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Matrix Composites (matrix + composite)
Kinds of Matrix Composites Selected AbstractsDielectric Properties of a Printed Sol,Gel Matrix Composite,ADVANCED ENGINEERING MATERIALS, Issue 5 2010Tobias Lehnert Low temperature processable materials with high dielectric constants are required for application on flexible organic substrates, for example, in printed electronics. To date, mainly organic polymers with embedded functional particles have been investigated for this purpose. For the first time, we present a printable dielectric composite material composed of ferroelectric high permittivity particles (BaTiO3) bonded by a mainly inorganic sol,gel derived network. The exemplary optimization of the properties by varying the sol,gel precursor illustrates the potential of sol,gel chemistry for printable functional materials. An operational gravure printed capacitor including printed silver electrodes is presented. The measured dielectric constants are among the highest reported in literature for low temperature cured films with moderate dissipation factors. Besides these promising dielectric properties, this composite film shows a ferroelectric response. [source] Biomimetic Formation of Hydroxyapatite/collagen Matrix CompositeADVANCED ENGINEERING MATERIALS, Issue 1-2 2006Y. Wang A composite of collagen (COL) and hydroxyapatite(HA) was prepared using a biomimetic approach, which performs a direct nucleation of HA on self- assembled collagen matrix. This research may be helpful to understand the possible mechanisms for collagen-mediated mineralization in general and the COL/HCA composite can be considered a new particularly attractive material for human bone tissue implantation. [source] Processing and Properties of a Porous Oxide Matrix Composite Reinforced with Continuous Oxide FibersJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2003Magnus G. Holmquist A process to manufacture porous oxide matrix/polycrystalline oxide fiber composites was developed and evaluated. The method uses infiltration of fiber cloths with an aqueous slurry of mullite/alumina powders to make prepregs. By careful manipulation of the interparticle pair potential in the slurry, a consolidated slurry with a high particle density is produced with a sufficiently low viscosity to allow efficient infiltration of the fiber tows. Vibration-assisted infiltration of stacked, cloth prepregs in combination with a simple vacuum bag technique produced composites with homogeneous microstructures. The method has the additional advantage of allowing complex shapes to be made. Subsequent infiltration of the powder mixture with an alumina precursor was made to strengthen the matrix. The porous matrix, without fibers, possessed good thermal stability and showed linear shrinkage of 0.9% on heat treatment at 1200°C. Mechanical properties were evaluated in flexural testing in a manner that precluded interlaminar shear failure before failure via the tensile stresses. It was shown that the composite produced by this method was comparable to porous oxide matrix composites manufactured by other processes using the same fibers (N610 and N720). The ratio of notch strength to unnotch strength for a crack to width ratio of 0.5 was 0.7,0.9, indicating moderate notch sensitivity. Interlaminar shear strength, which is dominated by matrix strength, changed from 7 to 12 MPa for matrix porosity ranging from 38% to 43%, respectively. The porous microstructure did not change after aging at 1200°C for 100 h. Heat treatment at 1300°C for 100 h reduced the strength for the N610 and N720 composites by 35% and 20%, respectively, and increased their brittle nature. [source] Crystallization behaviors of carbon fiber reinforced BN-Si3N4 matrix compositeCRYSTAL RESEARCH AND TECHNOLOGY, Issue 7 2007Bin Li Abstract The crystallization behaviors of a new carbon fiber reinforced composite with a hybrid matrix comprising BN and Si3N4 prepared by precursor infiltration and pyrolysis were investigated by Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy. The results show that the as-received composite is almost amorphous, and its main composition is BN and Si3N4. When heat treated at 1600°C, the composite is crystallized and shows a much better crystal form. When heat treated at 2100°C, Si3N4 in the matrix is decomposed, and BN exhibits a relatively complete crystallization. The existence of B4C and SiC is detected, which indicates the interfacial chemical reactions between nitride matrices and carbon fibers. The surface morphology of carbon fibers in the composite changed significantly when heated from 1600 to 2100°C, which also proved the occurrence of interfacial chemical reactions. