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

Competing impurities and reentrant magnetism in La(2-x)Sr(x)Cu(1-z)Zn(z)O(4) revisited. The role of the Dzyaloshinskii-Moriya and XY anisotropies

We study the order-from-disorder transition and reentrant magnetism in La(2-x)Sr(x)Cu(1-z)Zn(z)O(4) within the framework of a long-wavelength nonlinear sigma model that properly incorporates the Dzyaloshinskii-Moriya and XY anisotropies. Doping with nonmagnetic impurities, such as Zn, is considered according to classical percolation theory, whereas the effect of Sr, which introduces charge carriers into the CuO(2) planes, is described as a dipolar frustration of the antiferromagnetic order. We calculate several magnetic, thermodynamic, and spectral properties of the system, such as the antiferromagnetic order parameter, the Neel temperature, the spin-stiffness, and the anisotropy gaps, as well as their evolution with both Zn and Sr doping. We explain the nonmonotonic and reentrant behavior experimentally observed for T_N by Hucker et al. in Phys. Rev. B 59, R725 (1999), as resulting from the reduction, due to the nonmagnetic impurities, of the dipolar frustration induced by the charge carriers (order-from-disorder). Furthermore, we find a similar nonmonotonic and reentrant behavior for all the other observables studied. Most remarkably, our results show that while for x=2% and z=0 the Dzyaloshinskii-Moriya gap \Delta_{DM}=0, for z=15% it is approximately \Delta_{DM} = 7.5 cm^(-1). The later is larger than the lowest low-frequency cutoff for Raman spectroscopy (~ 5 cm^(-1)), and could thus be observed in one-magnon Raman scattering.Comment: 13 pages, 10 figure

Low-field microwave absorption and magnetoresistance in iron nanostructures grown by electrodeposition on n-type lightly-doped silicon substrates

In this study we investigate magnetic properties, surface morphology and crystal structure in iron nanoclusters electrodeposited on lightly-doped (100) n-type silicon substrates. Our goal is to investigate the spin injection and detection in the Fe/Si lateral structures. The samples obtained under electric percolation were characterized by magnetoresistive and magnetic resonance measurements with cycling the sweeping applied field in order to understand the spin dynamics in the as-produced samples. The observed hysteresis in the magnetic resonance spectra, plus the presence of a broad peak in the non-saturated regime confirming the low field microwave absorption (LFMA), were correlated to the peaks and slopes found in the magnetoresistance curves. The results suggest long range spin injection and detection in low resistive silicon and the magnetic resonance technique is herein introduced as a promising tool for analysis of electric contactless magnetoresistive samples.Comment: 12 pages, 5 figure

A new methodology for the characterization of mode II fracture of pinus pinaster wood

In this study, the End Notched Flexure (ENF) fracture test was used to obtain the mode II Rcurve of the Pinus pinaster wood in the RL crack propagation system. The test method was numerically and experimentally analyzed. In the numerical study, three (3D) and twodimensional (2D) finite element analyses were conducted to determine the mode II critical strain energy release rate (GIIc) and the respective R-curve. Firstly, the 3D analysis was performed in order to obtain the strain energy release rates distributions at the crack tip, and consequently, to identify the presence of spurious fracture modes that could affect the measured GIIc. The P-δ-a values determined from the 3D model were compared with the same values obtained from the 2D model. The main objective was to validate the 2D model, which is computationally less expensive. On the other hand, measurement of the crack length in the ENF test is quite difficult in wood because crack tends to close during propagation. To avoid this experimental problem a Compliance-Based Beam Method (CBBM), based on equivalent crack approach, is proposed. Moreover, this method does not require additional experimental tests to obtain the elastic properties. Experimental tests were also executed in order to verify the numerical results. The aim is to introduce the CBBM as a standard data reduction scheme in order to measure the GIIc value

Non-Newtonian fluid flow through three-dimensional disordered porous media

We investigate the flow of various non-Newtonian fluids through three-dimensional disordered porous media by direct numerical simulation of momentum transport and continuity equations. Remarkably, our results for power-law (PL) fluids indicate that the flow, when quantified in terms of a properly modified permeability-like index and Reynolds number, can be successfully described by a single (universal) curve over a broad range of Reynolds conditions and power-law exponents. We also study the flow behavior of Bingham fluids described in terms of the Herschel-Bulkley model. In this case, our simulations reveal that the interplay of ({\it i}) the disordered geometry of the pore space, ({\it ii}) the fluid rheological properties, and ({\it iii}) the inertial effects on the flow is responsible for a substantial enhancement of the macroscopic hydraulic conductance of the system at intermediate Reynolds conditions. This anomalous condition of ``enhanced transport'' represents a novel feature for flow in porous materials.Comment: 5 pages, 5 figures. This article appears also in Physical Review Letters 103 194502 (2009

Balanço de energia durante o crescimento inicial de um cultivo irrigado de cana-de-açúcar no Semiárido.

Objetivou-se analisar o balanço de energia em um cultivo irrigado de cana-de-açúcar durante a fase inicial de crescimento. O experimento foi conduzido no município de Juazeiro, BA, Semiárido brasileiro. Foram obtidas medidas micrometeorológicas e aplicado o método do balanço de energia com base na razão de Bowen. Quatro dias após o último evento de irrigação (4, 12, 17 e 21 dias), foram escolhidos para analisar os padrões horários dos componentes do balanço de radiação e de energia. Com os resultados, verificou-se que a redução da disponibilidade de água no solo, resultante dos dias após o último evento de irrigação, e o déficit de pressão de vapor d?água, devido as condições meteorológicas locais, modificam o balanço de energia da cana-de-açúcar irrigada no semiárido brasileir

Controle da evapotranspiração da cana-de-açúcar irrigada no Semiárido brasileiro.

O objetivo deste trabalho é analisar variação sazonal do controle da cana-de-açúcar ao processo de evapotranspiração sob as condições climáticas do Semiárido brasileiro. O experimento foi realizado no município de Juazeiro, Bahia. A evapotranspiração da cultura foi quantificada por meio do método do balanço de energia com base na razão de Bowen. Para analisar o controle da cana-de-açúcar ao processo de evapotranspiração foi utilizado o fator de desacoplamento. Para o ciclo, os valores de Ω foram, em média, iguais a 0,68, demonstrando um desacoplamento moderado. Observou-se pouca alteração no valor médio final, sendo igual a 0,69, quando se retirou o efeito do tombamento da cultura. Estes resultados indicam que, o sistema clima induziu ao maior controle da cana-de-açúcar no processo de troca de vapor d?água com a atmosfera