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

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

Procedimento para análise lignocelulósica.

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Procedimentos para análise lignocelulósica.

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MODE I FRACTURE CHARACTERIZATION: WOOD SEN-TPB

The single edge notched beam loaded in three-point-bending (SEN-TPB) was used in this study to induce mode I fracture in wood (Picea abeas L.). Numerical analyses of stress profiles along the specimen length revealed a stress relief region as crack grows in size. Based on this data, beam theory and crack equivalent concepts were employed to develop an expedite data reduction scheme to estimate the Resistance-curve, taking advantage of a simplification performed on the revealed stress relief region. Besides allowing the evaluation of wood fracture toughness without crack length monitoring during loading, the developed procedure provides a user-friendly method when compared to other sophisticated procedures. Experiments involving the SEN-TPB were performed to evaluate fracture toughness in wood

Fracture characterization of wood under Mode I loading using the SEN-TPB Test

Mode I fracture characterization was induced in wood (Picea abies L.) using the single-edge-notched beamloaded in three-point-bending. A developed data reduction scheme based on the equivalent linear elasticfracture mechanics was used to evaluate the Resistance-curve instead of classical methods. The method isfound on beam theory and crack equivalent concept taking into account the triangular stress relief regionthat develops in the crack vicinity. The method dispenses crack length monitoring in the course of theloading process, providing a complete Resistance-curve which is essential for a clear identification of thefracture energy. The validation of the procedure has been performed numerically using a bilinear cohesivedamage model, thus allowing the simulation of both damage initiation and growth. The numerical modelalso provided the critical specimen dimensions that permit the attainment of accurate evaluation of thefracture toughness in wood

Rendimento do óleo essencial de Ocimum selloi benth. submetido a diferentes adubos orgânicos em associação ou não à adubação verde.

Este trabalho teve por objetivo verificar o efeito de diferentes adubos orgânicos em associação ou não com adubo verde no rendimento de óleo essencial 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). Os óleos essenciais das folhas foram extraídos por hidrodestilação em aparelho tipo Clevenger modificado. Avaliou-se o rendimento de óleo essencial sobre o rendimento de fitomassa seca. O elineamento experimental adotado foi o esquema fatorial 2x4, com quatro repetições (DBC). As médias obtidas foram submetidas à análise de variância seguida de teste de médias (Tukey). Não foram observadas diferenças significativas no rendimento do óleo essencial de folhas de O. selloi submetidas ou não à adubação verde, em associação aos diferentes tipos de adubo orgânico quando os mesmos foram comparados à testemunha. Com base nos resultados obtidos, pode-se concluir que, nas condições ensaiadas, as adubações verde e orgânica não influenciaram no rendimento do óleo essencial de Ocimum selloi

Wood beam repairing with carbon-epoxy composites

Wood damaged beams submitted to bending loads were repaired using carbon-epoxy patches. The effect of patch thickness as well as adhesive filleting were both studied experimentally and numerically. The objective was to verify the influence of these aspects on the strength and failure of the repaired structural components. Cohesive zone modeling considering mixedmode (I+II) loading was carried out to simulate the observed experimental behavior. It was concluded that repair can successful recover the original bearing capacity, although patch thickness and adhesive filleting did not reveal a significant gain on strength