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Microstructural Characteristics of an AZ91 Matrix-Glassy Carbon Particle Composite,ADVANCED ENGINEERING MATERIALS, Issue 7 2010Anita Olszówka-Myalska This paper presents the results of a microstructural investigation of a new type of ultralight glassy carbon particles (Cp)-AZ91 magnesium alloy matrix composite manufactured by the powder metallurgy method. Glassy Cp with unmodified surfaces and surfaces modified with SiO2 amorphous nanocoating were used in the experiment. The composite microstructure, with an emphasis given on the interface, was characterized by scanning electron microscope (SEM), TEM, and HRTEM microscopy. Uniform distribution of the particles in the matrix and their good bonding with the metal matrix were observed. A continuous very thin MgO oxide layer containing needle-like Al2MgO4 phase was detected at the glassy carbon,AZ91 interface. An increase of aluminum concentration at the interface as a result of Mg and Al diffusion into the SiO2 nanolayer was observed in the case of particles modified with SiO2. Crystalline phases containing carbon were not detected at the interface. [source] Microstructural analysis of iron aluminide formed by self-propagating high-temperature synthesis mechanism in aluminium matrix compositeJOURNAL OF MICROSCOPY, Issue 1 2006ANITA OLSZÓWKA-MYALSKA Summary An aluminium matrix composite with iron aluminide formed in situ as a result of self-propagated high-temperature synthesis was examined. The structural characteristics of the reinforcement investigated by scanning electron microscopy and transmission electron microscopy methods are presented. Iron aluminide particles with a very fine grain size and of two shapes, cubic and needle-like, were observed. No differences in their phase composition were found by the selective electron diffraction pattern method. The composite reinforcement formed in the early stage of self-propagating high-temperature synthesis consisted only of the Al3Fe phase. [source] In Situ Synthesis and Microstructures of Tungsten Carbide-Nanoparticle-Reinforced Silicon Nitride-Matrix CompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2004Tateoki Iizuka A W2C-nanoparticle-reinforced Si3N4 -matrix composite was fabricated by sintering porous Si3N4 that had been infiltrated with a tungsten solution. During the sintering procedure, nanometer-sized W2C particles grew in situ from the reaction between the tungsten and carbon sources considered to originate mainly from residual binder. The W2C particles resided in the grain-boundary junctions of the Si3N4, had an average diameter of ,60 nm, and were polyhedral in shape. Because the residual carbon, which normally would obstruct sintering, reacted with the tungsten to form W2C particles in the composite, the sinterability of the Si3N4 was improved, and a W2C,Si3N4 composite with almost full density was obtained. The flexural strength of the W2C,Si3N4 composite was 1212 MPa, ,34% higher than that of standard sintered Si3N4. [source] Temperature Dependence of Tensile Strength for a Woven Boron-Nitride-Coated Hi-NicalonÔ SiC Fiber-Reinforced Silicon-Carbide-Matrix CompositeJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2001Shuqi Guo The temperature dependence of tensile fracture behavior and tensile strength of a two-dimensional woven BN-coated Hi-NicalonÔ SiC fiber-reinforced SiC matrix composite fabricated by polymer infiltration pyrolysis (PIP) were studied. A tensile test of the composite was conducted in air at temperatures of 298 (room temperature), 1200, 1400, and 1600 K. The composite showed a nonlinear behavior for all the test temperatures; however, a large decrease in tensile strength was observed above 1200 K. Young's modulus was estimated from the initial linear regime of the tensile stress,strain curves at room and elevated temperatures, and a decrease in Young's modulus became significant above 1200 K. The multiple transverse cracking that occurred was independent of temperature, and the transverse crack density was measured from fractographic observations of the tested specimens at room