Edson Cocchieri Botelho

A review on the development and properties of continuous fiber/epoxy/aluminum hybrid composites for aircraft structures

Weight reduction and improved damage tolerance characteristics were the prime drivers to develop new family of materials for the aerospace/aeronautical industry. Aiming this objective, a new lightweight Fiber/Metal Laminate (FML) has been developed. The combination of metal and polymer composite laminates can create a synergistic effect on many properties. The mechanical properties of FML shows improvements over the properties of both aluminum alloys and composite materials individually. Due to their excellent properties, FML are being used as fuselage skin structures of the next generation commercial aircrafts. One of the advantages of FML when compared with conventional carbon fiber/epoxy composites is the low moisture absorption. The moisture absorption in FML composites is slower when compared with polymer composites, even under the relatively harsh conditions, due to the barrier of the aluminum outer layers. Due to this favorable atmosphere, recently big companies such as EMBRAER, Aerospatiale, Boing, Airbus, and so one, starting to work with this kind of materials as an alternative to save money and to guarantee the security of their aircrafts.

Characterization of cure of carbon/epoxy prepreg used in aerospace field

Carbon/epoxy 8552 prepreg is a thermoplastic toughened high-performance epoxy being used in the manufacture of advanced army material. Understanding the cure behavior of a thermosetting system is essential in the development and optimization of composite fabrication processes. The cure kinetics and rheological behavior were evaluated using a differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and a rheometer. Values of the kinetic parameters were obtained from dynamic DSC scans using an nth order reaction model. Rheological measurements as a function of temperature and time were made for the prepreg system. The manufacturers recommended cure cycle was evaluated and considered adequate to consolidated the studied system.

Hygrotermal effects evaluation using the iosipescu shear test for glare laminates

Fiber-metal laminates (FML) composed of alternating layers of unidirectional fiber-reinforced plastic (FRP) laminae and aluminum-alloy sheets offer some superior mechanical properties, compared with either conventional laminates consisting of only FRP laminae or high-strength monolithic aluminum alloys. The environmental factors can limit the applications of composites by deteriorating the mechanical properties during service. Usually, polymeric matrix absorbs moisture when exposed to humid environments and metals are prone to surface corrosion. On the other hand, FML laminates presents more resistance of moisture when compared with their constituents. Evaluation of shear properties is particularly important in the design of mechanically fastened parts and components, which are subject to parallel and opposing loads. In this work, the shear behavior was studied for Glare laminates and its constituents in dry and wet conditions.

Correlation between degree of crystallinity, morphology and mechanical properties of PPS/carbon fiber laminates

The crystallization degree in semi-crystalline thermoplastics plays an important role in determining the final properties of structural composite material (e.g. toughness, stiffness and solvent resistance). The main purpose of this work is to study different induced degrees of crystallinity in carbon fiber (CF) reinforced polyphenylene sulfide (PPS) composites, by using three different cooling rates during hot compression molding processing (51%, 58% and 62% of crystallinity). In this study, the morphology, thermal and mechanical properties of the produced laminates were investigated and compared. The results showed an increase in the storage modulus (9.8%), Youngs modulus (9.2%) and ILSS (14.2%) for the lower cooling rates. Evidences of fiber/interface improvement and crystallites nucleation on the fiber reinforcement surface were also identified.

Atmospheric Plasma Treatment of Carbon Fibers for Enhancement of Their Adhesion Properties

Plasma processing of carbon fibers (CFs) is aimed to provide better contact and adhesion between individual plies without decrease in the CF mechanical resistance. This paper deals with surface modification of CFs by an atmospheric pressure dielectric barrier discharge (DBD) for enhancing the adhesion between the CF and the polymeric matrix. The scanning electron microscopy of the treated samples revealed many small particles distributed over entire surface of the fiber. These particles are product of the fiber surface etching during the DBD treatment that removes the epoxy layer covering as-received samples. The alteration of the CF surface morphology was also confirmed by the Atomic force microscopy (AFM), which indicated that the CF roughness increased as a result of the plasma treatment. The analysis of the surface chemical composition provided by X-ray photoelectron spectroscopy showed that oxygen and nitrogen atoms are incorporated onto the surface. The polar oxygen groups formed on the surface lead to the increasing of the CF surface energy. The results of interlaminar shear strength test (short beam) of CFs/polypropylene composites demonstrated a greater shear resistance of the composites made with CFs treated by DBD than the one with untreated fibers. Both the increase in surface roughness and the surface oxidation contribute for the enhancement of CF adhesion properties.

