Micromechanics of 3D printed Metals

Metal additive manufacturing (AM) is a unique, emerging manufacturing technology that facilitates customisation, flexible production and complex, lightweight components. In order to fully utilise the high potential of metal AM, a fundamental understanding of the produced material microstructure and its mechanical behaviour must be achieved. This PhD thesis investigates the anisotropic mechanical properties of 316L austenitic stainless steel and Ti-6Al-4V titanium alloy, produced by laser powder bed fusion (LPBF) process. Various computational methods are employed at different length scales to gain insight into the mechanical properties of the material based also on experimental testing. The micromechanical characteristics are studied through crystal plasticity simulations using periodic representative volume elements (RVEs) that are specific to each material. The applied crystal plasticity model is based on a simple viscoplastic power law, neglecting grain boundary effects. Numerical predictions for the mechanical anisotropy are obtained based on the crystallographic texture. For both materials, the crystal plasticity parameters are calibrated against tensile tests carried out on dog-bone specimens printed with different orientations relative to the build direction. The calibrated RVEs are subjected to virtual material testing under multiple load cases to determine different anisotropic yield criteria. Finally, 316L elastically isotropic truss lattices are investigated, when subjected to uniaxial tensile load. The experimental results are supported by finite element analyses, which employ the anisotropic material parameters determined by crystal plasticity simulations. The influence of geometrical imperfections are investigated numerically in order to study failure mechanisms and fracture patterns of the lattices.