PSI - Issue 68

Xiangnan Pan et al. / Procedia Structural Integrity 68 (2025) 1038–1044 X. Pan et al. / Structural Integrity Procedia 00 (2025) 000–000

1042

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where ε is the engineering strain, σ is the engineering stress, σ f and δ f are the engineering stress and the elongation at fracture, respectively. For R = –1, while σ max < σ 0.2 , i.e. stress-related fatigue (Schijve, 2009), Eq. (1) can be idealized as Eq. (4),

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where E is the elastic modulus. By rearranging Eq. (4), we obtain Eq. (5),

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which allows us to estimate the fatigue life. 3.2. Intrinsic fatigue resistances at different stages

Fig. 2. Tensile (a) and S-N (b) curves for Ti-6Al-4V with different microstructures.

We select a titanium alloy (Ti-6Al-4V) with three different conditions, one is conventionally made and with EM, the other two are produced by AM (PBF-LB) with and without HIP (Tao et al., 2024), as test materials targeting to compare the effect of microstructure on OCF (Fig. 2a), HCF and VHCF (Fig. 2b). As shown in Fig. 2a, EM has the lowest UTS of σ u = 927 MPa and the highest elongation of δ f = 19.3 %, AM without HIP has the highest UTS of σ u = 1185 MPa and the lowest elongation of δ f = 3.0 %, AM with HIP has the medium UTS and elongation of σ u = 998 MPa and δ f = 13.5 %. Fig. 2b is not only includes the three conditions, but also adds a group of S-N results for Ti 6Al-4V produced by conventional manufacturing and with a BM (Heinz et al., 2013; Heinz and Eifler, 2016), whose σ 0.2 = 920 MPa, σ u = 1010 MPa and δ f = 17.5 %. In HCF regime, the BM has the best performance, followed by AM with HIP and then EM and AM without HIP, their fatigue resistances are as σ f-7 = 639, 578, 554 and 302 MPa. In VHCF regime of N f > 10 8 cycles, the EM has the best performance, followed by BM and AM with HIP, which are