Evaluation of decomposition kinetics of poly (ether-ether-ketone) by thermogravimetric analysis

The non-isothermal thermogravimetric methods have been used extensively for the determination of kinetic parameters in polymers. The poly (ether ketones) are used as matrix in advanced high performance composites due its high thermal stability, excellent environmental performance and superior mechanical properties. In this work, the non-isothermal decomposition kinetics of the polymer poly (ether ether ketone) (PEEK) was evaluated in nitrogen and synthetic air atmospheres, using the Flynn-Wall-Ozawa and Coats Redfern models. The results showed that the necessary time for the material decomposes in 5% is approximately 216 years if it is submitted to temperatures of 350 °C in nitrogen atmosphere. On the other hand, if the material is submitted to air atmosphere, this decomposition time drops to about 1,05 years in the same temperature and for the same conversion rate. The decomposition kinetics study by Coats Redfern showed that the D3 mechanism (three-dimensional diffusion (Jander equation)) had better adjustment to the decomposition kinetics of the material in nitrogen atmosphere, while in synthetic air the R1 mechanism (phase boundary controlled reaction (one-dimensional movement)) has better adjustment to the decomposition kinetics of the material.

Nonoxidative thermal degradation kinetic of polyamide 6,6 reinforced with carbon nanotubes

The thermal degradation of the polyamide 6,6 (abbreviated henceforth as PA 6,6) reinforced with different concentrations of carbon nanotubes (CNTs) was investigated by means of thermal analysis. In this study, the nanostructured composites were produced using 0.1, 0.5 and 1.0 wt% of CNT. X-ray diffraction analyses were performed in order to evaluate the crystallographic properties of nanostructured composite. The degradation kinetics of PA 6,6/CNT nanostructured composites were measured by thermogravimetric analysis at different heating rates under nitrogen flow. TGA experiments were performed to elucidate the thermal behavior and supply the data that characterize the degradation kinetic. The degradation parameter kinetics was determined using the Ozawa–Wall–Flynn (O-W-F) methods, which do not require knowledge of the reaction mechanism. In this work, the results show that the addition of CNT up to the amount of 0.5 wt% increases the thermal stability of PA 6,6.

Processing and mechanical characterization of titanium-graphite hybrid laminates:

Titanium/carbon fiber/epoxy (CF—E) laminates offer many advantages when compared to the traditional metal—fiber laminates and polymer matrix composites for use on aerospace structures. They have many of the advantages of traditional composites such as good strength and stiffness-to-weight ratios. This article displays the mechanical experimental results demonstrating the advantageous influence of titanium/CF—E laminates on specific characteristics of CFRP materials, GLARE® and CARALL®. This hybrid laminate was produced with CF—E prepreg and by titanium foil inside of autoclave system. According to this study, the tensile stress, tensile modulus, shear stress, and shear modulus values for titanium/CF—E laminates are superior when compared with GLARE® and CARALL® laminates, showing the superiority of this laminate in aerospace applications.

Evaluation of weather influence on mechanical and viscoelastic properties of polyetherimide/carbon fiber composites

In order to investigate how environmental degradation affects the mechanical and thermal performance of polyetherimide/carbon fiber laminates, in this work different weathering were conducted. Additionally, dynamic mechanical analysis, interlaminar shear strength tests and non-destructive inspections were performed on this composite before and after being submitted to hygrothermal, UV radiation and thermal shock weathering. According to our results, hygrothermally aged samples had their glass transition temperature and elastic and storage moduli reduced by plasticization effect. Photooxidation, due to UV radiation exposure, occurred only on the surface of the laminates. Thermal shock induced a reversible stress on the composite’s interface region. The results revealed that the mechanical behavior can vary during weather exposure but since this variation is only subtle, this thermoplastic laminate can be considered for high-performance applications, such as aerospace.

The effect of the ocean water immersion and UV ageing on the dynamic mechanical properties of the PPS/glass fiber composites

Nowadays, the poly(phenylene sulfide) thermoplastic matrix composites have being utilized by most of the aerospace companies in order to replace a great quantity of the components made of aluminum, thermoset composites, or both and it is the reason they are being strongly considered to be utilized into marine structures, however, are quite often exposed to the environmental conditions that can damage them irreversibly, minimizing their qualities and compromising their performance. Depending on the aviation industry policy and requirements to learn more about these possible damages and increase the performance and the safety, this work aims to evaluate how the salt water and the UV light radiation conditioning affect the viscoelastic properties of the PPS/glass fiber laminates. Those viscoelastic experiments were performed by a DMA instrument before and after to submit the specimens to the conditioning and the experiments results were compared. Additionally, the moisture absorption mechanism after immersion in the artificial ocean solution and the material surface analysis after UV conditioning were investigated. According to the results found in this work, it can be concluded that the PPS/glass fiber absorbed approximately 0.3% of moisture into artificial ocean water conditioning under 60°C and this thermoplastic laminate exhibits moisture absorption according to the Fick’s law, since the n constant experimental value was around 0.5.