PSI - Issue 57

Jacques BERTHELLEMY et al. / Procedia Structural Integrity 57 (2024) 872–903 J. Berthellemy / Structural Integrity Procedia 00 (2023) 000 – 000

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Fig. 38: Fatigue test specimen used by Kunz et al.

Fig. 39: Example of chancroid notch observed at the surface of W steel

The chancroid notch with the geometrical ratio H/R = 0.35 was already studied by L. Kunz et al. with the Effective Notch stress method. This study was modelizing the chancroid notch using a perfect spherical geometry of the crater. As shown in Figure 39, the geometric parameter adopted in the present paper is R, where R² = 2  H – H² while  was preferred by Kunz et al. to build the model by substraction of the sphere from the initial solid surface. Kunz's study was initially reproduced identically, with the same results. The principal stress is multiplied by a factor 1.50 at the bottom of the chancroid notch.

Fig. 40-a : Spherical chancroid model H/R = 0.35 SCF = 1.50

Fig. 40-b: Probability of crack initiation during one cycle p = 9.3 E-7

Class = 100 / exp ( -0,3333 * ln ( 1/ ( 2E6 * 9.30E-7 ))) = 82 MPa

The calculated modified category of detail is around 80MPa instead of the original 125MPa category of the surface. This calculation corresponds approximately with the experimentaldata provided by Kunz et al. from tests. However the calculation result with a perfect spherical defect is too favorable, and the irregularities of the chancroid geometry shown by figure 39 was also modelized by using the rotation of a nurbs as presented in Figure 41 for H/R=0.350.