Orientador: Glaucia Amorim Faria / Resumo: Considerando que a intensidade de infestação (I.I.%) é um importante dado sobre o dano causado pela Diatraea saccharalis em cana-de-açúcar e que existem poucos trabalhos na literatura relacionados ao tamanho de ótimo de parcela para este tipo de amostragem, o objetivo deste trabalho foi estimar o tamanho ótimo de parcela em hectares e número de colmos que deverá ser utilizado no processo de amostragem de modo que represente a intensidade de infestação causada pelo ataque da D. saccharalis em cana-de-açúcar. Para os cálculos relativos ao tamanho da área a ser amostrada foram utilizados quatro métodos para o cálculo do tamanho de parcela: método de inspeção visual da curvatura máxima, método da máxima curvatura modificado, modelo linear segmentado com platô e modelo quadrático segmentado com platô. Para os cálculos referentes ao número de entrenós foi utilizado o método da estimativa da suficiência amostral. O método da máxima curvatura modificado foi o que proporcionou melhores resultados. De acordo com os resultados encontrados neste trabalho, podemos concluir que o número mínimo a ser amostrado é o de 36 entrenós por hectare e a área máxima a ser amostrada é a de 27,5 hectares. / Abstract: Infestation intensity (II%) is an important data on the damage caused by Diatraea saccharalis in sugarcane. There are few studies in the literature related to the optimal plot size for this type of sampling. The objective of this work is to estimate the optimal plot size in hectares and number of stems to be used in the sampling process to represent the intensity of infestation caused by D. saccharalis attack on sugarcane. For the calculation of the size of the minimum sampled area, four methods were used: 1. visual inspection method of maximum curvature; 2. modified maximum curvature method; 3. segmented linear model with plateau and; 4. quadratic segmented model with plateau. For the calculations referring to the number of internodes, the method of estimating the sample adequacy was used. The modified maximum curvature method presented the best results. According this study, the minimum number to be sampled is 36 trains per hectare and the maximum area to be sampled is 27.5 hectares. / Mestre

Three testing methods are proposed to characterize properties of fuel cell materials that affect the mechanical durability of proton exchange membranes (PEMs). The first two methods involved measuring the in-plane biaxial strength of PEMs and the biaxial hygrothermal stresses that occur in PEMs during hygrothermal cycles. The third method investigated the nonuniform thickness and compressibility of gas diffusion media which can lead to concentrated compressive stresses in the PEM in the through-plane direction. Fatigue and creep to leak tests using multi-cell pressure-loaded blister fixtures were conducted to obtain the lifetimes of PEMs before reaching a threshold value of gas leakage. These tests are believed to be more relevant than quasi-static uniaxial tensile to rupture tests because of the introduction of biaxial cyclic and sustained loading and the use of gas leakage as the failure criterion. They also have advantages over relative humidity cycling test because of the controllable mechanical loading. Nafion® NRE-211 membrane was tested at three different temperatures and the time-temperature superposition principle was used to construct a stress-lifetime master curve. Tested at 90°C, extruded Ion Power® N111-IP membrane was found to have longer lifetime than Gore™-Select® 57 and Nafion NRE-211 membranes under the same blister pressure profiles. Bimaterial specimens fabricated by bonding a piece of PEM to a substrate material were used to measure the hygral stresses, compressive and tensile, in the PEM during relative humidity cycles. The substrate material and its thickness were carefully chosen so that stresses in the PEM could be obtained directly from the curvature of the bimaterial specimen without knowing the constitutive properties of the PEM. Three commercial PEMs were tested at 80°C by cycling the relative humidity between 90% and 0% and by drying the membrane to 0%RH after submersion in liquid water. Stress histories for all three membranes show strong time-dependencies and Nafion® NRE-211 exhibited the largest tensile stress upon drying. Besides in-plane stresses, hard spots in gas diffusion media (GDM) can locally overcompress PEMs in the out-of-plane direction and cause electrical shorting. In this study, GDM samples sealed with an impermeable Kapton® film on the surface were compressed with uniform air pressure and the nonuniform displacement field was measured with a three-dimensional digital image correlation technique. Hard spots as a result of the nonuniform thickness and compressibility of the GDM were found and their severities as stress risers are evident. Locally, a nominal platen compression (similar to bipolar plate land compression) of 0.68 MPa can lead to compressive stress as large as 2.30 MPa in various hard spots that are in the order of 100s µm to 1 mm in size. / Ph. D.

