1,720,958 research outputs found
Stretch-induced softening in filled elastomers: A review on Mullins effect related anisotropy and thermally induced recovery
No full textThe Mullins effect of filled elastomers, corresponding to their softening under stretching, has been widely
explored and several models have been proposed to reproduce it. However, the observed anisotropy in the
material mechanical response induced by a stretch and the thermally induced recovery of the pristine material
behaviour are two aspects of the phenomenon that are difficult to model. In this review, an update collection of
the main results from literature experimental works about these topics is reported, with the aim to provide a
support for the improvement of existing models or the formulation and validation of new ones. A part of the
review details testing methods used to investigate the anisotropic mechanical response induced by differently
pre-stretching the materials. Another part, focused on studies highlighting the recovery of the original behavior
after a thermal treatment of the stretch-softened material, is aimed at approaching a more comprehensive understanding of the phenomena. The results of literature studies are summarized emphasizing the type of rubber
and filler, the filler content as well the applied stretching conditions. An overview of physical interpretations of
stretch-induced anisotropy and thermal recovery is provided, which could be useful for the development of the
physically based models
Fracture behavior of filled elastomers: How do strain induced softening and its thermally induced recovery affect the fracture toughness?
Full text linkIn this work, two peroxide-crosslinked hydrogenated nitrile butadiene rubbers for hydrogen system applications have been studied. Both elastomers are carbon black filled and one of these also contains a small quantity of polyamide. At the beginning, a preliminary analysis of the strain rate effect on the mechanical response and of the strain-induced softening is reported. Moreover, the dissipated and stored energies involved in the deformation of both the virgin and softened materials are evaluated. The thermally induced recovery of the strain-softening is analyzed by performing two treatments. In the second part of the work, the fracture behaviour of the two materials is compared and the effects of softening and its thermally induced recovery on fracture behavior are evaluated on one of the two compounds. The main finding is that softened material has a lower fracture toughness compared to the virgin material, while toughness of the thermally treated softened material is comparable to that of the virgin one
Is J-integral at crack onset an intrinsic property of filled elastomers? Experimental testing and finite element modelling for fracture toughness evaluation
No full textThe fracture behaviour of two filled NBR based compounds, differing in filler type (carbon black or silica) and content (75 and 60 phr respectively) has been evaluated performing fracture tests under different loading conditions. Single edge notched tension (SENT) tests, tests in pure shear (PS) deformation conditions on single edge notched specimens and equibiaxial (EB) tensile tests on centre-notched square shaped specimens have been carried out at room temperature at a nominal deformation rate of 1 min-1. Different approaches were adopted for the material’s fracture toughness evaluation. From both SENT and PS tests, for which analytical expressions for the tearing energy are available, the material’s tearing energy was evaluated. From PS tests, J-integral at fracture onset was also evaluated, since also this energy-based parameter can be determined analytically in this case. Further, once defined the materials’ constitutive equations, J-integral has been numerically evaluated at fracture onset in uniaxial tensile, PS and EB tests. A comparison between the different parameters have been performed for the two materials in relation to the evaluation method adopted
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
Stretch induced anisotropy and fracture toughness: An experimental study on a silica- filled NBR compound
No full textAnisotropic pre-stretching of a filled rubber compound is responsible for the anisotropic behaviour of the stretched material, which is commonly evidenced by evaluating only the tensile response of the prestretched material. In this work, an evaluation of the effects of stretch-induced anisotropy on the fracture behaviour of the material was also carried out. Preliminary pre-stretching of silica-filled SBR-based compounds was performed by deforming the material under uniaxial or equibiaxial tensile conditions or under pure shear deformation conditions, up to different strain levels. The tensile and fracture behaviour of the softened material was evaluated along two perpendicular directions and correlated with both the principal strains applied and the biaxiality index defined to characterize the anisotropy of preliminary stretchin
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