and elevated temperatures. The temperature dependence of the effective interfacial shear stress was estimated from the measurements of the transverse crack density. The temperature dependence of in situ fiber strength properties was determined from fracture mirror size on the fracture surfaces of fibers. The decrease in the tensile strength of the composite up to 1400 K was attributed to the degradation in the strength properties of in situ fibers, and to the damage behavior exception of the fiber properties for 1600 K. [source] Untersuchungen zur Herstellung siliziumkarbid-partikelverstärkter Aluminiumpulver durch Hochenergiekugelmahlen.MATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 6 2010Fabrication of silicon carbide reinforced aluminium powders by high-energy ball-milling High-energy ball milling; Aluminium matrix composite; AA2017; SiC particle reinforcement; Microstructure Abstract Die Herstellung von Siliziumkarbid-Aluminium-Verbundpulver stellt die erste Stufe der pulvermetallurgischen Herstellungsroute für partikelverstärkte Aluminiumwerkstoffe dar. Der Prozess der Verbundpulverausbildung beim Mahlen in einer Hochenergiekugelmühle und der Einfluss von Prozessparametern werden anhand der Al-Legierung EN AW-2017 mit 10 und 15 Vol.-% Siliziumkarbidteilchen der Kornfraktion <2 ,m untersucht. Die Gefügeentwicklung des Pulvers wird materialografisch charakterisiert. Bestimmte Prozessparameter beeinflussen den Verbundpulverzustand zum Teil gegenläufig, so dass der erreichte Optimierungsstand als Kompromiss anzusehen ist. Lösungsvarianten für eine weitere Verbesserung werden aufgezeigt. The fabrication of aluminium silicon-carbide composite powder is the first step of the powder metallurgical production of particle-reinforced aluminium material. This paper deals with the production of silicon-carbide reinforced aluminium matrix (AA2017) composite powder through an high energy ball milling process by using simoloyer- and planetary high energy mills. The Stages of composite powder formation during the high-energy ball milling process will be shown by means of materialographic studies and by micro hardness. Major factors of influence as well as typical problems are discussed. [source] Bulk and patch ferrite resonator antennas based on the ceramic matrix composite: GdIGx YIG1- xMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 6 2009P. B. A. Fechine Abstract In this study, the dielectric properties of the GdIGXYIG1,X ferrite composite material at radio frequency (RF) and microwave frequency bands were studied. These measurements were carried out in different sample geometries: thick films and cylindrical ceramic bulk ferrite resonator. In the RF range, we observed that the material is rather stable because of its short changes as a function of temperature and frequency range. The temperature capacitance coefficient values for all the samples (thick films and cylindrical ceramic bulk samples) presented short positive values at the RF range. The GdIG0.5YIG0.5 thick film was used as a substrate for the microstrip antenna device, where the upper Ag electrode served as a circular patch antenna and a microstrip line was used as a feed line. The microstrip antenna operates in this configuration at 8.185 GHz. In the study of the dielectric properties of the composites antenna geometry, with the same ferrite composite, a bulk cylindrical geometry was investigated. A numerical study, together with the experimental, was done, and the dielectric characteristics of the composite like ,r, tg,E, and ,r were obtained. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1595,1602, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24395 [source] Reverse piezoelectric behavior of carbon fiber thermoplastic-matrix compositePOLYMER COMPOSITES, Issue 5 2002Zhen Mei The reverse piezoelectric effect was observed in the through-thickness direction of a continuous carbon fiber nylon-6 matrix composite. The piezoelectric coupling coefficient was 2.2 × 10,6 m/V, as determined up to an electric field of 261 V/m. The effect was largely reversible upon turning off the field and was unaffected by field reversal. It is attributed to the electric dipoles in the nylon-6 matrix. [source] Preparation of Tip-Protected Poly(oxyphenylene) Coated Carbon-Fiber UltramicroelectrodesELECTROANALYSIS, Issue 23 2006El-Deen Abstract A high-yield, reliable, and reproducible method has been successfully