PSI - Issue 79

Déborah de Oliveira et al. / Procedia Structural Integrity 79 (2026) 248–258

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cycles) at maximum stresses of 384 MPa for horizontal samples and 436 MPa for vertical samples, whereas Pimenta (2022) found a fatigue strength (horizontal sample) of only 302.04 MPa. The anisotropy results reported by Ermakova et al. (2023) were opposite to those observed in the present study, with vertical samples exhibiting higher fatigue resistance. Moreover, the fatigue strength values for horizontal samples were 21.3% higher than those found by Pimenta. These discrepancies can be attributed to factors such as specimen geometry, as the stress concentrator inherent to rectangular specimens may have adversely affected fatigue resistance. Additionally, factors including non-compliance with surface finish standards and slight differences in deposition parameters and testing conditions (e.g., load ratio) may have contributed to the variations observed. In Fig. 5 the comparison between both curves is presented. The comparative curve clearly highlights the anisotropic behavior of the material, with the horizontal specimens exhibiting higher fatigue resistance across all points on the curve. Among the fractured specimens from both tests, at a stress level of 350 MPa, the horizontal specimen (H5) endured 2.23 times more cycles than the vertical specimen (V3), underscoring the anisotropic effects inherent to the material, or small defects from the deposition process (Araujo et al., 2023). Ayan and Kahraman (Ayan and Kahraman, 2022) also investigated fatigue behavior of ER70S-6 wire in vertical and horizontal samples but performed bending fatigue tests on rectangular specimens. From their test data, an S-N curve comparing vertical and horizontal samples was generated. In their study, vertical samples showed higher fatigue resistance up to 10^6 cycles; however, at 10^7 cycles, the fatigue behavior was similar in both orientations, with endurance limits of 178 MPa for vertical samples and 176 MPa for horizontal samples. The higher fatigue strength in vertical samples aligns with the findings of Ermakova et al. (2023) but differs from the results presented in this work.

Fig. 5. Comparison between vertical and horizontal specimens.

To evaluate the fracture, some specimens were selected V2 since it presented the lowest life, V6 for presenting similar characteristics as V3, V4 and V5 and V1 for having the highest resistance. Specimen V2 was subjected to a maximum stress of 384 MPa, withstanding only 901 cycles. Similar to H1 this sample did not exhibit well-defined fracture zones. As shown in Fig. 6, the fracture surface appears relatively homogeneous, likely featuring dimple structures. The fracture characteristics of this specimen closely resemble those observed in static tests, which can be attributed to the very low number of cycles compared to conventional fatigue test values. Despite the significant discrepancy in cycle count relative to the other samples, optical microscopy analysis did not reveal any distinct defect or contributing factor that could justify V2 poor performance.