Tearing of free-standing graphene

We examine the fracture mechanics of tearing graphene. We present a molecular dynamics simulation of the propagation of cracks in clamped, free-standing graphene as a function of the out-of-plane force. The geometry is motivated by experimental configurations that expose graphene sheets to out-of-plane forces, such as back-gate voltage. We establish the geometry and basic energetics of failure and obtain approximate analytical expressions for critical crack lengths and forces. We also propose a method to obtain graphene's toughness. We observe that the cracks' path and the edge structure produced are dependent on the initial crack length. This work may help avoid the tearing of graphene sheets and aid the production of samples with specific edge structures.CAPESNational Science Foundation DMR 1002428Physic

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

Aspectos climáticos da captação de água de chuva no Estado de Pernambuco.

Captação de água de chuva tem sido uma técnica popular em muitas partes do mundo, especialmente em regiões áridas e semi-áridas (que são aproximadamente 30% da superfície da terra). A captação de água de chuva é especialmente usada em áreas semi-áridas, onde a precipitação ocorre somente durante em alguns meses e em diferentes locais, como o semi-árido do Estado de Pernambuco, Brasil. O governo brasileiro está construindo 1 milão de cisternas para fornecer água de beber para 1 milhão de famílias do Semi-Árido brasileiro. Em Pernambuco serão construidas 22% do total de cisternas. A variabilidade da precipitação no Estado é decisiva para determinar a área de captação ideal para o abastecimento das cisternas nas diferentes regiões do estado. Esse estudo usou dados de precipitação anual para o estado de Pernambuco. Foi estimada a ocorrência de probabilidade de chuva usando a Distribuição Normal de Probabilidade dos quantis. Os resultados mostraram que em anos normais, nas áreas mais secas do estado, a precipitação média foi 400 mm. Este valor deve ser considerado para escolha do tamanho da cisterna e da área de captação para diferentes regiões de estado. A cisterna construída pelo governo tem capacidade para armazenar 16m³, para isso, é necessária uma área de captação de 60m² para garantir a eficiência e o abastecimento de água nas regiões mais secas de Pernambuco, com garantia em 80% dos anos

Detecting hydroclimatic changes using spatio-temporal analysis in the sub-medium São Francisco-PE basin, Brazil.

The São Francisco river basin is the third largest drainage basin of Brazil and the only one entirely within its frontiers

Topological insulator particles as optically induced oscillators: towards dynamical force measurements and optical rheology

We report the first experimental study upon the optical trapping and manipulation of topological insulator (TI) particles. By virtue of the unique TI properties, which have a conducting surface and an insulating bulk, the particles present a peculiar behaviour in the presence of a single laser beam optical tweezers: they oscillate in a plane perpendicular to the direction of the laser propagation, as a result of the competition between radiation pressure and gradient forces. In other words, TI particles behave as optically induced oscillators, allowing dynamical measurements with unprecedented simplicity and purely optical control. Actually, optical rheology of soft matter interfaces and biological membranes, as well as dynamical force measurements in macromolecules and biopolymers, may be quoted as feasible possibilities for the near future.Comment: 6 pages, 5 figures. Correspondence and requests for Supplementary Material should be addressed to [email protected]