New insights for materials science characterisation using different complementary techniques combined with x-ray absorption spectroscopy

The combination of x-ray absorption spectroscopy (XAS) with UV-Vis and Raman spectroscopies or with Differential Scanning Calorimetry (DSC) has been recently carried out on the D44 beamline of DCI-LURE. The different set-ups used to perform such combinations are described and examples of combined investigations belonging to different field of materials science (coordination chemistry, sol-gel and catalysis) are presented. © Physica Scripta 2005.

Preparation and characterization of PVDF/CaCO3 composites

The contribution of new materials, involving composites and blends, has been reaching the most varied fields of science, as much of the scientific as technological point of view. This is due to the man's needs in applications, especially in medicine areas. Thus, this work shows the preparation and characterization of poly(vinylidene fluoride) (PVDF) and calcium carbonate (CaCO3) Composite films in order to analyse the incorporation of CaCO3 in PVDF for future application in bony restoration and bony filling. The films were prepared by casting method, where the PVDF pellet shape was dissolved in dimethylacetamide (DMA) and in a separate container CaCO3/DMA emulsion was also made. Soon afterwards they were mixed in several proportions 100/00, 95/05, 85/15, 70/30 in weight and left to dry in greenhouse. Homogeneous and flexible films were obtained and structurally characterized by attenuated total reflection infrared spectroscopy (FT-IR/ATR), thermal analyses (DSC, TGA), X-ray diffractometry, optical and scanning electron microscopies. The results showed that the material was a composite with good thermal stability until around 400 degrees C, the crystallinity of PVDF was non-polar alpha-phase and the obtained films were porous, being these filled with CaCO3. (c) 2006 Elsevier B.V. All rights reserved.

Processing and hygrothermal effects on viscoelastic behavior of glass fiber/epoxy composites

Fiber reinforced epoxy composites are used in a wide variety of applications in the aerospace field. These materials have high specific moduli, high specific strength and their properties can be tailored to application requirements. In order to screening optimum materials behavior, the effects of external environments on the mechanical properties during usage must be clearly understood. The environmental action, such as high moisture concentration, high temperatures, corrosive fluids or ultraviolet radiation (UV), can affect the performance of advanced composites during service. These factors can limit the applications of composites by deteriorating the mechanical properties over a period of time. Properties determination is attributed to the chemical and/or physical damages caused in the polymer matrix, loss of adhesion of fiber/resin interface, and/or reduction of fiber strength and stiffness. The dynamic elastic properties are important characteristics of glass fiber reinforced composites (GRFC). They control the damping behavior of composite structures and are also an ideal tool for monitoring the development of GFRC's mechanical properties during their processing or service. One of the most used tests is the vibration damping. In this work, the measurement consisted of recording the vibration decay of a rectangular plate excited by a controlled mechanism to identify the elastic and damping properties of the material under test. The frequency amplitude were measured by accelerometers and calculated by using a digital method. The present studies have been performed to explore relations between the dynamic mechanical properties, damping test and the influence of high moisture concentration of glass fiber reinforced composites (plain weave). The results show that the E' decreased with the increase in the exposed time for glass fiber/epoxy composites specimens exposed at 80 degrees C and 90% RH. The E' values found were: 26.7, 26.7, 25.4, 24.7 and 24.7 GPa for 0, 15, 30, 45 and 60 days of exposure, respectively. (c) 2005 Springer Science + Business Media, Inc.

Hygrothermal effects on the shear properties of carbon fiber/epoxy composites

The environmental factors, such as humidity and temperature, can limit the applications of composites by deteriorating the mechanical properties over a period of time. Environmental factors play an important role during the manufacture step and during composite's life cycle. The degradation of composites due to environmental effects is mainly caused by chemical and/or physical damages in the polymer matrix, loss of adhesion at the fiber/matrix interface, and/or reduction of fiber strength and stiffness. Composite's degradation can be measure by shear tests because shear failure is a matrix dominated property. In this work, the influence of moisture in shear properties of carbon fiber/epoxy composites ( laminates [0/0](s) and [0/90](s)) have been investigated. The interlaminar shear strength (ILSS) was measured by using the short beam shear test, and Iosipescu shear strength and modulus (G(12)) have been determinated by using the Iosipescu test. Results for laminates [0/0](s) and [0/90](s), after hygrothermal conditioning, exhibited a reduction of 21% and 18% on the interlaminar shear strenght, respectively, when compared to the unconditioned samples. Shear modulus follows the same trend. A reduction of 14.1 and 17.6% was found for [0/0](s) and [0/90](s), respectively, when compared to the unconditioned samples. Microstructural observations of the fracture surfaces by optical and scanning electron microscopies showed typical damage mechanisms for laminates [0/0](s) and [0/90](s).

