Abstract: Considering the fact that plastic volume's change do not be neglected in many kinds of metal, the constitutive equations which taking account of the effect of plastic volume's change are established. In order to obtain the elasto-plastic stress from the measured data on total strain, plastic strain is separated from total strain and gave the calibration method of parameters in the constitutive equations. Comparing with the traditional theory which does not consider the plastic volume's change, it is a better basis for measuring elasto-plastic stress in structures.

Key words: Elasto-plastic stress measurement, Plastic poisson ratio, Plastic volume's change, Strain space