177,252 research outputs found
LCF assessment on heat shield components of nuclear fusion experiment “Wendelstein 7-X” by critical plane criteria
No full textThe Wendelstein 7-X modular advanced stellarator has started operations at the Max Planck Institute for Plasma Physics in
Greifswald, Germany, in 2016. In the first phase, the machine operated restricting the plasma pulses to low power and short
lengths. Plans to achieve actively cooled components are scheduled to start in 2020 when the machine will operate in steady-state
at full power. FEM simulations for steady-state operations revealed high plastic strains at several locations, for most of all the
rigidly supported Plasma Facing Components; therefore, there is the risk of a premature fatigue failure before the end of the
scheduled operations of the machine. The aim of this study is to analyse, by means of the commercial code ABAQUS, the
behavior of such critical components estimating, eventually, their fatigue life by means of the commercial code fe-safe
Nonlinear fatigue crack propagation in a baffle module of Wendelstein 7‐X under cyclic bending loads
Get PDFSimulation of the fatigue crack propagation in a Wendelstein 7‐X baffle module is performed in this study using both a finite element method‐based software and the UniGrow nonlinear model for small‐scale yielding (SSY) conditions. Some experimental fatigue tests of several cracked baffle modules have been performed through a servo‐hydraulic machine. One of these experimental tests
has been considered to simulate fatigue crack propagation in the baffle module. Before starting the experimental test, a first crack partly contained in the welding seam and partly in the steel pipe is found. Subsequently, owing to the applied load, the crack propagated both into the welding seam and into the steel pipe until the plastic zone in the near field attains SSY conditions.
Finally, owing to the increase in the extension of the plastic zone, SSY conditions are not more valid, and the breakage of the steel pipe is produced by plastic collapse
FEM-DBEM approach to analyse crack scenarios in a baffle cooling pipe undergoing heat flux from the plasma
No full textWendelstein 7-X is the world’s largest nuclear fusion experiment of stellarator type, in which a hydrogen plasma is confined by a magnet field generated with external superconducting coils, allowing the plasma to be heated up to the fusion temperature. The water-cooled Plasma Facing Components (PFC) protect the Plasma Vessel (PV) against radiative and convective heat from the plasma. After the assembly process of heat shields and baffles, several cracks were found in the braze and cooling pipes. Due to heat load cycles occurring during each Operational Phase (OP), thermal stresses are generated in the heat sinks, braze root and cooling pipes, capable to drive fatigue crack-growth and, possibly, a water leak through the pipe thickness. The aim of this study is to assess the most dangerous initial crack configurations in one of the most critical baffles by using numerical models based on a FEM-DBEM approach
Enzyme activities in liver and muscle biopsy specimens from thyrotoxic and hypothyroid patiens
Get PDFAppropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Data files for ab initio calculations of the lattice parameter and elastic stiffness coefficients of bcc Fe with solutes
No full textAbstractWe present computed datasets on changes in the lattice parameter and elastic stiffness coefficients of bcc Fe due to substitutional Al, B, Cu, Mn, and Si solutes, and octahedral interstitial C and N solutes. The data is calculated using the methodology based on density functional theory (DFT) presented in Ref. (M.R. Fellinger, L.G. Hector Jr., D.R. Trinkle, 2017) [1]. All the DFT calculations were performed using the Vienna Ab initio Simulations Package (VASP) (G. Kresse, J. Furthmüller, 1996) [2]. The data is stored in the NIST dSpace repository (http://hdl.handle.net/11256/671)
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
Get PDFBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
Crack modelling in baffle modules of nuclear fusion experiment "wendelstein 7-X"
No full textStructural analyses are performed on subassemblies of so-called baffle modules, critical plasma facing components of the "Wendelstein 7-X" stellarator, where the presence of detected large cracks can drastically reduce the expected fatigue life. Such baffle modules are designed to remove heat coming from the hot plasma, heated up to nuclear fusion temperatures, and are made of graphite tiles bolted onto a structure of CuCrZr heat sinks that, in turn, are brazed on water-cooled stainless steel pipes. High plastic deformations occurred during the shaping process of the pipes were responsible for crack initiation at the roots of the braze. Such cracks, if propagating under fatigue thermomechanical loads, could penetrate into the cooling pipes and cause leakage of the coolant fluid, with consequent damages and interruption of operations. In this work, the geometry of one of these cracks has been reconstructed by CT scans and analysed using the Dual Boundary Element (DBEM) method, in order to forecast its potential impact on the component life
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Coupled FEM–DBEM approach on multiple crack growth in cryogenic magnet system of nuclear fusion experiment ‘Wendelstein 7-X’
No full textAt the Max Planck Institute for plasma physics in Greifswald, Germany, the world's largest nuclear fusion experiment of modular stellarator type Wendelstein 7-X has started plasma operation. The hot hydrogen plasma is confined in a plasma vessel by an electromagnetic field generated by 50 non-planar and 20 planar superconducting coils. The superconducting coils are encased in cast stainless steel housings. The coils are bolted onto a central support ring and welded together by so called lateral support elements (LSEs). In this paper, a procedure, based on a global–local finite element method (FEM)–dual boundary element method (DBEM) approach, is developed to simulate the propagation of multiple cracks detected in LSEs and undergoing a fatigue load spectrum. The global stress analysis on the superconducting coils is performed by FEM whereas the sub-modelling approach is adopted to solve the crack propagation in the DBEM environment. The boundary conditions applied on the DBEM submodel are the displacements calculated by the FEM global analysis, in correspondence of the cut surfaces (there are no body forces nor external loads applied on the submodel volume). Two cracks are simultaneously introduced, and a linear elastic fracture mechanics analysis is performed. Results in terms of cracks growth rates and evolving crack shapes are provided, and the residual life of the component is forecast
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