This set of Mechanical Behaviour Questions and Answers for Entrance exams focuses on “Variables Affecting Fatigue”.
1. Which element has a maximum effect on fatigue strength in steel?
a) Ni
b) Ag
c) C
d) Au
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Explanation: Carbon in steel has the maximum effect on fatigue strength. It is due to solid solution strengthening.
2. What causes an increase in fatigue strength of steel?
a) Vacancies
b) Micro cracking
c) Bridging
d) Strain ageing effect
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Explanation: C in steel increases maximum fatigue strength. It is because of solid solution strengthening along with strain ageing effect.
3. What increases fatigue life?
a) Decarburized region
b) Machine marking
c) Polishing surface
d) Inclusions
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Explanation: Decarburized regions, inclusions and machine markings cause an increase in surface irregularity. It decreases fatigue life. Polishing surface improves fatigue life.
4. What decreases fatigue life?
a) C in steel
b) Polishing
c) Strain ageing
d) Porosity
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Explanation: Porosity includes irregularity on a surface. It reduces fatigue life. It reduces fatigue life. Polishing and strengthening improve fatigue life.
5. What improves fatigue strength of the component?
a) Electroplating
b) Buffing
c) Indentation
d) Softening
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Explanation: Buffing improves fatigue strength of the component. Electroplating generally lowers the fatigue strength. Indentation and softening also lower fatigue life.
6. What is not improved by case hardening?
a) Surface hardness
b) Wear resistance
c) Flexibility
d) Fatigue life
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Explanation: Steels are case hardened. It improves surface hardness, wear resistance and fatigue life.
7. The ___________ part of the cyclic stress assists crack opening and its propagation.
a) Normal
b) Shear
c) Tensile
d) Compressive
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Explanation: The tensile part of the cyclic stress assists crack opening and its propagation. Residual stresses thus are dangerous if are of tensile type.
8. What is a way to introduce compressive residual stresses?
a) Micro cracking
b) Bridging
c) Shot peening
d) Heating
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Explanation: Shot peening is the best way to introduce compressive residual stresses. It increases fatigue life. Micro cracking will decrease fatigue life.
9. For steel, fatigue strength is __________ of tensile value.
a) Twice
b) Thrice
c) Half
d) Quarter
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Explanation: Fatigue strength of steel is near 50% of its tensile value. Fatigue ratio hence is ½ for steel.
10. With increase in stacking fault energy, fatigue strength of material __________
a) Increases
b) Decreases
c) Remains constant
d) First Increases and then decreases
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Explanation: For materials with high stacking fault energy, dislocations can easily cross glide. It helps in the development of extrusion and intrusions. It decreases fatigue strength.
11. Non-ferrous metals have fatigue ratio of 0.35.
a) True
b) False
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Explanation: Non-ferrous metals have fatigue ratio of 0.35. Fatigue ratio is a ratio of fatigue strength and tensile strength.
12. Hard surface materials have low fatigue strength.
a) True
b) False
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Explanation: Hard surfaces are difficult to yield. It delays the initiation of a fatigue crack. It improves fatigue strength.
13. Which condition is okay to use in cyclic stresses?
a) Low hardness surface
b) Machined surface
c) High SFE
d) Coarse grain structure
View Answer
Explanation: Machining of surface reduces its roughness and hence crack nucleation sites. It improves fatigue life. High surface hardness, low SFE and fine grain structure are preferred.
Sanfoundry Global Education & Learning Series – Mechanical Behaviour & Testing of Materials.
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