313 research outputs found
Modelling surface roughening during plastic deformation of metal crystals under contact shear loading
No full textDuring plastic deformation, metal surfaces roughen and this has a deleterious impact on their tribological performance. It is therefore desirable to be able to predict and control the amount of roughening caused by subsurface plasticity. As a first step, we focus on modelling plastic deformation during contact shearing of an FCC metallic single crystal, employing a finite strain Discrete Dislocation Plasticity (DDP) formulation. This formulation allows us to capture the finite lattice rotations induced in the material by shearing and the corresponding local rotation of the crystallographic slip planes. The simulations predict a pronounced material pile-up in front of the contact and a sink-in at its rear, which are strongly crystal-orientation dependent. By comparing finite and small strain DDP, we can assess the effect of slip plane rotation on surface roughening and on metal plasticity in general. Results of the simulations are also compared with crystal plasticity, which is also capable of predicting a pile-up and sink-in, but not the crystal-orientation dependency of roughening.Accepted Author Manuscript(OLD) MSE-
Plastic contact of self-affine surfaces: Persson's theory versus discrete dislocation plasticity
No full textPersson's theory allows for a fast and effective estimate of contact area and contact stress distributions when a flat and a self-affine rough surface are pressed into contact. For elastic bodies, the results of the theory have been shown to be in very good agreement with rather costly simulations. The theory has also been extended to plastic bodies. In this work, the results of Persson's theory for plastic bodies are compared with those of discrete dislocation plasticity. The area–load curves obtained by theory and simulations are found to be in good agreement when the rough surface has a very small root-mean-square (rms) height. For larger rms heights, which are more realistic for metal surfaces, the agreement is no longer good unless in the theory, instead of a size-independent material strength, one uses a rms height- and resolution-dependent yield strength. A modification of this type, i.e., the use of a yield strength dependent on size, does however not lead to agreement between the probability distributions of the contact stress, which is much broader in the simulations than in the theory. The most likely reason for this discrepancy is that the theory, apart from neglecting plasticity size dependence, only applies to elastic-perfectly plastic bodies and therefore, neglects strain hardening.</p
Modeling adhesive contacts under mixed-mode loading
No full textExperiments show that when an adhesive contact is subjected to a tangential load the contact area reduces, symmetrically or asymmetrically, depending on whether the contact is under tension or compression. What happens after the onset of sliding is more difficult to be assessed because conducting experiments is rather complicated, especially under tensile loading. Here, we provide through numerical simulations, a complete picture of how the contact area and tractions of an adhesive circular smooth punch evolve under mixed-mode loading, before and after sliding. First, the Green's function molecular dynamics method is extended to include the description of the interfacial interactions between contacting bodies by means of traction–separation constitutive laws that enforce coupling between tension (or compression) and shear. Next, simulations are performed to model sliding of a circular smooth punch against a flat rigid substrate, under tension and compression. In line with the experimental observations, the reduction in the contact area during shear loading is found to be symmetric under tension and asymmetric under compression. In addition, under tensile loading, full detachment is observed at the onset of sliding with a non-zero value of the tangential force. After the onset of sliding and the occurrence of slip instability, the contact area abruptly increases (reattachment), under both tension and compression. For interfaces with high friction, the reattachment occurs only partially. However, a full reattachment is attainable when friction is low.(OLD) MSE-
Knowledge representation within information systems in manufacturing environments