Hygrothermal effects on damping behavior of metal/glass fiber/epoxy hybrid composites

Continuous fiber/metal laminates (FML) offer significant improvements over current available materials for aircraft structures due to their excellent fatigue endurance and low density. Glass fibers/epoxy laminae and aluminum foil (Glare) are commonly used to obtain these hybrid composites. The environmental factors can limit the applications of composites by deteriorating the mechanical properties during service. Usually, epoxy resins absorb moisture when exposed to humid environments and metals are prone to surface corrosion. Therefore, the combination of the two materials in Glare (polymeric composite and metal). can lead to differences that often turn out to be beneficial in terms of mechanical properties and resistance to environmental influences. In this work. The viscoelastic properties. such as storage modulus (E') and loss modulus (E'), were obtained for glass fiber/epoxy composite, aluminum 2024-T3 alloy and for a glass fiber/epoxy/aluminum laminate (Glare). It was found that the glass fiber/epoxy (G/E) composites decrease the E' modulus during hygrothermal conditioning up to saturation point (6 weeks). However, for Glare laminates the E' modulus remains unchanged (49GPa) during the cycle of hygrothermal conditioning. The outer aluminum sheets in the Glare laminate shield the G/E composite laminae from moisture absorption. which in turn prevent, in a certain extent, the material from hygrothermal degradation effects. (c) 2005 Elsevier B.V. All rights reserved.

Evaluation of fatigue behavior on repaired carbon fiber/epoxy composites

The continuous use of structural polymer composites in aeronautical industry has required the development of repairing techniques of damages found in different types of laminates. The most usually adopted procedure to investigate the repair of composite laminates has been by repairing damages simulated in laminated composite specimens. This work shows the influence of structural repair technique on mechanical properties of a typical carbon fiber/epoxy laminate used in aerospace industry. When analyzed by tensile test, the laminates with and without repair present tensile strength values of 670 and 892 MPa, respectively, and tensile modulus of 53.0 and 67.2 GPa, respectively. By this result, it is possible to observe a decrease of the measured mechanical properties of the repaired composites. When submitted to fatigue test, it is observed that in loads higher than 250 MPa, this laminate presents a low life cycle (lower than 400,000 cycles). The fatigue performance of both laminates is comparable, but the non-repaired laminate presented higher tensile and fatigue resistance when compared with the repaired laminate.

Influence of moisture absorption on mechanical behaviour of composites

Because of their application that normally demands high mechanical strength combined with low weight, the fibre/matrix interface became an important parameter concerning structural life. The problem of moisture absorption in materials has received attention in experimental studies on a composite systems as well as from a theorical point of view. The fibre/matrix interface plays an important role in the structural behaviour of composites due to the fact that load transfer from matrix to reinforce occurs at the interface. In this case the study of compatibility of fibre/matrix/environmental is essential to ensure a product that attend structural objectives, many times without failure possibilities. The composite used in this investigation is the carbon fibre/matrix epoxy composite, which was immersed in sea water standard during 94 days at 60 degrees C, submitted to tensile and compressive tests to study the influence of moisture absorption on mechanical behaviour. The interface was investigated through fracture surface analysis by SEM and a strong interface and a good adhesion fibre/matrix was observed.

Evaluation of hygrothermal effects on the shear properties of Carall composites

Fiber metal laminates are the frontline materials for aeronautical and space structures. These composites consists of layers of 2024-T3-aluminum alloy and composite prepreg layers. When the composite layer is a carbon fiber prepreg, the fiber metal laminate, named Carall, offers significant improvements over current available materials for aircraft structures. While weight reduction and improved damage tolerance characteristics were the prime drivers to develop this new family of materials, it turns out that they have additional benefits, which become more and more important for today's designers, such as cost reduction and improved safety. The degradation of composites is due to environmental effects mainly on the chemical and/or physical properties of the polymer matrix leading to loss of adhesion of fiber/resin interface. Also, the reduction of fiber strength and stiffness are expected due to environmental degradation. Changes in interface/interphase properties leads to more pronounced changes in shear properties than any other mechanical properties. In this work, the influence of moisture in shear properties of carbon fiber/epoxy composites and Carall have been investigated by using interlaminar shear (ILSS) and Iosipescu tests. It was observed that hygrothermal conditioning reduces the Iosipescu shear strength of CF/E and Carall composites due to the moisture absorption in these materials. (c) 2006 Elsevier B.V. All rights reserved.

