Fatigue and Damage Tolerance Questions and Answers

Answer: A

Correct answer: About 7 per cent

\[ \frac{30 - 28}{30} = 0.067, \] that is about seven per cent. This is a very small margin against unstable fracture. Since the stress intensity grows as the square root of the crack length, a very small further extension consumes what remains, and any overload during that period would take the structure straight past the toughness.

Answer: B

Both are true and the second explains the first. Since no stress is safe indefinitely, an aluminium structure is quoted with a fatigue strength at a stated number of cycles and managed through inspection rather than declared immune.

Answer: C

Both statements are true and the second is the reason for the first. Cold working, interference-fit fasteners and careful hole preparation all address this directly, and they are standard practice in fatigue-critical structure.

Answer: D

Both are true and the second explains the first. Applied tensile cycles must first overcome that compression before the hole edge experiences tension, and improvements of three to five times in life are routinely achieved.

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.

Answer: B

Both are true and the second explains the first. Sequence effects, particularly overload retardation, mean the same set of cycles applied in different orders gives different lives. The rule remains useful as a first estimate because of its simplicity.

Answer: C

Both statements are true and the second is the reason for the first. Without inspection there is nothing to catch the crack, so the interval calculation is an inseparable part of the design rather than a maintenance afterthought.

Answer: D

Both are true and the second explains the first. With the Paris exponent typically around three, a rising stress intensity feeds a rapidly rising growth rate, so most of the crack growth life is spent while the crack is still small.

Answer: A

Both statements are true and the second is the reason for the first. A lower toughness means a smaller critical crack, and therefore a shorter inspection interval, so the strongest alloy is frequently not the best choice for a tension surface.

Answer: B

Both are true and the second explains the first. If many similar details crack at once the alternative paths are cracking too, and the linking of adjacent cracks can produce a failure far larger than any single-crack analysis predicted.