Axial-torsional testing and cyclic plasticity modelling of wire arc additively manufactured steel

Wire arc additive manufacturing (WAAM) is a metal 3D printing technique with the potential to produce structural steel elements in a cost-effective fashion. However, there is currently a paucity of data concerning the mechanical behaviour of WAAM steel under uniaxial and multiaxial cyclic loading. This study aims to address this gap via a comprehensive experimental investigation and constitutive modelling of the multiaxial cyclic behaviour of WAAM steel. Cyclic testing featuring axial and torsional loading was conducted on WAAM Grade ER70S-6 steel, and a constitutive model to describe the multiaxial cyclic behaviour of the examined material is proposed. First, radial loading in the biaxial stress plane was conducted to identify the shape of the initial yield surface and the strain development paths of the material. Uniaxial and biaxial cyclic loading tests were performed to investigate the hardening of the material. The experimental results show that WAAM steel exhibits a von Mises isotropic yield surface, with plastic strain developing in the direction normal to the yield surface. The proposed modified two-surface plasticity model accurately reproduces both the uniaxial and multiaxial cyclic stress-strain responses, while offering improved accuracy for the multiaxial ratcheting behaviour compared with the conventional model. The results of this study show that the classical plasticity theory used for conventional steel is also applicable to WAAM steel.