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

The abundance and diversity of larval and juvenile fish in a Tropical estuary

The larval and juvenile fish of the Cayenne river estuary (French Guiana, South America) were sampled at two stations from June 1989 until October 1990. A total of 52989 individuals from 59 species, some still incompletely identified, were collected. Three families, #Engraulidae, #Gobiidae and #Scianidae$, accounted for over 97% of the total number of juveniles. The analysis of data over this period showed low diversity, and a difference in diversity between the two sampling locations (H' = 1.24 and 1.68). The results conform to some theoretical models of abundance that suggest a relative equilibrium of juvenile assemblages. In contrast, the seasonal variations in diversity and abundance and the results of a correspondence analysis showed significant differences in species distribution and in their relative abundance at the two sampling locations at certain periods, mainly in the rainy season. Our study indicates that, in spite of an apparent stability, the year to year variation in salinity and freshwater inputs could affect juvenile recruitment of some species and induces modifications in the composition of larval and juvenile estuarine fish assemblages. (Résumé d'auteur

Quantitative sampling of freshwater shrimps : comparison of two electrofishing procedures in a Caribbean stream

Two electrofishing procedures (point abundance sampling and removal sampling) for estimating community structure and the abundance of freshwater shrimps (#Decapoda : #Natantia) were compared at five sites in the Grand-Carbet River, Guadeloupe, French West Indies, on the basis of species richness, species frequency and the length of caught individuals. Sampling was carried out using battery-powered portable electric fishing gear. Both point abundance sampling and removal procedures highlighted a steep longitudinal gradient related to the shrimp fauna and non consistent discrepancy was observed between the two procedures in the different sites. Thus, the choice of one of these two procedures will depend only on the study objective. The benefits and disadvantages of these two electrofishing procedures are concisely discussed. (Résumé d'auteur

Plantas medicinais e aromáticas como defensivos naturais.

201

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

Influência da adubação verde e diferentes adubos orgânicos na produção de fitomassa aérea de atroveran.

Resumo: Este trabalho teve por objetivo verificar o efeito de diferentes adubos orgânicos em associação ou não com adubo verde na produção de folhas de Ocimum selloi Benth., planta nativa do Brasil. O experimento foi conduzido na área experimental da Embrapa Meio Ambiente (CNPMA), localizado no município de Jaguariúna, em duas áreas distintas, sendo uma delas submetidas anteriormente ao plantio e incorporação de adubo verde (Crotalaria juncea). Os tratamentos utilizados foram: T1 - testemunha (solo sem adubação), T2 - cama de aviário (5 kg/m2), T3 - hidrolisado de peixe (produto comercial Fishfértil - 5 mL/m2) e T4 - composto orgânico (4 kg/m2). A colheita foi realizada 180 dias após o plantio, em Janeiro de 2011, sendo colhidas as plantas úteis (quatro plantas por parcela). Avaliou-se o rendimento de fitomassa fresca e seca. O delineamento experimental adotado foi o esquema fatorial 2x4, com quatro repetições (blocos). As médias obtidas foram submetidas à análise de variância seguida de teste de médias (Tukey). Com base nos resultados obtidos, pode-se concluir que a cama de aviário apresentou resultados mais satisfatórios quanto à produção de folhas de Ocimum selloi quando comparados aos demais tratamentos orgânicos, não observando-se incremento nos resultados pela associação com o adubo verde Crotalaria juncea. Abstract: Influence of green manure and different organic manure on production of aereal phytomass of Ocimum selloi. The aim of this work was to avail the effect of different manures in association or nor with green manure on yield of leaves of Ocimum selloi Benth. The assay was accomplished on experimental area of Embrapa Environmental (Jaguariúna district), at two different spaces (with or without green manure Crotalaria juncea). The treatments used were: T1 - witness (no manure), T2 - chicken manure (5 kg/m2), T3 - commercial product Fishfértil - 5 mL/m2) and T4 - composting (4 kg/m2). The cut was realized on 180 days after the planting (January - 2011), and were collected four plants/ plot. The yield of dried and fresh Ocimum selloi phytomass was availed. The experimental design was factorial scheme (2x4), with four repetitions. The treatment with chicken manure showed best results on treatments, but did not was influence by using Crotalaria juncea