Equi-Biaxial Loading Effect on Austenitic Stainless Steel Fatigue Life

Abstract

Fatigue lifetime assessment is essential in the design of structures. Under-estimated predictions may result in unnecessary in service inspections. Conversely, over-estimated predictions may have serious consequences on the integrity of structures. In some nuclear power plant components, the fatigue loading may be equibiaxial because of thermal fatigue. So the potential impact of multiaxial loading on the fatigue life of components is a major concern. Meanwhile, few experimental data are available on austenitic stainless steels. It is essential to improve the fatigue assessment methodologies to take into account the potential equi-biaxial fatigue damage. Hence this requires obtaining experimental data on the considered material with a strain tensor in equibiaxial tension. Two calibration tests (with strain gauges and image correlation) were used to obtain the relationship between the imposed deflection and the radial strain on the FABIME2 specimen. A numerical study has confirmed this relationship. Biaxial fatigue tests are carried out on two austenitic stainless steels for different values of the maximum deflection, and with a load ratio equal to -1. The interpretation of the experimental results requires the use of an appropriate definition of strain equivalent. In nuclear industry, two kinds of definition are used: von Mises and TRESCA strain equivalent. These results have permitted to estimate the impact of the equibiaxiality on the fatigue life of components.

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

“…The first one was of an experimental nature: It allowed us to link the displacement imposed in the center of the specimen to the radial strain. This experimental calibration step is described in the following reference [19]. At the end of this first step, an experimental calibration curve, carried out on specimens of the same material as the one to be studied, was thus defined.…”

“…Unfortunately, testing on structures representative of real plant components is expensive but should be increased to help contribute to the general understanding of the various aggravating effects [7][8][9][10][11][12][13][14]. In order to obtain fatigue strength data under structural loading, biaxial test devices with and without a PWR environment were developed at LISN [15][16][17][18][19].…”

PWR Effect On Crack Initiation Under Equi-biaxial Loading

“…• Determination of the value of the radial strain corresponding to the imposed deflection from the strain-deflection calibration curve obtained in the paper [14]. With a similar mechanical behavior, the calibration curve can be used for the two materials.…”

“…Unfortunately, testing on structures representative of real plant components is expensive but should be today increased to help contribute to the general understanding of the various aggravating effects [6][7][8][9][10]. In order to obtain fatigue strength data under structural loading, biaxial test means with and without PWR environment were developed at LISN [11] [13][14]. Two kinds of fatigue devices have been developed.…”

Environmental Fatigue Behavior of a Z3CN20.09M Stainless Steel in High Temperature Water

“…It indicates that the involvement of corrosive medium or the interactions of corrosive medium with applied load might be responsible for the decrease in the fatigue life of the Z3CN20.09M ASS [16,17]. At the same strain amplitude, the decrease in strain rate yielded a lower fatigue life [15,[18][19][20][21]. For example, at 0.8% strain amplitude, the decrease in strain rate from 0.04% to 0.004%/s led to 3.5 times lower in the fatigue life.…”