No full textThis thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.Representing knowledge as information content alone is insufficient in providing us with an understanding of the world around us. A combination of context as well as reasoning of the information content is fundamental to representing knowledge in an information system. Knowledge Representation is typically concerned with providing structures and theories that are used as a basis for intelligent reasoning. For this research however, the author defines an alternative meaning, which is related to how knowledge is used in a given context. Thus, this dissertation provides a contribution to the field of knowledge within information systems, in terms of the development of a frame-of-reference that will support the reader in navigating through the different forms of explicit and tacit knowledge use within the manufacturing industry. In doing so, the dissertation also presents the generation of a novel classification of three forms of knowledge (Structural, Interpretive and Evaluative forms); the development of a conceptual framework which highlights the drivers for knowledge transformation; and the development of a conceptual model which seeks to envelop both the content as well as the context of knowledge (Semiotic as well as Symbiotic factors). This is established through the use of an Empirical, Quantitative case study approach, that seeks to explore an interpretivist view of knowledge representation within two information systems contexts, within two UK manufacturing organisations. The first case study presents how a-priori knowledge assumptions are used in a computer aided engineering decision-making task within a high technology manufacturing company. The second case study shows how knowledge is used within the IT/IS investment evaluation decision making process, within a manufacturing SME. In doing so, both case studies attempt to elucidate the inherent, underlying relationship between explicit and tacit knowledge, via a frame-of-reference developed by the author which defines key drivers for knowledge transformation
On the proportionality between area and load in line contacts
No full textThe relative contact area of rough surface contacts is known to increase linearly with reduced pressure, with proportionality factor κ. In its common definition, the reduced pressure contains the root-mean-square gradient (RMSG) of the surface. Although easy to measure, the RMSG of the entire surface does not coincide, at small loads, with the RMSG over the actual contact area g¯ r, which gives a better description of the contact between rough surfaces. It was recently shown that, for Hertzian contacts, linearity between area and load is indeed obtained only if the RMSG is determined over the actual contact area. Similar to surface contacts, in line contacts, numerical data are often studied using theories that predict linearity by design. In this work, we revisit line contact problems and examine whether or not the assumption of linearity for line contacts holds true. We demonstrate, using Green’s function molecular dynamics simulations, that κ for line contacts is not a constant: It depends on both the reduced pressure and the Hurst exponent. However, linearity holds when the RMSG is measured over the actual contact area. In that case, we could compare κ for line and surface contacts and found that their ratio is approximately 0.9. Finally, by analytically deriving the proportionality factor using g¯ r in the original model of Greenwood and Williamson, a value is obtained that is surprisingly in good agreement with our numerical results for rough surface contacts.(OLD) MSE-
Preface
No full textThe University of Pennsylvania Working Papers in Linguistics (PWPL) is an occasional series published by the Penn Graduate Linguistics Society. The series has included volumes of previously unpublished work, or work in progress, by linguists with an ongoing affiliation with the Department, as well as volumes of papers from NWAV and the Penn Linguistics Colloquium/Conference. This volume contains selected papers from the 41st Penn Linguistics Conference, held from March 24-26, 2017 in Philadelphia, PA, at the University of Pennsylvania. Thanks go to Luke Adamson, Ryan Budnick, Andrea Ceolin, Nattanun Chanchaochai, Ava Creemers, Aletheia Cui, Kajsa Djärv, Amy Goodwin Davies, Helen Jeoung, Wei Lai, Nari Rhee, Caitlin Richter, Ollie Sayeed, Lacey Arnold Wade, Yosiane White, Hong Zhang for their help in editing. Since Vol. 14.2, PWPL has been an internet-only publication. As of September 2014, the entire back catalog has been digitized and made available on ScholarlyCommons@Penn. Please continue citing PWPL papers or issues as you would a print journal article, though you may also provide the URL of the manuscript. An example is below: Adamson, Luke 2018. Denominal verbs: past tense allomorphy, event frames and zero-categorizers. In University of Pennsylvania Working Papers in Linguistics 24.1, ed. Ava Irani and Milena Šereikaitė, 1-10. Available at: http://repository.upenn.edu/pwpl/vol24/iss1 Publication in the University of Pennsylvania Working Papers in Linguistics (PWPL) does not preclude submission of papers elsewhere; copyright is retained by the author(s) of individual papers. The PWPL editors can be contacted at: U. Penn Working Papers in Linguistics, Department of Linguistics, 3401-C Walnut Street, Suite 300, C Wing, Philadelphia, PA 19104-6228 and [email protected]. Ava Irani and Milena Šereikaitė, Issue Editor
Preface
