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.
Crack statically growing would induce the re-distribution of the stress and strain at the crack tip for power hardening materials, and the process of crack statically growing would be affected by the change of the stress and strain at the crack tip. To understand the effect of crack statically growing on the stress and strain at the crack tip, a simulation and analysis of the stress and strain at the stable growing crack tip is performed by using elastic-plastic finite element software for the power hardening materials in this paper, which establishes a foundation for improving the capability of predicting environmentally assisted cracking growth rate in key structural materials of nuclear power plants.
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.
Feature selection has become the focus of research areas of applications with high dimensional data. Nonnegative matrix factorization (NMF) is a good method for dimensionality reduction but it cant select the optimal feature subset for its a feature extraction method. In this paper, a two-step strategy method based on improved NMF is proposed.The first step is to get the basis of each catagory in the dataset by NMF. Added constrains can guarantee these basises are sparse and mostly distinguish from each other which can contribute to classfication. An auxiliary function is used to prove the algorithm convergent.The classic ReliefF algorithm is used to weight each feature by all the basis vectors and choose the optimal feature subset in the second step.The experimental results revealed that the proposed method can select a representive and relevant feature subset which is effective in improving the performance of the classifier.
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