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Development of a 3D microstructure sensitive crystal plasticity model for aluminum
Full text linkA dislocation density based crystal plasticity finite element model (CPFEM) has been developed in which different dislocation densities evolve on all octahedral slip systems in aluminum. Based upon the kinematics of crystal deformation and dislocation interaction laws, dislocation generation and annihilation are modeled. Dislocation densities evolve in form of closed loops and are tracked as state variables in the model, leading to spatially inhomogeneous dislocation densities that show patterning in the dislocation structures. A generalized Taylor equation is used as the hardening law in which hardening coefficients are based on the reactions between dislocations on co-planar and non-planar slip systems. The hardening coefficients for reactions involving latent slip systems are determined using 3D discrete dislocation dynamics. The model is validated using distinct hardening behavior of {100} and {111} single crystals of aluminum. The phenomenon of overshooting in aluminum is predicted using the model. Effect of collinear interactions of dislocations is shown to enhance the overshooting behavior. Evolution of crystallographic texture during plane strain deformation of polycrystalline aluminum is predicted. The crystallographic texture shows characteristic texture components observed in the rolling texture in the experiments reported in the literature. Description of dislocation densities is presented in form of pole figures along with evolution of crystallographic texture which shows increasing heterogeneity in microstructure with increasing deformation. Simulations of plane strain deformation on bicrystals are performed which predict rotations of crystallites during deformation and orientation spread at the final stage of deformation reasonably well as compared with the experimental observation. Similar studies are done for more complex grain topology in 2D columnar multicrystals. Overall, the model predicts heterogeneous evolution of accumulated plastic strain which is found to be consistent with the accumulated dislocation density, shear strain, dislocation density evolution rate and the Taylor factor in the corresponding grains
A phase-field study of crack propagation and branching in functionally graded materials using explicit dynamics
No full textConstitutive behavior of as-cast aluminum alloys AA3104, AA5182 and AA6111 at below solidus temperatures
No full textModeling of Deformation Microstructure - Strain Hardening and Crystallographic Reorientation of Crystallites in a Columnar Polycrystal
No full textIn this work microstructure evolution in a columnar polycrystal of pure aluminum is studied using a microstructure sensitive crystal plasticity finite element model (CPFEM). In the model, based upon the kinematics of crystal deformation and dislocation interaction laws, dislocation generation and annihilation are modeled. Dislocation densities evolve in the form of closed loops and are tracked as state variables, leading to spatially inhomogeneous dislocation densities that show patterning in the dislocation structures. The hardening law is based on the strength of junctions between dislocations on specific slip systems. The CPFEM model is able to show the anisotropic hardening behavior of aluminum single crystals. The measures of accumulated plastic strain in the experiment and the simulation are compared with varying degrees of success.</jats:p
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
USAF Characteristic K Approach: A Robust Tool for Predicting Fatigue Crack Growth under Various Underload Spectra
No full textThis paper forms part of an ongoing investigation into the tools required in linear elastic fracture mechanics (LEFM) for evaluating the durability of components designed for limited life replacement. In this study, we demonstrate that the USAF ‘Characteristic K’ method, when combined with the Hartman–Schijve adaptation of the NASGRO crack growth formula, can predict the impact of underloads on the propagation of small cracks in aluminum alloy AA7050-T7451 with reasonable accuracy. The published da/dN versus ΔK small crack growth curves associated with five specific underload spectra are examined. It is found that, in each case, there is reasonably good agreement between the predicted and the measured curves. To the best of the author’s knowledge, this paper is the first to highlight the ability of the USAF Characteristic K approach, when coupled with the Hartman–Schijve equation, to reasonably accurately predict the growth of small cracks subjected to a range of underload spectra
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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