Material Constitutive Law for Large Strains and Strain Rates

This note comments on a strain rate pattern found in tensile tests. This strain rate pattern readily suggests that the Cowper-Symonds equation relating the static and dynamic flow stresses with the strain rate is not valid for a broad range of strains unless its coefficients change. A modification of the Cowper-Symonds equation is proposed, and good prediction of the dynamic flow stress at any strain and strain rate level was obtained.