Unified full-range plasticity till fracture of meta steel and structural steels

This paper investigated mechanical behaviors and monotonic plasticity of a new type of high strength and high ductility meta steel with negative Poisson's ratio effect (termed as NPR steel in this study). NPR steel can postpone necking initiation, so it has a high uniform elongation of 55.3% and a high elongation till fracture of 61.7% in this study. Classical plasticity theory postulates that metals have a constant Poisson's ratio of 0.5 under plastic straining, but Poisson's ratio of NPR steel decreases from around 0.5 to 0.44 at the plastic stage. In this paper, experimental and numerical studies on the new material were conducted, and four types of conventional engineering steels were also investigated for comparison. For each type of steel, coupons of three different gauge lengths were tested to examine the size effect. Full-range true stress - true strain relationships of the five types of steels under monotonic tension were obtained by a unified post-necking modification method newly proposed in this study, and numerical results compared well with the corresponding experimental ones. Finally, a unified plasticity model and ductile fracture parameters were presented for the steels.