On the strain rate sensitivity values of superplastic materials

Some problems arising in experimental determination of the strain rate sensitivity of the flow stress, a, on the strain rate, ξ, are considered. It is pointed out that the strain rate sensitivity index, m, entering the standard power relation σ = Kξ m , is not identical to the slope M = ∂ (log σ)/∂ (log ξ) of the sigmoidal superplastic curve. The difference between m and M is to be taken into consideration in treating the results of the mechanical tests.