1,720,980 research outputs found
Root rotations and root displacements in bimaterial layers and thin films
No full textAn elasticity technique to derive compliance coefficients describing crack tip root rotations and displacements in end-loaded, bimaterial, isotropic and orthotropic layers has been recently proposed in Ustinov and Massabò (Int. J. Solids Struct., 2022). The coefficients define the boundary conditions which account for the near tip deformations when using beam (plate) theories to describe the detached layers. The coefficients, collected into 6x6 compliance matrices, relate crack tip kinematic variables describing relative displacements and rotations between the detached and intact parts, and six elementary crack tip loadings, which combine to describe general end loadings. The steps necessary to use the coefficients in the solution of statically determined problems, when the forces acting on the layer are known through equilibrium, is presented here with reference to classical fracture mechanics specimen
The effects of shear on the fracture parameters of face/core debonds in sandwich beams
No full textThe effects of shear on energy release rate and mode mixity in a debonded sandwich beam are investigated through a semi-analytic approach which uses exact two-dimensional elasticity and structural theories. The expressions for the shear components of the energy release rate and mode mixity will be combined with earlier results for three-layers subjected to bending-moment and axial forces to obtain solutions for general loading conditions
Fracture mechanics solutions and operative formulae for isotropic bi-material layers with large elastic mismatch
No full textFollowing previous works in the literature on the fracture of layered composites, semi-analytical expressions for energy release rate and mode-mixity phase angle in isotropic bi-material layers subjected to arbitrary end loadings are extended to materials characterized by a large elastic mismatch described by Dundurs’ parameters |α| ≤ 0.99 and |β| ≤ 0.4. The solutions depend on elementary bending, axial and shear loads acting at the crack tip cross section, elastic constants and relative thickness of the layers, and dimensionless coefficients describing the fracture parameters of single elementary loads. The coefficients associated to the shear forces are presented in the literature only for combinations with β = 0; here they are determined numerically for different values β not =0 to describe materials used in current applications. Simplified fitting formulae having general validity, as polynomials, which highlight the dependence on Dundurs’ parameters and are practical to support laboratory tests, are derived for layers with mid-thickness delaminations and thin layers on semi-infinite substrates. Applications to some mixed mode fracture specimens highlight the effects of β not = 0 on the fracture parameters and the limitations of estimates based on the commonly adopted assumption β = 0. As expected, the results for mid-thickness delaminations show that such effects are stronger on mode-mixity phase angle than on energy release rate
An improved analysis of a STB specimen for fracture characterization of laminates and foam-cored sandwich composites under mode III loads
No full textThis work presents the development of an improved data reduction method for the shear-torsion-bending (STB) test designed for monolithic laminates. The analytical derivation extends the applicability of the STB rig to composite sandwich specimens subjected to an out-of-plane shear loading. The data reduction method consists of an analytical model that expresses the global energy release rate in terms of applied loads, specimen geometry and material properties. The mathematical derivation of the energy release rate relies on first order shear deformation theory, Vlasov theory for non-uniform torsion of beams and near tip effects are also taken into consideration by the analytical model. Face sheets and core are modelled as homogeneous, linear elastic and orthotropic materials. The analytical expression is verified using the energy release rate extracted from a high-fidelity 3D FE based fracture mechanics model of the specimen. A compliance based method is used to generate global predictions, while local predictions are extracted using a displacement-based mode separation method. Local predictions are used to discuss accuracy and limitations of the approximate analytical model.</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
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