Luciano Machado Gomes Vieira

Geometric effects of sustainable auxetic structures integrating the particle swarm optimization and finite element method

The development of new materials based on industrial wastes has been the focus of much research for a sustainable world. The growing demand for tyres has been every year exacerbating environmental problems due to indiscriminate disposal in the nature, making a potentially harmful waste to public health. The incorporation of rubber particles from scrap tyres into polymeric composites has achieved high toughness and moderate mechanical properties. This work investigates the geometric effects (thickness, width and internal cell angle) of auxetic structures made of recycled rubber composites based on experimental and numerical data. The response surface models integrated with the swarm intelligence and finite element analysis were proposed in order to obtain a range of solutions that provides useful information to the user during the selection of geometric parameters for reentrant cells. The results revealed the cell thickness ranges from 39-40 mm and 5.98-6 mm, and the cell angle range from -0.01 to -0.06o maximize the ultimate strength. The same parameters were able to optimize the modulus of elasticity of rubber auxetic structures, excepting for the angle factor which must be set between -30o and 27.7o. The optimal Poissons ratio was found when the cell angle ranged from -30o to -28.5o, cell width ranged from 5-5.6 mm and 2 mm in thickness.

EVALUATION OF MECHANICAL PROPERTIES OF LOW COST FMLs FABRICATED WITH COIR FIBRE-REINFORCED COMPOSITES

Fibre Metal Laminates (FMLs) are composite structures that comprise alternating metal layers and fibre-reinforced polymer composites (FRCs) combining their distinct physical-mechanical properties. Traditional FMLs are based on synthetic (carbon, glass and aramid) fibres. However, alternative FMLs based on natural fibre-reinforced composites have been developed to take advantage of available natural resources. A new ecofriendly FML sandwich based on random coir fibre-reinforced epoxy and polyester resin was developed in this research. Mechanical tests revealed that the tensile properties were fully dominated by the aluminium sheets, which were treated with alkali for degreasing and wash primer in order to enhance interfacial bonding. Such treatment efficiently reduced delamination and increased the flexural modulus (~67%). A similar increase in flexural (~22.94%) and impact strength (~99.16%) as well as in skin stress (~20.89%) of the new FMLs proposed was observed owing to the flexural and impact strength of composite cores and better core-layer stress transfer upon the aluminium treatment. keywords: FML-sandwich composites, epoxy, polyester, coir fibre, mechanical properties.

Impact Behaviour of Hybrid Carbon Fibre Composites Reinforced with Silica Micro- and Functionalized Nanoparticles

This work investigates the effect of silica nanoparticles functionalized with poly-diallyldimethylammonium chloride (PDDA) and silica microparticle inclusions (1.0 wt% and 3.5 wt%) on the impact resistance of hybrid carbon fibre reinforced composite laminates (HCFRCs) and tensile modulus of particle reinforced polymers (PRPs) via Full-Factorial Design of Experiments. The data were analysed with Analysis of Variance (ANOVA). The inclusion of particles led to reduced impact absorption of HCFRCs, except for composites with 1.0 wt% of silica in microscale, which provides an increase of 11.75% in the impact resistance. Microstructural analysis of fractured impact samples revealed pull-out as the predominant fracture mode in 1.0 wt% silica microparticle composites. Such mechanism leads to impact energy dissipation which may explain the increased impact resistance of these samples.