Environmental Effect on Fatigue Crack Initiation under Equi-Biaxial Loading of an Austenitic Stainless Steel

Cédric Gourdin,Jean-Christophe Le Roux,Laurent De Baglion,Hager Dhahri,Grégory Perez

doi:10.3390/met11020203

Abstract

The lifetime extension of nuclear power stations is considered an energy challenge worldwide. That is why the risk analysis and the study of various effects of different factors that could potentially prevent safe long-term operation are necessary. These structures, often of great dimensions, are subjected during their life to complex loading combining varying multiaxial mechanical loads with non-zero mean values associated with temperature fluctuations under a PWR (pressure water reactor) environment. Based on more recent fatigue data (including tests at 300 °C in air and a PWR environment, etc.), some international codes (RCC-M, ASME, and others) have proposed and suggested a modification of the austenitic stainless steels fatigue curve combined with a calculation of an environmental penalty factor, namely Fen, which has to be multiplied by the usual fatigue usage factor. The determination of the field of validation of the application of this penalty factor requires obtaining experimental data. The aim of this paper is to present a new device, “FABIME2e” developed in the LISN (Laboratory of Integrity of Structures and Normalization) in collaboration with EDF (Electricity of France) and Framatome. These new tests allow the effect of a PWR environment on a disk specimen to be quantified. This new device combines structural effects such as equibiaxiality and mean strain and the environmental penalty effect with the use of a PWR environment during fatigue tests.

Highlights

The question of assessing the margins and safety factors in fatigue analyses, which are widely used today (ASME BPV III, RCC-M, JSME, EN-13445-3, etc. [1,2,3,4,5]), is a very challenging one.The fatigue rules used today in the nuclear industry were initially built and integrated into the ASME code in the 1960s
This paper focused on the description of two kinds of experimental devices to perform fatigue tests on spherical specimens with or without the effect of a water environment
The first device (FABIME2) is devoted to study of the effect of biaxiality and mean strain/stress on fatigue life

Summary

Introduction

The question of assessing the margins and safety factors in fatigue analyses, which are widely used today (ASME BPV III, RCC-M, JSME, EN-13445-3, etc. [1,2,3,4,5]), is a very challenging one.The fatigue rules used today in the nuclear industry were initially built and integrated into the ASME code in the 1960s. Establishing fatigue rules is a challenge in itself since fatigue degradation depends on the wear of components that undergo repeated cycling. As a result, testing is, in practice, conducted on small laboratory specimens, which raises the question of how to extrapolate results to a full-size component. Another difficulty is that the rules need to remain easy to apply in order to be used in industrial engineering calculations. On the curves presented in the NUREG report [1], the PWR water environment effect on the fatigue lifetime of material used in the manufacture of reactor components is illustrated

Objectives

Results

Discussion

Conclusion