A novel and simple method for the measurement of plane strain work hardening

For the measurement of plane strain work hardening, a number of test methods are available. The plane strain compression test is a well-known and widely used method. However, the measured hardening data is not accurate enough for defining material models in sheet forming processes. This is due to many experimental uncertainties such as friction and other poorly defined boundary constraints, such as inhomogeneity during deformation. As an alternative, the use of plane strain tensile testing avoids many of the inherent problems of the compression test. However, inhomogeneity in the strain distribution at specimen edges requires extra analysis with regard to data interpretation. In addition, strain measurement is time consuming even when an automatic strain measurement device is used. At Corus Research, Development & Technology, a novel test procedure, which can be performed simply and quickly, has been developed using specimens of different gauge widths and an extensometer for instantaneous strain measurement. This procedure has been validated experimentally. A further simplified method using specimens of one gauge width has been proposed. This simplified version has been modelled using FEM code Dieka using various yield loci. The resulting FEM output indicates that the stress and strain data measured in the plane strain tensile test gives a slight overestimation in true work hardening but this is less than 2% if there is no slip between specimen and clamp.