PSI - Issue 57

Stéphan Courtin et al. / Procedia Structural Integrity 57 (2024) 4–13

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Author name / Structural Integrity Procedia 00 (2019) 000 – 000

Fig. 3. Evolution of the propagated crack lengths for the thermal loading #1.

3. Numerical protocol and modelling assumptions

3.1. Description of the  J approach

As mentioned above, international codes and standards only provide inadequate and very conservative methods for dealing with the thermal fatigue crack growth associated with austenitic stainless steel large nuclear components, with high thicknesses, experiencing cyclic LSY due to mechanical and thermal loadings during their service life. Non-codified alternatives, recently discussed by Li et al. (2019) or Hojo and Kumagai (2022), then appear to be good candidates for assessing plasticity phenomena occurring during the thermal fatigue crack growth beyond SSY. These approaches, promising to reduce the conservatism of codified methods, propose to extend the use of classical Paris laws by the evaluation, by FEA , of a parameter ΔJ, derived from the J-integral parameter introduced by Eshelby (1956), and developed by Cherepanov (1967) and Rice (1968). As reminded by Li et al. (2019), note that the J-integral concept is mathematically valid only for monotonically increasing loading in nonlinear elastic range. The  J approach considered in this paper and using the EDF code_aster FE software and Salome-Meca platform, is based on the one reported by Li et al. (2019), the overall fatigue crack growth evaluation scheme being as follows: • Thanks to elastic FEA with pre-cracked meshes, determination of the minimum (K min ) and maximum (K max ) stress intensity factors for the thermal loadings considered. • Definition of virtual monotonically increasing thermal loadings from K min and K max in order to assess elastic plastic ΔJ value s, thermal loadings being from 0°C to ΔT, where :

o T Kmin is the thermal state generating K min o T Kmax is the thermal state generating K max o ΔT is the difference between the two thermal states: ΔT = T Kmax - T Kmin • Determination of effective stress intensity factors ΔK eff (see Eq.1):

(1)

where: o E and  are respectively Young’s modulus and Poisson coefficient of the material o ሺ ሻ is the closure effect correction proposed by the French RSE-M code (2014), with R= K min / K max