Constitutive relations of structure steel under nonproportional loading

The mechanical properties of metals in the inelastic range may generally be described by mathematical relationships. Many such constitutive relationships or plasticity models were formulated based on limited experimental data and were at best validated by static or uniaxial cyclic loading tests. Very few of the mathematical models have been substantiated by test results under biaxial and nonproportinal loading conditions because experimental information was not available. This is particularly true for structural steel. This paper is concerned with the improvement of a plasticity model of the two-surface type for structural steel based on experimentally observed features of annealed A-36 steel specimens tested under biaxial cyclic and nonproportional loading conditions at room temperature. This two surface plasticity model for A-36 steel is then used to predict numerically the experimental curves covering the entire strain histories of the tests. Excellent correlations are obtained.