Chaboche viscoplastic material model for process simulation of additively manufactured Ti-6Al-4 V parts

For the estimation and further optimization of the residual stress and distortion state in additively manufactured structures during and after the wire arc additive manufacturing (WAAM) process, thermomechanical simulation can be applied as a numerical tool. In addition to the detailed modelling of key process parameters, the used material model and material data have a major influence on the accuracy of the numerical analysis. The material behaviour, in particular the viscoplastic behaviour of the titanium alloy Ti-6Al-4 V which is commonly used in aerospace, is investigated within this work. An extensive material characterization of the viscoplastic material behaviour of the WAAM round specimen is carried out conducting low cycle fatigue (LCF) and complex low cycle fatigue (CLCF) tests in a wide temperature range. An elasto-viscoplastic Chaboche material model is parameterised, fitted, and validated to the experimental data in the investigated temperature range. Subsequently, the material model is implemented in the thermomechanical simulation of a representative, linear ten-layer WAAM structure. To finally determine the effect of the fitted material model on the estimation accuracy of residual stress and distortion, simulation results using the standard material model and the elaborated Chaboche model from this study are compared to experimental data in the substrate. The thermomechanical simulation with the Chaboche model reveals a better agreement with the experimental distortion and residual stress state, whereby the standard material model tends to an overestimation. The estimation accuracy with respect to the maximum distortion is improved from an error of 60% with the standard model to an acceptable error of about 6% using the elaborated model. Additionally, the estimated residual stress state shows a sound agreement to the experimental residual stress in the substrate.