Issue 77

S. Spiller et alii, Fracture and Structural Integrity, 77 (2026) 386-404; DOI: 10.3221/IGF-ESIS.77.22

of the investigation revealed that due to the specimens’ extensive porosity and poor surface roughness, the detrimental effect of the notch on the fatigue behavior of the specimens was minor.

Max σ max at run-out [MPa]

Thickness [mm]

σ max 50% [MPa]

Specimen series

T σ

k

ρ [mm]

k tn

q

k f

S1 S5 S3

1 5 3 3 3

197 231 277

300 300 300

1.26 2.85 1.64 1.91 1.46

3.05 3.79 5.12 5.62 4.63

N90 N30

89 61

--

0.2 0.1

5.17 7.67

0.75 0.60

4.14 5.03

50

Table 2: Fatigue properties for all tested specimens.

Figure 12: Fractography analysis of the notched specimens. N90-5: SEM image overview of the fracture surface, a), and magnified details in b) and d). N30-3: overview of the fracture surface e), and magnified details s in c) and f). Fig. 12 reports representative fracture surfaces for both the notched series. Through the magnified details, it is possible to observe the morphology of the surfaces of the sintering cracks that are well-developed from both sides in the N30-3 specimen. On the contrary, in the N90-5 specimen, only a very limited portion of material shows the morphology of the sintering crack as depicted in detail in Fig. 12c. These examples demonstrate that fatigue cracks tend to originate from the sintering crack tips. Otherwise, the fatigue initiation points can be located at the notch root without a preferential location. This suggests that in the presence of notched geometries, irregularities such as deformed corners and rough top surfaces are not as critical as they were proven in the previous section in the case of smooth fatigue specimens.

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