PSI - Issue 82

L. Mata et al. / Procedia Structural Integrity 82 (2026) 16–23 Mata et al./ Structural Integrity Procedia 00 (2026) 000–000

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N f (cycles)

Fig. 5. Relationship between the nominal stress amplitude and the number of cycles to failure for different loading scenarios (bending-torsion and tension-torsion), s⁄t ratios (s⁄t = 4/3 and s⁄t = 2) and material conditions (untreated and stress relieved). B-T: bending-torsion; T-T: tension torsion; UT: untreated condition (black series); SR: stress-relieved condition (blue series). Experimental results obtained from Cunha (2024). Comparing both loading scenarios, i.e. bending-torsion and tension-torsion, it is evident that, regardless of the σ⁄τ ratio, for the same normal stress amplitude, the specimens subjected to tension-torsion (hollow markers) showed considerably smaller fatigue lives compared to those subjected to bending-torsion (filled markers). This behaviour was also independent of the application of the residual stress relief treatment. Fig. 5 also compares the experimental fatigue lives reported by Cunha (2024) with the numerical predictions obtained in this study for bending-torsion loading under s ⁄ t ratio = 2. It is clear from the figure that the numerical predictions are close to the corresponding experimental values, particularly at higher stress levels. At lower stress amplitudes, the predictions are slightly unconservative but remain acceptable from a fatigue design perspective. 4. Conclusions The main purpose of the present work was the numerical prediction of fatigue life in notched tubular AlSi10Mg aluminium alloy specimens produced by selective laser melting subjected to proportional bending-torsion and tension torsion cyclic loadings. The notch consisted of a through-thickness hole machined by CNC after the additive manufacturing stage. Two different normal-to-shear stress ratios (σ⁄τ = 4⁄3 and σ⁄τ = 2) were studied for each loading scenario considering pulsating loading conditions. Two material conditions were also studied, namely untreated and stress-relieved. Based on the numerical simulations, the crack initiation locations, the early-stage crack directions and the fatigue lives were predicted. The following conclusions can be drawn: • Fatigue crack initiation was characterised by the nucleation of two diagonally opposite cracks around the hole surface, which were satisfactorily predicted based on the maximum value of the first principal stress in the notch region; • For both loading scenarios, the location of the crack initiation locations was significantly affected by the σ⁄τ ratio. The crack initiation angles and the early-stage crack directions increased with decreasing σ⁄τ ratios, relative to the line normal to the longitudinal axis of the specimen;