Modelling Stress-Strain Behaviour of Low-Yield-Point Steels

Abstract

Unlike low carbon or alloy steels, low-yield-point steels are characterized with very low yield strength but very high capacity of strain hardening and deformation capacity. In order to develop their advantages in energy dissipation systems, accurate modeling of the stress-strain behavior of low-yield-point steels are imperative for structural analysis and performance evaluation. Previous experimental investigations have revealed the prominent cyclic hardening response and there generally exists an initial yield plateau. Based on these observations, a cyclic plasticity model was developed to describe the stress-strain responses under monotonic and various cyclic loadings. Both isotropic hardening and kinematic hardening were found to be nonlinear. Exponential function was used to describe the transient hardening under cyclic loading, while evolution of backstresses based on the Armstrong-Frederick rule was used to trace the significant Bauschinger effect in unloading-reloading cycles. Both isotropic and kinematic hardening rules were decomposed into short-range and long-range components to capture the stress-strain responses in yield plateau and strain-hardening regions, respectively, but using formulations of different parameters. In addition, an impermanent bounding surface in stress space and a memory surface in plastic strain space were established to correctly describe the yield plateau stress and duration. A calibration procedure by tension coupon test was established, which makes it convenient to determine model parameters in practical application. Close agreement between the experimental and the modeling stress-strain curves was obtained. Therefore, the developed cyclic plasticity model can be used for further elasto-plastic analysis of structural components or systems using low-yield-point steels to yield accurate predictions.