This set of Mechanical Behaviour Multiple Choice Questions & Answers (MCQs) focuses on “Geometry of Dislocations”.
1. Dislocations are generated mostly when ______ takes place.
a) Slip
b) Twinning
c) Annealing
d) Heating
View Answer
Explanation: Dislocations are generated during slip mostly. Slip causes shear in the crystal. This shear introduces dislocations at high shear stress.
2. Dislocations during solidification produces due to ______
a) Impurity atoms
b) Voids
c) Cooling
d) Metal atoms
View Answer
Explanation: Dislocations may produce during solidification. It may be due to impurity atoms. It may also be due to thermal vibrations.
3. Which term is used for the line which lies between the slipped and unslipped regions?
a) Dislocation line
b) Slip line
c) Free surface
d) Grain boundary
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Explanation: The line which lies between the slipped and unslipped regions is known as the dislocation line. It is the line of mismatch. It separates the slipped region.
4. Screw dislocation line moves ______ to applied stress.
a) Parallel
b) Perpendicular
c) At angle < 90°
d) At angle > 90°
View Answer
Explanation: Screw dislocation line moves perpendicular to the applied force. In this dislocation, the segment of the dislocation line is parallel to the Burgers vector.
5. Dislocations are classified in ____ types based on geometry.
a) 2
b) 4
c) 5
d) 6
View Answer
Explanation: Dislocations are classified into two types based on geometry. These are edge and screw dislocations. These are further subdivided into positive and negative dislocations.
6. Edge dislocation ______ cross slip and _____ climb.
a) Can, can
b) Can, cannot
c) Cannot, can
d) Cannot, cannot
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Explanation: Edge dislocation, when face problem in gliding, can climb. Thus it changes its slip plane. While it can’t cross slip.
7. Screw dislocation _____ cross slip and _____ climb.
a) Can, can
b) Can, cannot
c) Cannot, can
d) Cannot, cannot
View Answer
Explanation: Screw dislocation, when encountering any barrier, can cross slip. Thus it can change its slip plane. While it can’t climb.
8. A dislocation can’t terminate _____
a) Within crystal
b) In free surface
c) Ingrain boundary
d) With another dislocation
View Answer
Explanation: A dislocation can’t terminate inside an otherwise perfect crystal. It can terminate at free surface or grain boundary. It can also annihilate with another dislocation.
9. What is the angle between applied stress and mixed dislocation line?
a) 0°
b) <90°
c) 90°
d) >90°
View Answer
Explanation: In a mixed dislocation, the direction of motion lies in between edge and screw. The angle is less than 90°. That’s why it is called mixed dislocation.
10. An edge dislocation can be characterized as _________
a) The angle between the dislocation line and its Burgers vector is 0°
b) The angle between the dislocation line and its Burgers vector is 45°
c) The angle between the dislocation line and its Burgers vector is 90°
d) The angle between the dislocation line and its Burgers vector is 120°
View Answer
Explanation: In the edge dislocation, Burgers vector is perpendicular to dislocation. Edge dislocation line moves parallel to applied stress. It is of two types, positive and negative.
11. Below the edge of an extra half plane of edge dislocation, bonds are broken.
a) True
b) False
View Answer
Explanation: Below the edge of the extra half plane, atoms are found in the tension state. While above slip plane atoms are in the compression state. Bonds are broken on this plane.
12. The screw dislocation in which the atomic displacement occurs in the forward direction is a counterclockwise dislocation.
a) True
b) False
View Answer
Explanation: The screw dislocation in which the atomic displacement occurs in the forward direction is a clockwise dislocation. It is also known as positive screw dislocation. This can be understood by using a screw.
Sanfoundry Global Education & Learning Series – Mechanical Behaviour & Testing of Materials.
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