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Peridynamic modeling of inelastic materials for aerospace applications
Get PDFStudy of the mechanical behavior of ductile materials is essential in engineering and materials science due to the widespread use of these materials in industry. Ductile materials are known for their ability to deform significantly before fracture, and this has contributed to their extensive adoption in many industrial sectors such as aerospace, automotive, and structural engineering.
Ductile materials undergo elastoplastic deformation prior to fracture. This process reduces the stiffness of the material before failure. When a material is loaded, it initially exhibits elastic behavior. A surface in the stress space known as the yield surface controls the initiation of the plastic deformation. Plastic deformation occurs when the stress in the material remains on the yield surface throughout the loading process. Furthermore, to reflect the real behavior observed in most ductile materials, the size of the yield surface is controlled by adding a hardening/softening assumption to the formulation.
The linear elastic fracture mechanics (LEFM) approach, which neglects yielding at the crack front, is not reliable for simulating the mechanical behavior of ductile materials that undergo significant deformation under service loads. In contrast, the elasto-plastic fracture mechanics (EPFM) approach considers the impact of yielding at crack tips and characterizes the plastic behavior of the material. Consequently, it is appropriate for analysing ductile materials.
Moreover, the deformation of all metals is, to some extent, time-dependent. This behavior can be effectively characterized by elasto-viscoplasticity. This framework accounts for the time-dependent inelastic strains observed in solids. The Perzyna constitutive law, with its simple formulation, accurately simulates the evolution of viscous effects and is thus widely employed in engineering applications.
Classical continuum mechanics is a theory that establishes the mathematical foundation for the study of the mechanical behavior of ductile materials. However, fracture analysis is challenging, especially when it is approached within the framework of the classical mechanics theory because this theory uses partial derivatives in the equation of motion, which require continuity of the displacement field. This assumption becomes problematic when dealing with discontinuities such as cracks.
Peridynamics is a nonlocal theory of solid mechanics designed for discontinuous problems. It is well suited to failure analysis because it uses integral equations rather than partial differential equations. It redefines the equation of motion and improves its suitability for solving problems involving cracks. However, since it is a recently introduced theory, Peridynamics is not equipped with all constitutive laws normally available for classical continuum mechanics.
Therefore, it is reasonable to develop a peridynamic elastoplastic model for the study of the mechanical behaviour of ductile materials. The main purpose of this dissertation is to develop peridynamic approaches to simulate both elastoplastic materials and elasto-viscoplastic materials with strain hardening. The elastoplastic model is based on the classical theory of plasticity. The model is capable of simulating the elastoplastic behavior of materials with isotropic, kinematic and combined hardening. The elasto-viscoplastic peridynamic model is based on the Perzyna constitutive law. For materials with hardening, the yield surface changes with any change in plastic strain, a behavior observed in most materials. This effect is duly taken into account in the proposed models. We shall briefly show that the proposed approaches are well suited for fracture analysis of ductile materials. Several examples, including 2D plane stress and plane strain, and 3D cases, are performed to demonstrate the capabilities of the proposed approaches
Elastoplastic peridynamic formulation for materials with isotropic and kinematic hardening
Get PDFWe present an ordinary state-based peridynamic model in 2D and 3D consistent with rate-independent J2 plasticity with associated flow rule. The new contribution is the capability of the elastoplastic law to describe isotropic, kinematic and mixed hardening. The hardening formulations follow those available in the literature for classical elastoplasticity. The comparison between the results obtained with the peridynamic model and those obtained with a commercial FEM software shows that the two approaches are in good agreement. The extent of the plastic regions and von Mises stress computed with the new model for 2D and 3D examples match well those obtained with FEM-based solutions using ANSYS
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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