1,720,962 research outputs found
A model for predicting plastic strain and surface cracks at steady-state wear and ratcheting regime
No full textUnidirectional plastic strain accumulation (ratcheting) is one of the main causes of surface crack nucleation in rails and wheels in dry condition. It is related to frictional forces which develop at the contact interface due to sliding, especially in curve and in braking. Surface cracks generated by ratcheting can subsequently lead to severe damage when environmental fluid contaminants (such as rain or snow) are added at the contact interface, due to the complex solid-fluid interaction, which can enhance crack growth.
In dry condition, wear and ratcheting can reach an equilibrium, such that the strain field and the crack depth are stationary. Understanding such steady-state deformation regime can be a key factor for predicting the expected crack depth and scheduling a correct maintenance programme.
In this paper a model for predicting the strain field at steady-state regime is proposed. Such model, based on an integral equation, allows predicting the strain field and crack morphology at high cycle number with no need of iterative numerical simulation. The potentiality of the model was proven both in characterizing the cyclic plasticity behaviour of materials and in predicting the maximum expected crack depth in full scale railway wheels
A Model for the Assessment of Wheel–Rail Contact in the Presence of Solid Contaminants
No full textAn analytical model for the assessment of a contact in the presence of a solid contaminant is presented, mainly aimed at studying the damage to railway wheels and rails operating in third-bodycontaminated environments. The model, developed under 2D plane strain idealization, includes multiple evenly spaced rigid cylindrical contaminant bodies entrapped between two elastic cylinders. It allows a very fast calculation of the pressure distribution on the surfaces in contact and it can be used for evaluating the stress field in the subsurface region, at both the small scale of the contact between the main body and the contaminant body and the full scale of the contact between the two main bodies. The model was validated by comparison with finite element (FE) analyses, showing its accuracy. Some examples of application showed the model’s ability to predict the limit of the influence of the solid contaminant bodies and the depth where cyclic plasticity phenomena occur in wheel–rail contacts
Metal Inert Gas (MIG)–Cold Metal Transfer (CMT) and Fiber Laser–MIG Hybrid Welds for 6005A T6: Experimental and Numerical Comparison
No full textAbstract: The microstructural and hardness properties of welded joints of AA 6005-T6 aluminum alloy obtained with metal inert gas (MIG), fiber laser–MIG hybrid, and cold metal transfer (CMT) welding were analyzed immediately after welding and after 3 years of natural aging. The fine hardening precipitation within the heat-affected zone, fusion zone, and base material was characterized by differential scanning calorimetry for the three different welding techniques. The elastic–plastic properties of the welded joints were characterized by means of finite element. For all investigations, the analysis on AA6005 aluminum alloy confirms a better behavior of CMT and fiber laser–MIG hybrid joints with respect to the conventional MIG processes. Graphic Abstract: [Figure not available: see fulltext.]
Study of wheel/rail material coupling in presence of solid contaminants
No full textThe purpose of this work is to evaluate the effect of changing cyclic yield strength levels of either wheels or rails on the plastic strain through FEM analysis. The simulations have been carried out with implicit two-dimensional finite element models both in clean contact conditions and in presence of solid contaminants. The materials used are some of the most traded in Europe and in America, with the addition of SANDLOS®S, an innovative steel designed specifically for sandy environments. FEM results were correlated to worn mass and optical micrographs previously achieved in rolling contact tests performed on small-scale specimens
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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
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