developed to fabricate poly(oxyphenylene)-coated carbon fiber ultramicroelectrodes (POCF UMEs) with tip radii r<2,,m. During the insulation process, the tip of the electrochemically etched electrode is protected by inserting it into an inert polymer while the remainder of the electrode is insulated by electrochemical deposition of a 1,3,,m thick poly(oxyphenylene) film. Optimum conditions for poly(oxyphenylene) deposition are developed and the resulting carbon fiber UMEs showed good cyclic voltammetric behavior even after storage for more than one year. These UMEs were tested for use as amperometric scanning electrochemical microscopy (SECM) tips and successfully imaged Au/Kel-F and Al/SiCp metal matrix composites. [source] Carbon Long Fiber Reinforced Aluminum Matrix Composites , Parameter Studies and Numerical Simulations of the Infiltration Process,ADVANCED ENGINEERING MATERIALS, Issue 7 2010Heiko Ballmes Within this work, the development of a cost efficient and reliable production technique for infiltrating carbon fibers with aluminum using a conventional cold chamber die casting machine is reported. Results are presented that demonstrate the large potential of pressure die casting as a low cost manufacturing process for carbon fiber reinforced aluminum matrix composites. The influence of process parameters on the infiltration behaviour is investigated and compared to results gained by numerical simulation. [source] Processing of Carbon Nanofiber Reinforced ZrB2 Matrix Composites for Aerospace Applications,ADVANCED ENGINEERING MATERIALS, Issue 7 2010Jorge Barcena Ceramic matrix composites (CMCs) based on zirconium diboride (ZrB2) reinforced by vapor grown carbon nanofibers are a potential constituent of reusable thermal protection systems. A manufacturing procedure was devised that involved the fabrication of thin films by tape casting to obtain a layer that could be integrated into a more complex system. Higher thermal conductivities and improved toughness can be expected for nanofiber additions, as compared to the matrix alone. Consolidation by hot-pressing was more effective than pressureless sintering, in terms of the final relative density and flatness of specimens. Examination of microstructures showed that few carbon nanofibers were present in the matrix after consolidation by sintering, which was attributed to a reaction between the nanofibers and zirconium oxide present on the surface of the ZrB2 powder. As a solution, oxygen impurities from the boride powders were removed by reduction with carbon coatings derived from phenolic resin. The deleterious reaction was avoided, but residual carbon remained at the grain boundaries, likely from decomposition of the binder. The use of an alternative binder (PMMA vs. PVB) will be used in future studies to reduce the residual carbon content. Further, consolidation by Spark Plasma Sintering (SPS) will be explored to further reduce the reaction of surface oxides with the nanofibers. Finally, characterization of the microstructure at the nanometric level and further determination of the mechanical and thermal properties will be conducted as part of future studies. [source] In Situ Damage Detection With Acoustic Emission Analysis During Cyclic Loading of Wire Reinforced EN AW-6082,ADVANCED ENGINEERING MATERIALS, Issue 7 2010Kay André Weidenmann In the field of lightweight construction, hybrid structures such as reinforced metal matrix composites are highly qualified materials. The direct composite extrusion process allows for continuous manufacturing of wire reinforced aluminum matrix profiles. The aim is to increase the stiffness and specific strength in a way that the composite material shows better mechanical properties than the single matrix material. To determine and locate damage evolution during cyclic loading of spring steel reinforced EN AW-6082 matrix the acoustic emission analysis is used. Furthermore it allows for getting more information about the damage mechanisms during fatigue of the matrix and the final failure of the reinforcing element. The current work also includes the determination of damage evolution using strain measuring methods. [source] Cost-Efficient Metal,Ceramic Composites,Novel Foam-Preforms, Casting Processes and Characterisation,ADVANCED ENGINEERING MATERIALS, Issue 3 2010Gisela Standke Because of their dissatisfactory cost-performance ratio metal matrix composites (MMCs) are still not