International audienceStrain-aging constitutive models are suitable to simulate the formation and propagation of Lüders bands in complex specimens and components. The identification of the corresponding material parameters is difficult because the strain localization phenomena associated with the Lüders behavior must be taken into account. The spurious mesh dependence of standard finite element simulations of Lüders band propagation is illustrated in the present work and removed using a strain gradient plasticity model. Furthermore the gradient approach introduces a characteristic size corresponding to the finite dimension of the Lüders band front as observed from strain field measurements. The parameters are identified from the experimental measurement of the peak stress and plastic strain carried by the band for a C-Mn steel over a temperature range from −150°C to room temperature and for several strain rates. The validity of the model is tested on 3D simulations of the Lüders band propagation in a strain gradient plasticity medium

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The RSE-M Code provides rules and requirements for inservice inspection of French Pressurized Water Reactor power plant components. Appendices 5.3 and 5.4 of the Code give non mandatory guidance for analytical evaluation of flaws, i.e. fracture mechanics analyses based on simplified methods. Flaw assessment aims to calculate the initiation and the subsequent propagation of the crack under cyclic loading (fatigue analysis) and then to assess the crack stability, by comparing the applied J integral to the toughness of the material. This paper shows an overview of the R&D work undergone to make possible an analytical approach: • analytical formulas for the elastic stress field in elbows under in-plane, out-of-plane and torsion moments, • stress intensity factors solutions based on the influence coefficient method for surface and embedded cracks in pipes, • simplified methods to estimate the J integral for various configurations of piping, flaws and loading. These methods are shortly presented, including their field of application and their validation.

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