1,720,968 research outputs found
Damage characterizations and simulation of selective laser melting fabricated 3D re-entrant lattices based on in-situ CT testing and geometric reconstruction
No full textIn recent years, metal additive manufacturing (AM) are widely employed for industrial applications, such as: biomedical, aerospace, automotive, marine and offshore sections. AM demonstrated superior manufacturing efficiencies and economic advantages for advanced lightweight industrial components with unlimited arbitrary topological layouts and complex internal microstructures, and are also employed for fabrication of auxetic materials and structures. In this paper, damage characterizations and mechanical behaviors of selective laser melting (SLM) fabricated 3D re-entrant lattices are investigated based on in-situ interrupted micro-CT test, and simulation based on geometric reconstructed models are performed for exploring the underlying failure mechanisms. Firstly, theoretical models for predicting the mechanical properties of 3D re-entrant lattice are developed, such as stiffness, Poisson's ratio and strength, etc. Secondly, the geometrical errors and fabrication defects of 3D reentrant lattices are analyzed based on 3D micro-CT scanning, in-situ micro-CT interrupted compression tests are performed for studying the deformation process and failure mechanisms. Finally, image finite element models with the detailed information of the shape, position and distribution of defects of the 3D reentrant lattices are constructed from 3D tomographic images, and numerical simulations are performed for studying the effects of the defects on the mechanical performances of the SLM additive manufactured 3D re-entrant lattice structures. It is shown that the failure behavior of the reentrant lattice is governed not only by its topology, but also by the geometric defects and surface defects. Moreover, the proposed interrupted in-situ micro-CT mechanical loading experiments and image finite element approaches can also shed lights on the relations between fracture failure around the edge and the powder adhesion. The damage evolution process is compared with the numerical simulation results to verify the materials failure modes
Mechanostructures: Rational mechanical design, fabrication, performance evaluation, and industrial application of advanced structures
No full textThe rapid progress of advanced manufacturing, multidisciplinary integration and artificial in-telligence has ushered in a new era of technological development in the design of lightweight, well-integrated, multifunctional, intelligent, flexible and biomimetic materials and structures. The traditional approach in structural research poses several intrinsic limitations on the practical performance of devices and instruments in harsh industrial environments, due to factors such as the disconnection between structural design and manufacturing, low efficiency in the manufac-ture of complex structures, reduced actual mechanical integrity and reliability of manufactured structures compared to the theoretical values obtained from structural design, insufficient level of multifunctional structural integration, and excessive economic cost. In addition, the advanced materials and structures incorporated in industrial equipment often need to withstand extreme service environments, and it is increasingly important to further integrate the design, manufac-ture, function, performance evaluation and industrial application of advanced structures, to provide the theoretical and technical bases for optimizing their fabrication. In view of the above, the authors propose a new research paradigm of "mechanostructures," which aims to achieve target mechanical responses of structures, devices and equipment in extreme service environ-ments by integrating their structural design, manufacturing and performance evaluation. By designing novel structures based on desired static and dynamic mechanical responses and considering the mechanical behavior throughout the whole deformation process, the new field of "mechanostructures" pursues an application-oriented structural design approach. As a typical example of mechanostructures, lightweight multifunctional lattice structures with high stiffness, strength, impact resistance, energy absorption capacity, shock wave attenuation and noise reduction show great potential for applications in aerospace, transportation, defense, biomedical,energy, machinery, equipment and other industrial fields. In this respect, the mechanical design of lattice metastructures inspired by polycrystalline microstructures is presented, starting with a discussion on typical mechanical properties and multifunctional performance conflicts, and demonstrating the scientific merits of "mechanostructures" based on the innovative structural design, manipulation of the multifunctional mechanical properties, and elaboration of the un-derlying physical mechanisms
In-situ SEM investigation on fatigue behaviors of additive manufactured Al-Si10-Mg alloy at elevated temperature
No full textIn-situ high temperature measurement in a scanning electron microscopy (SEM) environment is an important technique for exploring the microstructure evolution and crack propagation within refractory materials and other advanced alloys. In this paper, in-situ tensile fatigue experiments under SEM environment at room temperature and elevated temperature are performed for studying the fatigue performance and crack propagation process of selective laser melting (SLM) additive manufactured Al-Si10-Mg materials. Firstly, in-situ SLM additive manufactured Al-Si10-Mg fatigue tensile samples are prepared, and micro-CT are employed for the characterization of void defects within SLM additive manufactured Al-Si10-Mg with different laser scanning speeds and laser energy; Secondly, in-situ fatigue experiments are carried out under SEM environment at 25 degrees C, 100 degrees C, 200 degrees C, 300 degrees C, 400 degrees C, 500 degrees C and 600 degrees C, respectively. The fatigue mechanical behaviors, microstructure evolution and crack propagations of as-fabricated Al-Si10-Mg samples are characterized. Finally, micro-CT tomography 3D imaging techniques are employed for exploring the link between SLM defects and fatigue performances
Mechanical behaviors of SLM additive manufactured octet-truss and truncated-octahedron lattice structures with uniform and taper beams
No full textIn this paper, three-dimensional lattice structures composed of octet-truss and truncated-octahedron unit cells with regular and tapered beams are proposed, and their mechanical properties are investigated through experiments and simulation comparisons. Firstly, analytical closed form expressions of the relative density functions are derived for different lattice structures. Secondly, in-situ compression samples are fabricated via Selective Laser Melting (SLM) 3D printing technique, monotonic compression experiments are performed for studying the effects of tapered beams on the mechanical properties of lattice structures with ordinary uniform beams, and SEM characterizations of fracture surface morphology are performed for understanding the underlying failure mechanisms. Afterwards, asymptotic homogenization (AH) method is used for evaluating the anisotropy properties of these lattice structures, closed form expression of the mechanical behaviors of unit cells is derived and solved with ABAQUS (R) using surface traction method. Asymptotic homogenization analysis shows that node enforcement can significantly enhance the modulus and reduce the anisotropy of the lattice
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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