1,720,963 research outputs found
Constitutive Equations for Hot Extrusion of AA6005A, AA6063 and AA7020 Alloys
No full textConstitutive equations relate thermo-mechanical parameters, i.e. strain (ε), strain rate (έ) and temperature (T), with flow stress (σ). The most popular constitutive relationship, among those
used in the study of hot deformation, is the phenomenological sinh Garofalo equation. In recent years several papers described the hot deformation of aluminum alloys by mean of hot torsion testing.
However, sinh constitutive parameters are seldomly available in literature even for the commonest
aluminum alloys used today by the extrusion industry. This paper presents the result of the
torsion tests providing constitutive equations for AA6005A, AA6063 and AA7020 alloys. The relative extrudabilities of these alloys were estimated by means of FEM simulation carried out by the HyperXtrude® software
Back.end and front-end scrap in direct extrusion: an estimation by means of finite element analysis
No full textFinite elements analyses are offering to extrusions a big opportunity: to estimate accurately not only the charge weld extension but also the billet skin contamination. The present work examined the dynamics of the back-end and front-end defect in the direct extrusion of a solid profile through the use of FE analyses. Numerical results have been compared with industrial experiments with the aim to understand the effect of the selected boundary conditions on the accuracy of the predictions
Back-End and Front-End Scrap in Direct Extrusion; an Estimation by Means of Finite Elements Analysis
No full textFinite elements analyses are offering to extrusions a big opportunity: to estimate accurately not only the charge weld extension but also the billet skin contamination. The present work examined the dynamics of the back-end and front-end defect in the direct extrusion of a solid profile through the use of FE analyses. Numerical results have been compared with industrial experiments with the aim to understand the effect of the chosen boundary conditions on the accuracy of the predictions
EVOLUTION OF THE CHARGE WELDS: TOWARDS A NOVEL ANALYTICAL FORMULATION
No full textCharge welds are, together with the seam welds, defects generated during the
continuous extrusion of metallic materials. However, while the seam welds can
exhibit the same resistance of the basic material if proper levels of pressure, contact time and temperature
are applied, charge welds are always contained parts of the profile with lower mechanical
properties. Indeed, at the end of each process stroke, the back end of the old billet material
that completely fill the die starts to interact with the front side of the new billet loaded into the
press that is usually contaminated by oxides, dust or lubricant thus producing a transition zone
that extends to a variable length. It comes then clear that the length of the profile marked by
the charge welds need to be scrapped and an accurate prediction and reduction of this portion
become mandatory, not only for the final user of the profile, in order to avoid in-service
product failures, but also for extruders and die makers to increase process efficiency.
In this context, aim of the present work was to compare the experimental -numerical investigations
performed by the authors in terms of charge welds extensions with the predictions of
the analytical models nowadays reported in literature. The final global aim work was
to assess the applicability of these models in the everyday industrial practice
QUALITY ASSESSMENT AND OPTIMIZATION OF AN INDUSTRIAL EXTRUDED PROFILE
No full textThe extrusion process is an economic maunfacturing method used to produce profiles with a constant section. However, even when simple components are considered, many process and product issues can emerge such as low mechanical properties or distorsions of the exit profile, die premature failure and/or low production rates. These problems are related to the complex nature of the process that has to guarantee, at the same time, proper conditions for a good welding (in case of hollow profiles), absence of profile distorsions, an acceptable die stress and as much as possible fast extrusion. In addition, all these conditions have to be reached in the short extrusion time of each single billet and can emerge to be conflicting one each other’s. Usually, the optimization of the extrusion process is performed
by the operators on the basis of consolidated experience and empirical rules. However, in this way, it is extremely difficult to control all the process and geometrical parameters involved and then to control the final outputs. This explains the number of works in literature aimed to develop numerical and analytical models for the extrusion process optimization. In this context, the authors recently presented a novel procedure for the multi-goal optimization of extrusion dies based on meta-models that was preliminary validated on the experimental results available for a simple round tube profile. In this work, two additional test cases are presented with the aim to extended the validation cases of the proposed procedure to a more complex industrial profil
Scrap Prediction in Direct Extrusion
No full textThe continuous, direct extrusion is an economical and efficient process to
manufacture high-quality aluminum profiles. However, because of multiple billets processing, transient defects (coring and charge welds) can be generated, affecting portions of the profiles and deteriorating their mechanical properties. In the case of structural applications, the reliable prediction of the onset and the extent of these portions is therefore mandatory to be scrapped by the commercialized length. In this context, the present work has been aimed at examining the dynamic evolution of the coring and charge weld defects in the direct extrusion of a solid profile.
Both experimental and numerical activities have been performed, and results evaluated in terms of coring and charge weld defects evolution achieving good agreement for both phenomena. Results have been compared with the outcomes of the analytical models available in the literature. For the charge weld extension, the analytical model returned poor predictably, while a very good match with numerical data was obtained for the coring defect
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
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