Abstract
Several biaxial fatigue tests are conducted up to 10 6 cycles at room temperature in the context of a collaboration LMT-Cachan / EDF / AREVA / SNECMA / CEA. Malteses cross specimens of 304L steel, designed to initiate crack in the bulk, are loaded by a triaxial testing machine. A Digital Image Correlation technique is used to measure strain during loading and detect crack initiation early. A special optical assembly and a stroboscopic sampling method are set up in this purpose. Several types of loadings are performed: equibiaxial with a loading ratio R = 0.1, equibiaxial with loading ratio R = -1, pseudo uniaxial (cyclic loading at R= 0.1 in one direction and constant loading in the other). First results are commented.
Highlights
Some parts of the cooling circuits of nuclear power plants are subject to high thermomechanical fluctuations because of the turbulent mixings of water at different temperatures. This may lead to thermal fatigue phenomena and the appearance of thermal cracking on the inner surface of tubes [1]. This phenomenon is the subject of numerous studies, from the understanding of thermomechanical loading to the prediction of structure failure
A first approach consists in reproducing the real thermomechanical loadings as accurately as possible [2], whereas the other consists in loading the samples mechanically in order to reproduce the typical stress states due to thermal loading
This second method is justified by the fact that the rather low temperature variation has little influence on High Cycle Fatigue (HCF) behavior [3]
Summary
Some parts of the cooling circuits of nuclear power plants are subject to high thermomechanical fluctuations because of the turbulent mixings of water at different temperatures This may lead to thermal fatigue phenomena and the appearance of thermal cracking on the inner surface of tubes [1]. A first approach consists in reproducing the real thermomechanical loadings as accurately as possible [2], whereas the other consists in loading the samples mechanically in order to reproduce the typical stress states due to thermal loading This second method is justified by the fact that the rather low temperature variation has little influence on High Cycle Fatigue (HCF) behavior [3]. The 304L austenitic stainless steel is elasto-plastic in the HCF regime and the cyclic behavior never reaches a stabilized state This material is viscous at room temperature. The experimental campaign is used to identify a damage model (DAMAGE2005) [4] and to better understand/model the multiaxial cyclic behavior of 304L steels
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