Stress corrosion cracking (SCC) is one of the key issues of welded structure failure in nuclear power plants. To understand the effect of strength matching on SCC growth rate in welded joint of primary coolant circuit safe end in pressured water reactor, a model of the safe end welded joint with mismatched strength was established by using elastic-plastic finite element method (EPFEM).The effect of weld strength matching on SCC growth rate was analyzed in this paper, by adopting crack tip strain rate as SCC mechanical driving force. The investigated results indicate that the distribution of plastic strain and plastic strain rate nearby the crack front is similar when the crack located at welded metal, and the driving force of SCC along the crack front in the over-match, even-match and under-match welded joint are from small to large, respectively, which implicit SCC growth rate along the crack front in the over-match, even-match and under-match welded joint also are from slow to fast, respectively. The investigating establishes a foundation for improving the predicting capability of SCC growth rate in nuclear power structures.
Intergranular stress corrosion cracking is one of important failure form of structural materials in nuclear power plants, and the initiation and development of crack at grain boundary are affected by the grain size of materials. The macroscopic model and mesoscopic model of crack propagation was established by using finite element method, and the effects of grain size on fracture parameters such as Mises stress, the maximum principal stress and equivalent plastic strain nearby crack tip were studied. The results indicate that the distribution of Mises stress and equivalent plastic strain are discontinuity at grain boundary, and the maximum principal stress locates at grain boundary. The Mises stress, maximum principal stress and equivalent plastic strain nearby crack tip increase with the increasing of grain size.
Solar photovoltaic cell demand is great in the whole world and its manufacturing cost is also high. The main reason that slicing cost is too high, because of the low slicing efficiency and large kerf loss.Therefore, many scholars are studying new slicing method in order to reduce the cost. In this paper, we summarize conventional and new slicing method for solar silicon wafer, and think that new slicing method widely apply in photovoltaic industry, which needs to solve some technical problems. At present, multi-wire saw technology still is mainly slicing method in photovoltaic industry.
The welded joint is the critical area in the structure integrity investigation. To understand the influence of the mechanical heterogeneous on the fracture parameters in welded joint, the represented way of the welded mechanical heterogeneity and its effect on the mechanical parameters at the crack tip are analyzed by using an elastic-plastic finite element analysis software in this paper. The investigated results indicate that continuous change of material mechanical properties could express the effect of the actual welded mechanical heterogeneity on the fracture mechanical parameters change in the welded joint more accurately, which provide a new approach on the fracture problem investigation in welded joints.
This paper proposes a hydraulic sleepless speed system for a invariable fertilizing application based on PLC, in order to enhance the stability of the hydraulic sleepless speed system and eventually achieve precise fertilizing. With particular emphasis on the stability of the hydraulic circuit and the actuation control method, mathematical model and simulation model for hydraulic sleepless speed system are established. More specifically, hydraulic sleepless speed system with stable oil circuit and oil pressure sensor is designed to ensure hydraulic system stability, while PID control algorithm is employed to compensate transmission error according to the mathematical model. The hydraulic sleepless speed system is then simulated in different PID control parameters. Simulations show that the results are reasonable and applicable, providing some theoretical guidance to the characteristics anticipation and test of hydraulic sleepless speed system. It is also found that when the PID parameter is chosen as =10, =0.08, =8, the fertilizing precision will be satisfied.
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