PSI - Issue 71

Shohei Matsuda et al. / Procedia Structural Integrity 71 (2025) 4–9

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Fig. 3. Non-propagating cracks emanating from the end edge of 4-hole defects in four specimens runout for N = 2 × 10 7 under σ a = 100-112.5 MPa, as shown in Fig. 1

Fig. 4. Macroscopic view of the fracture surface of the specimen with a 4-hole defect; =120 MPa, =573538 . Red lines in the right-hand figure indicate the facet boundaries

5. Conclusions Rotating bending fatigue tests were performed on the cast aluminum alloy (JIS AC4C-T6) specimens containing artificial defects with identical shapes and dimensions. The S-N data obtained showed a large scatter, and the √ parameter model gave a non-conservative prediction for the fatigue limit. The surrounding grains were comparable to or larger than the artificial defects. Therefore, the grains around the defect significantly affected the conditions for crack initiation and subsequent crack propagation. The fracture surface near the artificial defect comprised many smaller facets with different inclinations to the maximum principal stress plane. This feature of the fracture surface is supposed to be responsible for the large scatter in the fatigue strength and the unsatisfactory prediction of fatigue limit based on the √ parameter model. The scatter in fatigue strength is a characteristic of this type of material. From a perspective of practical fatigue design, it will be essential to study the fatigue strength evaluation method, focusing not on the average value of fatigue strength obtained experimentally but on the statistical nature of the lower bound of the scatter.