# Mechanical Behaviour Questions and Answers – Dislocation Intersection

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

1. Which of the following jog is a type of jog that has the ability to glide?
a) glissile
b) sessile
c) kink
d) partial

Explanation: Glissile jog is a type of jog that can glide in a particular plane with the rest of the dislocation line.

2. Formation of jog __________ energy related to dislocations.
a) increases
b) decreases
c) doesn’t affect
d) can Increase or decrease

Explanation: Intersection of dislocations results in the formation of jogs. It increases the length of dislocation. Which increases the energy of dislocation.

3. The movement of jogged dislocations is ___________ than dislocations having no jogs.
a) easier
b) more difficult
c) equally difficult
d) easy and difficult

Explanation: The intersection of dislocations involves external energy. So the movement of jogged dislocations in a crystal is more difficult than dislocations having no jogs.

4. Which is the most important type of intersection from viewpoint of plastic deformation?
a) The intersection of edge dislocations having b perpendicular to each other
b) The intersection of edge dislocations having b parallel to each other
c) The intersection of edge dislocation with a screw dislocation
d) The intersection of screw dislocations

Explanation: Intersection of two screw dislocations produces jogs of edge nature on screw dislocations. These dislocations can move only by the climb. That’s why this intersection is important.

5. A __________ is a sharp break in the dislocation line which remains in the slip plane.
a) jog
b) kink
c) dislocation loop

Explanation: A jog is a sharp break in the dislocation moving it out of the slip plane. While kink is a sharp break in the dislocation line which remains in the plane. The difference is of slip plane.
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6. __________ in dislocations are unstable.
a) Jogs
b) Kinks
c) Vacancies
d) Interstitials

Explanation: Kinks in dislocations are unstable. Kinks during glide can line up. These then annihilate the offset.

7. What is the energy of a jog of length b2 and Burgers vector b1?
a) 0.2G1b12b2
b) 0.5Gb1b2b2
c) Gb1b2b2
d) Gb12b2

Explanation: The energy of jog is given by E = α G1b12b2.
Here, G is Shear modulus, b1 is Burgers vector and b2 is length of jog. α = 0.2 for metals.

8. What is step height of super jog?
a) 1-2b
b) 1-4b
c) 5-30b
d) more than 30b

Explanation: Under high stress condition, jogs are forced to come together. These hence form super jog. Its step height is 5–30b.

9. Screw dislocations with jogs are __________ mobile than edge dislocations. Screw dislocations without jog move __________ from one plane to another than edge dislocation.
a) more, easily
b) more, hardly
c) less, easily
d) less, hardly

Explanation: Screw dislocations with jogs can only move by the climb. It is a thermally activated process. While screw dislocation without jog moves easily.

10. What is energy required for forming a vacancy at a jog in fcc metal?
a) 0.7 eV
b) 1.4 eV
c) 2.7 eV
d) 4.8 eV

Explanation: Dislocations move by leaving behind vacancies. The energy required to form a vacancy in fcc metal is 4.8 eV. While energy to form an interstitial atom is 0.7 eV.

11. During the jog movement, vacancy formation is faster than interstitial atom formation.
a) True
b) False

Explanation: Vacancy formation occurs readily than interstitial atom formation. The energy required for vacancy formation (0.7 eV in fcc metals) is less than interstitial atom formation (4.8 eV). It is during jog movement.

12. Forest dislocations make deformation easy.
a) True
b) False

Explanation: Formation of junctions and intersection between moving dislocations is known as dislocation forest. This provides a barrier to gliding dislocations. Hence it makes deformation difficult.

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