This set of Mechanical Behaviour Multiple Choice Questions & Answers (MCQs) focuses on “Dislocation Intersection”.
1. Jog, which is able to glide is called __________ jog.
Explanation: Jog, which is an edge in nature, is called glissile. It means it is able to glide. These glide in particular plane with the rest of dislocation line.
2. Formation of jog __________ energy related to dislocations.
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 energy of dislocation.
3. The movement of jogged dislocations is ___________ than dislocations having no jogs.
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 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 climb. That’s why this intersection is important.
5. A __________ is a sharp break in the dislocation line which remains in the slip plane.
c) dislocation loop
d) frank-Read source
Explanation: A jog is 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.
6. __________ in dislocations are unstable.
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?
Explanation: The energy of jog is given by E = α G12b2.
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?
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 move 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 jog movement, vacancy formation is faster than interstitial atom formation.
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.
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.
Sanfoundry Global Education & Learning Series – Mechanical Behaviour & Testing of Materials.
To practice all areas of Mechanical Behaviour & Testing of Materials, here is complete set of 1000+ Multiple Choice Questions and Answers.