A nonlinear finite element analysis was performed for an axial loaded reinforced concrete column subjected to biaxial bending taking into account second-order effects. According to Eurocode there are two ways to take second-order effects into consideration: nonlinear FE analysis and hand calculation based on the simplified methods explained in Eurocode 2. Since simulating this kind of structures in ABAQUS is difficult, several simulations were made to find the correct model with satisfying accuracy. The nonlinear analysis focused on material modelling of concrete and its nonlinear behaviour. The simulation took into consideration the inelastic behaviour of concrete along with the confinement effect from transverse reinforcement. The finite element model was verified by comparing the obtained results from FEA to the results from a benchmark experiment. The mean values needed for simulating the FE model was derived from the mean compressive strength of concrete. After verification, another FE model using design parameters was analysed and the results were compared to the results from calculations based on simplified methods according to Eurocode 2 to see how much they agreed with each other. In a parametric study, the effect of eccentricity, compressive and tensile strength of concrete, fracture energy, modulus of elasticity, column cross-section dimension and length, steel yield stress and stirrup spacing were studied. A comparison between outcomes from the simplified methods and ABAQUS, calculated with design parameters showed that the bearing capacity from FE analysis was 21-34 % higher than the one obtained with the simplified methods. It is recommended that in further studies, analyse different slender reinforced concrete column with different L/h with FE-simulation to investigate if FEA always gives a more accurate result. For this case, and probably for columns with complex geometries, a finite element analysis is a better choice. / En icke-linjär finitelementanalys för en armerad betongpelare utsatt för tvåaxlig böjning genomfördes med hänsyn till andra ordningens effekter. Enligt Eurokoder finns det två sätt att iaktta andra ordningens effekter: icke-linjär analys och handberäkning baserad på de förenklade metoderna förklarad i Eurokod 2. Eftersom det är svårt att simulera den här typen av konstruktioner i ABAQUS, så har flera simuleringar utgjorts för att finna ett modell med acceptabelt noggrannhet. Den icke-linjära analysen fokuserade på korrekt materialmodell av betong och dess icke-linjära beteende. Modellen tog hänsyn till betongens oelastiska beteenden och inkluderade fleraxiella effekten. Finitelementmodellen verifierades genom att jämföra de erhållna resultaten från FEA till resultaten från ett försök. Värden som behövdes för att simulera FE-modellen härleddes från betongens medeltryckhållfasthet. Efter att referensmodellen var verifierad, ytterligare en FE-modell, som inkluderade designparametrar, analyserades och resultaten jämfördes med resultaten från beräkningar baserade på förenklade metoderna enligt Eurokod 2 för att se hur mycket de stämde överens med varandra. I en parameterstudie har effekten av excentricitet, tryck- och draghållfasthet av betong, brottenergi, elasticitetsmodul, pelarens tvärsnittsdimension och längd, stålsträckgränsen och centrumavstånd på byglar studerat. En jämförelse mellan resultaten från de förenklade metoderna och ABAQUS, beräknade med designparametrar visade att bärighetförmågan från FE-analys var 21-34% högre än den som erhålls med de förenklade metoderna. Det rekommenderas att i fortsatta studier, analysera flera slanka armerade betongpelare med olika L/h med FE-simulering för att undersöka om FEA alltid ger ett nogrannare resultat. För denna studie, och förmodligen för pelare med komplexa geometrier, är en FE-analys ett bättre val.