1,720,982 research outputs found
Identification of the parameters contained in a cyclic cohesive zone model for fatigue crack propagation
No full textCyclic cohesive zone models provide a useful tool to describe fatigue driven crack propagation,
covering a wide range of engineering applications. For a proper use of these models, particular
attention must be devoted to the correct calibration of the parameters contained, considering that
some of these can be characterized by a large variability and/or by the absence of a precise
physical meaning so that they are not amenable to a direct measurement. This paper proposes a
robust inverse analysis procedure, to investigate the identifiability of the model parameters
governing the fatigue induced damage evolution, in a recently proposed cyclic cohesive zone
model. A novel control for compact test specimens providing more meaningful experimental
information is proposed. The identification problem is formulated by considering fatigue crack
propagation curve and deformations measurements in a discrete number of points of the specimen
surface as input data of the inverse algorithm. The finite element operator, adopted to simulate
the experimental tests, has been substituted by a proper calibrated meta model to reduce the
computational cost of the forward operator and, thus, to solve the inverse problem in a stochastic
context through Monte Carlo like procedures. Representative results, obtained starting from
virtual data affected by different levels of noise, are reported to highlight the identifiability of the
model parameters on the basis of the experimental data adopted. Indications regarding the
minimum number of measurements needed to make the inverse problem well-posed are also
provided, supporting possible planning of measurements setups for laboratory investigations
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
Fast 3D Adaptive Limit Analysis of Masonry Arch Bridges Interacting with Backfill
No full textIn this paper, a novel three-dimensional approach for the evaluation of the load carrying capacity of masonry arch bridges with arch-backfill interaction is proposed. An adaptive upper bound limit analysis procedure is followed. NURBS solids are adopted for representing the geometry ofboth arch and backfill, allowing an accurate representation of the structure. These elements are idealized as rigid blocks with energy dissipation occurring only at interfaces, in turn represented by planar or curved NURBS surfaces. An initial mesh is obtained by subdividing the NURBS solids through additional surfaces. Then, a Genetic Algorithm mesh adaptation scheme is applied to reproduce the real collapse mechanism. As numerical example, the analysis ofatwo-ring skew arch with backfill is reported
Stochastic Calibration of a Cyclic Cohesive Zone Model Through Monte Carlo Analysis
No full textFatigue induced crack propagation is still an open issue, relevant to many engineering applications. Cyclic loading produces damage accumulation at a localized region which results first in the formation of micro-cracks and finally leads to the creation of macro-cracks. The modeling of fatigue induced crack propagation can be done according to different approaches, such as the Paris law, where the rate of crack growth is dependent on fracture mechanics parameters, e.g., the stress intensity factor or the strain energy release rate. Other approaches are the empirical methods, typically S-N approach and the micromechanical models describing the accumulation of damage based on material microstructure changes. Another approach involves the definition of phenomenological models where the fatigue crack growth is described by adopting cohesive zone laws. In this paper a damage-based irreversible cyclic cohesive zone model is adopted, where damage healing is considered during the fatigue damage evolution. The model presents different parameters, some of which are characterized by a large variability, do not possess a precise physical meaning and then they are not amenable to direct measurement. In this context, this paper aims to provide a robust procedure for the calibration of these model parameters, based on a Monte Carlo stochastic approach. Indications regarding the minimum number of experimental measurements are also provided, to support the planning of tests setups for laboratory investigations. Finally, the definition of a well posed inverse problem allows an efficient identification of all the sought model parameters reducing then the experimental costs
Three-dimensional adaptive limit analysis of masonry arch bridges interacting with the backfill
No full textIn this paper, the collapse behavior of masonry arch bridges interacting with the backfill is investigated through an adaptive procedure based on the kinematic theorem of limit analysis and a NURBS (Non-Uniform Rational B-Spline) representation of the geometry. The initial model is subdivided into few macro-blocks considered rigid and with dissipation occurring only along element interfaces, in turn represented by planar or curved NURBS surfaces. The properties of the materials are considered using homogenized failure domains and the initial mesh subdivision is then adjusted by means of a Genetic Algorithm. Particular attention is focused on the characterization of the arch-backfill interaction problem. The backfill is here represented first in terms of equivalent vertical and horizontal loads and then by following a direct modeling through NURBS curved macro-blocks. In particular, this latter approach allows to take into account the backfill contribution also in terms of internal dissipation. However, material parameters must be defined with particular attention: the use of a very rough discretization with the assumption of rigid blocks requires the utilization of equivalent ultimate resistance values for backfill-backfill interfaces to correctly estimate the internal dissipation at failure. Meaningful numerical examples dealing with different geometries and considering both load-carrying capacity and foundation settlement problems are reported. Finally, two geometrically complex examples are analysed through a recently presented modeling strategy via NURBS solids
An optical and electron microscope study of the growth and etching behavior of electrolytic amorphous germanium.
No full textVariations 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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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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