relative to aluminium, so in the presence of an electrolyte the aluminium corrodes preferentially. A glass fibre layer or a sealant is used to isolate the two wherever they meet.
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Lightning strike protection on a composite aircraft is needed because
Answer: C
An aluminium skin conducts a strike away readily, whereas carbon composite does not, so the energy can burn through or damage the laminate. A conductive mesh or foil is incorporated in the outer surface to provide the path.
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The building block approach to composite certification means
Answer: D
Because composite failure is not predicted from first principles as reliably as metal yielding, confidence is built up through a pyramid of tests of increasing complexity and decreasing number. The approach is far more test-intensive than metallic certification.
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