1,720,961 research outputs found
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
ANALYSIS OF THE TRIBOLOGICAL BEHAVIOUR OF TITANIUM FASTENERS UNDER DIFFERENT TIGHTENING STRATEGIES
No full textThe present work aims at investigating the tribological behaviour of Ti6Al4V, M6 screws, applied to cast aluminium underhead and threads, when subjected to different tightening strategies. All tightenings have been performed in the dry condition, after degreasing of the cast parts by means of a commercial spray degreaser. Namely, a standard steady tightening operation at 20 rpm has been compared to a mixed high speed – standard speed strategy (200 rpm – 20 rpm), observing the tribological output in terms of underhead and thread friction coefficients at first tightening. All measurements have been performed by means of a tightening test bench that allows sampling the separate frictional contributions at the underhead and at the thread. For each specimen, force – torque diagrams have been plotted and observation of the underhead surfaces have been performed (before and after first tightening). The underhead and thread friction coefficients have been sampled at both 25% and 100% of the target tightening torque. The main outcomes of the study are: (i) the frictional behaviour of the Ti6Al4V screw, mating to aluminium substrates is nearly the same for both tightening strategies, in terms of average total coefficient of friction; (ii) in the case of mixed high – low speed strategy, a slightly better behaviour in terms of stick slip occurrence has been observed at first tightening, (iii) both processes allow achieving friction coefficients in the range suggested by the relevant standards
Fatigue response of AlSi10Mg by laser powder bed fusion: influence of build orientation, heat, and surface treatments
Full text linkThe aim of this study is to analyze how the fatigue behavior of AlSi10Mg by laser powder bed fusion is affected by build orientation, heat, and surface treatments. A three-by-three factorial plan has been arranged for this purpose. Particularly, regarding the heat treatment, three levels were considered (as built, age hardening, and stress relief); whereas, for the surface treatment, three levels were investigated (micro-shot-peening, micro-shot-peening plus fine blasting, and machining and lapping following laser powder bed fusion). Regarding the build orientation, the specimens were manufactured using three different build orientations (0 degrees, 45 degrees, and 90 degrees). The obtained data have been statistically analyzed by a three-factor ANOVA-based method. The results, supported by fractographic and micrographic microscopy analyses, indicate that the age-hardening treatment yields the maximum benefits, whereas stress relief may even have a detrimental effect. As for surface treatments, a positive influence of shot-peening has been found
Fretting fatigue of interference fitted joints: development of a novel specimen for four-point rotating-bending tests and experimental results
Full text linkInterference-fitted joints are widely used to join a shaft and a hub. The contact pressure produced by the interference induces stress concentration on the shaft at the hub end. FEA can be helpful in evaluating the related stress concentration factor. However, fretting damage may be generated and may arise from micro-sliding between the mating surfaces. It is currently not feasible to take this occurrence into account and to properly and reliably address this phenomenon by a standard numerical simulation. In order to tackle this question, an ad hoc specimen was designed for four-point rotating bending fatigue testing. The new specimen has three main advantages: the first one is the reduced dimensions with respect to the usually tested shafts, the second is the possibility of controlling the average contact pressure, and the third is the capability of easily dismounting the specimen without damaging the coupled surfaces. The specimen has been then tested. The study focused on C40 normalized steel, whose fretting fatigue limit was experimentally evaluated by the aforementioned device. The mating surfaces could also be carefully analyzed for fretting damage detection after cycling. The fatigue limit retrieved was 254 MPa and fretting damage and induced cracks were detected in the specimens, which proves the effectiveness of the introduced testing rig at reproducing fretting fatigue damage
AN INVESTIGATION ABOUT THE AGEING BEHAVIOUR OF PRE-APPLIED THREADLOCKERS
No full textPre-applied threadlockers are widely adopted in industrial applications, due to their favorable features in terms of handling of the fastener and savings in terms of assembly-line dosing systems. In the practice, fasteners with the pre-applied adhesive may undergo storage and/or shipping in harsh environmental conditions, both in terms of temperature and humidity. Questions may arise as to whether such thermal-hygroscopic aging (prior to assembly): (i) affects the tribological properties of the fastener at tightening and/or (ii) the breakaway torque of the fastener after curing. By means of an experimental approach, this work primarily aims at answering the first question, indeed scarcely covered by the literature. As for the second question, measurement of the breakaway torque is carried out for the sake of comparison with the data provided by the adhesives datasheets, where available. Based on a common bolt and plate configuration, the study involves different pre-applied threadlockers in terms of strength grade, among several hygrothermal conditions, representative of frequent storage/shipping conditions. The experimental data have been analyzed by means of the ANOVA tools to assess the effectiveness of the input parameters (adhesive type and aging conditions) on the response in terms of both thread friction coefficient at tightening and breakaway torque of the fastener after tightening completion and complete polymerization. Guidelines useful to the design engineer are reported in the conclusions
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
EXPERIMENTAL INVESTIGATION ON THE FATIGUE STRENGTH FOR DIFFERENT TIGHTENING PROCEDURES AND MATERIALS IN METRIC SCREWS
No full textThe aim of this present paper is to investigate the influence of some joint design parameters on the fatigue strength of metric screws. This investigation involved different screws strength grades (8.8 and 12.9). The experimental tests were carried out on black oxidized M6 screws, coupled with steel nuts of the corresponding strength class. Both screws and nuts were tested in “as received” lubrication condition. The screws were tested untightened and tightened with the tightening torque causing yielding (100% of the yield stress). A preliminary test to evaluate the tightening torque providing the desired equivalent stress on the screw was carried out. A tightening machine bench which was able to measure the tightening load and the friction coefficients both in the underhead and in the thread was used. The tests were run controlling the tightening torque and the spindle speed. In the following tests, the screws were tightened at the desired tightening torque and then untightened by means of the aforementioned tightening machine bench. Then the screws and the nuts were assembled on an ad hoc test fixture and tested on a resonant testing machine in order to evaluate the screw fatigue limit according to the international standard ISO 3800. The experimental results were processed by means of statistical tools of two-way ANOVA and Fisher Test in order to evaluate the effect of each parameter on the fatigue response of the screws
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
Fretting Fatigue in Mechanical Joints: A Literature Review
Full text linkFretting fatigue is a fatigue damage process that occurs when two surfaces in contact with each other are subjected to relative micro‐slip, causing a reduced fatigue life with respect to the plain fatigue case. Fretting has now been studied deeply for over 50 years, but still no univocal design approach has been universally accepted. This review presents a literature study that involves the three main types of mechanical joint affected by fretting fatigue (press‐fitted shaft hub joints, dovetail joints, and bolted joints) aiming at giving insight into the progress made in terms of design guidelines for engineers
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