Numerical and experimental analyses of biocomposites reinforced with natural fibres

n the last decades the biocomposites have been widely used in the construction, automobile and aerospace industries. Not only the interface transition zone (ITZ) but also the heterogeneity of natural fibres affects the mechanical behaviour of these composites. This work focuses on the numerical and experimental analyses of a polymeric composite fabricated with epoxy resin and unidirectional sisal and banana fibres. A three-dimensional model was set to analyze the composites using the elastic properties of the individual phases. In addition, a two-dimensional model was set taking into account the effective composite properties obtained by micromechanical models. A tensile testing was performed to validate the numerical analyses and evaluating the interface condition of the constitutive phases

Influence of Displacements on Calculus of the Longitudinal Modulus of Elasticity of Pinus Caribaea Structural Round Timber Beams

Round timber shows great potential for use as a building material, having the advantage of not being proc-essed, such as the sawn wood. In Brazil, the normative standards that deal with the existing round timber elements are mainly headed for the pole market, being in force for at least twenty years without technical review, recommending char-acterization of this material by destructive methods, using small specimens with no defects and a cantilever beam structural model[2]. This paper aims to determine the longitudinal modulus of elasticity of Pinus caribaea structural round timber beams using static three-point bending test under physical and geometrical linearity conditions (non-destructive methodol-ogy) which evaluates the effect of the L/200 and L/300 displacement measurements for this purpose[6]. The results achieved by the confidence interval show the statistical equivalence between the values of the modulus of elasticity, being possible in this case, the use of both limits in displacement measurements

Influência da mudança da posição de peças roliças estruturais de Eucalyptus no cálculo do módulo de elasticidade longitudinal

A madeira roliça possui grande emprego nas construções civis, desempenhando a função de vigas, colunas, fundações, postes para distribuição de energia elétrica entre outras, apresentando a vantagem de não ser processada, como é o caso da madeira serrada. O projeto envolvendo elementos roliços requer, além de outras variáveis estruturais, o conhecimento do módulo de elasticidade longitudinal. No Brasil, os documentos normativos que tratam da determinação das propriedades de rigidez e resistência para peças roliças de madeira estão em vigência há mais de vinte anos sem revisão técnica. As peças roliças por mais próximas de uma geometria tronco-cônica podem apresentar eixo com curvatura não nula, conduzindo a valores de elasticidade diferentes para posições distintas do elemento estrutural. Este trabalho tem como objetivo, através do ensaio de flexão a três pontos, avaliar a influência da mudança da posição das peças estruturais roliças de Eucalyptus no cálculo do módulo de elasticidade longitudinal. Os resultados encontrados indicaram a necessidade da realização do ensaio para pelo menos duas posições distintas da peças

Polymer-cementitious composites containing recycled rubber particles

Waste from scrap tires is one of the most environmentally harmful waste since it leads to significant soil and air pollution. This work investigates the effect of recycled rubber particles incorporation into cementitious composites modified with epoxy polymer. A Design of Experiment (DoE) was conducted to identify the effect of epoxy polymer inclusion (35 and 50?wt%), rubber inclusion (10, 15 and 20?wt%) and rubber particle size (coarse and fine particles) factors on the bulk density, mechanical strength and stiffness of the composites. Third-order interaction effects were obtained, except for density which was affected by two second-order interactions. Larger epoxy polymer and rubber amounts decreased the bulk density of the composites. Epoxy polymer contributes to cement hydration, even without water content. Higher incorporation of coarse rubber particles leads to reduced mechanical performance. In general, lower amounts of epoxy polymer and finer rubber aggregates provide superior mechanical strength and modulus. The use of epoxy polymer also enhances the adhesion between cement and rubber aggregates. This rubber polymer-cementitious composite achieved promising results, being a feasible alternative to reuse end-of-life rubber tyres into structural applications

Assessment of compacted-cementitious composites as porous restrictors for aerostatic bearings

Cementitious composites reinforced with silica, silicon carbide or carbon microfibres are designed, manufactured, characterised and tested as porous restrictor for aerostatic bearings. Carbon microfibres are residues obtained from the cutting process of carbon fibre-reinforced polymers. Porosity, permeability, flexural strength and stiffness are quite relevant in the design of aerostatic porous bearings. A 3141 full factorial design is carried out to identify the effects of particle inclusion and water-to-cement ratio(w/c) factors on the physical and mechanical properties of cementitious composites. Higher density material is achieved by adding silicon carbide. Higher porosity is obtained at 0.28 w/c level when silica and silicon carbide are used. Carbon microfibres are not effective under bending loads. Higher compressive strength is reached especially when silica particles are combined with 0.33 or 0.35 w/c. According to the permeability coefficient values the cementitious composites consisted of CMF (0.28 w/c), silica (0.30 w/c) or silicon carbide (0.30 w/c) inclusions are promising as porous restrictor; however, carbon microfibre porous bearings achieved the lowest air gap variation under the tested working conditions

Ageing of autoclaved epoxy/flax composites:effects on water absorption, porosity and flexural behaviour

International audienceThis work investigates the effects of ageing on autoclaved composites made with unidirectional prepreg epoxy and flax tape in environments with 50% and 100% of relative humidity. A Design of Experiment (DoE) has been used first to determine the effect of the ageing time (0,2, 4, 6, 8 and 16 days), type of bending (3-point and 4-point bending) and fibre orientation (longitudinal and transverse) on the water absorption and flexural properties of 50% saturated composites. A second experiment at 100% humidity has been also performed to further characterise the composites and to identify the equivalent ageing time that provides the mechanical behaviour of the 50% humidity samples after sixteen days. The water absorption and apparent porosity levels increase progressively with the ageing time, in particular for the case of transverse laminates; these features compromise the flexural properties of the composites. The laminates subjected to 4-point bending showed increased water absorption levels and improved flexural properties compared to the samples under 3-point bending. The flexural properties of flax composites at 50% humidity after 16 days are equivalent to those shown by composites immersed in water for less than one day