1,721,258 research outputs found
Loss of Bifurcation and Multiple Shapes of Thin [0/90] Unsymmetric Composite Plates Subject to Thermal Stress
No full textThe shape of thermally loaded thin [0/90] composite plates predicted by the classical lamination theory is a saddle, with a value of curvature independent of the in-plane dimensions of the structure. Including the effect of geometrical nonlinearities reveals the occurrence of bifurcation of the saddle solution for a critical value of in-plane dimensions (or temperatures), depending on material properties. In the post-bifurcation regime, the saddle shape becomes unstable, while two cylindrical configurations develop on the stable branches. One cylinder can be snapped into another by applying an external force. In the present paper the behaviour of [0/90] plates under thermal stress is simulated with an ABAQUS Finite Element Model and results are compared to a Rayleigh-Ritz model. For square plates, results from the FEM model are in good agreement with the Rayleigh-Ritz model and only small discrepancies are found. The introduction of imperfections, such as asymmetry in thickness, produces a loss of bifurcation which is predicted by the Rayleigh-Ritz and by the ABAQUS model. The range of existence of the cylindrical solutions can also be predicted. For rectangular plates the FEM model predicts a loss of bifurcation which is not found by the Rayleigh-Ritz model. It is found that the length-to-width ratio (aspect ratio) plays a crucial role in the existence and stability of the cylindrical shapes. Numerical simulations are supported by experimental results on thin [0/90] unsymmetric plates with length-to-width ratio equal to 1
Development of Curvature during the Cure of AS4/8552 [0/90] Unsymmetric Composite Plates
No full textThe development of residual stresses in [0/90] unsymmetric flat laminates (AS4/8552 composite system) was monitored by stopping the cure cycle at pre-determined points and evaluating the related level of deformation. Cylindrical shapes of consistent curvature are obtained and the “cured” curvature can be eliminated by re-heating samples up to a certain temperature, designated as the stress free temperature, Tsf. The stress free temperature has also been measured after the interrupted cure cycles: the evolution of the stress free temperature during the cure cycle allowed the vitrification point to be estimated. Both curvature and Tsf increase with increasing cure but level off after the vitrification point, attaining a constant value. The stress free temperature of samples cured beyond vitrification is systematically higher than their cure temperature. It is evident that a certain percentage of non-thermoelastic stress is present in the structure, possibly due to resin chemical shrinkage. The “cured” curvature is mostly driven by the transverse coefficient of thermal expansion, α2. From curvature–temperature profiles, it is found that α2 is almost constant during the cycle, below Tg. Post-cure of laminates that have not been fully cured tends to increase their “residual” curvature, but the effect of the post-cure is relatively small for specimens cured beyond the vitrification poin
Generation of Residual Stresses and Distortion during the Cure of Polymer Matrix Composites
No full textMechanisms Generating Residual Stress and Distortion during Manufacture of Polimer-Matrix Composite Structures
No full textMethods of monitoring fatigue damage under variable amplitude loading in CFRP composites
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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
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