Ductile fracture modelling of L-PBF printed 316L stainless steel using computed tomography

This study presents an experimental approach for determining the parameters of the Gurson-Tvergaard-Needleman (GTN) damage model. The research involved tensile testing of additively manufactured 316L stainless steel (SS316L). For additive manufacturing (AM) to effectively complement or replace traditional manufacturing methods, a comprehensive understanding of damage evolution in AM metallic components is essential. Furthermore, the microstructure of AM materials is distinct from that of metals processed through conventional means. The inherent porosity of AM metallic components motivates the use of porous metal plasticity models to describe their damage behaviour, particularly the GTN model. In addition to conducting complete tensile tests, interrupted tests were performed to assess void formation at various elongation stages. Computed tomography, with a pixel size of 3 μm, was employed to investigate void evolution across different elongation values. Six parameters were derived from the CT scans: initial porosity (f₀), nucleated porosity (f_N), true strain at the potential maximum for nucleated voids (ε_N), standard deviation of the nucleated voids (S_N), critical porosity (f_c), and final porosity (f_f). To validate these parameters obtained from CT scans, a finite element model (FEM) was developed to simulate uniaxial tensile tests. The discrepancies between the FEM predictions and experimental results were minimal, indicating that the proposed methodology and derived parameters are suitable for modelling ductile fracture in AM SS316L. The FEM analysis suggested that both the nucleation and growth of intrinsic voids in AM SS316L can be accurately predicted for a specified equivalent strain. Notably, the rate of intrinsic void growth increased significantly once a critical void volume fraction was exceeded, which was attributed to the coalescence of developed voids, thereby indicating that the void growth mechanism is influenced by stress triaxiality.