When music wire (100% pearlite) is cold drawn, the pearlite spacing is reduced in proportion to the wire diameter. That is, d/do = D/Do, where d is the pearlite spacing and D is the wire diameter. The o subscript indicates original conditions. Assuming that the ?ow stress, σ , is given by σ = σ o! + k!d-1/2, derive an expression for σ as a function of the strain, ε.