PRECISE EXPERIMENTAL RESULTS AND AN ANALYTICAL FORMULATION OF THE SUBSEQUENT PLASTIC DEFORMATION OF MILD STEEL SUBJECTED TO PRE-STRESSING

Abstract

Thin-walled tubular specimens of annealed mild steel were prestressed plastically by tension or torsion, unloaded perfectly and reloaded proportionally by combined loadings of axial load and torque, as fundamental examples of investigating the plastic properties of the material used in received condition. The experimental results show that the shapes of equi-strain curves for the reloading on the deviatoric stress plane differ considerably from Mises' circle for smaller equivalent strains less than 0.5 %. This means that the isotropic and kineproperty of the material mentioned above. Then, a new expression of plastic stress-strain relation is proposed based on the general tensor equation between noncoaxial tensors. The plastic strain tensor for the reloading is expressed as a function of the tensors of the prestress and the reloading stress. The relation obtained approximates closely the experimental results.