1,721,294 research outputs found
Contraddizione, paraconsistenza e dialeteismo. Note su F. Berto, L. Bottai, Che cos'è una contraddizione, Roma, Carocci, 2015, pp. 123.
No full textRecensione al volume: F. Berto, L. Bottai, Che cos'è una contraddizione, Roma, Carocci, 2015, pp. 123
Contraddizione, paraconsistenza e dialeteismo. Note su F. Berto, L. Bottai, Che cos'è una contraddizione, Roma, Carocci, 2015, pp. 123.
No full textRecensione al volume: F. Berto, L. Bottai, Che cos'è una contraddizione, Roma, Carocci, 2015, pp. 123
Analytical models for fatigue life prediction of metals in the stress life approach
Full text linkQuesta tesi fornisce una raccolta di modelli stress-life (S/N) per la valutazione della vita a fatica di componenti metallici sia lisci che intagliati sottoposti a sollecitazioni di ampiezza sia costante che variabile. Il documento è suddiviso in cinque capitoli, il primo è una panoramica della fatica in generale e, nello specifico, degli strumenti necessari nei capitoli successivi. Nel capitolo 2 la transizione di da intaglio di tipo "crack like" a "blunt" è adattata all'approccio stress-life attraverso la teoria delle distanze critiche, quindi viene definita una nuova curva S/N modellante tale transizione. Il capitolo 3 si basa sul nuovo modello di curva S/N per il carico a fatica ad ampiezza variabile, dimostrando che la valutazione della vita a fatica in queste condizioni può essere eseguita attraverso uno shift costante della curva di Wöhler se si adotta la regola del danno cumulativo lineare. Il metodo è abbastanza generale poiché non è necessario ipotizzare vincoli specifici sulla della storia di carico in quanto il fattore di shift tiene conto degli effetti di tensione media, sebbene siano chiari i limiti della regola del danno cumulativo lineare alla base del lavoro. Si è anche osservato che, adottando una regola di danneggiamento cumulativo bilineare, il modello introduce in maniera naturale il concetto di limite di fatica, pur mantenendo costante il fattore di shift già definito. I modelli proposti sono stati validati sperimentalmente attraverso i dati del programma di test SAE Keyhole, disponibili pubblicamente online all'indirizzo https://www.efatigue.com/benchmarks/SAE_keyhole/SAE_keyhole.html.
Il capitolo 4 discute i limiti di validità dell regola del danno cumulativo lineare, prestando particolare attenzione al suo rapporto con le leggi di propagazione di cricca del tipo "Paris generalizzato". In particolare, il capitolo dimostra come il supporre danno cumulativo lineare corrisponda esattamente all'integrare una legge di potenza della sollecitazione e delle dimensioni della cricca in forma di legge di Paris o Walker. Ergo, questo risultato è valido anche per tensione media diversa da zero, ma non considera né la sequenza di applicazione del carico né effetti di chiusura della cricca. Di conseguenza, nonostante alcune chiare limitazioni, non si prevede alcuna differenza in termini di accuratezza tra l'applicazione di una del danno cumulativo lineare rispetto all'integrazione di un'equazione di propagazione della cricca. Infine, il capitolo 5 presenta un'indagine sui vantaggi dell'applicazione di una curva S/N a quattro parametri (forse più realistica rispetto ad una pura legge di potenza) ottenuta direttamente ipotizzando che la curva a due parametri corrisponda alla derivata prima della precedente nel suo punto di flesso. L'accuratezza della nuova curva è stata dunque confrontata con la legge di potenza troncata utilizzando una campagna sperimentale di dati di fatica su acciaio e lega di alluminio condotta dal National Advisory Committee for Aeronautics (NACA).This Thesis provides a collection of stress-life (S/N) models for fatigue life evaluation of both pristine and notched metallic components. The document is subdivided into five Chapters, the first being a Literature Overview of fatigue in general, and, in the specific, of the tools needed in the subsequent Chapters. In Chapter 2 the “crack like to blunt” notch transition is adapted to the stress-life approach using the theory of the critical distances, therefore a new S/N curve to model this transition is defined. Chapter 3 relies on the new S/N curve model for variable amplitude fatigue loading by demonstrating that fatigue life assessment under these conditions can be performed through a constant shift of the Wöhler curve if adopting a linear damage accumulation rule. The method is quite general since there is no need of hypothesizing specific constraints on loading history as the shift accounts for mean stress effects, albeit suffering from the weaknesses of the underlying linear damage accumulation rule. The models proposed have been experimentally validated through the SAE Keyhole test program data, publicly available online at https://www.efatigue.com/benchmarks/SAE_keyhole/SAE_keyhole.html.
Chapter 4 discusses the limits of validity of a linear damage accumulation rule, giving special attention to its relationship with crack propagation laws of the generalized Paris type. Specifically, the Chapter proves that supposing a linear damage accumulation exactly corresponds to integrating a power law of the stress and the crack size in the form of Paris’ or Walker’s law. Ergo, this result is valid even for non-zero mean stress, yet neither accounting for load sequence nor for crack closure is considered. Thenceforth, despite some clear limitations, no difference in terms of accuracy is expected between the application of a linear damage accumulation rule vs. integration of a crack growth equation. Finally, Chapter 5 presents an investigation of the advantages in the application of a (maybe more realistic) four parameters S/N curve directly obtained postulating that the two parameters curve corresponds to the first derivative of the former one in its inflection point. The accuracy of the new curve is compared with the former employing an experimental campaign fatigue data on steel and aluminum alloy conducted by the National Advisory Committee for Aeronautics (NACA)
Notch stress intensity factors in an array of narrow V-Notches under tension by means of local strain energy density and coarse meshes
No full textFatigue limit prediction of a compression fork-pin coupling of a front motorbike suspension under fully reversed bendino load
No full textThe fork-pin compression coupling of the front suspension of a motorbike is very important for the reliability and the safety of the vehicle. The failure of this component is very dangerous because it would make the vehicle unmanageable, and it could cause severe injuries to the driver. Therefore, the designer’s aim is to assure its reliability keeping at the same time the production costs low.
One of the most important causes of failure is due to fatigue under fully reversed bending load. In this work, fatigue behaviour of fork-pin couplings, produced by the Paioli Meccanica S.p.a. of Bologna, is analysed, and the results of the tests carried out on an ad-hoc testing system are summarised. The Sines’ method for multiaxial fatigue is applied to predict fatigue life and to estimate the stress concentration factor (Kf) of the coupling
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
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