Numerical modeling of stress-strain relationships for advanced high strength steels

Abstract

As a result of altered chemical composition, multiphase microstructures, and other micromechanical change, advanced high strength steel (AHSS) has three to five times the strength of conventional mild steels. Developed for automotive applications, AHSS has high potential for application in cold-formed steel construction. However, the material properties must be properly understood and quantified for application to structural design with economic efficiency. A series of tensile coupon tests were carried out to determine typical AHSS material properties. Existing stress-strain models, designed for steels with gradual strain hardening, were studied and recalibrated to the AHSS test data. No existing method provided an accurate fit for all cases. An updated two-stage plus linear stress-strain model, based on the Ramberg-Osgood expression, was developed. The predictive equations for the parameters required by the new model were provided based on the statistical analysis of AHSS test data. In addition, from the discussion of the new model, a novel proof stress was recommended to represent the yield strength of AHSS. Energy was used to compare the AHSS experimental stress-strain curves with conventional steel stress-strain models to examine the rationality of the proposed proof stress as the yield strength in design.