1,720,976 research outputs found
A numerical approach for the modelling of forming limits in hot incremental forming of AZ31 magnesium alloy
Full text linkMagnesium alloys, because of their good specific material strength, can be considered attractive by different industry fields, as the aerospace and the automotive one. However, their use is limited by the poor formability at room temperature. In this research, a numerical approach is proposed in order to determine an analytical expression of material formability in hot incremental forming processes. The numerical model was developed using the commercial software ABAQUS/Explicit. The Johnson-Cook material model was used, and the model was validated through experimental measurements carried out using the ARAMIS system. Different geometries were considered with temperature varying in a range of 25–400 °C and wall angle in a range of 35–60°. An analytical expression of the fracture forming limit, as a function of temperature, was established and finally tested with a different geometry in order to assess the validity
Ceramic materials wear mechanisms when cutting nickel-based alloys
No full textIn this paper the performances of some commercial ceramic inserts when cutting AISI 310 steel are investigated and compared to those of a traditional carbide based tool. The most important wear mechanism in the ceramic inserts is related to the segmented edges of the chips that abrade a notch at the end of the cut zone. Alumina-zirconia inserts are very sensitive to this kind of wear, whereas tools made of Sialon and alumina with SiC whiskers exhibit slightly better performances despite the concomitant chemical wear mechanisms. (C) 1999 Elsevier Science S.A. All rights reserved
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
Low‐cost, High‐Capability, Embedded Systems for CNC Education and Research
Full text linkTeaching of CNC and CAD/CAM technologies has recently taken a great importance, due to their development, to the great number of solutions available on the market, and to the frequent updates. Nevertheless, one of the most urgent need is to improve the quality of education coping with a rapidly growing number of students.
Nowadays, in comparison to the past, many Open-Source technical solutions, both hardware and software, are available to realise easily and cheaply some scaled-down prototypes of numerical control machine tools: these are able to work perfectly and can be employed as a learning method.
This paper shows some past experiences regarding the development of some degree thesis works. In particular, it is shown how to implement a numerical control (LinuxCNC) in two specific cheap embedded systems (Raspberry Pi and BeagleBone Black). In this way, a student has the possibility of simulating the working of a complete Numerical Control and of learning interactively its way of programming.
The final result and student response have shown an excellent effectiveness of these experiences and easy to use as powerful tool in engineering education
Meta-heuristic Algorithms for Nesting Problem of Rectangular Pieces
Full text linkNesting problems consist of placing multiple items onto larger shapes finding a good arrangement. The goal of the nesting process is to minimize the waste of material. It is common to assume, as in the present work, that the stock sheet has fixed width and infinite height, since in the real world a company may have to cut pieces from a roll of material. The complexity of such problems is often faced with a two-stage approach, so-called “hybrid algorithm”, combining a placement routine and a meta-heuristic algorithm. Starting from a given positioning sequence, the placement routine generates a non-overlapping configuration. The encoded solution is manipulated and modified by the meta-heuristic algorithm to generate a new sequence that brings to a better value of the objective function (in this case the height of the strip). The proposed method consists in placing the rectangles inside a strip and in combining the meta-heuristic algorithms with the No Fit Polygon algorithm. The software has been developed in Python language using proper libraries to solve the meta-heuristic techniques (Inspyred) and the geometric problems (Polygon). The results show the effectiveness of the proposed method; moreover, with regard to problems reported in literature employed as benchmark of the nesting algorithms, the degree of occupation values (Efficiency Ratio, ER) are shown to be higher than 90%
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
An Efficient NURBS Path Generator for a Open Source CNC
No full textIn this paper a NURBS path generator (on the plane XY) is proposed to be developed for those
CNC machine tools and robot which are Open Source or Opening Architecture. The goal is to use simple and
efficient techniques to manufacture geometries which are very complex, whose main feature is the presence of
free-form surfaces and contours. To reach this goal, the NURBS path generator has been optimized in order to
enable the user to select among three different options to generate the tool path, using a specific parameter. The
three options are respectively called “NURBS interpolation with constant increments of u parameter” (NICU),
“NURBS interpolation with constant displacement increments by linear motion”(NICL), “NURBS interpolation
with constant displacement increments by circular motion” (NICC). The NURBS path generator has been
implemented for an Open Source Numerical Control (LinuxCNC) in order to evaluate its efficiency, by
simulations and experimental tests, in terms of computational complexity, comparison between the trajectory
covered and the path programmed, capability to follow speed and path trends
A more efficient method for clustering sheet metal shapes
No full textThe nesting of two-dimensional irregular shapes is a common problem which is frequently encountered by a number of industries where raw material has to be, as economically as possible, cut from a given stock sheet. A frequently recurring problem as far as cutting stock is concerned, is how to obtain the best nesting of some pieces of flat patterns which occupy minimal-area convex enclosure. The area of convex enclosure is related to the convex hull of the union of patterns which can be imagined as a large rubber band surrounding the set of all polygons.
Our goal is to automatically obtain the smallest area convex shape containing all the patterns.
As a matter of fact, Cheng and Rao have proposed an heuristic “stringy effect” procedure for clustering which follows a descending order of area of patterns. The “stringy effect” is able to put each new piece in a position which minimises the value of the distance between the centroid of each added piece and the centroid of the already formed cluster.
The procedures till now shown in literature are quite complex. They make use of sliding techniques, and are not able to effectively work with relatively multiply-connected figures. In particular, the different procedures proposed are based on the No Fit Polygon computation of non-convex polygons, which often generates holes.
This work is a proposal for a more efficient method, which can be used in heuristic procedure.
In this paper a new procedure for the calculation of “No Fit Polygon” (NFP) of non-convex polygons is presented. Given two non-convex polygons, the algorithm is able to calculate their NFP very quickly and without any approximation by a polygon clipping method. By iterating this procedure with every polygon of our set, and positioning them using the “stringy effect” technique, it is so possible to obtain a convex shape that contains all the patterns, having the minimal area
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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