PSI - Issue 38

10

Jacques Berthellemy / Structural Integrity Procedia 00 (2021) 000 – 000

Jacques Berthellemy et al. / Procedia Structural Integrity 38 (2022) 428–446

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2. 3 Evaluation of the stress concentration factor along the cut The point with of the strongest probability of crack initiation along the cut is determined using the signed von Mises criterion as scalar function in order to determine the probability of crack initiation during one cycle of stress variation. During this cycle presented in Fig. 15, a time varying factor is applied to the set of stresses that constitute the loading and for instance for the longitudinal stress  , the amplitude of stress is of 50 MPa which means in other words that the  stress range is of 100 MPa.

Figure 15 : History of stress variation that is used to evaluation the crack initiation probability

Along a rounded cutting line, the von Mises function avoids us to have to look for the governing principal stress. The quality of the cut is assumed to be 125 MPa and Code_Aster presents directly as a result the probability of crack initiation. This zone is very limited and corresponds to the zone with the red color of Fig. 18 in the web along the cut. The principles of 3D-volume modeling presented here were developed at Cerema for the European research program Precobeam. These principles made it possible to find by calculation the classes of fatigue of the Eurocodes based on experimental results as presented in [22,23,24,25]. It produces good results for fatigue classes under 71 MPa. In this case the class of detail is obtained with the Woehler model used in EN 1993-1-9 [17] represented by equation (1): Class = 100 . ( ( 1 . 2 6 3 ) ) MPa ( eq. 1 ) where p is the probability of crack initiation during the used cycle and 100 MPa is the stress range of this cycle. Note in the following results, that when t 2 = t 1 and  = 0 then the class 71 MPa is obtained which confirms the pertinence of Table 8.2 of EN 1993-1-9 [17] and of the present calculations as well.