Rodrigo Teixeira Santos Freire

A Statistical Analysis of Epoxy Polymer Reinforced with Micro Ceramic Particles

A significant amount of research has been focused on the use of ceramic nano/micro particles to enhance the strength and stiffness of polymeric matrices. This work evaluates the effect of Portland cement or crystalline silica (quartz) particle inclusions into epoxy polymer. Two experiments were conducted based on a full factorial design analysis. Experiment I investigated the effect of Portland cement amount (ASTM III), two types of hardeners (HY 951 and 956) and two curing times (7 and 28 days) on the compressive behaviour and density of particulate composites. Experiment II evaluated the incorporation of quartz or cement particles by mixing different mass fraction levels, considering 28 days of curing time and HY 951 hardener. The samples were prepared in a randomized manufacturing process and tested in compression. The mechanical properties were significantly affected by the type of hardener used. Both particles, considered in appropriate level set, can enhance the compressive strength and stiffness of the composites.

EPOXY POLYMERS REINFORCED WITH CARBON POWDER WASTES

This paper investigates the incorporation of recycled carbon micro fibres obtained from the cutting process of laminate composites into epoxy polymers at different mass fractions (0, 2.5, 5, 7.5 and 10%). The elastic modulus and strength under tensile, compressive, flexural and impact loadings were investigated via Analysis of Variance (ANOVA). The tensile (compressive) modulus progressively increases up to 36.6% (28.6%) with the inclusion of carbon powder wastes. The inclusion of 5% mass fraction waste resulted in an increase of 27% (19%) in tensile (compressive) strength. The flexural strength also increased 28.6% when 10wt% carbon powder wastes were added. Carbon powder waste led, however, to a dramatic decrease (approx. 50%) in impact resistance attributed to the increase in stiffness.

COLD-PRESSED HYBRID COMPOSITES REINFORCED WITH COIR FIBRES AND CEMENT PARTICLES: A STATISTICAL APPROACH

The mechanical properties of polyester hybrid composites reinforced with treated and untreated coir fibres and 15 wt.% of cement microparticles at different locations were investigated in this work. A Full Factorial Design (2131) was conducted to identify the effect of the chemical treatment of coir fibres and location of cement inclusions on the tensile (and flexural) strength and modulus. In general, the alkaline treatment led to increased tensile properties and flexural strength compared to untreated fibre composites. The inclusion of cement particles, especially added throughout the whole sample, increased the tensile and flexural strength and tensile modulus of untreated coir fibre composites. A significant increase in flexural modulus was observed only in composites made with treated coir fibres along with the incorporation of cement particles in the whole sample.

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.

Investigations on short coir fibre–reinforced composites via full factorial design

Over the last few decades, a significant amount of research has been focused on the use of natural fibres as reinforcement in polymers, due to their intrinsic properties such as sustainability, easy availability and processing, biodegradability and moderate mechanical strength. Among natural fibres, coir is a low-cost fibre extracted from coconut palm which is extensively produced in Brazil. A full factorial design was carried out to investigate the effects of the manufacturing and composition parameters on the mechanical and physical properties of short coir fibre–reinforced composites (SCoirFRCs). The random short fibres were mixed with epoxy polymer and compacted by uniaxial pressure. The physical and mechanical responses, namely, apparent density, impact resistance, flexural strength and modulus, were investigated under a design of experiment approach. SCoirFRCs fabricated with 35% of fibre volume fraction, 375 g/m2 of fibre grammage and HY956 epoxy hardener type achieved higher flexural modulus and impact resistance, while those consisting of 30 vol% of coir fibres, HY956 type and 300 g/m2 of grammage revealed higher flexural strength. The findings revealed that the mechanical properties of SCoirFRCs are substantially dominated by the properties of the matrix phase and fibre wettability.

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.