PSI - Issue 66

María Moreno-Rubio et al. / Procedia Structural Integrity 66 (2024) 362–369 Author name / Structural Integrity Procedia 00 (2025) 000 – 000

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align with the central line. However, if the estimated lives are greater than the experimental ones, the points will appear above this line; conversely, they will fall below it if the estimated lives are shorter. The "x2" and "x3" lines mark where an estimated life is twice or three times the experimental life. Similarly, the lines symmetric to the central one indicate estimated lives that are half or a third of the experimental life. These lines provide a reference for assessing the accuracy of the fatigue life predictions. It can be observed that most of the RT estimates, represented by blue points, fall within the range of a factor of 2, with the majority lying below the central line, suggesting that the prediction model is conservative. However, this is not the case for higher life regimes, near one million cycles, where the predicted lives become infinite. For the HT case, represented by red points the values also fall within the factor of 2 range, but they are generally less conservative, with most points above the central line. Additionally, for axial stress values below 350 MPa, the estimated life tends to infinity. 4. Conclusion This research investigated the behavior of Inconel 718 at both low and high temperatures (650ºC) under simple and fretting fatigue conditions, subjected to various load levels. The methodology for conducting the different types of tests was validated in the laboratory. To begin with, a comparison between simple and fretting fatigue at both temperatures reveals that for life regimes exceeding 2·10⁴ cycles, corresponding to axial stresses below 1000 MPa, the fatigue life under fretting fatigue is shorter than under simple fatigue. Furthermore, when examining each type of test independently to evaluate the impact of temperature on the material, it is noted that in simple fatigue, the life is similar for cycles beyond 10⁵, while at lower cycles, it decreases. On the other hand, in the case of fretting fatigue, the curves remain nearly parallel, which is not seen in simple fatigue, and the life is reduced by approximately four times at high temperature. Finally, it is worth noting that the life estimation model employed, which combines the initiation and propagation phases, aligns well with the experimental data. The model is more conservative at room temperature than at 650ºC. However, it should also be mentioned that the model struggles to accurately predict life estimates exceeding one million cycles. Acknowledgements The authors would like to thank the Fondo Europeo de Desarrollo Regional, Ministerio de Ciencia e Innovación and the Agencia Estatal de Investigación for the funding of the project RTI2018 – 096059-B-I00. References Ciavarella, M., & Demelio, G. (2001). A review of analytical aspects of fretting fatigue, with extension to damage parameters, and application to dovetail joints. International Journal of Solids and Structures, 1791-1811. Connolley, T., Reed, P., & Starink, M. (2002). Short crack initiation and growth at 600ºC in notches specimens of Inconel 718. Material Science & Engineering. Erena, D., Vázquez, J., Navarro, C., & Domínguez, J. (2020). Fatigue and fracture analysis of a seven ‐ wire stainless steel strand under axial and bending loads. Fatigue & Fracture of Engineering Materials & Structures, 149-161. Erena, D., Vázquez, J., Navarro, C., & Domínguez, J. (2022). A fretting fatigue model based on self-streered cracks. Theoretical and Applied Fracture Mechanics, 117(103144). Golden, P. (2009). Development of a dovetail fretting fatigue fixture for turbine engine materials. International Journal of Fatigue, 620-628. Jahanmir, S. (1993). Friction and wear of ceramics. CRC Press. Moreno-rubio, M., Vázquez, J., Navarro, C., & Domínguez, J. (2023). Experimental study on the fretting fatigue of Inconel 718 superalloy. Tribology International. Mouritz, P. (2012). Introduction to aerospace materials. Woodhead Publishing Limited. Navarro, C., Muñoz, S., & Domínguez, J. (2014). Fracture mechanics approach to fretting fatigue behaviour of coated aluminium alloy components. J Strain Anal Eng, 49(2), 66-75.