Fábio de Oliveira Braga

Charpy Toughness Behavior of Eucalyptus Fiber Reinforced Polyester Matrix Composites

This work investigated the toughness behavior of polyester matrix composites reinforced with up to 30% in volume of long, continuous and aligned fibers extracted from the eucalyptus wood by means of Charpy impact tests. It was found that the addition of eucalyptus fibers results in a marked increase in the absorbed impact energy of the composites. Macroscopic observation of the post-impact specimens and SEM fracture analysis showed that longitudinal rupture through the Eucalyptus fiber interface with the polyester matrix is the main mechanism for the remarkable toughness of these composites.

Evaluation of the Diameter Influence on the Tensile Strength of Pineapple Leaf Fibers (PALF) by Weibull Method

The fiber extracted from pineapple leaf (PALF) displays relevant mechanical properties that are motivating investigations for possible engineering application as polymer composite reinforcement. As any natural lignocellulosic fiber, the PALF presents non-uniform dimensions and heterogeneous properties with a significant dispersion of values. In fact, a marked variation in the tensile strength has been reported, which represents a problem for the design of a PALF reinforced composite. In several other lignocellulosic fibers, the diameter dimension was found to affect the value of the tensile strength. This work investigated the precise diameter dependence of the PALF tensile strength using the Weibull statistic method. The results showed a mathematical hyperbolic type of inverse correlation between the PALF strength and its diameter, which was found to be similar to that commonly obtained in other lignocellulosic fibers.

Flexural Behavior of Epoxy Matrix Composites Reinforced with Malva Fiber

Polymer composites reinforced with natural fibers have been increasingly investigated and applied as engineering materials owing to their economical, technical, societal and environmental advantages. The malva fiber, particularly an important resource in the Amazon region in Brazil, only recently begin to be investigated as possible composite reinforcement for engineering application. However, the mechanical properties of composites reinforced with malva fiber are still unknown. In this paper, the flexural behavior of epoxy matrix composites reinforced with continuous malva fiber was for the first time investigated. Specimens of continuous malva fibers aligned along an epoxy matrix were press-molded. Three-points bending test were performed and the fractured specimens were analyzed by SEM. The results showed a marked improvement in the composites flexural properties with the increase in the amount of reinforced malva fiber. This improvement was found to match the Rule of Mixtures, which revealed the unique potential of malva composites for engineering applications.

Pullout Tests Behavior of Polyester Matrix Reinforced with Malva Fiber

The interface between a composite matrix and the reinforcing fiber plays an important role in the efficiency by which an applied load is transmitted throughout the composite structure. The shear stress at the fiber/matrix interface can be associated with this load transference and, consequently, will affect the composite strength. In the present work, pullout tests were used to evaluate the interfacial shear stress of malva fiber in polyester matrix composites. A small critical length was found for the malva fiber embedded in polyester, which corresponds to a relatively weak fiber/matrix bond and lower interfacial strength.

Correlation between the Density and the Diameter of Fique Fibers

Environmental considerations in addition to technical, economical and societal benefits are contributing to promote the substitution of natural fibers for glass fiber in polymer matrix composites. However, natural fibers are heterogeneous in their dimensions, specially the cross section diameter, which plays an important role in their physical properties. The fibers extracted from the leaf of the fique plant (Furcraea andina) are a promising stiff natural fiber for composite reinforcement. In this work, a statistical analysis of the density of fique fibers using the Weibull methodology was performed. An attempt to correlate the fiber density with the diameter, precisely measured by means of a profile projector, was carried out. The results revealed an inverse dependence, adjusted to a hyperbolic equation, between the fique fiber diameter and corresponding density.

Tensile and Impact Properties of Two Fiber Configurations for Curaua Reinforced Composites

Natural fibers have been extensively investigated in the past decades, due to their good properties, lightweight, low cost and renewable nature. From the ananas erectifolius plant, high strength and high modulus curaua fibers can be obtained. Their remarkable properties make them adequate to several high performance applications. In the present work, tensile and impact properties of two fiber configurations for curaua reinforced composites were investigated: a non-woven fiber fabric (NWFF) and high percentage continuous and aligned fiber (HPCAF) composites, using epoxy and polyester as polymeric matrix, respectively. The results showed that the fabric configuration does not effectively reinforce the polymer on tensile load, in spite of promoting significant improvement on the impact properties of the composite. The latter configuration results in both high strength and tough composites, however, its ability to resist to impacts depends on the direction of load.

Fracture Behavior of 316 Stainless Steel under Creep at 600 and 800°C

The fracture characteristics of two AISI 316 austenitic stainless steels, creep-tested at constant load and temperatures of 600 and 800°C, were studied by scanning electron microscopy. The morphological aspects of the fracture were analyzed and correlated to the ductility level attained under creep. In one of the 316 steels, a marked change from ductile to intergranular mode of fracture was observed in going from 600 to 800°C. It is proposed that the condition for crack nucleation at precipitates as well as grain boundary oxidation are responsible for these microstructural changes.

Evaluation of a Tacking Stage for Adherence, between Mortar and Ceramic Brick

The civil construction industrial sector is one of the most important in Brazil both for job opportunity and amount of utilized materials. However, it is also the sector that produces one of the highest volume of waste materials. In fact, it is estimated that total wastes to be around 30% of the raw materials supplied to the constructions. Several factors have been indicated as responsible for this wastage in civil construction, from lack of qualified labor to inappropriate technical procedures. One of the constructive stages, which has been the subject of doubt, is the previous preparation of a crude brick wall to receive a layer of mortar before painting. This previous preparation is known as tacking, which consists of coating the bricks surface with a light mixture of water, cement and sand to improve the mortar adherence. Since the tacking increases the masonry construction cost in approximately 2%, the present work evaluated its necessity. Tests were conducted without and with tack between the bricks and the mortar. The results showed a tendency to increase the adherence with time after tacking.

Density Weibull Analysis of Pineapple Leaf Fibers (PALF) with Different Diameters

Societal, economical, technical and environmental advantages are today justifying the replacement of synthetic fibers by natural fibers. However, natural fibers obtained from plants do not present the same dimensional uniformity. In fact, they show large dispersion of values, as compared to synthetic fibers. In the case of the lignocellulosic fiber extracted from the pineapple leaf, limited information exists regarding the correlation between its properties and dimensional characteristics. In particular, so far, no investigation has been carried out on the influence of the diameter and the density of pineapple fibers. Therefore, the objective of this work was to measure the density of pineapple fibers and to define, by means of the Weibull statistic method, its dependence on the corresponding fiber diameter.

Photoacoustic Thermal Characterization of Banana Fibers

Natural fibers are attracting the interest of engineering sectors owing to specific advantages such as lightweight and lower cost as well as for their inherent condition of being renewable, biodegradable, recyclable and neutral with respect to CO2 emission. In particular, the fiber extracted from the malva plant stem is nowadays recognized as one of the strongest lignocellulosic fibers. However, the thermal properties of the malva fibers have yet not been fully investigated. The present work had as its objective to investigate, by photoacoustic spectroscopy and photothermal techniques the thermal properties of diffusivity, specific heat capacity and conductivity of a pressed malva fibers sample. The results revealed that these fibers showed a superior thermal insulation capacity.