# Mechanical Behaviour Questions and Answers – Deformation at Elevated Temperature

This set of Mechanical Behaviour Questions and Answers for Aptitude test focuses on “Deformation at Elevated Temperature”.

1. On _________ temperature slip may also occur on non-close packed planes.
a) Sub-zero
b) Elevated
c) Melting
d) Low

Explanation: At low temperature, plastic deformation occurs by slip on slip planes. But on elevated temperature, it can also occur on non-close packed planes.

2. In aluminum _________ planes are only active slip planes at low temperature.
a) {1 1 1}
b) {1 0 0}
c) {1 1 2}
d) {1 1 0}

Explanation: {1 1 1} planes are only active slip planes in aluminum at low temperature. On high temperature, {1 1 0} and {1 1 2} also become active.

3. The tendency of slip band formation __________ with an increase in temperature.
a) Increases
b) Decreases
c) Remains constant
d) First increases, then decrease

Explanation: The tendency of slip band formation increases with an increase in temperature. Coarse slip bands are also observed at elevated temperatures.

4. Slip band spacing _________ with increasing temperature.
a) Increases
b) Decreases
c) Remains constant
d) First increases, then decrease

Explanation: Slip band spacing increases with increasing temperature. Coarse slip bands form on higher temperatures.

5. Slip band spacing _________ with increasing stress.
a) Increases
b) Decreases
c) Remains constant
d) First increases, then decrease

Explanation: Slip band spacing increases with lowering stress. It is a similar effect that of high temperature.
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6. _________ stress and _________ temperature conditions favor large subgrain formation.
a) Low, low
b) Low, high
c) High, low
d) High, high

Explanation: Low stress and high temperature conditions favor large subgrain formation. The size of subgrains depends on the stress and temperature.

7. What is the reason for decreasing creep rate during primary creep?
a) Subgrain formation
b) Dislocation annihilation
c) Recovery
d) Recrystallization

Explanation: Subgrain formation causes the increased number of low angle grain boundaries. These act as barrier for dislocation motion. Hence creep rate decreases.

8. _________ is a creep recovery process.
a) Subgrain formation
b) Dislocation pile up
c) Grain boundary migration
d) Slip

Explanation: Grain boundary migration is a creep recovery process. It allows the distorted material to undergo further deformation.

9. Which of the following is a principal deformation process?
a) Multiple slips
b) Kink bands formation
c) Subgrain formation
d) Fold formation

Explanation: Subgrain formation is a principal deformation process. Multiple slips, kink bands formation and fold formation are secondary deformation processes.

10. Which of the following is a secondary deformation process?
a) Slip
b) Subgrain formation
c) Grain boundary sliding
d) Multiple slips

Explanation: Multiple slips is a secondary deformation process. Slip, subgrain formation and grain boundary sliding are primary.

11. What is the rate controlling factor in high temperature creep?
a) Dislocation glide
b) Grain boundary sliding
c) Dislocation climb
d) Slip

Explanation: Dislocation climb is the rate controlling factor in high temperature creep. Formation of subgrain structure supports this fact.

12. Creep rate is higher for α-iron than for ϒ-iron.
a) True
b) False

Explanation: α-iron has much higher self-diffusion. That’s why creep rate is higher for α-iron than ϒ-iron.

13. Cross slip of screw dislocations occurs only on low temperatures.
a) True
b) False

Explanation: Deformation by a thermally cross slip of screw dislocation also results at high temperatures. Climb also requires thermal activation.

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