# Mechanical Behaviour Questions and Answers – Deformation by Twinning

This set of Mechanical Behaviour Multiple Choice Questions & Answers (MCQs) focuses on “Deformation by Twinning”.

1. The extend of deformation due to mechanical twinning is ___ than due to slip.
a) smaller
b) larger
c) equal
d) smallest

Explanation: The volume of any given crystal which is reoriented by mechanical twinning is quite small. The total amount of deformation is smaller. While deformation extent is larger in slip.

2. In ___ crystals, slip systems are limited to three, making slip difficult.
a) BCC
b) FCC
c) HCP
d) SC

Explanation: In HCP crystals, slip systems are limited. Slip planes are basal planes {0 0 0 1}. Limited number of slip planes makes slip difficult.

3. The plane passing through the twinning axis and separating the region of twinning from undeformed part is called ___ planes.
a) Twinning
b) Slip
c) Basal
d) Close packed

Explanation: Twinning takes place along twinning axis. The plane passing through twinning axis is called twinning plane. This plane separates the twinning region from the undeformed region in crystal.

4. What is twinning plane in FCC metals?
a) {1 1 1}
b) {1 0 0}
c) {1 1 0}
d) {2 1 1}

Explanation: Twinning plane for FCC metals is {1 1 1} plane. These are known as octahedral planes. Twinning can only occur on this plane family.

5. What is twinning plane for BCC metals?
a) {1 1 1}
b) {1 0 0}
c) {1 2 3}
d) {1 1 2}

Explanation: Twinning plane for BCC metals is {1 1 2}. Twinning can take place only on these planes.

6. What is twinning plane for HCP crystals?
a) {0 0 0 1}
b) {1 0 1 0}
c) {1 0 1 2}
d) {1 1 1 1}

Explanation: In HCP crystals, twinning plane is {1 0 1 2}. Twinning occurs on these planes. {0 0 0 1} are slip planes.

7. What is twinning plane for rhombohedral crystals?
a) {1 1 1}
b) {1 1 0}
c) {1 1 2}
d) {0 1 1}

Explanation: {0 1 1} are the twinning planes for rhombohedral crystals. In these crystals, twinning is only possible in these planes. {1 1 1} is twinning plane for FCC crystals.

8. What is associated with a cry of tin?
a) Slip
b) Thermal vibration
c) Twinning
d) Quenching

Explanation: The cry of tin is referred to a cracking noise. It is associated from copious formation of twins. It results from the bending of tin rod.

9. The stress-strain curve of single crystal undergoing twinning shows ____
a) No irregularity
b) Jagged irregularities
c) Sudden drop in the curve
d) Peaks

Explanation: The stress-strain curve of a single crystal undergoing twinning shows sharp, jagged irregularities. Each irregularity corresponds to a small permanent deformation. These are created because of twins.

10. Which of the following statement is false?
a) Annealing twins occur during annealing heat treatment
b) Mechanical twins generate due to plastic deformation
c) Annealing twins form in high stacking fault energy metals
d) Annealing twins are mostly observed in FCC metals

Explanation: Annealing twins form in low stacking fault energy metals. These are mostly observed in FCC metals, example of this is brass, copper and austenitic stainless steels.

11. Annealing twins largely effect strain hardening properties.
a) True
b) False

Explanation: Annealing twins form during annealing of low stacking fault energy metals. These twins have an insignificant effect on strain hardening of the material. It is due to the small contribution to deformation.

12. Deformation by twinning is not a dominant mode of deformation in FCC metals.
a) True
b) False

Explanation: FCC metals consist of many slip systems at room temperature. Thus slip is easy in these metals. So twinning is not a dominant mode of deformation.

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

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