1,720,957 research outputs found
Analysis of prospective SIF and shielding effect for cylindrical rough surfaces obtained by L-PBF
Full text linkFatigue properties of parts built by Additive Manufacturing (AM) are strictly related to process-induced defects and complex surface morphology. Several studies have proved that surface valleys act as crack initiation sites, similarly to surface micro-notches. However, different roughness parameters have been considered in literature for the depth of the surface notches, together with the adoption of a shielding factor. The aim of this study is to understand how the surface complexity of L-PBF (Laser-Powder Bed Fusion) AlSi10Mg cylindrical specimens in as-built condition can affect the fatigue behaviour. In detail, CT (Computer Tomography) scans were adopted to characterize the surface quality and 2D FE (Finite Element) analyses were used to calculate the local stress intensity factor at the most critical valleys in the surface. The results of the FE analyses were compared with a shielding factor determined for regularly spaced notches. In spite of the significant scatter, the average geometric factor value for surface notches in L-PBF surfaces is correctly predicted by the traditional shielding factor
Orientation-dependent fatigue assessment of Ti6Al4V manufactured by L-PBF: Size of surface features and shielding effect
Full text linkThe fatigue behaviour of as-built parts produced by means of Laser-Powder Bed Fusion process (L-PBF) is primarily influenced by the presence of stress raisers on the surface, whose morphology strongly depends on the relative orientation between the surface and the build direction. This study aims to shed light into the factors representing the surface morphology that correlate with the fatigue performance of L-PBF Ti6Al4V specimens manufactured in four different orientations. A Fracture Mechanics-based model based on measurable roughness parameters was employed for the prediction of the fatigue properties in both the finite life and endurance limit regions. The fatigue model considers an initial equivalent defect corresponding to the roughness parameter Rv,max. In addition, it includes a geometric factor F accounting for the shielding present at the roots of the micro-notches which was calculated starting from profile roughness parameters determined by X-ray Computer Tomography (XCT) scans. The predicted stress–life curves show that the adoption of the maximum profile depth Rv,max and the shielding factor F yields precise life predictions considering the effect of the surface orientation
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
A comparison of fatigue analysis methods for L-PBF net-shape surfaces in Ti6Al4V parts
Full text linkThe fatigue performance of additive manufacturing components is strongly limited by the surface topology, in particular considering the effect of the surface orientation. In the present study, Ti6Al4V laser powder bed fusion (L-PBF) net-shape specimens were printed considering four critical orientations to investigate and compare HCF fatigue properties and two different fatigue assessment methods.
Detailed X-ray Computer Tomography (XCT) allowed us to carry out numerical simulations of the 4-Point Bending test samples, by adopting the critical distance method (TCD method). Endurance limit predictions based on the most critical valleys were performed by TCD and compared to predictions made with a Fracture Mechanics model that relies on simple profile roughness parameters.
Comparison of the methods show that TCD inherently includes the shielding effect and it can better account for isolated features, while FM is more rapid and conservative
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
Fatigue strength estimation of net-shape L-PBF Co–Cr–Mo alloy via non-destructive surface measurements
No full textOne of the primary challenges in utilizing additive manufacturing for load-bearing metal components in the aerospace industry lies in the relatively low fatigue strength and significant variability stemming from the typically rough as-built surfaces. The goal of this research is to develop a model able to robustly correlate parameters obtained by non-destructive measurements to the fatigue strength of a generic surface state for a cobalt-chrome alloy manufactured via laser powder bed fusion (L-PBF). The results show that a relatively accurate estimation of fatigue strength of a generic surface quality can be performed via high-quality non destructive roughness measurements coupled with statistical considerations and fracture mechanics-based assessments. This provides the capability of comparing different surface states and selecting the best option for fatigue strength with limited experimental effort and might prospectively set the basis for qualification of L-PBF components in the presence of rough surfaces
- …
