Crack initiation under thermal fatigue: An overview of CEA experience. Part I: Thermal fatigue appears to be more damaging than uniaxial isothermal fatigue

Abstract

International audienceFor nuclear reactor components, uniaxial isothermal fatigue curves are used to estimate the crack initiation under thermal fatigue. However, such approach would be not sufficient in some cases where cracking was observed. To investigate differences between uniaxial and thermal fatigue damage, tests have been carried out using the thermal fatigue devices SPLASH and FAT3D: a bi-dimensional (2D) loading condition is obtained in SPLASH and crack initiation is defined as the first 150-μm surface cracks, whereas a tri-dimensional (3D) loading condition is obtained in FAT3D and crack initiation refers to the first 2-mm surface crack. All the analysed tests clearly show that for identical levels of strain, the number of cycles required to achieve crack initiation is significantly lower in thermal fatigue than in uniaxial isothermal fatigue. The enhanced damaging effect probably results from a pure mechanical origin: a nearly perfect biaxial state corresponds to an increased hydrostatic stress. In that frame, a Part II accompanying paper will be dedicated to investigate accurately on multiaxial effect, and to improve thus estimation of crack initiation under thermal fatigue

High cycle thermal fatigue of austenitic stainless steel

“…2.-(2)) is used to measure the 2D temperature field and the 3D displacement fields with a high magnification lens allowing for a pixel resolution of 15µm. Two fast pyrometers (KGA740-LO, ∈ [3,5 ], Fig. 2.-(3)) are used to measure and monitor within the impacted zone the temperature variation on a 2.5mm central area.…”

“…mechanical strain amplitude) as in standardized isothermal strain controlled push-pull mechanical fatigue tests. From previous thermal fatigue results obtained at CEA [3,4], it appeared that this approach could be nonconservative, namely, the number of cycles to crack initiation in thermal fatigue experiments could be lower than in push-pull isothermal fatigue tests for the same levels of equivalent strain amplitude.…”

Numerical simulation of thermal fatigue behavior in a cracked disc of AISI H-11 tool steel

“…Some of the setups include a disc heated by induction on the periphery [1][2][3][4][5][6][7][8][9][10][11][12], triangular blade heated by induction [13], electrical heating of tube followed by water splashing to induce thermal shock [14][15][16][17][18], hot dipping of cylinders in molten aluminum [19,20], laser heating [21,22], focused halogen lamps heating [23,24], convection/combustion heating [25,26], furnace heating with water quenching [27,28] and actual dies [29,30]. Out of these experimental setups most researchers have worked on the heated disc problem.…”

Fatigue life prediction for broad-band multiaxial loading with various PSD curve shapes

“…To assess the risk of thermal fatigue damage [1,2] resulting from the machining of the pipes inner surface (pre-hardening gradient, residual stresses and scratches) , experimental tests on tubular specimens (named INTHERPOL tests), were developed by EDF R&D. Other tests facilities were also developed by CEA [3]. Recently, experimental investigations at room temperature on the fatigue behaviour of pre-hardened stainless steel were carried out by Taleb and Hauet [4], Taheri et al [5].…”