established in industry, although they show improved properties compared to pure metals in some application fields. The present paper describes the development of enhanced MMCs based on silicon carbide (SiC) foams made by the Schwartzwalder process. Therefore, foams with cell sizes of 30, 45 and 60,ppi based on pressure less sintered SiC (SSiC) were developed. They were coated with layers of coarse SiC particles, which form a rough strut surface. The ceramic content of the foams could be increased to values of 20,30,mass%. Additionally, foam preforms based on clay-bonded SiC (as they are known from molten metal infiltration) were tested. The preforms were infiltrated with aluminium alloys AlSi9Cu3 and AlSi7Mg0.6 and cast iron EN-GJSA-XNiCr35-5-2 and EN-GJL-250. For aluminium alloys high pressure die casting (HPC) as well as gravity casting was applied, whereas iron was only infiltrated by gravity casting. For HPC an excellent interlocking of metal and preform was observed because of the microporosity of the rough surface of the SSiC foam struts. By the use of gravity casting preform cells up to 45,ppi could be well infiltrated. Microporosity in the ceramic coating and the typical hollow struts of the foams did not show metal infiltration. Even by use of moderate ceramic volume fractions pressure-infiltrated aluminium matrix composites showed a high specific stiffness of up to E/,,=,42,GPa,cm3,g,1 compared to conventional Al or Mg alloys (E/,,=,25,27,GPa,cm3,g,1). Ceramic foam based MMCs produced by pressure less casting showed no advantages in mechanical properties compared to pure metals. Nevertheless it can be expected that they can provide improved wear resistance and lower thermal expansion coefficients. [source] 3D Architecture and Load Partition in Eutectic Al-Si Alloys,ADVANCED ENGINEERING MATERIALS, Issue 12 2009Guillermo Requena Abstract The changes of the three dimensional architecture of a eutectic AlSi12 alloy during heat treatment are revealed by means of synchrotron holotomography. The non-destructive nature of the holotomography technique allows to analyze the same volumes in different thermal conditions. The results show a disintegration of the interconnected eutectic Si-lamellae into isolated elongated particles. The load carrying capacity of both types of Si morphologies is studied by in situ neutron diffraction during compression tests. The experimental results are compared to those obtained using a micromechanical model developed for metal matrix composites based on a homogenization approach. The correlation between experiments and calculations shows that the interconnectivity of Si must be considered to account for the strength exhibited by the eutectic alloy. The present study bridges the gap between the already available two-dimensional studies of architecture and properties of the binary AlSi12 alloy and new three-dimensional studies of more complex systems based on this alloy. [source] High Strength (Ti58Ni28Cu8Si4Sn2)100,xMox Nanoeutectic Matrix,, -Ti Dendrite, BMG-Derived Composites with Enhanced Plasticity and Corrosion ResistanceADVANCED ENGINEERING MATERIALS, Issue 11 2009Hesham E. Khalifa Semi-solidly processed(Ti58Ni28Cu8Si4Sn2)100,xMox nanoeutectic matrix composites utilize a ductile dendritic , -Ti phase to achieve enhanced plasticity up to 15% total strain while maintaining fracture strengths up to 2300 MPa. The choice of Mo as the , -Ti stabilizer plays an important role in enhancing the work hardening exponent as well as the corrosion resistance in these alloys. [source] Microstructures and Mechanical Properties of ZrC Reinforced (Zr-Ti)-Al-Ni-Cu Glassy Composites by an In Situ Reaction,ADVANCED ENGINEERING MATERIALS, Issue 5 2009Tao Liu Wetting behaviors of TiC and ZrC by a molten Zr55Al10Ni5Cu30 alloy were investigated in order to give an instruction in synthesizing the glassy composites using a liquid casting route. The (Zr-Ti)55Al10Ni5Cu30 bulk metallic glass matrix composites, reinforced by in situ ZrC particles were then fabricated by copper mold casting. The microstructure and mechanical properties were investigated systematically. [source] Novel Nanoparticle-Reinforced Metal Matrix Composites with Enhanced Mechanical PropertiesADVANCED ENGINEERING MATERIALS, Issue 8 2007C. Tjong Abstract This paper summarizes and reviews the state-of-the-art processing methods, structures and mechanical properties of the metal matrix