French recent developments in support to rules for creep and creep-fatigue analyses

RCC-MR proposes Design rules for creep and creep-fatigue damage evaluation in zones with no geometrical discontinuities. Rules have been developed, based on the σd concept, in order to consider zones with geometrical discontinuities. Rule for Weld are proposed in the paragraph relative to shell design rules and reduction coefficient due to material properties are given in Appendix A9. For fatigue analysis, last version of RCC-MR (1993) has proposed a reduction factor on fatigue curves (Jf value), derived from preliminary tests performed within European program. Studies have been carried out in order to have a better understanding of the phenomena involved in these fatigue reduction factors. Tests have been performed on large plates, with varying applied displacements, weld geometry, plate thickness, weld direction. It appears that material effect is not the only purpose to be considered but that it is necessary to think about the geometrical effect, linked to the welded zone dimensions, and the elastic follow-up effect between the two materials: base metal and weld metal. As a first approach, simplified calculations have been achieved with precise material characterization. Roche's method and Zarka method's give conservative result in comparison to tests results. (author). 3 refs, 4 tabs