1,721,046 research outputs found
Thermo-mechanical modelling of Dynamic Tensile Extrusion test
No full textRecently, the researchers of the Los Alamos National Laboratory (LANL) have been developed a technique to investigate high strain-rates in which a sphere is launched at high speed (300-800 m/s) through a conical die (Dynamic Tensile Extrusion test). The system can use a set-up similar to a Taylor test (like a light gusgun) but induces in the material high levels of tensile stresses and allows to investigate the fracture and damage of the material in these extreme conditions. Due to the high strain-rates and hydrostatic component of stress that occur during the extrusion in the die, the material is also subject to a rapid heating. In this work, the DTE test has been simulated with the explicit Lagrangian code LSDYNA. In order to correctly reproduce the various aspects of the test it is necessary to use an elasto-plastic material model that takes into account strain-rate, thermal softening, pressure influence and damage and that adequately describes the thermal coupling effects and the equation of state (EOS) of the material. Besides, due to the high distortion of the Lagrangian mesh, the use of a mesh adapting technique is absolutely necessar
Plastic Behavior of Laser-Deposited Inconel 718 Superalloy at High Strain Rate and Temperature
Full text linkNickel-based superalloys have several applications for components exposed to high temperatures and high strain rate loading conditions during services. The objective of this study was to investigate the tensile properties of Inconel 718 produced using the laser metal deposition technique. Specimens with different heat treatments were investigated. Experimental tests were performed at the DYNLab at Politecnico di Torino (Italy). The temperature sensitivity was investigated between 20 °C and 1000 °C on a Hopkinson bar setup at a nominal strain rate of 1500 s−1. The specimens heating was obtained by means of an induction heating system, and the temperature control was performed by thermocouples, an infrared pyrometer, and a high-speed infrared camera. The thermal images were analyzed to check the uniformity of the heating and to investigate the presence of adiabatic self-heating. The results showed that the materials strength exhibited a significant drop starting from 800 °C. The strain rate influence was investigated at room temperature, and limited sensitivity was found covering six orders of magnitude in the strain rate. A preliminary analysis of the fracture mode was performed. Finally, different solutions for the strength material modeling were proposed and discussed with the aim of identifying models to be used in finite element simulations
Numerical simulations of components produced by fused deposition 3D printing
Full text linkThree-dimensional printing technology using fused deposition modeling processes is becoming more and more widespread thanks to the improvements in the mechanical properties of materials with the addition of short fibers into the polymeric filaments. The final mechanical properties of the printed components depend, not only on the properties of the filament, but also on several printing parameters. The main purpose of this study was the development of a tool for designers to predict the real mechanical properties of printed components by performing finite element analyses. Two different materials (nylon reinforced with glass or carbon fibers) were investigated. The experimental identification of the elastic material model parameters was performed by testing printed fully filled dog bone specimens in two different directions. The obtained parameters were used in numerical analyses to predict the mechanical response of simple structures. Blocks of 20 mm × 20 mm × 160 mm were printed in four different percentages of a triangular infill pattern. Experimental and numerical four-point bending tests were performed, and the results were compared in terms of load versus curvature. The analysis of the results demonstrated that the purely elastic transversely isotropic material model is adequate for predicting behavior, at least before nonlinearities occur
Bi-material joining for car body structures: experimental and numerical analysis
No full textCrashworthiness is an important issue in car body design: it describes the ability of the vehicle structure to behave efficiently by absorbing and dissipating energy in a stable and controlled manner during a crash event. Energy management during frontal impact is mainly done through crash boxes in the front rails. These crash boxes are usually slender, thin-walled steel columns, progressively collapsing during impact. Due to a trend in lightweight materials use, it is necessary to gain knowledge about the material behaviour and alternative joining systems. The use of an adhesive as a joining system for different materials was investigated by means of experimental tests on specimens and simple components, made of aluminium and deep drawing steel. A numerical simulation technique was developed to describe and understand the phenomenon. Furthermore, since the behaviour is influenced by the loading rate and the materials used in this application are known to be strain-rate sensitive, static and impact loading conditions were examine
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
- …
