Plastic behavior of additively manufactured Ti6Al4V ELI: Mechanical characterization, engineering scale modeling, and validation using free-end torsion tests

This paper is devoted to the study of Ti6Al4V ELI (Extra Low Interstitials) processed by electron beam melting (EBM). The experimental investigation includes quasi-static uniaxial tension and compression tests and free-end torsion tests. It was found that the horizontally and vertically printed specimens have the same yield stresses and similar overall stress-strain response. Irrespective of the printing direction the material displays strength differential effects. During monotonic compression tests, a slight anisotropy in plastic strains in compression was revealed by online optical measurements. This slight anisotropy was confirmed by conducting interrupted compression tests and further measuring the deformed cross-sections. Although the material anisotropy is weak, the torsional response cannot be captured with the von Mises yield function. On the other hand, using the isotropic Cazacu and Barlat (2004) yield function that involves only one additional parameter that can be determined solely from uniaxial tension and compression tests, both strength differential effects and the material's torsional response are predicted with accuracy. Furthermore, a transversely isotropic extension of this yield criterion involving only two additional anisotropy coefficients that can be determined using analytical formulas from uniaxial data, enables to account for both the mild anisotropy and the material's tension compression asymmetry and to obtain good predictions for all test conditions investigated.