5. Structures and Materials

Fatigue — Quiz

Test your understanding of fatigue with 5 practice questions.

Practice Questions

Question 1

Which phenomenon best distinguishes low-cycle fatigue (LCF) from high-cycle fatigue (HCF) in metallic aircraft structures?

Question 2

When a component experiences $2\times10^5$ cycles at stress level $S_1$ with fatigue life $N_1=1\times10^6$ cycles and $1\times10^5$ cycles at stress level $S_2$ with fatigue life $N_2=5\times10^5$ cycles, what is the total damage fraction according to Miner’s rule? Show your calculation.

Question 3

Using Paris’ law $\displaystyle \frac{da}{dN}=C(\Delta K)^m$, calculate the crack growth rate if $C=1\times10^{-12}\,\mathrm{m/(cycle\,(MPa\sqrt m)^m)}$, $m=3$, and $\Delta K=15\,\mathrm{MPa\sqrt m}$.

Question 4

For a material with threshold stress intensity factor range $\Delta K_{th}=5\,\mathrm{MPa\sqrt m}$, applied stress range $\Delta\sigma=80\,\mathrm{MPa}$, and geometry factor $Y=1.12$, what is the maximum crack length $a_{max}$ (in mm) below which fatigue crack growth will not occur? Use $\Delta K_{th}=Y\,\Delta\sigma\,\sqrt{\pi\,a_{max}}$. Show your calculation.

Question 5

Which of the following best explains how shot peening improves the fatigue life of metallic aircraft components?