1,720,962 research outputs found
Investigation of roughness induced crack closure effects in fatigue
No full textThe incidence of roughness induced fatigue crack closure has been studied by finite element modelling.Results show an increasing effect of crack path angle on closure levels with the closure mechanism being strongly dependent on residual plastic strains in the wake rather than global shear displacements of the fracture surfaces.An analytical expression for the functional dependence of roughness induced closure has been produced which shows reasonable agreement with the finite element results
Analytical modelling of the influence of local mixed mode displacements on roughness induced crack closure
No full textApplication of crack closure analytical modelling to predict the behavior of complex fatigue crack growth properties is limited partly due to restricted two-dimensional modelling approaches. An analytical model of roughness induced crack closure (RICC) is developed in the present paper considering a three-dimensional twisted and kinked crack path. Residual shear deformations at asperities in the crack wake affect the crack opening generating closure. These residual shear deformations are explicitly formulated from residual plastic deformation. The respective influence of the in-plane and out-of-plane deformation on RICC is discussed. The crack twisting is found to be a less significant effect on the RICC than the crack kinking, for similar deviation angles. However, these out-of-plane crack deflections are found to be non negligible particularly at low tilting angles. This analytical model is used to predict the closure stress intensity factor for a range of 2xxx aluminium alloys. Predictions are compared to experimental results obtained from low ?K fatigue crack growth tests. Experimental results show that fatigue performance scale with closure level and roughness of the failed fatigue specimen surfaces. Comparison of estimated and measured closure stress intensity factor show similar trends. <br/
Analytical and finite element modelling of roughness induced crack closure
No full textCrack closure is an established component of fatigue understanding, however, significant confusion remains in both experimental determination and micromechanical modelling. Analytical and finite element models of roughness induced crack closure (RICC) are developed in the present paper. A novel interpretation of RICC is explored where shear strains causing asperity contact arise explicitly from residual plastic deformation in the wake of a propagating crack, in a manner that is essentially analogous to plasticity induced crack closure (PICC). The analytical model estimates the crack opening along a simple deflected crack path, defined by a crack deflection angle and length, and residual shear at each asperity interfering with this opening to generate closure. The results from the analytical model are compared to finite element modelling and experimental results, with insight being provided into a controlling influence of the ratio of asperity size to plastic zone size on closure levels
Numerical modelling of roughness and plasticity induced crack closure effects in fatigue
No full textThe incidence of roughness induced fatigue crack closure has been studied by finite element modelling. Based on an analysis of both overall specimen compliance and node behaviour along the crack path the present modelling shows: (a) an increasing effect of crack path angle on roughness induced closure levels in keeping with the simple analytical model of Suresh and Ritchie; (b) the mechanism by which closure occurs is due to residual plastic strains in the wake, rather than global shear displacements of the fracture surfaces due to mixed-mode behaviour at the crack tip; and (c) the closure levels are relatively low compared to experimental data, consistent with the absence of environmental irreversibility in the finite element models and the idealised crack path morphologies that were used. Slip band simulations show a significant increasing effect of inhomogeneous deformation on closure levels, improving the apparent accuracy of the modelling results
Numerical modelling of combined roughness and plasticity induced crack closure effects in fatigue
Full text linkThe incidence of roughness induced fatigue crack closure has been studied by finite element modelling. Closure analyses in the literature have been reviewed and been shown to lack a reasonable treatment of: (a) propagating elastic-plastic cracks, and (b) the influence of the characteristically inhomogeneous plastic deformation associated with near-threshold crack growth in many materials. Based on an analysis of both overall specimen compliance and node behaviour along the crack path, the present modelling shows: (a) an increasing effect of crack path angle on roughness induced closure levels in keeping with the simple analytical model of Suresh and Ritchie; (b) the mechanism by which closure occurs is more strongly dependent on residual plastic strains in the wake than global shear displacements of the fracture surfaces due to mixed-mode behaviour at the crack tip; and (c) the closure levels are relatively low compared to experimental data, consistent with the absence of environmental irreversibility in the finite element models and the idealised crack path morphologies that were studied. Slip band simulations show a significant increasing effect of inhomogeneous deformation on closure levels, improving the apparent accuracy of the modelling results. <br/
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
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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