1,721,004 research outputs found
Numerical ductile fracture propagation control for pipelines transporting natural gases and CO-mixtures
No full textEinfluss des Spannungszustands auf die Entstehung von Separations
No full textAs of now, investigations regarding the origin of separations in pipeline steels has focused on microstructural characteristics of these steels. It is known that band-like occurrences in the microstructure or so-called segregation zones are necessary for separations to occur when transverse strain restraints emerge on hard microstructural components. The fracture mechanism causing separations is cleavage fracture. Based on this knowledge, the present work developed a damage-mechanical failure criterion capable of simulating separations without a predefined zone. This demonstrated that, in addition to the microstructure, the present stress state has a major influence on the formation of separations. The analysis of the fracture surfaces showed that in the Charpy impact test, separations only occur in the transition zone. Thus, as an initiation parameter, a critical separation stress defined as a function of the existing material coordinate system was calibrated precisely at this point. As separations also propagate through already ductile damaged regions in the material and stop only in regions of high deformation, a stress state dependent limiting strain was introduced as a confinement parameter. The stress- and strain-based criterion was implemented in the existing phenomenological MBW model and now enables to depict the occurrence as well as the influence of separations on the load-bending behavior in the Charpy impact test. Furthermore, in the Battelle drop weight tear test (BDWTT), it was shown that the stress state has a major influence on the formation of separations. A significantly larger specimen width and test speed result in a much more critical stress state and the transition range including the occurring separations shifts to higher temperatures. Although there are differences between the real fracture surface of the tested BDWT specimen and the simulated fracture surface, these are due to the microstructural inhomogeneities, which cannot be reproduced by a macroscopic model. Despite this slight deviation, the material behavior could be depicted by the previously calibrated separation criterion and thus the developed model extension was successfully validated. At the component scale, a pipe segment was simulated with an uncoupled pressure decay function in combination with the validated extended MBW model. In contrast to the model with purely ductile damage as well as failure, a significantly higher crack propagation rate was achieved with the separation criterion, especially in the crack initiation phase. As the crack propagated, the decreasing pressure lowered the stress state in the material, so that although separations still occurred in the simulation, they had less influence on the crack velocity and approached the velocity level of purely ductile crack propagation. Thus, although separations at the component scale have an impact on long-running cracks under the given boundary conditions and should also be taken into account in the design of pipelines, but they should not be considered as a general obstacle to the application of modern high-toughness pipeline steels
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
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Experimentelle und numerische Analyse des Schädigungsverhaltens von Hybridlaserschweißverbindungen
No full textThe recently observed widespread application of laser-hybrid welding process in different fields of manufacturing industry results from advantages of both laser welding and conventional arc beam welding processes. With growing application of laser-hybrid welding, the demand for characterisation of mechanical properties of laser-hybrid weld and of their influence on the structural performance increases constantly. The accurate fracture prediction is required for the utilisation of possible safety reserves thus providing economical and safe design of components. In the frame of this work experimental and numerical analyses are performed with objective to characterise ductile and brittle fracture behaviour of flawed laser-hybrid welds for three different constructional steels (S355, EH36 und RQT701). Micromechanically based GTN (Gurson, Tvergaard and Needleman) damage model has been successfully applied for numerical description of crack initiation and crack propagation. The required model parameters are determined and verified by means of combined numerical and experimental investigations (metallographic analyses and tests on the fracture mechanics and Wide Plate specimens). Subsequently, the phenomena of crack path deviation (CPD) frequently observed in laser and hybrid laser welds is numerically simulated and analysed by the verified GTN model. It can be confirmed, that the tendency to CPD depends strongly on the development of stress triaxiality and plastic strains at the interface between base and weld metal. Regarding component safety, the CPD can be evaluated positively due to the crack resistance increase resulting from higher energy consumption necessary for the crack deviation in the base metal. Besides the ductile fracture behaviour, the influence of the laser-hybrid weld on the toughness properties in low shelf and transition temperature region has been investigated by means of fracture mechanics tests and subsequent evaluation with master curve concept. The results show significant dependence of determined reference temperature T0 on the stress triaxiality varied by different specimen geometry and initial crack size. The two parameter criterion seems to be suitable to provide a conservative prediction of brittle behaviour of low constraint fracture mechanics specimens and thus flawed hybrid welded components. The accuracy of this prediction becomes higher with increasing failure probability. Furthermore the Beremin-model has been evaluated with respect to describe the onset of cleavage process of laser-hybrid welds. It can be concluded, that the estimation of the cleavage failure is only possible by modifying the original model, e.g. by introducing temperature dependence of the Weibull parameter. The safety assessment of investigated Wide Plate specimens according to FITNET procedure shows, that the accuracy of failure prediction can be increased by knowledge of measured residual stresses and toughness values of shallow crack specimens. The advantages of numerical damage analysis for design of hybrid welded components when compared to FITNET procedure are demonstrated on different examples for practical application of laser-hybrid welds
Experimentelle und numerische Analyse des Schädigungsverhaltens von Hybridlaserschweißverbindungen
No full textThe recently observed widespread application of laser-hybrid welding process in different fields of manufacturing industry results from advantages of both laser welding and conventional arc beam welding processes. With growing application of laser-hybrid welding, the demand for characterisation of mechanical properties of laser-hybrid weld and of their influence on the structural performance increases constantly. The accurate fracture prediction is required for the utilisation of possible safety reserves thus providing economical and safe design of components. In the frame of this work experimental and numerical analyses are performed with objective to characterise ductile and brittle fracture behaviour of flawed laser-hybrid welds for three different constructional steels (S355, EH36 und RQT701). Micromechanically based GTN (Gurson, Tvergaard and Needleman) damage model has been successfully applied for numerical description of crack initiation and crack propagation. The required model parameters are determined and verified by means of combined numerical and experimental investigations (metallographic analyses and tests on the fracture mechanics and Wide Plate specimens). Subsequently, the phenomena of crack path deviation (CPD) frequently observed in laser and hybrid laser welds is numerically simulated and analysed by the verified GTN model. It can be confirmed, that the tendency to CPD depends strongly on the development of stress triaxiality and plastic strains at the interface between base and weld metal. Regarding component safety, the CPD can be evaluated positively due to the crack resistance increase resulting from higher energy consumption necessary for the crack deviation in the base metal. Besides the ductile fracture behaviour, the influence of the laser-hybrid weld on the toughness properties in low shelf and transition temperature region has been investigated by means of fracture mechanics tests and subsequent evaluation with master curve concept. The results show significant dependence of determined reference temperature T0 on the stress triaxiality varied by different specimen geometry and initial crack size. The two parameter criterion seems to be suitable to provide a conservative prediction of brittle behaviour of low constraint fracture mechanics specimens and thus flawed hybrid welded components. The accuracy of this prediction becomes higher with increasing failure probability. Furthermore the Beremin-model has been evaluated with respect to describe the onset of cleavage process of laser-hybrid welds. It can be concluded, that the estimation of the cleavage failure is only possible by modifying the original model, e.g. by introducing temperature dependence of the Weibull parameter. The safety assessment of investigated Wide Plate specimens according to FITNET procedure shows, that the accuracy of failure prediction can be increased by knowledge of measured residual stresses and toughness values of shallow crack specimens. The advantages of numerical damage analysis for design of hybrid welded components when compared to FITNET procedure are demonstrated on different examples for practical application of laser-hybrid welds
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