composites reinforced with ceramic nanoparticles. The metal matrices of nanocomposites involved include aluminum and magnesium. The processing approaches for nanocomposites can be classified into ex-situ and in-situ synthesis routes. The ex-situ ceramic nanoparticles are prone to cluster during composite processing and the properties of materials are lower than the theoretical values. Despite the fact of clustering, ex-situ nanocomposites reinforced with very low loading levels of nanoparticles exhibit higher yield strength and creep resistance than their microcomposite counterparts filled with much higher particulate content. Better dispersion of ceramic nanoparticles in metal matrix can be achieved by using appropriate processing techniques. Consequently, improvements in both the mechanical strength and ductility can be obtained readily in aluminum or magnesium by adding ceramic nanoparticles. Similar beneficial enhancements in mechanical properties are observed for the nanocomposites reinforced with in-situ nanoparticles. [source] Hot-Pressed Glass Matrix Composites Containing Pyrochlore Phase Particles for Nuclear Waste Encapsulation,ADVANCED ENGINEERING MATERIALS, Issue 7 2003A.R. Boccaccini As alternative immobilization materials for Pu-bearing nuclear waste, lead-containing glass matrix composites with homogeneously distributed lanthanum zirconate pyrochlore particles (up to 30,% by volume) have been developed. Fabrication by hot pressing at the relatively mild temperature of 610,°C leaves the pyrochlore structure of the La zirconate unchanged, which is crucial for the containment of radioactive nuclei. The Figure, an SEM image of a polished sample with 30,% La2Zr2O7, demonstrates the homogeneous particle distribution and absence of pores. [source] Preliminary study of the crack healing and strength recovery of Al2O3 -matrix compositesFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 2 2004L. JUN ABSTRACT This study focused on the crack-healing behaviour of three commercial Al2O3,ceramic-matrix composites: TiCP/Al2O3, ZrO2/Al2O3 and SiCW/Al2O3. Vickers indentation was used to introduce surface flaws with different loads of 49, 98 and 196 N. Then the cracked specimens were annealed in air for 1 h at 1000, 1200 and 1400 °C. The annealing treatment was also conducted at 1200 °C in vacuum for 1 h. Results showed that the annealing treatments increased the indentation strength, but the extent of the increase was different. When annealed in air, the main crack-healing mechanism of TiCP/Al2O3 and SiCW/Al2O3 composites was chemical reaction. When annealed in vacuum, stress relaxation caused much less strength recovery. The main crack-healing mechanism of ZrO2/Al2O3 was the existence of low melting eutectic and the rearrangement of grains caused by ZrO2(m), ZrO2(t) transformation in the crack-opening process zone. The effects of annealing temperature, atmosphere and indentation load on the degree of strength recovery were all related to the crack-healing mechanisms. [source] Ceramic Matrix Composites: A Challenge in Space-Propulsion Technology ApplicationsINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 2 2005Stephan Schmidt Various technology programs in Europe are concerned, besides developing reliable and rugged, low-cost, throwaway equipment, with preparing for future reusable propulsion technologies. One of the key roles for realizing reusable engine components is the use of modern and innovative materials. One of the key technologies that concerns various engine manufacturers worldwide is the development of fiber-reinforced ceramics,CMCs (ceramic matrix composites). The advantages for the developers are obvious,the low specific weight, the high specific strength over a large temperature range, and their great damage tolerance compared with monolithic ceramics make this material class extremely interesting as a construction material. Over the past few years, the EADS-ST Company (formerly DASA) has, together with various partners, worked intensively on developing components for hypersonic engines and liquid rocket propulsion systems. In the year 2000, various hot-firing tests with subscale (scale 1:5) and full-scale nozzle extensions were conducted. In this year, a further decisive milestone was achieved in the sector of small thrusters, and long-term tests served to demonstrate the extraordinary stability of the C/SiC material. Besides developing and