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Metodo della Rosetta Micrometrica per la misura multidirezionale degli stress residui tramite tecnologia a fascio ionico focalizzato
Full text linkIn questo lavoro è presentato un metodo innovativo per il calcolo dello stato tensionale residuo di un materiale.
Il metodo, denominato Rosetta Micrometrica (Micrometric Rosette, MR), applica i cui principi validati in
precedenti pubblicazioni degli stessi autori [13, 14, 15], e consiste nell’utilizzo combinato del fascio ionico
focalizzato (FIB), del microscopio elettronico a scansione (SEM) e della correlazione digitale di immagini (DIC).
La tecnica consente la valutazione dello stress residuo di un materiale misurando il rilassamento dello stesso
a seguito della rimozione del volume circostante che lo costringe e lo mantiene in tensione. L’implementazione
del metodo, presentata in questo lavoro, consiste nella capacità di analizzare il rilassamento del materiale
lungo qualsivoglia direzione nel piano della superficie del campione, e la capacità di individuarne le direzioni
principali di tensione, consentendo così la valutazione completa dello stato tensionale residuo con un solo unico
test di misura. La procedura è realizzata con una ripetizione ciclica di rimozione del materiale consentendo
la valutazione del profilo dello stress residuo in funzione dell’affondamento. La risoluzione del gradiente è
dell’ordine di 100 nm. La procedura sviluppata è semi automatizzata, grazie alla realizzazione, da parte degli
stessi autori, di uno script per il continuo controllo e riallineamento degli strumenti coinvolti. Lo script permette
di variare le dimensioni dell’area di materiale analizzato, il numero di cicli eseguiti, l’affondamento relativo di
ogni ciclo, la numerosità e l’orientazione delle direzioni da analizzare, consentendo di adattare perfettamente la
misura alle peculiarità del provino che deve essere studiato.
Il metodo viene eseguito su un materiale caratterizzato da uno stato tensionale non equibiassiale, un laminato.A new method for the calculation of the residual stress state of materials is presented in this work.
The method, named Micrometric Rosette (MR), applies the principles validated in previous publications by the same
authors [13, 14, 15], and consists of the combined use of focused ion beam (FIB), the scanning electron microscope
(SEM) and the digital correlation of images (DIC). The technique allows the evaluation of the residual stress of a
material by measuring the relaxation of the same after the removal of the volume surrounding that forces him and
keeps it in tension. The implementation of the method, presented in this work, consists in the ability of analyzing the
relaxation of the material along any direction in the plane of the surface of the material, and the ability to identify the
main directions of tension, thereby enabling the complete evaluation of the residual stress state with one and only
test measurement.
The measure is carried out with a cyclic repetition of removal of the material, as shown in fig 5, allowing the realization
of a profile of residual stress as a function of the sinking. The resolution of the gradient is of the order of 100 nm.
The developed procedure is semi-automated thanks to the implementation, by the same authors, of a script for the
continuous control and realignment of the instruments. The script allows to vary the size of the area being analyzed,
the number of cycles performed, the relative sinking of each cycle, the numerosity and the orientation of the directions
to be analyzed, allowing to perfectly adapt the test to the peculiarities of the specimen which is to be studied.
In this work the method was executed on a material characterized by a non equi biaxial stress state, a rolled sheet
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
Residual micro-stress distributions in heat-pressed ceramic on zirconia and porcelain-fused to metal systems: Analysis by FIB-DIC ring-core method and correlation with fracture toughness
No full textObjectives The production of fixed partial dentures (FPDs) induces complex residual stress profiles, due to both the thermal expansion coefficient mismatch between the veneering ceramic and the framework and to the thermal gradients occurring during the final cooling. Detailed knowledge of residual stress distributions in the veneering ceramics is important to understand the interface phenomena with the framework and the consequences of the different firing systems. The first objective of this study was to analyse the residual stress distribution in heat-pressed ceramic on zirconia core with micrometer spatial resolution, with also a focus on the stress at the interface versus porcelain-fused-to-metal samples. The second purpose was to correlate the residual stress with the fracture toughness. Methods The micron-scale focused ion beam (FIB) ring-core method was used to map the residual stress over the cross-sections of the veneering ceramics. The methodology is based on FIB micro-milling of annular trenches, combined with high-resolution in situ scanning electron microscope (SEM) imaging, a full field strain analysis by digital image correlation (DIC) and numerical models for residual stress calculation. Fracture toughness was evaluated by using high load Vickers indentation and hardness/modulus were measured by nanoindentation testing also across the interfaces. Results Both prosthetic systems showed a compressive stress at the ceramic surface on a micron-scale. The stress profile for porcelain fused to metal (PFM) showed a transition to tensile stress at the half of the layer, whilst the stress in proximity of the interface was more compressive in both the cases. Residual stress on a micron scale are higher in magnitude than the corresponding macro-scale values reported in the literature, due to the stress relaxation given, at larger scales, by micro-voids and cracks. The stress field was directly correlated with the indentation fracture toughness, which was higher in those areas where the compressive stress is greater. Stress analysis in correspondence of interfacial porosity for the zirconia sample also showed that micro-defects could induce local modifications of the residual stress field, which may even locally generate a tensile stress state. Significance The interfacial stress in dental systems was analysed on a micron scale and can give further insights into the process/property/performance correlation for this class of materials. In particular, interfacial and/or local modifications of the residual stress are expected to have a significant influence on crack nucleation mechanism in correspondence of micro-defects. A direct correlation between residual stress distribution and fracture toughness was proposed. It is noteworthy that the method can be used to study real crowns and bridges. In fact, complex geometries can be easily analysed by this procedure
Characterization of Metal-Ceramic and Zirconia-Ceramic Prosthetic: Microhardness at the Interface Systems
No full textSelective nanoindentation mapping to evaluate mechanical properties of battery materials
No full textVariations 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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