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Flow-induced vibration of PWR steam generator tubes is one of the key problems to be considered in nuclear engineering. In this paper, the dynamics of tubes subjected to cross flow is investigated. A fully coupled model for fluid dynamics and structure is used to analyze this fluid–structure problem. The study begins with an analysis of a single tube subjected to cross flow, and the dynamics and flow patterns of the system are investigated. Time trace, power spectral density (PSD), phase-plane plot and Poincare map are used to characterize the motion of the tube. Then, the dynamical behaviours of two tubes with in-line and parallel configuration are studied, and the mutual influence of the two tubes is analyzed. The relationship between pitch-to-diameter ratio and non-dimensional displacement for two contiguous tubes is investigated. Finally, the interactions within a 3 × 3 tube bundle in cross flow, and the vibration responses of the 9 tubes are investigated.

A model to calculate the welding temperature and residual stress was built using finite element code ABAQUS, and a subroutine of creep damage was also developed. Based on the coupling of welding residual stress and creep damage, the welding residual stress and creep damage of a tube made of Cr5Mo steel were simulated. This method can obtain the distributions of complex residual stress, creep damage and stress relaxation, which provide a reference for discussing the effect of residual stress on creep damage. The results show that the welding residual stress is very large at initial stage, then it is relaxed in a short time at high temperature. The distribution of creep and damage is mainly decided by the as-welding residual stress. Welding residual stress has a great effect on the creep and damage, which provides a reference for the design and life prediction of high temperature component.

Creep–fatigue interaction damage evolution of the nuclear engineering materials modified 9Cr–1Mo steel is studied with Continuum Damage Mechanics (CDM) theory. Based on the Norton creep damage and fatigue dissipate potential theory, an effective stress controlled creep–fatigue interaction damage model has been developed in this paper, in which the creep and fatigue damage function are both considered as nonlinear variables. The damage evolution function consists of the stress amplitude and the range of mean strain. The damage parameters in the model have clear physical meaning and can be determined easily. A stress controlled creep–fatigue interaction experiment has been performed with the P91 steel to obtain the damage model. The experimental results indicated that the damage model is applicable to describe the damage evolution for creep–fatigue interaction.

Experiments and numerical simulations with Phase Field Model and Finite Element Analysis were carried out to investigate the phase separation dynamic properties and the corresponding thermal aging degradation mechanism. Experimental results from transmission electron microscopy and atomic force microscopy show that thermal aging causes the Cr-rich phase precipitate and form clusters. A phase field dynamic model was developed with constitutive relations and empirical potential functions to investigate the phase separation dynamics in the ferrite phase. Numerical results integrated with cell dynamical system method show clearly the micro structure morphology and the phase separation coarsening with aging time. The evolution process of the phase separation was quantitatively illustrated and reproduced macroscopically. The scattering pattern becomes clearer and the corresponding radius becomes smaller along with the increasing aging time. The average characteristic length increases firstly then decreases and enters a more stable stage. With the increment of the local Cr concentration, the evolution of the phase morphology was quite different. Finite Element Analysis simulation results with the Gurson–Tvergaard–Needleman void model show that the damage initiated more easily in the ferrite matrix for the Cr atoms forming clusters with increasing aging time. The phenomenological simulations with Phase Field Model and Finite Element Analysis were in remarkably good agreement with experimental results and analytical considerations.

Besides the macro-mechanical properties for thermal aging effect published in “Thermal aging effect on Z3CN20.09M Cast Duplex Stainless Steel” (Nuclear Engineering and Design 239(2009) 2217-2223), the thermal aging damage mechanism is investigated in this paper through nano-indentation tests and micro-structures evolution examination. Numerical simulations were carried out with GTN continuum damage model to investigate the different crack propagation process for aging. The nano-indentation hardness values increase with aging time for both phases while the hardness values of the ferrite phase are much higher and increase much more. The nano-indentation energy indicating the toughness decreases for both phases with aging time. TEM results show that the Cr-enriched α′ phase precipitates in the ferrite phase which is considered as the critical reason making the dislocation slip difficult and causing the increase of the strength and reduction of the toughness. The crack initiates from the ferrite phase instead of the austenite phase from the SEM observation and FEA simulation results, which reflects the change of the fracture mechanism for thermal aging.

Instrumented impact tests were performed on Z3CN20.09M Cast Duplex Stainless Steel (CDSS) aged at 400 °C for up to 3000 h. The material was cut from the primary pipe of a PWR to investigate the accelerated thermal aging embrittlement effect on the dynamic fracture properties. The load–deflection curves from the instrumented impact tests described both the loading and the fracture stages, from which the dynamic ultimate loading level and the dynamic ultimate strengths were calculated as a function of increased aging time. The increase in the dynamic ultimate strengths with aging time is much higher than those for the static ultimate strengths. With the increment of the aging time, both the crack initiation energy and the crack propagation energy decrease, which are separated form the total impact energy taking the maximum loading level as the crack initiation point. It is shown that the reduction tendency of the fracture propagation energy is the predominant reason for the reduction of the impact energy. With the increment of the aging time, the unloading slopes reflecting the crack propagation speed increase and the fracture surface patterns change from ductile fracture with shallow dimples to cleavage brittle fracture caused by dislocations piling up in the ferrite matrix. Mechanical properties of inner wall with fine equi-axed grains are much better than those of the outer wall with coarse columnar structures.

Small punch (SP) tests have been performed at room temperature on round specimens with six kinds of thicknesses. Experimental results show that the SP energy, the fracture strain and the fracture toughness increase with the thickness of the SP samples. Fracture surface displays typical ductile fracture, and the outer surface of the hemispherical bulk part punched off is full of little bowings around which there are many microcracks caused by the stretch stress under biaxial strain/stress state. From the view point of the energy dissipation, the fundamental theoretical model of fracture toughness is proposed, according to which the ductile fracture toughness is obtained from the SP energy, the plastic deformation and the experimental fractography. The fracture strain and the fracture energy density criteria are introduced into the local failure model. With the continuum damage model, the FEA simulations provide the results of the crack propagation process which agree with the experimental results and can verify the fracture model.