1,721,016 research outputs found
Analytical formulation of the contact pressure evolution for interference joints under creep regime
No full textAn analytical formulation to evaluate the contact pressure evolution in interference fit joints working under high temperature regime, is proposed. The phenomenon is mainly due to the stress relaxation related to the creep behaviour of materials used to realize this kind of joints. Despite extensive researches on the topic, the decay of contact pressure due to creep relaxation is commonly not considered or evaluated only by numerical methods. The proposed analytic solution correlates the contact pressure to the creep material properties and could be largely used to improve the design or the fitness-for-service assessment of joints that transmit load thanks to the interference fit. The formulation assumes the plane strain condition for the inner element and the plane stress condition for the outer one. It was validated by finite element analysis (FEA) and gives accurate prediction of the contact pressure evolution both in plane and axisymmetric simulations
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
Stress Relaxation Behavior of Additively Manufactured Polylactic Acid (PLA)
Full text linkIn this work, the stress relaxation behavior of 3D printed PLA was experimentally investigated and analytically modeled. First, a quasi-static tensile characterization of additively manufactured samples was conducted by considering the effect of printing parameters like the material infill orientation and the outer wall presence. The effect of two thermal conditioning treatments on the material tensile properties was also investigated. Successively, stress relaxation tests were conducted, on both treated and unconditioned specimens, undergoing three different strains levels. Analytical predictive models of the viscous behavior of additive manufactured material were compared, highlighting and discussing the effects of considered printing parameters
3D strip model for continuous roll-forming process simulation
Full text linkThe paper addresses the complexities for a reliable numerical simulation of the roll forming process. During the process, the material is progressively bent accumulating plastic deformation at each forming step. Strain hardening limits the material formability and may causes flaws of the final shape. A simplified method for the FEM modeling of the process has been developed introducing a narrow-strip 3D model. This approach leads better performance than the classical modeling method, in terms of results reliability and low computational time. In order to verify the proposed model, an experimental campaign of testing, for a specific roll forming production process, was carried out. On the quasi-static regime, the post necking behavior of the sheet metal was characterized. The Vickers hardness and the plastic strain of uniaxial tests were empirically correlated. By the hardness correlation, the plastic strain accumulated at different stages of the process was evaluated and compared with the numerical results. Further possible improvements of the method are highlighted
Influence of SLM parameters on the compressive behaviour of lattice structures in 17-4PH stainless steel
No full textAdditive manufacture (AM) technologies allow innovative structural design, including complex lattice structures. Selective laser melting (SLM) is an AM process that enables the manufacture of space filling lattice structures. Lattice structures are topologically ordered, three-dimensional open-celled structures composed of one or more repeating unit cells. From a mechanical designer viewpoint, a great advantage offered by cellular materials is high strength accompanied by a relatively low mass. Due to their complex structure, fine geometry and the absence of supports structures, the setting of the best parameters to print lattice structures is difficult and could negative influence their mechanical response. This study investigated how different parameters settings influence the compression behaviour of lattice structures in stainless steel 17-4PH (AISI-630) printed by SLM. A comparison between compressive response of structures printed with different parameters is presented and considerations about their behaviour exposed
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
Design of adaptive optics by interference fitting: Theoretical background
No full textInterference-fit joints are typically adopted to produce permanent assemblies among mechanical parts. The resulting contact pressure is generally used for element fixing or to allow load transmission. Nevertheless, some special designs take advantage of the contact pressure to induce desiderata deformation or to mitigate the stress field inside the structure. Biased interference fitting between a planar mirror and an external ring could be used to induce the required curvature to realize new adaptive lens for optical aberration correction. Recently, thermally-actuated deformable mirror on this principle based, was proposed and prototyped. Although the feasibility and utility of such innovative lens was demonstrated, no comprehensive theory was developed to describe mirror behavior and predict their curvature. Nowadays, the use of approximated numerical approach, such as the finite element method, is the only way to study the interaction between biased and interference fitted bodies. The paper aims to give the theoretical background for the correct design of adaptive lens actuated by interference fitting. A new formulation for the curvature prediction is proposed and compared with finite element analysis and available experimental measurements
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
An Experimental-Numerical Study on Curling Process for Metallic Caps Production
No full textIn the field of food industry, adoption of metallic caps for the storage of agri-food products is widespread. This type of caps is obtained through a sequence of forming processes executed on a tinplate. First, the plane metal sheet is deep drawn to obtain a cup whose edge is slightly shaped inward, then a curling process forms the edge into a hollow ring. This paper is focused on the curling, which allows to assess the final cap shape immediately before the application of the cups on the jars. Since the process is generally made on packaging lines with high production rates, the design of a proper curling machine needs to consider the effect of fatigue as well as maximum load values. Because of the different cap dimensions and shapes contemporary worked on the line, the loads definition is not easy. The scope of this work is the development of a model for the prediction of curling loads for different cap shapes and sizes. The analytical solutions, available in literature, together with numerical simulations of the process were compared to experimental compression tests made on two different caps type. Considerations on caps geometry and size influence on curling force represent a contribution to the fitness for service evaluation as well as a starting point for the design of new curling machines
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