Question

The elastic strain energy of a unit length of an edge dislocation as compared to that of a screw dislocation is

• A. Less
• B. More
• C. Equal
• D. Double

Hint:

Elastic strain energy of edge dislocations is \textbf{slightly more} than screw dislocations due to their extra volumetric distortion component.

Answer 1

The Correct Option is B

Step 1: Understanding dislocations Dislocations are line defects in crystals. There are primarily two types: - \textit{Edge dislocation:} extra half-plane of atoms inserted into the crystal. - \textit{Screw dislocation:} result of shear distortion. Step 2: Energy of dislocations The elastic strain energy per unit length \( E \) of a dislocation is given approximately by: \[ E \propto Gb^2 \] where \( G \) is the shear modulus and \( b \) is the magnitude of the Burgers vector. For edge dislocations, the energy involves both shear and volumetric (dilatational) components, whereas screw dislocations involve only shear strain. Conclusion: Since edge dislocations include both shear and volumetric strain, their total elastic strain energy is higher than that of screw dislocations.