Question

Two parallel edge dislocations of the same sign (same Burger's vector) are located on the same slip plane. As they approach each other, what happens?

• A. Energy decreases; Force is attractive
• B. Energy increases; Force is repulsive
• C. Energy remains constant; Force is zero
• D. Energy increases; Force is attractive

Hint:

Like dislocations (same sign on same slip plane) repel each other.
Unlike dislocations (opposite signs on same slip plane) attract and can annihilate each other, which decreases the system's energy.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question relates to the elastic interactions between two dislocations in a crystalline lattice.
Specifically, we are looking at two parallel edge dislocations of the same sign sharing the same slip plane.

Step 2: Key Formula or Approach:
Dislocations introduce strain fields in the lattice, resulting in compressive stress above the slip plane and tensile stress below it (for positive edge dislocations).
The force per unit length between two parallel dislocations can be analyzed using Peach-Koehler equation principles or strain energy overlap.

Step 3: Detailed Explanation:

• When two edge dislocations of the same sign are on the same slip plane, their compressive stress fields (located on the same side of the slip plane) begin to overlap as they approach each other.

• This overlapping of identical stress fields significantly increases the total elastic strain energy of the crystal lattice.

• Since physical systems spontaneously tend to minimize their potential energy, the system will resist this approach.

• This resistance manifests as a repulsive force between the two dislocations, pushing them apart.

• Consequently, bringing them closer together requires doing work against this repulsion, which increases the strain energy of the system.

Step 4: Final Answer:
As they approach each other, the energy increases and the force is repulsive.