Investigations on the cumulative fatigue life for a type 304-L stainless steel used for pressure water reactor

Les circuits des Réacteurs à Eau Pressurisée peuvent être soumis à la fatigue thermique. Les chargements rencontrés en service sont complexes. Aussi, le conservatisme des prévisions ne paraît pas toujours garanti. Un programme expérimental d'essais de fatigue a été réalisé à amplitude de déformation imposée sur l'acier 304-L avec des séquences à plusieurs niveaux. La loi de cumul linéaire de dommage ne permet pas d'estimer a durée de vie pour l'acier 304-L. Un effet d'histoire est mis en évidence. La loi bilinéaire proposée par Manson permet d'obtenir d'assez bonnes estimations

A computational lifetime prediction of a thermal shock experiment. Part II: discussion on difference fatigue criteria

The SPLASH experiment has been designed in 1985 by the CEA to simulate thermal fatigue due to cooling shocks on steel specimens and is similar to the device reported by Marsh in Ref. [1]. The purpose of this paper is to discuss the application of different fatigue criteria in this case. The fatigue criteria: dissipated energy, Manson Coffin, Park and Nelson, dissipated energy with a pressure term, are determined for the experiment using results from FEM computations presented in the first part of the paper (Part I) and compared with results from uniaxial and multiaxial experiments from literature. The work emphasizes the evolution of the triaxiality ratio during the loading cycle

A computational lifetime prediction of a thermal shock experiment. Part I: thermomechanical modelling and lifetime prediction

The SPLASH experiment has been designed in 1985 by the CEA to simulate thermal fatigue due to short cooling shocks on steel specimens and is similar to the device reported by Marsh in Ref. [1]. The purpose of this paper is to discuss the mechanical and the fatigue analysis of the experiment using results from FEM computations. The lifetime predictions are obtained using a modified dissipated energy with a maximal pressure term and agree with the experimental observations. The numerical analysis of the mechanical state shows an important evolution of the triaxiality ratio during the loading cycle. Further comparisons and discussions of the fatigue criteria are provided in the second part of the paper (Part II)

Comparaison de modélisations numériques appliquées à une expérience de fatigue sous choc thermique

International audienceThis paper is dedicated to the comparison of several numerical models for estimating the mechanical state in a thermal fatigue experiment known as the SPLASH test, in terms of their prediction capacity with respect to several fatigue criteria. The numerical methods are either completely nonlinear or combine approximate elastic solutions obtained from minimizing a potential energy or closed form solutions with a Neuber or Zarka technique to estimate directly the elastoplastic state. The fatigue criteria used are Manson, dissipated energy and dissipated energy combined with a hydrostatic pressure term. The latter had provided a best prediction over a series of anisothermal and isothermal LCF experiments in a classical fatigue analysis. The analysis shows that for this criteria we obtain a systematic and conservative error.Ce travail présente une comparaison de plusieurs modèles numériques pour déter-miner le cycle mécanique de l'expérience de fatigue thermique SPLASH. On s'intéresse en particulier à la précision des différents modèles lorsqu'on les utilise pour une analyse de fatigue. Les techniques numériques étudiés sont : (i) la résolution du problème élasto-plastique non-linéaire complet par calculs Eléments Finis, (ii) des solutions élastiques approchées cou-plées à une règle de Neuber modifié (iii) la méthode de calcul simplifié des structures de Zarka et al. Les critères de fatigue utilisés sont : (1) le critère de Manson, (2) un critère sur l'énergie dissipée par cycle, (3) un critère sur l'énergie dissipée modifiée par la pression hydrostatique. Ce dernier est le plus pertinent du point de vue de la fatigue au regard des résultats obtenus sur une série d'essais multiaxiaux et uniaxiaux. L'analyse présentée ici montre que ce critère est conservatif et ne propage pas les erreurs dues à la technique de calcul du cycle stabilisé utilisé

A comparison of lifetime prediction methods for a thermal fatigue experiment

This paper is dedicated to the comparison of several numerical models for estimating the lifetime in a fatigue experiment. The models simulate the SPLASH experiment, which produces thermal fatigue by locally quenching stainless steel specimens. All models predict first a stabilized mechanical state (plastic shakedown) and then a lifetime prediction using several fatigue crack initiation criteria.The numerical methods are either completely nonlinear or combine approximate elastic solutions obtained from minimizing a potential energy or closed form solutions with a Neuber or Zarka technique to estimate directly the elastoplastic state.The fatigue criteria used are Manson, dissipated energy and dissipated energy combined with a hydrostatic pressure term. The latter had provided a best prediction over a series of anisothermal and isothermal LCF experiments in a classical fatigue analysis.The analysis shows that for fatigue criteria taking into account the triaxiality of the mechanical response we obtain a systematic and conservative error. As a consequence of this work, we show that simplified models can be used for lifetime prediction. Moreover the paper provides a general technique to asses from the point of view of the design engineer the combination between a numerical method and a fatigue criterion

Investigations into the cumulative fatigue life of an AISI 304L austenitic stainless steel used for pressure water reactors: Application of a double linear damage rule

International audienceIn order to investigate cumulative damage in fatigue, a multi-level fatigue programme has been carried out on an austenitic stainless steel AISI 304L. All the tests have been performed under controlled strain-amplitude conditions, with several changes of levels up to rupture; values of strain-amplitude were included between 0.20% and 0.80%. The present experimental programme shows that applying a linear damage rule (LDR), also referred to as Palmgren–Miner’s rule, has been demonstrated to be unreliable in some cases. A loading sequence (loading history) effect is clearly shown for the two-level sequence tests; application of the LDR leads to residual fatigue-life overestimation for high-to-low loading (H–L) sequences whereas residual fatigue-life is underestimated for low-to-high loading (L–H) sequences. The multi-level and block tests, undertaken in this campaign, confirm also a possible non-verification of the LDR.Within this framework, the double linear damage rule (DLDR) has been tested. Its application would seem to be promising as an additional approach in certain situations. However, complex sequences and random fatigue tests are still needed to draw a conclusion, and to more clearly evaluate the conditions where use of the LDR would not be sufficient