Prediction of the longitudinal tensile strength of polymer matrix composites

A micromechanical model was developed for the prediction of the longitudinal tensile strength of polymer matrix composites. The model considers successive fibre breaks within an infinitely wide Li-long representative volume element (RVE), Li being the so-called ineffective length. An elastic-plastic stress transfer model is used to define Li and fibre strength is described by a Weibull distribution. The composite strength is obtained by solving numerically an equation for the maximum RVE stress. A simplified closed-form solution derived proved to be in very good agreement with the base formulation. Although there is still significant uncertainty over model input data, predictions agreed well with experimental strengths of carbon fibre composites

A new data reduction scheme to obtain the mode II fracture properties of Pinus Pinaster wood

In this work a numerical study of the End Notched Flexure (ENF) specimen was performed in order to obtain the mode II critical strain energy released rate (GIIc) of a Pinus pinaster wood in the RL crack propagation system. The analysis included interface finite elements and a progressive damage model based on indirect use of Fracture Mechanics. The difficulties in monitoring the crack length during an experimental ENF test and the inconvenience of performing separate tests in order to obtain the elastic properties are well known. To avoid these problems, a new data reduction scheme based on the equivalent crack concept was proposed and validated. This new data reduction scheme, the Compliance-Based Beam Method (CBBM), does not require crack measurements during ENF tests and additional tests to obtain elastic properties.FCT - POCTI/EME/45573/200

Finite element analysis of the ECT test on mode III interlaminar fracture of carbon-epoxy composite laminates

In this work a parametric study of the Edge Crack Torsion (ECT) specimen was performed in order to maximize the mode III component (GIII) of the strain energy release rate for carbon-epoxy laminates. A three-dimensional finite element analysis of the ECT test was conducted considering a [90/0/(+45/-45)2/(-45/+45)2/0/90]S lay-up. The main objective was to define an adequate geometry to obtain an almost pure mode III at crack front. The geometrical parameters studied were specimen dimensions, distance between pins and size of the initial crack. The numerical results demonstrated that the ratio between the specimen length and the initial crack length had a significant effect on the strain energy release rate distributions. In almost all of the tested configurations, a mode II component occurred near the edges but it did not interfere significantly with the dominant mode III state.FCT - POCTI/EME/45573/200

Interlaminar fracture under mixed-mode II + III and I + III

This paper presents two new interlaminar fracture test methods for mixed-mode II + III and I + III loadings. Both tests involve biaxial bending of edge pre-delaminated plate specimens with a cross-ply lay-up. The tests allow the coverage of a wide range of mode mix ratios. However, they require finite element analyses for selecting specimen configurations and experimental data reduction. Moreover, a relatively complicated fixture is needed for the mixed-mode I + III test, while geometric non-linearity is significant in the mixed-mode II + III one. Nevertheless, realistic fracture envelopes were obtained for carbon/epoxy laminates.FCT/FEDER EU fund - POCI/EME/57956/200

Mixed mode I + II interlaminar fracture of carbon/epoxy laminates

This paper describes a study of the mixed mode I + II fracture of carbon/epoxy unidirectional and multidirectional specimens with symmetric, quasi-symmetric and markedly asymmetric legs. A beam model was developed for predicting the compliance and total strain energy release rate, G. Model predictions agreed well with three-dimensional finite element results for double cantilever beam, end-notched flexure and mixed mode bending tests. The mode mix was evaluated from a virtual crack closure technique limit analysis, which overcomes ambiguity in delaminations between differently oriented plies. Experimental specimen compliances were in good agreement with beam model predictions. Initiation critical strain energy release rates Gc were plotted against the mode II ratio GII/G. Fracture loci of specimens with symmetric and quasi-symmetric legs had practically identical shapes, showing a linear Gc increase with GII/G > 25 %. Moreover, Gc values of multidirectional specimens with quasi-symmetric and markedly asymmetric legs were very similar.FCT/FEDER EU fund - POCI/EME/57956/200

de Broglie-Proca and Bopp-Podolsky massive photon gases in cosmology

We investigate the influence of massive photons on the evolution of the expanding universe. Two particular models for generalized electrodynamics are considered, namely de Broglie-Proca and Bopp-Podolsky electrodynamics. We obtain the equation of state (EOS) $P=P(\varepsilon)$ for each case using dispersion relations derived from both theories. The EOS are inputted into the Friedmann equations of a homogeneous and isotropic space-time to determine the cosmic scale factor $a(t)$. It is shown that the photon non-null mass does not significantly alter the result $a\propto t^{1/2}$ valid for a massless photon gas; this is true either in de Broglie-Proca's case (where the photon mass $m$ is extremely small) or in Bopp-Podolsky theory (for which $m$ is extremely large).Comment: 8 pages, 2 figures; v2 matches the published versio

Sistematização de dados bibliográficos relacionados aos impactos ambientais da produção agrícola sobre as águas fluviais no corredor de Nacala, Moçambique.

Resumo: As atividades do bolsista foram desenvolvidas no escopo do ProSAVANA-TEC (Projeto de Melhoria da Capacidade de Pesquisa e de Transferência de Tecnologia para o Desenvolvimento da Agricultura no Corredor de Nacala em Moçambique), organizando levantamentos bibliográficos de informações disponíveis na internet sobre a qualidade da água superficial nas bacias hidrográficas localizadas na região do Corredor de Nacala e em Moçambique como um todo. A organização do material bibliográfico foi realizada por meio dos programas computacionais "ZOTERO", "MENDELEY.COM" e "MENDELEY- DESKTOP". Por fim, obteve-se uma coletânea de material bibliográfico, organizado digitalmente, para otimizar as consultas bibliográficas dos membros da equipe do ProSavana, assim como de outros interessados nos temas desta coletânea, assim facilitada pelo uso da ferramenta computacional selecionada. Abstract: The activities of the grantee have been developed within the scope of ProSavana-TEC (Project Capacity Enhancement of Research and Technology Transfer for the Development of Agriculture in the Nacala Corridor in Mozambique), organizing bibliographic information available on the internet about the surface water quality in the river basins located in the region of the Nacala Corridor as well as Mozambique as a whole. The organization of the bibliographic material was performed by the use of the softwares"Zotero", "MENDELEY.COM" and "Mendeley-DESKTOP". Finally, we obtained a collection of bibliographic material, that was digitally organized, to optimize the bibliographic queries of theProSavana team members as well as queries of other people interested in topics of this collection , which access will be facilitated by the use of the selected computational tools

Citros: a podridão floral.

Introducao; Causa; Sintomas; Disseminacao; Controle; Estudo economico.bitstream/item/44463/1/CPATC-DOCUMENTOS-07-CITROS-A-PODRIDAO-FLORAL-FL-13125a.pd