1,720,952 research outputs found
On the two-potential constitutive modelling of rubber viscoelastic materials
Get PDFU of I Only Restriction Lifted for Item 93166 on 2018-07-08T09:15:36Z."This work lays out the specialization of the two-potential constitutive framework --- also known as the ""generalized standard materials'' framework --- to rubber viscoelasticity. Inter alia, it is shown that a number of popular rubber viscoelasticity formulations, introduced over the years following different approaches, are special cases of this framework. As a first application of practical relevance, the framework is utilized to put forth a new objective and thermodynamically consistent rubber viscoelastic model for incompressible isotropic elastomers. The model accounts for the non-Gaussian elasticity of elastomers, as well as for the deformation-enhanced shear thinning of their viscous dissipation governed by reptation dynamics. The descriptive and predictive capabilities of the model are illustrated via comparisons with experimental data available from the literature for two commercially significant elastomers."Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2018-05-01The student, Aditya Kumar, accepted the attached license on 2016-04-21 at 16:42.The student, Aditya Kumar, submitted this Thesis for approval on 2016-04-21 at 17:40.This Thesis was approved for publication on 2016-04-25 at 13:53.DSpace SAF Submission Ingestion Package generated from Vireo submission #9421 on 2016-07-07 at 13:50:34Made available in DSpace on 2016-07-07T20:27:55Z (GMT). No. of bitstreams: 2
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Previous issue date: 2016-04-25Embargo set by: Seth Robbins for item 93166
Lift date: 2018-07-07T20:28:14Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 93166
Lift date: 2018-07-07T20:35:34Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD syste
Nucleation and propagation of fracture and healing in elastomers
No full textU of I OnlyThe main objective of this dissertation work is to introduce a macroscopic theory capable of describing, explaining, and predicting the nucleation and propagation of fracture and healing in elastomers undergoing arbitrarily large quasistatic deformations. Elastomers are assumed to behave as purely elastic isotropic solids. The proposed theory, which can be viewed as a generalization of the phase-field approximation of the variational theory of brittle fracture of Francfort and Marigo (1998) to account for physical attributes innate to elastomers that have been recently unveiled by experiments at high spatiotemporal resolution, rests on two central ideas. The first one is to view elastomers as solids capable to phase transition to another solid of vanishingly small stiffness: the forward phase transition serves to model the nucleation and propagation of fracture while the reverse phase transition models the possible healing. The second central idea is to take those phase-transitions to be driven by the competition of the elasticity, the strength, and the critical energy release rate of the elastomer under investigation.
Two models based on the general formulation are presented which account for the strength of elastomers in different manners. The first and simpler model accounts only for the hydrostatic strength of elastomers. The second and more elaborate model accounts for a generic strength surface in the entire stress space and as a result is capable of describing fracture nucleation at large, be it within the bulk (under arbitrary states of stress, not just hydrostatic), from large pre-existing cracks, small pre-existing cracks, or from smooth and non-smooth boundary points. The descriptive and predictive capabilities of both models are examined by confronting their predictions with a wide range of famed --- but hitherto unexplained --- and new experimental results.
From an applications point of view, the proposed theory amounts to solving a system of two coupled and nonlinear PDEs for the deformation field and a phase field. A numerical scheme is presented to generate solutions for these PDEs in and 3 space dimensions. This is based on an efficient non-conforming finite-element discretization, which remains stable for large deformations and elastomers of any compressibility, together with an implicit gradient flow solver, which is able to deal with the large changes in the deformation field that can ensue locally in space and time from the nucleation of fracture.
Beyond its pertinence to elastomers, the proposed theory seems to provide a complete framework for the description of fracture nucleation and propagation in elastic brittle materials at large. Evidence of this remarkable generality is provided by direct comparisons with experiments on fracture nucleation and propagation in a broad spectrum of materials, including numerous ceramics and hard polymers.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2022-12-01The student, Aditya Kumar, accepted the attached license on 2020-09-11 at 14:35.The student, Aditya Kumar, submitted this Dissertation for approval on 2020-09-11 at 14:57.This Dissertation was approved for publication on 2020-09-17 at 17:15.DSpace SAF Submission Ingestion Package generated from Vireo submission #15808 on 2021-03-04 at 16:18:43Made available in DSpace on 2021-03-05T21:40:34Z (GMT). No. of bitstreams: 3
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Previous issue date: 2020-09-17Embargo set by: Seth Robbins for item 117177
Lift date: 2023-03-05T21:40:52Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 117177
Lift date: 2023-03-05T21:43:00Z
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Numerical Study of a Microswimmer using an Immersed boundary method
No full textThe environment in which microscopic organisms live in is dominated by viscous forces because of their small length scales. Inertial forces are of little use to them in their propulsion mechanisms. As a consequence of this, an organism such as the scallop which moves through time-reversible deformations of its body would not propel itself in a regime dominated by visocus forces. Hence, microscopic organisms use appendages like cilia and flagella that are not time reversible to move forward. However, inertial effects become important to microscopic organisms at the relevant time and length scales. For example, inertia is used by a microscopic organism such as Paramecium to escape/attack its predator/prey.The effects of inertia on the model of a spherically ciliated micro-organism are studied numerically using an Immersed Boundary Method (IBM) in the present work. In this model ,the distortions of the envelope that is generated by connecting all the tips of the cilia together, are prescribed. The unsteady Reynolds number which characterizes the influence of unsteady inertia that is generated by the beat of the organism, is varied from 0.025 to 18. The code which uses a Volume Penalization/Volume of Solid IBM to simulate the distorting sphere is validated for several test cases. The mean swimming velocity of the organism that is obtained numerically from the code is in agreement with the analytical model for two cases of the unsteady Reynolds number. The mean swimming velocity is found to decrease at increasing inertia. The flow pattern that is obtained in the near-field as a result of the distorting sphere is significantly different from those obtained with the existing models available in literature
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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