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 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

Uso do SOC na análise de modelos lineares multivariados.

bitstream/item/76201/1/CNPTIA-COM.TEC.-8805-88.pd

Genetic diversity in a germplasm bank of Oenocarpus mapora (Arecaceae).

Oenocarpus mapora is an Amazonian palm species commonly used by native populations for food and in folk medicine. We measured genetic variability, using RAPD markers, of material kept in a germplasm bank composed of accessions sampled from the Brazilian Amazon. These included 74 individuals from 23 accessions sampled from 9 localities in three States of the Brazilian Amazon. Jaccard genetic similarities were calculated based on 137 polymorphic bands, amplified by 15 primers. Dendrograms constructed based on the genetic similarities among individuals and sample localities demonstrated genetic separation of Acre State from the States of Amazonas and Pará. Two models in three hierarchical levels were considered for AMOVA: one considering the grouping of sampling sites in each state, and the other considering sampling sites in each subgroup formed by the dendrograms. The first model showed no significant genetic variation among states. On the other hand, genetic variation among subgroups was significant. In this model, the within-sample-site genetic diversity was 47.15%, which is considered to be low, since O. mapora is allogamous. By means of Bayesian analysis, the sample sites were clustered into five groups, and their distribution was similar to what we found in the dendrograms based on genetic similarity

Repetibilidade e número mínimo de medições para caracteres de cacho de bacabi (Oenocarpus mapora).

A bacabi (Oenocarpus mapora H. Karsten) é uma palmeira perene nativa da Amazônia, que produz cachos com centenas de frutos que apresentam grande potencialidade à agroindústria de polpa, mas tem sido pouco estudada. Os objetivos deste trabalho foram estimar os coeficientes de repetibilidade e determinar a previsibilidade e o número de medições necessárias para caracteres de cacho dessa palmeira. Foram avaliados 27 indivíduos de bacabi pertencentes ao Banco de Germoplasma de Oenocarpus/Jessenia da Embrapa Amazônia Oriental, em Belém-PA. De cada planta, foram colhidos três cachos em maturação completa para a mensuração de seis caracteres: peso total do cacho (PTC) e de frutos por cacho (PFC), número de ráquilas por cacho (NRC), comprimento da ráquis por cacho (CRC), peso de 100 frutos (PCF) e rendimento de frutos por cacho (RFC). As estimativas de repetibilidade foram obtidas pelos métodos estatísticos da análise de variância, componentes principais e análise estrutural. Em todos os caracteres, as estimativas de repetibilidade apresentaram valores muito semelhantes nos três métodos. As estimativas dos coeficientes de repetibilidade e as previsibilidades foram relativamente altas (r > 0,60 e R2 > 81,7%) para os caracteres número de ráquilas e rendimento de frutos por cacho, demonstrando regularidade dos genótipos nas várias medições (cachos), em todos os métodos. Para esses caracteres, o número mínimo de cachos necessários para a avaliação do real valor dos genótipos foi de treze (RFC) e cinco (NRC) cachos com confiabilidade de 95%, tornando-os factíveis no uso de inferências genéticas para as condições do estudo. Os demais caracteres exibiram repetibilidades e coeficientes de determinação de médias a baixas magnitudes, indicando necessidade de maior controle ambiental para suas mensurações

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

Design and Development of an Adhesive Joint Testing Apparatus for Mixed-Mode Evaluation

The present work is dedicated to the development and design of a load jig inspired in theproposed solution by Fernlund and Spelt in order to characterize fracture of bonded joints undermixed-mode I+II loading. The jig allows for easy alteration of the mode-mixity and permits coveringthe full range of mixed-mode I+II combinations. A data reduction scheme based on specimencompliance, beam theory and crack equivalent concept is proposed to overcome several difficultiesinherent to the test analysis. The development was based in a design methodology using numericalvalidation based on experimental data obtained with a Dual Loading Frame from Virginia Tech. Thismethodology is presented and then validated with the experimental application of the jig

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