# Mechanical Behaviour Questions and Answers – Equicohesive Temperature

This set of Mechanical Behaviour Multiple Choice Questions & Answers (MCQs) focuses on “Equicohesive Temperature”.

1. At low temperature, metals under stress deform by ________
a) Slip and twin
b) Softening
c) Rupture
d) Residual stresses

Explanation: At low temperature, metals under stress deform by slip and twin. These temperatures are about one half of the absolute melting temperature.

2. The fracture through grains is known as ________
a) Rupture
b) Trans granular
c) Inter crystalline
d) Intergranular

Explanation: If applied stress is sufficiently large, fracture occurs through grains. It is known as trans granular fracture.

3. A fracture through grain boundaries is _________
a) Trans granular
b) Trans crystalline
c) Cohesive
d) Intergranular

Explanation: On higher temperatures, grain boundaries become weak. Now crack propagate through grain boundaries. This is an intergranular fracture.

4. At _________________ the grain boundaries of polycrystalline metals act as ________ for cracks.
a) Low temperature, barrier
b) High temperature, barrier
c) High stress, barrier
d) High stress, nucleation sites

Explanation: At lower temperatures, the grain boundaries of polycrystalline materials are stronger than grains and it acts as a barrier for dislocation movement.

5. Which temperature is more important for alloys?
a) Melting temperature
b) Boiling temperature
c) Recrystallization temperature
d) Sub-zero temperature

Explanation: Recrystallization temperature is more important than melting temperature. It decides the phase transformation.

6. Why grain boundaries become weak on high temperatures?
a) Mobility of atoms
b) Partial melting
c) Dislocation pile up
d) Substructure

Explanation: The mobility of atoms in the grain boundary regions becomes high. Grains still maintain their stability. Hence grain boundaries are weaker.

7. With an increase in temperature, the cohesiveness of grain boundary ________
a) Increases
b) Decreases
c) Remains constant
d) First increases, then decrease

Explanation: On higher temperature, atoms become more mobile. The cohesiveness of the grain boundary decreases.

8. Grain boundary ________ occurs at a high temperature causing an intergranular fracture.
a) Gliding
b) Strengthening
c) Sliding
d) Twinning

Explanation: At high temperatures, atomic mobility increases in grain boundaries. It causes grain boundary sliding causing an intergranular fracture.

9. Which of the following temperature is used to differentiate transgranular and intergranular modes of fracture?
a) Recrystallization
b) Equi-cohesive
c) Curie
d) Critical

Explanation: Equicohesive temperature is the temperature at which the strength of grain and grain boundary is the same. It is used to differentiate the mode of fracture, which has transgranular fracture below equicohesive temperature and intergranular fracture at above equicohesive temperature.

10. With increasing strain rate, ECT _________
a) Increases
b) Decreases
c) Remains constant
d) First increases, then decrease

Explanation: On decreasing strain rate, ECT lowers. Hence the tendency for intercrystalline fracture increases.

11. Which process doesn’t occur at high temperature?
a) Sub grain formation
b) Recovery
c) Recrystallization
d) Slip and twinning

Explanation: At low temperatures, metals under stress deform principally by slip or twinning. Sub grain formation recovery and recrystallization occur at high temperature.

12. Equicohesive temperature is twice that of recrystallization.
a) True
b) False

Explanation: For most of the metals, the equicohesive temperature is equal to recrystallization temperature. Recrystallization temperature is fixed while equicohesive temperature has a range.

13. Below the equicohesive temperature, the strength of grain boundaries are higher than grains.
a) True
b) False

Explanation: At equicohesive temperature, the strength of grains and grain boundary is equal. Below the equicohesive temperature, grain boundaries are stronger than grains.

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

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