PSI - Issue 75

S.S. Penkulinti et al. / Procedia Structural Integrity 75 (2025) 1–9 Author name / Structural Integrity Procedia (2025) detailed in section 2.4 . The material behavior was assumed to be linear elastic and isotropic with a Young ’ s modulus E = 110 GPa and Poisson ’ s ratio = 0.34. All FE calculations have been performed using the FE code Z-set. 4

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Fig. 2. Schematic illustration of the numerical procedure (a) mesh generation (b) cyclic loading conditions (from Penkulinti et al. (2025))

2.3. Fatigue Criterion In order to determine whether or not the applied loading would initiate a fatigue crack, a multiaxial fatigue criterion is used as a post-processing procedure. For ease of implementation in the FE tools, the Crossland criterion (Crossland 1956) is used. A Fatigue Indicator Parameter (FIP) is computed at each Gauss point of the mesh following equation (2). This FIP involves the 2 nd invariant of deviatoric stress tensor 2, , the maximum of hydrostatic stress ℎ, over a loading cycle, and a material parameter . The calculation of 2, is obtained by a double maximisation over a loading period as expressed in equation (3), where S is the deviatoric stress tensor. ℎ, is given by equation (4). = √ 2, + ℎ, (2) √ 2, = 2√ 1 2 ∈ { ∈ (√( ( ) − ( )) : ( ( ) − ( )))} (3) ℎ, = 1 3 ∈ ( ( ( ))) (4) It is assumed that a crack initiation would occur if FIP reaches a threshold value . The and parameters used in the present study have been determined from the experimental fatigue strengths at 2 ×10 6 cycles under tension and torsion loading assessed in Vayssette et al. (2020) for defect-free Ti64 processed by L-PBF and subjected to HIP ( = 0.707 and =417 MPa). The FE problem being fully linear, the macroscopic fatigue strength Σ at 2 ×10 6 for a given loading type can be directly determined from the computed results using equation (5): = (5)