This set of Mechanical Behaviour Multiple Choice Questions & Answers (MCQs) focuses on “Creep Strength”.
1. _____ occurs when metal is subjected to a constant tensile load at an elevated temperature?
a) Fatigue
b) Creep
c) Impact
d) Wear
View Answer
Explanation: Creep takes place at constant tensile load on elevated temperature. It is a time-dependent deformation. While fatigue is a failure of material caused by repeatedly applied loads.
2. Creep is a ____ dependent phenomenon.
a) Temperature
b) Time
c) Load
d) Stress cycle
View Answer
Explanation: Creep occurs at all temperatures. This deformation occurs at constant stress. It is a time-dependent phenomenon.
3. Creep occurs due to sliding of _____
a) Vacancies
b) Voids
c) Grain boundaries
d) Dislocations
View Answer
Explanation: Creep deformation occurs due to the sliding of grain boundaries. At elevated temperatures, grain boundaries become weaker than grains. To enhance creep strength, this sliding is checked by various methods.
4. Which one of the following, is a static mechanical property?
a) Impact strength
b) Creep strength
c) Fatigue strength
d) Rebound hardness
View Answer
Explanation: Properties, which are measured on a constant external force, are static Mechanical properties. Creep strength is measured under constant stress. Impact strength, fatigue strength and rebound hardness are dynamic properties.
5. The ______ the melting point and the _____ the elastic modulus, the higher is creep strength.
a) Lower, lower
b) Lower, higher
c) Higher, lower
d) Higher, higher
View Answer
Explanation: Creep deformation is easy in lower melting point materials. With an increase in elastic modulus, creep strength of material improves. It is because deformation is difficult in high elastic modulus materials.
6. In _____ creep, atoms diffuse along grain boundaries and grains elongate in stress axis.
a) Dislocation
b) Nabarro-Herring
c) Coble
d) Solute drag
View Answer
Explanation: Coble creep is a diffusion controlled creep. It increases with increasing temperature. It is highly dependent on grain size.
7. Which of the following factors is inversely proportional to the magnitude of creep?
a) Temperature
b) Time
c) Grain size
d) Stress
View Answer
Explanation: With a decrease in grain size, magnitude of creep increases. It is because grain boundaries become weak at elevated temperatures and start to slide. With an increase in temperature, time and stress creep increases.
8. Crosslinking in Polymers increases creep strength.
a) True
b) False
View Answer
Explanation: Highly cross linked Polymers show good strength and elastic modulus. Thus these resist plastic deformations at high temperatures. Hence these show high creep resistance.
9. Which statement is correct regarding creep strength?
a) Wrought materials have higher creep strength than cast materials
b) With an increase in temperature, steady state creep rate decreases
c) Creep strength can be improved by precipitation hardening
d) Aromatic rings in polymer decrease creep strength
View Answer
Explanation: Cast materials show higher creep resistance. With increasing temperature, creep rate increases. Aromatic rings in Polymers increase creep resistance by cross linking.
10. Creep occurs only at high temperatures.
a) True
b) False
View Answer
Explanation: Creep occurs at all temperatures. Materials with low melting temperature (as lead and solder) begin to creep at room temperature. Plastics also creep at room temperature.
11. Nabarro-Herring creep predicts a strain rate which is a function of _____
a) D
b) D-2
c) D-3
d) D-1
View Answer
Explanation: Nabarro-Herring creep predicts a strain rate that is a function of D-3. Grain boundary creep predicts strain rate that is a function of D-2. Here strain rate is a function of grain size, D.
12. Match the following.
| Material | Creep temperature |
|---|---|
| i) Carbon steel | p) > 50-150°C |
| ii) Alloy steel | q) > room temperature |
| iii) Light metal and alloy | r) > 450°C |
| iv) tin | r) > 420°C |
a) i-r, ii-s, iii-p, iv-q
b) i-s, ii-r, iii-p, iv-q
c) i-r, ii-s, iii-q, iv-p
d) i-s, ii-r, iii-q, iv-p
View Answer
Explanation: For metals, creep is noticeable at 35% of melting temperature. For ceramics this is 45% of melting temperature. Some low melting point materials (here Sn) show creep at even room temperature.
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