PSI - Issue 75

S.S. Penkulinti et al. / Procedia Structural Integrity 75 (2025) 1–9 Author name / Structural Integrity Procedia (2025)

3

3

2. Materials and methods 2.1. Material and defect characterization

The alloy considered in this study is Ti64. In a previous experimental work, Ti64 samples have been processed by L-PBF (see Bonneric et al. (2025) for the detail of process parameters) and characterized using X-ray tomography with a voxel size of 4µm. Fig.1 shows the distributions in sizes (Feret diameter F 3d ) and shapes (Sphericity Ψ ) of a defect population obtained by CT-scan. Note that Feret diameter is the maximum possible distance between the parallel planes that are tangent to opposite sides of the defect geometry, while sphericity is given by equation (1) with is the volume of the defect and the surface area of the defect. = 1 3 (6 ) 2 3 / (1) 25 LoF defects and 10 gas pores from this population have been considered for the numerical simulations of the present study. These defects are highlighted in red in Fig. 1. The LoF defects correspond to low sphericity defects ( Ψ<0.6) and the gas pores to high sphericity defects ( Ψ>0.8 ). One can note that the number of considered gas pores was less than for the LoF defects, as it was assumed that the gas pores geometry was exhibiting less variability and would induce less scatter in the fatigue resistance.

Fig. 1. Distributions in sizes and sphericities of the defect population characterized by CT-scan. The defects considered for numerical simulations are highlighted in red.

2.2. Finite Element Modelling For each selected defect, a surface mesh was performed using the Avizo software. The defect was then positioned at the center of a cubic volume whose length is 5 times the size of the defect (see Fig. 2.a), before meshing the volume with quadratic tetragonal elements with GMSH software. The total number of elements is around 10 6 , with an element size at the vicinity of the defect of approximately 2.5µm. Multi-point Constraint (MPC) periodic boundary conditions were used to prescribe the cyclic loading applied to the cube. Three different loading types are considered in this study (see Fig. 2b), all corresponding to a loading ratio of R = -1. They are a) fully reverse tension ( ), b) fully reverse shear ( ), and c) in phase combined tension-shear stress with a biaxial stress ratio of Τ /Σ = 1 . In addition, for each loading type, multiple loading directions with respect to the defect have been considered, as