Leandro José da Silva

Statistical design of polymeric composites reinforced with banana fibres and silica microparticles

The study describes a design of experiment analysis performed on hybrid polymeric composites reinforced with unidirectional banana fibres and silica microparticles. Maleic anhydride was also evaluated as a chemical additive to improve the adhesion between phases. A full factorial design (2231) and the analyses of variance were performed to identify the significance of the microstructure constituents against different mechanical and physical properties in a total population of 120 biocomposites samples. The microstructure parameters considered were fibre volume fraction (30% and 50%), silica addition (0%, 20 wt% and 33 wt%) and maleic anhydride addition (0% and 2 wt%). The mechanical and physical properties of the composite considered as factorial and analyses of variance responses were the apparent density, apparent porosity, water absorption, modulus of elasticity and mechanical strength under tensile and flexural loading. The design of experiment analysis has shown that the volume fraction of the fibres significantly affects all responses, with the composite made from 30% of banana fibres exhibiting superior mechanical strength and modulus of elasticity. While the addition of silica has featured a statistically noticeable contribution to the porosity and the water absorption, the presence of the particles did not provide any significant enhancement to the composites mechanical strength. Maleic anhydride showed a significant contribution to the apparent density, water absorption and flexural modulus, not improving the adhesion between phases, with a consequent decrease of the Young’s modulus and increase of the water absorption within the composites.

Micromechanical analysis of hybrid composites reinforced with unidirectional natural fibres, silica microparticles and maleic anhydride

The work describes the analytical and experimental characterisation of a class of polymeric composites made from epoxy matrix reinforced with unidirectional natural sisal and banana fibres with silica microparticles and maleic anhydride fabricated by manual moulding. The analytical models, ROM rule of mixtures and Halpin-Tsai approach, have been used in conjunction with a Design of Experiments (DOE) analysis from tensile tests carried out on 24 different composites architectures. The following experimental factors were analyzed in this work: type of fibres (sisal and banana fibres), volume fraction of fibres (30% and 50%) and modified matrix phase by adding silica microparticles (0%wt, 20%wt and 33%wt) and maleic anhydride (0%wt and 2%wt). The ROM approach has shown a general good agreement with the experimental data for composites manufactured with 30%vol of natural fibres, which can be attributed to the strong adhesion found between the phases. On the opposite, the semi empirical model proposed by Halpin and Tsai has shown greater fidelity with composites manufactured from 50%vol of natural fibres, which exhibit a weak interfacial bonding. The addition of microsilica and maleic anhydride in the system did not enhance the adhesion between the phases as expected.

The effect of silica microparticles and maleic anhydride on the physic-mechanical properties of epoxy matrix phase

Abstract Thermoset polymers, especially epoxy resin, have been applied in several industrial applications in which high stiffness and adhesive strength are demanded. On the other hand, epoxy resin is rather brittle and has poor fracture toughness. For this reason, the addition of fibres/particles into thermoset polymer can be used to enhance strength and toughness for several structural applications. This work investigated the addition of silica microparticles and maleic anhydride (as a coupling agent between the phases) into epoxy resin, which will be used as the matrix phase of hybrid biocomposites. A full factorial design was conducted to evaluate the effect of silica microparticles and chemical additive into the epoxy matrix under compressive loadings. Apparent density was also evaluated. Experimental factors such as weight fraction of silica microparticles (0, 20, and 33.3 wt%) and weight fraction of maleic anhydride (0 and 2 wt%) were investigated. The statistical analysis revealed that the main factors ‘chemical additive’ and ‘silica addition’ significantly affected the compressive modulus of the composites.

Carbon nanotubes and superplasticizer reinforcing cementitious composite for aerostatic porous bearing

Cementitious composites are low cost and readily manufactured materials which can be used for specialist applications such as the production of aerostatic porous bearings. A design of experiment was used to identify the effects of superplasticizer additions and carbon nanotube inclusions on the physical and mechanical properties of cementitious composites which can be applied as porous restrictor in aerostatic thrust bearings. The presence of carbon nanotubes was able to increase the bulk density, the compressive strength and the modulus of elasticity, and also decrease the apparent porosity of the composites. The composite made with 0.4 wt.% of superplasticizer and 0.05 wt.% of carbon nanotubes achieved acceptable properties for the use as double-layered porous restrictor in aerostatic thrust bearings.

Different methods of three-point bending analysis of polymer epoxy reinforced with fiberglass laminated faces

The purpose of this paper is the study of mechanical behavior in three-point bending of polymer epoxy using different amount of glass fibers laminated faces as reinforcement. Therefore, it was used experimental method, numerical simulation using linear and non-linear method and analytical method of composite beams analysing force, displacement and normal stress. The specimens were prepared using hand lay-up process and vacuum bag compaction. It was realized tensile and flexural tests in the specimens obtaining mechanical properties used in numerical simulation and analytical method. The numerical simulation was performed using linear and non-linear method with 3D solid elements. The materials were considered isotropic. The results showed similar values between methods with emphasis for the non-linear simulation that most approached the experimental results.

Hybrid composites based on silica, glass and short sisal fibres

Studies of composite materials in recent years have focused on the use of natural fibres as an alternative to synthetic fibres. The attractive mechanical properties, sustainability, low cost and low weight are potential factors that have leveraged research in this area, due to the variety of applications in the engineering sector. A full factorial design (2161) was performed to identify the effect of silica inclusions and the stacking sequence of glass fibres and short sisal fibres. The response-variables, such as apparent density, tensile and flexural strength and modulus of elasticity, were assessed in this work. In general, the incorporation of silica particles improved the performance of composites containing larger amounts of sisal fibres. Hybrid composites with higher number of glass fibre layers achieved higher values of tensile and flexural strength (348 MPa and 663.28 MPa) and tensile and flexural modulus (22 GPa and 2.50GPa) and higher apparent density value (2.02 g/cm3).

Hydration and Dehydration of High Initial Strength Portland Cement Type CP V - ARI

It is known that the hydration of cement paste is influenced by a variety of factors, it is also known that some hydration products are gradually dehydrated at elevated temperatures. In doing so, different author studied the dehydration of hydrated cement pastes under different condition. In this work, samples of Hydrated Cement Paste (HCP) were prepared from Portland cement of high initial strength (CP V-ARI) with a water/cement ratio of 0.5. The morphological changes during hydration and dehydration by subsequent heat-treatments were analyzed by X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). Thermal Gravimetric Analysis (TGA) was used to study the thermal stability of the HCP. Dehydrated cement powder samples (DCP) were obtained heat treating samples of HCP at 300, 500, 700 and 900°C. After 7 days of curing HCP samples exhibited no significant changes in its structure. HCP dehydrated at 500°C showed the absence of Ca (OH)2 and calcium silicate hydrate. At 700°C the formation of β-2CaO.SiO2, 3CaO.SiO2 and CaO is observed. During heat treatment at 900°C the HCP revealed a significant mass loss of 36%.