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GATE 2024 MT – Question 24

Mechanical Behaviour of Materials · Dislocations and strengthening · 1 mark · Multiple choice

The figure shows a circular dislocation loop with fixed Burgers vector b (horizontal arrow). The dash-dot lines are horizontal and vertical diameters, and the arrow on the loop indicates its line vector. Identify the dislocation character at p, q, and r.

Diagram for GATE 2024 MT question 24
  1. p: pure edge, q: mixed, r: pure screw
  2. p: pure edge, q: pure screw, r: pure edge
  3. p: pure screw, q: mixed, r: pure screw
  4. p: pure screw, q: pure edge, r: pure screw

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Show answer and explanation

Correct answer: (A) p: pure edge, q: mixed, r: pure screw

Explanation

Dislocation character depends on angle between the local line tangent and fixed Burgers vector.

At p the tangent is vertical and perpendicular to horizontal b, giving pure edge.

At r it is horizontal and parallel to b, giving pure screw.

At q the angle is intermediate, giving mixed character. **A**.