Geometrically necessary dislocations induced size effect in the torsional stress relaxation behavior of thin metallic wires

Abstract

Torsional stress relaxation experiments on thin copper wires are performed. A size effect is observed. That is a faster relaxation deformation arises in a thinner wire. As the wire diameter increases, the activation volume increases but the strain rate sensitivity decreases. A greater effect of geometrically necessary dislocations on the relaxation deformation accounts for the size effect. In a thinner wire, geometrically necessary dislocations undergo fewer obstacles to reach the wire center and then neutralize, causing a more rapid evolution of mobile dislocations.