PSI - Issue 74

Mitra Delshadmanesh et al. / Procedia Structural Integrity 74 (2025) 9–16 Mitra Delshadmanesh / Structural Integrity Procedia 00 (2025) 000–000

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diameter of 2 mm. The specimen was aligned and glued across that hole as depicted in Fig. 3. During fatigue testing, the sample holder is excited to longitudinal vibrations with zero mean stress. The sample itself experiences the maximum stress at the location of the hole, where the support of the underlying sample holder is missing. The temperature of the sample and holder is kept well below 35°C with the use of a compressed air cooling system. The strain in the miniaturized samples was determined by strain gauge measurement at the sample holder in combination with Finite Element Analysis. The position of the strain gauge is indicated in Fig. 2. A plot of the stress distribution in the sample derived from a conventional Finite Element simulation can be seen in Fig. 3. The material parameters used for this simulation are summarized in Table 1.

Fig. 1. Sample types A, B, C, D, E, and F were designed with different notch radii in the range from 2 mm to 125 µm.

Fig. 2. Illustration of the ultrasonic fatigue testing system, schematically. The position of the strain gauge is at the height of the midsection at the side face of the holder.

Table 1. Material parameters used for conventional Finite Element Analysis.

Material

Density [kg/m 3 ]

Young’s modulus [GPa] Poisson ratio

CoCrFeNiMn

7960 4430

147

0.25

Ti6Al4V

113.8

0.342