Stress and strain anisotropy of CMT-WAAM 316 LSi stainless steel: Characterisation and modelling

A comprehensive experimental study was conducted to quantify and model the elastic and plastic anisotropy of stainless steel 316 LSi walls produced by Cold Metal Transfer Wire Arc Additive Manufacturing (CMT-WAAM). For the first time, the plastic strain anisotropy of WAAM produced components and the related modelling is systematically investigated. Using full-field strain data captured by digital image correlation (DIC), Young´s modulus, Poisson’s ratio, yield stress and Lankford’s coefficient were determined for tensile samples with orientations 0°, 45° and 90° relative to the print layer direction. Lankford's coefficient, as a measure of material anisotropy in plastic flow, was calculated considering the whole strain hardening region but also the initial plastic strain region. The results show the significant orientational dependence of the considered material properties and the evolution of the Lankford’s coefficient with the ongoing deformation process. In describing the elastic material behaviour an orthotropic linear elastic model was applied. The optimisation of the elastic material data utilised in the model calibration resulted in improved description of the material behaviour and confirmed the material’s orthotropic nature. The plastic material behaviour was described using phenomenological plasticity models based on associated or non-associated flow rule that utilise orthotropic Hill'48 stress function as yield function/plastic potential. The results show the advantage of the non-associated flow rule approach in predicting uniaxial tensile material behaviour. The analysis also underlined the need for the data related to biaxial stress states and the proper anisotropy characterisation for the reliable modelling and structural optimisation of WAAM components. • Elastic and plastic anisotropy of WAAM 316LSi stainless steel was characterised. • Stress and strain plastic anisotropy were assessed, being found stronger strain anisotropy. • Orthotropic elastic model calibrated using tensile data is provided. • r-values and yield stresses were determined and used to calibrate Hill'48 plasticity criteria. • Important differences in stress and strain anisotropy claim for non-associated plasticity.