PSI - Issue 79

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

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Fig. 6. V2 fracture (a) surface characteristics and (b) topography.

Specimen V6 was subjected to a maximum stress of 302.40 MPa (the same stress level as V1) and endured 821,180 cycles before failure. As mentioned, it presented similar surface characteristics as V3, V4 and V5, Fig. 7 reveals a clear distinction between brittle fracture regions (on the left) and ductile regions (on the right). The samples demonstrate a noticeable trend of increasing brittle crack growth zones as the number of cycles increases. Among the fractured vertical specimens, V6 exhibited the highest fatigue life despite not being tested under the lowest stress level. It also should be highlighted that distinct raised and recessed regions are observed, corresponding to ductile and brittle fracture mechanisms, respectively. In this case, however, the recessed (brittle) region is noticeably larger than in the other specimens, suggesting a greater extent of brittle behavior. This characteristic may have contributed to a slower crack propagation rate and, consequently, a higher fatigue life when compared to the others. For the vertical specimens subjected to fatigue loading, fracture mechanisms similar to those observed in the horizontal specimens were identified, with clearly defined brittle and ductile regions, consistent with descriptions in the literature. Additionally, for both orientations, specimens that failed after a low number of cycles exhibited fracture surfaces without well-defined zones and a predominance of dimples, indicating a primarily ductile failure mode. It should be highlighted that parts manufactured by AM And even small defects from the AM (de Araújo Soares et al., 2024) can impact on the part life (Araujo et al., 2024; da Silva et al., 2024).

Fig.7. V6 fracture (a) surface characteristics and (b) topography.

Specimen V1 was subjected to a maximum stress of 302.4 MPa, enduring 263,141 cycles before failure. The fracture observed in this specimen was similar to V3, V4 V5 and V6, exhibiting both brittle and ductile fracture regions, Fig. 8. As with the horizontal samples, the crack likely initiated at one of the specimens ends (near the fragile area) and propagated until a ductile failure occurred at the opposite end. It is also noteworthy that, at the same stress level, the horizontal samples exhibited "infinite life" (2 × 10^6 cycles). Fig. 8 (b) presents the topography of the fracture surface of V1. It reveals lower regions (on the left side) corresponding to crack initiation and propagation via a brittle mechanism. At the opposite end of the specimen, an elevated region is observed, which corresponds to the ductile failure mechanism.