# Mechanical Behaviour Questions and Answers – Fatigue Behaviour in Iron and Steel

This set of Mechanical Behaviour online test focuses on “Fatigue Behaviour in Iron and Steel”.

1. Fatigue strength of iron and steel _________ with an increase in temperature.
a) Increases
b) Decreases
c) Remains constant
d) First increases and then decreases

Explanation: Fatigue strength of materials increases with an increase in temperature above 100˚C. This value reaches a maximum value between 200˚C and 400˚C. After this decrease is seen.

2. Strain ageing process is associated with _________

Explanation: Strain ageing is a time dependent process. Dislocation movement is the important factor here. It is associated with static loading.

3. Which statement is true for steels?
a) These show distinct fatigue limit
b) Fatigue strength can’t be enhanced
c) Coaxing reduces their fatigue strength
d) Under stressing reduces their fatigue strength

Explanation: Steels show distinct fatigue limit. Their fatigue strength can be enhanced. It is by either coaxing or under stressing.

4. Which factor decreases the fatigue strength of iron and steel?
a) Under stressing
b) Coaxing
c) Temperature
d) Notching

Explanation: Notching decreases component’s fatigue strength. It is because of the stresses associated with it. Coaxing, under stressing and increasing temperature enhance fatigue strength of steels.

5. What temperature gives maximum fatigue strength of steels?
a) Below 100˚C
b) 100-200˚C
c) 200-400˚C
d) 500-600˚C

Explanation: Fatigue strength of steels increase with an increase in temperature. It increases above about 100˚C. It attains a maximum between 200 and 400˚C.

6. Which property is enhanced by strain ageing?
a) Tensile strength
b) Ductility
c) Stiffness
d) Yield strength

Explanation: Tensile curve shifts by strain hardening. It is time and temperature dependent. Its main motive is to enhance yield strength.

7. In which materials, increase in fatigue strength by coaxing is possible?
a) Ferrous
b) Strain ageable
c) Non-ferrous
d) Plastics

Explanation: Strain ageing is an important factor for coaxing. So fatigue strength enhancement is only possible for materials which can be strain aged.

8. A material is a fatigue tested below the fatigue limit for few millions of cycles and then retested at higher than fatigue limit. This process is known as ___________
a) Under stressing
b) Coaxing
c) Bridging
d) Toughening

Explanation: A material is a fatigue tested below the fatigue limit for few millions of cycles and then retested at higher than fatigue limit. This process is known as coaxing. For steels and irons, it enhances fatigue strength.

9. What is the diffusion rates of carbon and nitrogen atoms markedly dependent on?
a) Temperature
c) Crystal structure
d) Fatigue strength

Explanation: Diffusion rate is mainly dependent on temperature. It causes the strain ageing. It leads to strengthening.

10. Tensile strength decrease by strain ageing.
a) True
b) False

Explanation: Tensile strength is increased by strain ageing. Yield strength also increases because of tensile curve shifting.

11. Yield point phenomenon is more marked in annealed low carbon steels.
a) True
b) False

Explanation: Yield point phenomenon is seen in various non-ferrous materials too. But this is more marked in annealed low carbon steels due to the presence of carbon atoms.

Sanfoundry Global Education & Learning Series – Mechanical Behaviour & Testing of Materials.

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