PSI - Issue 68

Shahriar Afkhami et al. / Procedia Structural Integrity 68 (2025) 929–935 S. Afkhami et al. / Structural Integrity Procedia 00 (2025) 000–000

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Surface quality is another parameter influencing mechanical performance, especially under high-cycle fatigue loads. Accordingly, the arithmetic mean roughness ( Ra ) values, the maximum distance between the highest peaks and lowest valleys on the surface ( Rz ) of additively manufactured components, and aerial height maps are presented in Fig. 4 as measures of surface quality. According to these results, the surface quality of 316L and Al5X1 were similar on average, while Ti64 suffered from a higher Ra value and a relatively high Rz number. The relatively better surface quality of the components made of 316L and Al5X1 can be attributed to the shot blasting procedure performed on them after additive manufacturing. Further, according to the height maps in Fig. 4, Ti64’s (as-built) surface contained multiple relatively deep valleys, while (shot blasted) 316L and Al5X1 did not show such features on their surface. Surface characteristics of additively manufactured metals rely on various parameters; hence, the manufactured components in this study showed different surface features, although they were all processed using optimum additive manufacturing parameters recommended by raw materials and manufacturing system vendors [6]. In this regard, per Fig.4, shot blasting seems to improve the surface quality of the additively manufactured components significantly (and, consequently, their fatigue performance, as discussed in the following).

Fig. 4. The surface of additively manufactured components and their corresponding aerial height maps.

The fatigue test results are presented in Fig. 5 as applied load and cycles to failure data. Further, FEA was utilized to calculate local stress values at critical (failure) locations to transform load-cycle data into stress-cycle curves in Fig. 5. It should be noted that, when comparing the mechanical performance of the components, the weight of the components made of different metals differs from others (0.260 kg for Ti64, 0.257 kg for Al5X1, and 0.646 kg for 316L); also, as mentioned earlier, the strength of the raw metals are different and consequently, their corresponding component design (e.g., wall thickness and angles on the corners) are different between various metals, although the optimized designs seem similar in general (the design shown in Fig. 1). Hence, these slightly different angles and thickness values imposed various stress concentration factors (SCF) for the studied metals (1.85 for 316L, 0.37 for Al5X1, and 2.5 for Ti64). The summation of all these points makes the direct comparison of optimized components made of different metals impractical. It should be noted that all the components failed from the critical points normal to the applied load and with significant SCFs, as marked in Fig.6. In this regard, using Ti64 with the highest nominal strength seems to have not favored the fatigue performance of the component since the optimization software accordingly considered the sharpest local edge and highest SCF for this material. This issue, combined with the inferior surface quality of the as-built titanium, can significantly negatively influence the fatigue performance. Finally,