Effect of yarn cross-sectional shape on resin flow through inter-yarn gaps in textile reinforcements

Axial flow through gaps between aligned straight yarns with realistic cross-sectional shapes, described by power-ellipses, was analysed numerically. At a given fibre volume fraction, equivalent gap permeabilities have a maximum at minimum size of elongated tapering parts of the gap cross-section and a ratio of gap width to height near 1. When the yarn spacing is given in addition to the fibre volume fraction, calculated maximum and minimum values for the equivalent permeability of inter-yarn gaps, which occur at near-rectangular and lenticular cross-sections, differ by factors of up to 3.3. Novel approximations for the shape factor and the hydraulic diameter in Poiseuille flow were derived as a function of the fibre volume fraction, the yarn cross-sectional aspect ratio and the exponent describing the shape of the power-elliptical yarn cross-section. This allows the equivalent gap permeability to be predicted with good accuracy for any fibre volume fraction and yarn cross-section

Konzepte zur Erfassung der kulturellen Marginalität von Minderheiten

Einleitend werden die Begriffe Minderheit und Marginalität so definiert, daß von allgemeinen Begriffen ausgegangen wird. Zugleich wird vorgeschlagen, Minderheit und Marginalität deutlich zu trennen. Anschließend werden drei Typen von kultureller Marginalität beschrieben: die statische Marginalität; die dynamisch-zentrifugale Marginalität; die dynamisch-zentripetale Marginalität. Im fünften Abschnitt werden dann die Bedingungen und Funktionen der kulturellen Marginalität von Minderheiten skizziert, um abschließend Möglichkeiten der Überwindung zu diskutieren. Dabei werden im Hinblick auf die Kulturelle Integration vier Gesellschaftstypen unterschieden: demokratisch-integriert; oligarchisch-integriert; dissoziativ-desintegriert; förderalistisch-desintegriert. (RW

Multiscale modeling of combined deterministic and stochastic fabric non-uniformity for realistic resin injection simulation

The local fiber arrangement in a bi-directional fabric formed to a complex shape was modeled considering the stochastic arrangement of filaments within yarns, which determines axial and transverse yarn permeabilities, and the stochastic arrangement of yarns in a fabric, which determines the dimensions of interyarn gap spaces locally. To mimic the uncertainty in fabric forming, drape simulation was randomized in terms of start point and yarn start orientations. From yarn permeabilities and simulated local yarn spacing distributions, local fiber volume fractions and fabric permeabilities were approximated. This allowed resin injection into a deformed fabric to be simulated for different drape scenarios with different probabilities and different degrees of fabric randomness. The results indicate that variability in fabric properties and the forming process affects flow front shapes and times for complete impregnation of the reinforcement

Advanced geometry modelling of 3D woven reinforcements in polymer composites: processing and performance analysis

Numerical methods have become increasingly effective tools for analysis and design of composite materials. This study investigates how the inclusion of geometrical variations in modelling 3D woven fabrics affects the accuracy of numerical predictions. Based on micro-Computed Tomography data of 3D orthogonal woven composites, unit cell models were generated in TexGen at different levels of geometrical detail. Two types of analysis were implemented: (a) computational fluid dynamics (CFD) simulates resin flow during fabric impregnation in composites processing to predict permeability; (b) implicit static finite element analysis predicts in-plane tensile strength of the composites. By comparison with experimental data, the numerical predictions indicate that local geometrical variations, particularly in yarn cross-section, surface crimp and binder yarn path, have significant influence on both permeability and material strength. It is important to model the precise geometry in certain locations while the overall geometry can be simplified in order to maintain the practicality of model generation

Quantification of micro-scale variability in fibre bundles

Local variations in the random filament arrangement in carbon fibre bundles were determined by optical microscopy and automated image analysis. Successive steps of abrading, polishing and acquiring micro¬graphs of the sample surface made it feasible to analyse the micro-structure over a series of cross-sections along the fibre bundle path. Random and systematic changes in local filament arrangements were determined. Systematic changes were related to the interaction of a fibre bundle with an intersect¬ing binder thread leading to a local increase of the fibre volume fraction at the interface. Random clus¬tering of filaments in areas of high or low fibre volume fractions within the fibre bundles were found to be unaffected by the relative position of the bundle

Geometrical modelling of 3D woven reinforcements for polymer composites: prediction of fabric permeability and composite mechanical properties

For a 3D orthogonal carbon fibre weave, geometrical parameters characterising the unit cell were quantified using micro-Computed Tomography and image analysis. Novel procedures for generation of unit cell models, reflecting systematic local variations in yarn paths and yarn cross-sections, and discretisation into voxels for numerical analysis were implemented in TexGen. Resin flow during reinforcement impregnation was simulated using Computational Fluid Dynamics to predict the in-plane permeability. With increasing degree of local refinement of the geometrical models, agreement of the predicted permeabilities with experimental data improved significantly. A significant effect of the binder configuration at the fabric surfaces on the permeability was observed. In-plane tensile properties of composites predicted using mechanical finite element analysis showed good quantitative agreement with experimental results. Accurate modelling of the fabric surface layers predicted a reduction of the composite strength, particularly in the direction of yarns with crimp caused by compression at binder cross-over points

Modelling the permeability of random discontinuous carbon fibre preforms

A force-directed algorithm was developed to create representative geometrical models of fibre distributions in directed carbon fibre preforms. Local permeability values were calculated for the preform models depending on the local fibre orientation, distribution and volume fraction. The effect of binder content was incorporated by adjusting the principal permeability values of the meso-scale discontinuous fibre bundles, using corresponding experimental data obtained for unidirectional non-crimp fabrics. The model provides an upper boundary for the permeability of directed carbon fibre preform architectures, where predictions are within one standard deviation of the experimental mean for all architectures studied

O ensino da escrita visto pela ótica enunciativa: é possível ensinar uma ausência?

This text discusses the specificities of written enunciation that derive from our reading and understanding of Émile Benveniste’s work having in mind the context of Portuguese teaching. In order to do so, the first part of this text approaches the enunciative perspective of writing based on Dernières Leçons (2012), a book that gathers Benveniste’s notes to the classes he would teach in Collège de France. In the secondpart, the notions discussed previously are related to what is proposed by Dufour (2000) in relation to the trinity that constitutes language in orderto reflect on the relationship they establish with the teaching of writing. The hypothesis defended here is that reading in class texts produced by students is a midway path to the understanding of the specific properties of the aspects of person, time and space in written enunciation.Key words: writing, enunciative studies, teaching.Este texto discute a especificidade da enunciação escrita, derivada de nossa leitura e interpretação da obra de Émile Benveniste, tendo por escopo o ensino de língua portuguesa. Para tanto, aborda, em um primeiro momento, a perspectiva enunciativa da escrita com base em Dernières leçons (2012), livro que reúne anotações de Benveniste para as aulas que ministraria no Collége de France. Em um segundo momento, articula as noções discutidas com a proposta de Dufour (2000) sobre a trindade constitutiva da língua para, por fim, pensar a relação que estabelecem com o ensino de produção textual. A hipótese defendida é a de que a leitura, em sala de aula, dos textos produzidos por discentes se configura como um caminho intermediário para o entendimento das propriedades específicas dos aspectos de pessoa, tempo e espaço da enunciação escrita.Palavras-chave: escrita, enunciação, ensino