No full textThe University of Pennsylvania Working Papers in Linguistics (PWPL) is an occasional series published by the Penn Graduate Linguistics Society. The series has included volumes of previously unpublished work, or work in progress, by linguists with an ongoing affiliation with the Department, as well as volumes of papers from NWAV and the Penn Linguistics Colloquium/Conference. This volume contains selected papers from the 41st Penn Linguistics Conference, held from March 24-26, 2017 in Philadelphia, PA, at the University of Pennsylvania. Thanks go to Luke Adamson, Ryan Budnick, Andrea Ceolin, Nattanun Chanchaochai, Ava Creemers, Aletheia Cui, Kajsa Djärv, Amy Goodwin Davies, Helen Jeoung, Wei Lai, Nari Rhee, Caitlin Richter, Ollie Sayeed, Lacey Arnold Wade, Yosiane White, Hong Zhang for their help in editing. Since Vol. 14.2, PWPL has been an internet-only publication. As of September 2014, the entire back catalog has been digitized and made available on ScholarlyCommons@Penn. Please continue citing PWPL papers or issues as you would a print journal article, though you may also provide the URL of the manuscript. An example is below: Adamson, Luke 2018. Denominal verbs: past tense allomorphy, event frames and zero-categorizers. In University of Pennsylvania Working Papers in Linguistics 24.1, ed. Ava Irani and Milena Šereikaitė, 1-10. Available at: http://repository.upenn.edu/pwpl/vol24/iss1 Publication in the University of Pennsylvania Working Papers in Linguistics (PWPL) does not preclude submission of papers elsewhere; copyright is retained by the author(s) of individual papers. The PWPL editors can be contacted at: U. Penn Working Papers in Linguistics, Department of Linguistics, 3401-C Walnut Street, Suite 300, C Wing, Philadelphia, PA 19104-6228 and [email protected]. Ava Irani and Milena Šereikaitė, Issue Editor
On the load-area relation in rough adhesive contacts
No full textIt is well established that, at small loads, a linear relation exists between contact area and reduced pressure for elastic bodies with non-adhesive rough surfaces. In the case of adhesive contacts, however, there is not yet a general consensus on whether or not linearity still holds. In this work evidence is provided, through numerical simulations, that the relation is non-linear. The simulations here presented can accurately describe contact between self-affine adhesive rough surfaces, since they rely on Green's function molecular dynamics to describe elastic deformation and on coupled phenomenological traction-separation laws for the interfacial interactions. The analysis is performed for two-dimensional compressible and incompressible bodies under plane strain conditions. Interfaces with various roughness parameters and work of adhesion are considered.(OLD) MSE-7(OLD) MSE-
Todas as ilhas
No full textTodas as Ilhas, a work of poetry by Paraíba author Irani Medeiros, is a book that deserves to be celebrated. Published in 2001 by Idea, this book is part of the Paraíba Literária collection, a collection that pays homage to the literary talents of Paraíba. The work is a lyrical journey through a series of islands, each representing a different facet of the human experience. Medeiros uses the metaphor of the island to explore themes of isolation, community, love, loss, and redemption. His language is rich and evocative, painting vivid images that stay with the reader long after the book is closed. What truly sets Todas as Ilhas apart is Medeiros’ ability to capture the essence of the human experience in beautiful and moving verse. Each poem is an island unto itself, an entire world of emotions and images for the reader to explore. In short, Todas as Ilhas is a work of literary art that demonstrates the talent and depth of Paraíba authors. It is a valuable addition to the Paraíba Literária collection and a testament to the power of poetry to connect and move readers. I highly recommend it to all literature lovers.Todas as Ilhas, uma obra de poesia do autor paraibano Irani Medeiros, é um livro que merece
ser celebrado. Lançado em 2001 pela editora Idea, este livro faz parte da coleção Paraíba
Literária, uma coleção que homenageia os talentos literários da Paraíba.
A obra é uma viagem lírica através de uma série de ilhas, cada uma representando uma faceta
diferente da experiência humana. Medeiros usa a metáfora da ilha para explorar temas de
isolamento, comunidade, amor, perda e redenção. Sua linguagem é rica e evocativa, pintando
imagens vívidas que permanecem com o leitor muito depois de o livro ser fechado.
O que realmente distingue Todas as Ilhas é a habilidade de Medeiros em capturar a essência
da experiência humana em versos belos e comoventes. Cada poema é uma ilha em si, um
mundo inteiro de emoções e imagens que o leitor pode explorar.
Em resumo, Todas as Ilhas é uma obra de arte literária que demonstra o talento e a
profundidade dos autores paraibanos. É uma adição valiosa à coleção Paraíba Literária e um
testemunho do poder da poesia para conectar e comover os leitores. Recomendo vivamente a
todos os amantes da literatura
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