Structure, microstructure and dielectric properties of 100-x(Bi0.5Na0.5)TiO3-x[SrTiO3] composites ceramics

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Friction and wear properties of functionally graded aluminum matrix composites

Aluminum matrix composites are currently considered as promising materials for tribological applications in the automotive, aircraft and aerospace industries due to their great advantage of a high strength-to-weight ratio. A superior combination of surface and bulk mechanical properties can be attained if these composites are processed as functionally graded materials (FGM's). In this work, homogeneous aluminum based matrix composite, cast by gravity, and aluminum composites with functionally graded properties, obtained by centrifugal cast, are tested against nodular cast iron in a pin-on-disc tribometer. Three different volume fractions of SiC reinforcing particles in each FGM were considered in order to evaluate their friction and wear properties. The sliding experiments were conducted without lubrication, at room temperature, under a normal load of 5 N and constant sliding speed of 0.5 ms-1. The worn surfaces as well as the wear debris were characterized by SEM/EDS and by atomic force microscopy (AFM). The friction coefficient revealed a slightly decrease (from 0.60 to 0.50) when FGM's are involved in the contact instead of the homogeneous composite. Relatively low values of the wear coefficient were obtained for functionally graded aluminum matrix composites (≈10-6 mm3N-1 m-1), which exhibited superior wear resistance than the homogeneous composite and the opposing cast iron surface. Characterization of worn surfaces indicated that the combined effect of reinforcing particles as load bearing elements and the formation of protective adherent iron-rich tribolayers has a decisive role on the friction and wear properties of aluminum matrix composites.

Dispersed hydroxyapatite bioglass 45S5 composites: Comparative evaluation of the use of bovine bone and synthetic hydroxyapatite

The bovine bone and sintetic hydroxyapatite (HA) bioceramics are reference materials to employment as a bone substitute, however, their slow rate of degradation and its low rate of bioactivity index (Ib) are presented as limiting factors for application as bone graft. In contrast, the bioglass is a resorbable and osteoinductive material. the present work objective the development of composites of dispersed bovine bone or sintetic HA in silicate-phosphate bioglass, seeking to obtain a biomaterial with properties suitable for application as bone grafts. The composites were prepared by mixing between the powder components followed by sintering for 1h. Were used HA and bioglass (45S5) with particle size <240μm. The tested proportions of HA/45S5 were 20/80, 30/70 and 40/60 (wt%). The composites characterization was made employing scanning electron microscopy, Infra-Red Spectrometry and hydrolytic resistance test. The test results indicate the potential use of the materials developed for applications such as bone graft. © (2012) Trans Tech Publications, Switzerland.

A graphical tool for the tomographic characterisation of microstructural features on metal matrix composites

Research on the micro-structural characterization of metal-matrix composites uses X-ray computed tomography to collect information about the interior features of the samples, in order to elucidate their exhibited properties. The tomographic raw data needs several steps of computational processing in order to eliminate noise and interference. Our experience with a program (Tritom) that handles these questions has shown that in some cases the processing steps take a very long time and that it is not easy for a Materials Science specialist to interact with Tritom in order to define the most adequate parameter values and the proper sequence of the available processing steps. For easing the use of Tritom, a system was built which addresses the aspects described before and that is based on the OpenDX visualization system. OpenDX visualization facilities constitute a great benefit to Tritom. The visual programming environment of OpenDX allows an easy definition of a sequence of processing steps thus fulfilling the requirement of an easy use by non-specialists on Computer Science. Also the possibility of incorporating external modules in a visual OpenDX program allows the researchers to tackle the aspect of reducing the long execution time of some processing steps. The longer processing steps of Tritom have been parallelized in two different types of hardware architectures (message-passing and shared-memory); the corresponding parallel programs can be easily incorporated in a sequence of processing steps defined in an OpenDX program. The benefits of our system are illustrated through an example where the tool is applied in the study of the sensitivity to crushing – and the implications thereof – of the reinforcements used in a functionally graded syntactic metallic foam.

Monitoring of cure kinetic prepreg and cure cycle modeling

Cure kinetic model is an integral part of composite process simulation, which is used to predict the degree of curing and the amount of the generated heat. The parameters involved in kinetic models are usually determined empirically from isothermal or dynamic differential scanning calorimetry (DSC) data. In this work, DSC and rheological techniques were used to investigate some of the kinetic parameters of cure reactions of carbon/F161 epoxy prepreg and to evaluate the cure cycle used to manufacture polymeric composites for aeronautical applications. As a result, it was observed that the F161 prepreg presents cure kinetic with total order 1.2-1.9. (c) 2006 Springer Science + Business Media, Inc.

Fractography analysis and fatigue strength of carbon fiber/RTM6 laminates

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Chemical vapor deposition of multi-walled carbon nanotubes from nickel/yttria-stabilized zirconia catalysts

Multi-walled carbon nanotubes (MWNT) were produced by chemical vapor deposition using yttria-stabilized zirconia/nickel (YSZ/Ni) catalysts. The catalysts were obtained by a liquid mixture technique that resulted in fine dispersed nanoparticles of NiO supported in the YSZ matrix. High quality MWNT having smooth walls, few defects, and low amounts of by-products such as amorphous carbon were obtained, even from catalysts with large Ni concentrations (> 50 wt.%). By adjusting the experimental parameters, such as flux of the carbon precursor (ethylene) and Ni concentration, both the MWNT morphology and the process yield could be controlled. The resulting YSZ/Ni/MWNT composites can be interesting due to their mixed ionic-electronic transport properties, which could be useful in electrochemical applications.