PSI - Issue 83

Teresa Morgado et al. / Procedia Structural Integrity 83 (2026) 286–294

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to the average applied stress, frequency, temperature, and environment (Paris, Gomez and Anderson, 1961; Paris and Erdogan, 1963; Becker and Shipley, 2002). ௗ ௗ ே ௔ ൌ ܥ ሺο ܭ ሻ ௠ (7) The standard method for obtaining a steady-state solution for an elastoplastic structure subjected to cyclic loading is to apply a cyclic load periodically to the structure until a steady state is reached. At each point in time, Newton’s method is used to solve the nonlinear equations of equilibrium. As the complexity of the problem increases, it is expected that solving the nonlinear equations could consume nearly all of the computational capacity (Zienkiewicz et al, 2024). Therefore, this method requires significant computational power due to the application of numerous loading cycles until a stabilised response is achieved. To avoid high computational cost, the modified Newton method is used in combination with the Fourier representation of the solution and the residual vector to obtain a stabilised cyclic response. The ASTM E647-05standard recommends determining the SIF (SIFRef) experimentally for a single-edge notched bend (SENB) test by equations 8 and 9, where Pmax is the maximum load applied, S is the distance between the specimen supports, a is the pre-crack, W is the specimen height, and B is the thickness. ோ௘௙ ൌ ௉ ஻ ௠ௐ ௔௫ௌ యమ ቀ ௐ ௔ ቁ (8) ቀ ௐ ௔ ቁൌ൬2.9ቀ ௐ ௔ ቁ ଵଶ െ4.6ቀ ௐ ௔ ቁ ଷଶ ൅21.8ቀ ௐ ௔ ቁ ହଶ െ37.6ቀ ௐ ௔ ቁ ଻ଶ ൅38.7ቀ ௐ ௔ ቁ ଽଶ ൰ (9) 3. Material and geometric dimensions The first significant use of the Ti-6Al-4V alloy, also known as T64, was by Pratt & Whitney in the production of discs and blades for jet engines, instead of steel, which had traditionally been used in the design. The result was in savings of 945 kg per aircraft, as it is a less dense alloy (Levens & Peters, 2003; Boyer, 1995). Ti-6Al-4V is also commonly used in marine applications, particularly due to its good resistance to corrosion and fracture, regardless of chemical variations or the effects of pollution in seawater. In a study published by Gurrappa (2003) on the characterisation of a Ti-6Al-4V alloy for use in the chemical and marine industries. The author concluded that the TC4 alloy, as it pertains to marine applications, is capable of actively regenerating the protective oxide layer from low to high temperatures, provided it undergoes minimal surface treatment, and is not affected by pitting or the initiation of corrosion cracks. Totolin et al. (2016) reached the same conclusion; in their study on improving the tribocorrosive characteristics of the surface of a Ti-6Al-4V specimen in artificial seawater, they concluded that when the alloy is properly surface-treated, even in the face of abrasion, no corrosion cracks are observed. Regarding its applications in the maritime industry, an excellent example is offshore platforms, particularly in taper stress-joints. In this type of connection, extreme flexibility is essential due to the need to compensate for platform movement caused by waves, wind, and tides. Like the characteristics that taper stress-joints must possess, there are other components, also manufactured from Ti-6Al-4V, that are essential to the maritime industry, such as hydrofoils, propellers, certain shafts, and ship hulls (Froes, 2015; Leyens and Peters, 2003; Gurrappa, 2003). In the last decades, many authors studied the mechanical properties of the Ti-6Al-4V produced by Additive Manufacturing, namely Selective Laser Melting (SLM), as a function of build direction (Vilaro, 2011; Rafi et al., 2013; Simonelli et al., 2014; Cao et al, 2017; Hartunian and Esraghi, 2018; Kok et al, 2018; Baghi et al., 2021; Nguyen et al, 2022; Alves et al., 2024). The fatigue parameters for Ti-6Al-4V in function of build directions were experimentally determined also by several authors (Van Hooreweder et al., 2012; Cain et al., 2014; Edward and Ramulu, 2015; Hartunian and Esraghi, 2018). Table 1 presents the mechanical properties (Simonelli eta al, 2014) and Table 2 presents the fatigue parameters (Edward and Ramulu, 2015) of the Ti-6Al-4V used in this research.