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.

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Phase Transition and Monopoles Densities in a Nearest Neighbors Two-Dimensional Spin Ice Model

In this work, we show that, due to the alternating orientation of the spins in the ground state of the artificial square spin ice, the influence of a set of spins at a certain distance of a reference spin decreases faster than the expected result for the long range dipolar interaction, justifying the use of the nearest neighbor two dimensional square spin ice model as an effective model. Using an extension of the model presented in ref. [Scientific Reports 5, 15875 (2015)], considering the influence of the eight nearest neighbors of each spin on the lattice, we analyze the thermodynamics of the model and study the monopoles and string densities dependence as a function of the temperature.Comment: 11 pages, 8 figure