Method to determine the strain-rate sensitivity of a superplastic material from the initial slopes of its stress–strain curves

New method to estimate quantitatively the strain-rate sensitivity of a superplastic material is suggested. It is based upon measurements of the initial slopes of the stress–strain curves. In contrast with known techniques the method suggested is appropriate to apply to small deformations, so that the result obtained are to be assigned to the initial structural state of the material under consideration. The experimental verification of the method suggested is fulfilled in practice for the example of Wood's alloy. It is shown that the strain-rate sensitivity of this alloy decreases monotonically with increasing strain, e the value of m determined by means of the method suggested are in good agreement with that determined independently using standard techniques. An important feature of the method suggested is that in contrast with standard techniques its accuracy improves as the value of strain, e, becomes smaller, since the tilts of σ–e curves have a maximum when e→0. © 1998 Chapman & Hall