The Characterization of Materials by Precision Strain Rate Sensitivity

Abstract

Strain rate sensitivity is a measurement of the thermodynamic response of materials to changes in stress (τ). Correlations of the theoretical derivations to measured values are only valid if the strain rate (γ̇) is performed at constant structure (Σ). Thus transients during strain rate change obliterate the subtleties of the data especially since the strain rate sensitivity ∂lnτ∂lnγ̇T,Σ is of the order of 10−2. These transients, which are due to the inherent interactive nature of the testing frame of conventional tensile machines, can be nullified. This compensation results in a step-ramp in the displacement-time plot such that precision strain rate sensitivity can be measured. Moreover it is convincingly shown that the true elastic response of polyethylene including the unrelaxed modulus can be measured. Examples of evaluated material characteristics are: 1) the work to intersect dislocations at 0 K in dilute Al crystals. 2) the composition of interstitial solutes from which the solvus for NbCN in ferritic stainless steel can be determined. 3) the clustering in Al-4wt percent Cu during early GPI formation from which bond strength can be estimated.