PSI - Issue 53

João Alves et al. / Procedia Structural Integrity 53 (2024) 236–245 Author name / Structural Integrity Procedia 00 (2019) 000–000

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4.2. Life fatigue prediction models The requisite conditions were in place from the data presented to compare the existing models. The projected defect area and microhardness were employed as input to compute the values provided by the various models, summarized in Table 8.

Table 8. Results of prediction fatigue limit stress for different models. Authors: Models

Fatigue limit stress (MPa)

=1.43×( +120)/( √ ) 1 6 =1.43×( +75)/( √ ) 1 6 =1.43( +450)( √ ) 1 3 =0,55( +390)( √ ) 1 6 =1,53( +150)( √ ) 1 6

Murakami Y. (1989) Ueno et al. (2012)

440.50 397.40 506.76 268.89 502.05

Morgado et al. (2022)

Upon analyzing Table 8, it becomes evident that the fatigue limit stress obtained using the various proposed models is not valid compared to the experimental results. Therefore, new models based on the models of Murakami were developed to predict the fatigue limit stress of a Ti-6Al-4V alloy produced by SLM without heat treatment and are shown in Table 9. The two models developed are based on different principles. One of the equations presented was developed based on the same fundamentals used by the other authors, which are the adoption of projected defect area as an input. In contrast, a different equation was created using the surface defect, which counts the effects of defects in fatigue behaviour, through the geometry and not only in cross-sectional area.

Table 9. New life fatigue prediction models for a Ti-6Al-4V alloy, produced by SLM Area input New model developed Surface area of defect =0.424×( +100)/( √ ) 1 6 109.87 Projected area of defect =0.51×( +100)/( √ ) 1 6 109.90

Limit fatigue stress (MPa):

Error (%)

0.08 0.06

Thus, two new life fatigue prediction models were obtained that describe the fatigue behaviour of Ti-6Al-4V produced by SLM. 5. Conclusion Based on the results acquired through all the research, it can be concluded that: • The mechanical properties of Ti-6Al-4V manufactured by SLM seem superior to the same alloy produced by melting, casting, or powder metallurgy (traditional methods). • Ti-6Al-4V exhibited a strong plastic behaviour, according to the value of the straining hardening exponent. • Even though the value of the projected defect area is lower, highlighting the suitability of the proposed procedure, parameters and conditions used in manufacturing specimens. • The fatigue limit stress was approximately the same, although it was found to have fewer defects. • None of the models proposed by Murakami et al. (1989), Ueno et al. (2012), and Morgado et al. (2022) are appropriate to predict the fatigue limit of a Ti-6Al-4V produced by SLM in the condition as built. • Two new life prediction models were developed for a Ti-6Al-4V alloy produced by SLM and using nanotomography to inspect defects. References

ASTM E8/E8M-22. (2022). Standard Test Methods for Tension Testing of Metallic Materials. ASTM E384-22. (2022). Standard Test Method for Microindentation Hardness of Materials. https://doi.org/10.1520/E0384-17