Work hardening characteristics of copper from constant strain rate and stress relaxation testing

Tensile tests interrupted by stress relaxation periods were carried out on copper specimens at different temperatures and strain rates. Strain rates before and after stopping the cross-head were determined. Rather than interpreting the difference to be due to mechanically activated deformation, as has been considered elsewhere, deformation was considered to be thermally activated with a component responsible for hardening and a component unaccompanied by hardening. From a rate equation that can describe thermally activated glide controlled deformation, flow stresses were calculated from the strain rate differences together with the strains estimated to be due to the hardening component of deformation. Flow stress–strain curves so obtained were found to be independent of testing temperature and tensile strain rate. These curves were compared to hardening curves determined previously from constant force creep tests and were found to be similar.