1,720,977 research outputs found
Quasi-static and low-velocity impact biaxial flexural fracture of aluminosilicate glass — An experimental and numerical study
No full textIn this study, the quasi-static biaxial fracture behavior of aluminosilicate glass is investigated via Ball-On-Ring (BOR) and Ring-On-Ring (ROR) tests aided by a three-dimensional Digital Image Correlation (3D-DIC) technique. In-plane strain field and out of plane deformation distribution during the loading process can be obtained by this test system, overcoming the problem of inaccurate displacement data provided by the loading machine. During the loading process, a uniform strain distribution field is formed below the load ring of the ROR specimen while a gradient strain distribution is built for the BOR specimens. For dynamic loading conditions, low-velocity impact BOR tests are conducted at velocities of 2 m/s and 4 m/s showing a dynamic strengthening effect and high-speed cameras provide detailed fracture and failure sequences of the glass plates. Finite Element Method (FEM) simulations with the JH-2 material model are carried out showing good consistency with experimental results for the quasi-static loading conditions. FEM coupled to Smooth Particle Hydrodynamics (FEM-SPH) technique is utilized for dynamic simulations to solve the element distortion and non-physical problems. The influence of the tensile strain rate effect on low-velocity impact behavior of aluminosilicate glass is analyzed in detail. The original JH-2 model does not provide a reasonable prediction of the dynamic tensile response of brittle materials and the model requires further modifications to describe the dynamic tensile fracture behavior. By introducing rate-dependence maximum hydrostatic tensile strength σt,max to the updated model, better predictions for the contact force and projectile residual velocity histories of low-velocity impact tests can be provided
Investigation into different numerical methods in predicting the response of aluminosilicate glass under quasi-static and impact loading conditions
Get PDFThis paper presents a comparison of three numerical approaches for modeling brittle materials in both quasi-static and dynamic loading conditions. These methods include the Finite Element Method coupled to Smooth Particle Hydrodynamics (FEM-SPH), Discrete Element Method (DEM) and the elastic bond-based Peridynamics (PD). Numerical models for each method were built in the commercial software LS-DYNA. The parameters, associated to the mechanical behavior of aluminosilicate glass, were calibrated for each numerical model by means of experimental tests on material coupons. The experimental results from quasi-static three-point bending tests and ballistic impact tests were utilized for numerical models’ assessment. All methods provide comparable results under quasi-static flexural loading condition and for ballistic impact cases, the numerical results show the particular capability of each approach to capture the projectile residual velocity and the damage morphology of aluminosilicate glass tiles. However, considering all the loading conditions the FEM-SPH method replicates the mechanical response of aluminosilicate glass best
Effect of chemical strengthening residual stress on the flexural performance and fracture behavior of aluminosilicate glass
No full textIn this hybrid experimental, theoretical and numerical study the effect of chemical strengthening residual stress on the flexural strength and fracture behavior of aluminosilicate glass was investigated. Three-point bending tests were conducted on annealed and chemically strengthened glass specimens to obtain the flexural strength of both specimens and with the aid of high-speed cameras, the fracture and failure modes of these two kinds of specimens were analyzed and compared. A theoretical analysis based on the elastic fracture mechanics theory was employed to explain the strengthening effect of chemically strengthened glass. It is shown that the mechanical strength of chemically strengthened glass is highly related to the relation of the chemically strengthened layer depth and the surface flaw depth. Furthermore, this study provides an effective numerical approach to replicate the mechanical strength and failure modes for both annealed and chemically strengthened glass. The proposed finite element numerical method includes modeling techniques which consider the presence of pre-stress, random distributed surface flaws and the fracture onset in glass specimens. The residual stress pattern was defined exploiting the dynamic relaxation process for temperature-induced expansion of the elements before the loading process. Discrete distributed surface flaws were inserted in the model, the brittle fracture of glass was represented by the smeared crack method and the numerical results were compared to experimental data. It's illustrated that the proposed method can be used to represent both the discrete fracture behavior and the chemically-strengthening effect of silicate glass
Inhomogeneous FEM model for fracture simulation of aluminosilicate glass
Get PDFAluminosilicate glass possesses excellent mechanical and functional properties. It combines relatively low density, high hardness and strength in compression. However, the very low tensile strength and inherent brittleness are main concerns to its application. Due to the presence of microheterogeneity and randomly distributed surface flaws, the mechanical strength and failure mechanisms of silicate glasses varies considerably, even for the same glass products. In the present work, inhomogeneous FEM models were proposed and utilized to simulate the discrete failure strength and replicate the multiple crack patterns of aluminosilicate glass. Special attention was paid to the quasi-static three-point bending and ballistic impact loading conditions in this paper. The results from experiments and simulations were compared in detail and show that both the failure strength and fracture modes can be reproduced properly via the proposed numerical models both for three-point bending tests and for ballistic impact conditions. In the latter both the predicted residual velocity of projectile and the fragmentation behavior of glass tiles from the inhomogeneous FEM method show better matching than the homogeneous models
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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