1,720,965 research outputs found
Efficient equilibrium-based stress recovery for isogeometric laminated curved structures
No full textThis work extends the stress recovery for laminated composite solid plates, proposed in [1,2], to curved structures. Based on 3D Isogeometric Analysis (IGA) computations and equilibrium, this procedure uses a single element through the thickness in combination with a calibrated layer-by-layer integration rule or a homogenized approach, allowing for an inexpensive and accurate approximation in terms of in-plane stresses (and their derivatives), while through-the-thickness stress components are poorly approximated. Relying on the highorder continuity properties of IGA shape functions, an accurate out-of-plane stress state can also be recovered by means of direct integration of the equilibrium equations in strong form. The a posteriori step application, which is straightforward in the context of solid plates, is not trivial in the case of curved geometries. In fact, the notion of in-plane and out-of-plane directions is not clear when modeling this kind of structures in the global reference system, while adopting curvilinear coordinates to express the equilibrium gives rise to additional coupled terms that require an iterative process to resolve the balance of momentum equation. Therefore, we propose to apply the recovery locally, which, despite leading to more elaborated stress derivative terms because of the increasing geometry complexity, still allows for a direct reconstruction as the resolvent system is uncoupled. Several numerical results show the good performance of this approach particularly for composite stacks with significant radius-to-thickness ratio and number of plies.MN
Higher order phase-field modeling of brittle fracture via isogeometric analysis
Get PDFThe evolution of brittle fracture in a material can be conveniently investigated by means of the phase-field technique introducing a smooth crack density functional. Following Borden et al. (2014), two distinct types of phase-field functional are considered: (i) a second-order model and (ii) a fourth-order one. The latter approach involves the bi-Laplacian of the phase field and therefore the resulting Galerkin form requires continuously differentiable basis functions: a condition we easily fulfill via Isogeometric Analysis. In this work, we provide an extensive comparison of the considered formulations performing several tests that progressively increase the complexity of the crack patterns. To measure the fracture length necessary in our accuracy evaluations, we propose an image-based algorithm that features an automatic skeletonization technique able to track complex fracture patterns. In all numerical results, damage irreversibility is handled in a straightforward and rigorous manner using the Projected Successive Over-Relaxation algorithm that is suitable to be adopted for both phase-field formulations since it can be used in combination with higher continuity isogeometric discretizations. Based on our results, the fourth-order approach provides higher rates of convergence and a greater accuracy. Moreover, we observe that fourth- and second-order models exhibit a comparable accuracy when the former methods employ a mesh-size approximately two times larger, entailing a substantial reduction of the computational effort
Investigation of microscale brittle fracture opening in diamond with olivine inclusion using XFEM and cohesive zone modeling
No full textInclusions trapped in diamonds are a fundamental source of information to probe the Earth's interior, provided that the pressure conditions at which the diamond grew are correctly determined. This study explores the traditional assumptions in geothermobarometry for olivine-in-diamond host-inclusion systems by employing extended finite element methods (XFEM) and cohesive zone models (CZM) to quantify the contributions of brittle fractures to the relaxation of the residual stress of inclusions. Our analysis was performed assuming that the host-inclusion system does not contain fluids and that the unfractured minerals are elastically isotropic. Our models show that the damage initiation is solely dependent on the shape of the inclusion and on the fracture strength of the diamond host, while the fracture nucleation is influenced by both the size of the inclusion and the toughness of the diamond. Our findings indicate that, in dry systems, the amount of relaxation of residual stress of the inclusion due to the opening of brittle fractures is much lower than that due to the elastic interaction between the host and the inclusion. Moreover, the pressure release due to fractures is not substantially affected by the shape of the inclusion. We also show that the total relaxation of the residual pressure due to the combined effect of the elastic interaction and the brittle deformation is lower than what is observed in natural samples, even when assuming fracture strength and toughness lower than those reported from experiments on single crystals of diamond. Such discrepancies suggest that in natural olivine-diamond systems additional mechanisms such as viscous or plastic deformation and/or the presence of preexisting defects and fluids in the host might play a relevant role in the relaxation of the residual stress. These findings underscore the need for advanced numerical tools that consider the complex interplay of the geometry of the host-inclusion system, the fracture properties, and the presence of fluids and defects in order to build more accurate models to constrain the geological history of diamonds
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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