testing radiation-cooled nozzle components and small-thruster combustion chambers, EADS-ST worked on the preliminary development of actively cooled structures for future reusable propulsion systems. In order to get one step nearer to this objective, the development of a new fiber composite was commenced within the framework of a regionally sponsored program. The objective here is to create multidirectional (3D) textile structures combined with a cost-effective infiltration process. Besides material and process development, the project also encompasses the development of special metal/ceramic and ceramic/ceramic joining techniques as well as studying and verifying nondestructive investigation processes for the purpose of testing components. [source] Polymer characterization by ultrasonic wave propagationADVANCES IN POLYMER TECHNOLOGY, Issue 2 2008Francesca Lionetto Abstract The propagation of low-intensity ultrasound in polymers, acting as a high-frequency dynamic mechanical deformation, can be successfully used to monitor changes in the modulus of polymers associated with glass transition, crystallization, cross-linking, and other chemical and physical phenomena related to changes in the viscoelastic behavior, such as gelation phenomena. The velocity of sound is related to the polymer storage modulus and density, whereas the absorption of ultrasonic waves is related to the energy dissipation in the material and, therefore, to the loss modulus. Accordingly, ultrasonic measurements have been used by several authors to monitor the evolution of the viscoelastic moduli of polymers as a function of time or temperature and, recently, become a characterization technique of its own right, generally known as ultrasonic dynamic mechanical analysis (UDMA). Often the technique is used in conjunction with rheological methods as a means of providing a better insight into the viscoelastic behavior of polymer systems. As yet UDMA is underutilized primarily because of the low operating temperatures (usually below 100,C) of commercially available ultrasonic transducers, and also due to the requirement of a coupling medium to ensure an efficient energy transfer mechanism between the transducer and the test material. Despite these limitations, this paper shows that the use of ultrasonics is potentially a powerful method for the characterization of polymers, particularly as a tool for online monitoring of events occurring during polymer processing and in the manufacture of polymer matrix composites. The aim of this paper is to review the progress made in recent years, highlighting the potential and reliability of UDMA for monitoring physical transitions in polymers such as glass transition, melting, crystallization, as well as physical changes taking place during curing of thermosetting resins. © 2009 Wiley Periodicals, Inc. Adv Polym Techn 27:63,73, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20124 [source] A preliminary study on bladder-assisted rotomolding of thermoplastic polymer compositesADVANCES IN POLYMER TECHNOLOGY, Issue 1 2007A. Salomi Abstract In this preliminary work, a new process is examined for manufacturing hollow parts from continuous fiber-reinforced thermoplastic polymer. The new process combines the basic idea of bag forming (or bladder-assisted forming) with the rotation of the mold for the processing of thermoplastic matrix composites. A pressurized membrane is used to compact the composite on the inner wall of a mold, which is placed inside a forced convection oven. The mold is removed from the oven for the cooling stage. The process was initially developed by using a thermoplastic pre-preg obtained using yarns of commingled E-glass fibers with isotactic polypropylene (iPP). A preliminary characterization of the thermoplastic composite showed that the material can be consolidated with pressures as low as 0.01 MPa, which is readily achievable with the process of this study. The design of the mold and membrane was carried out on the basis of both structural analysis of the aluminum shell and thermal analysis of the mold. The mold thickness is of great importance with respect to both the maximum pressure allowed in the process and the overall cycle time. Molding was performed on stacks of three and six layers of yarn, varying the applied pressure between 0.01 and 0.05 MPa and maximum temperature of the internal air between 185°C and 215°C. The composite shells obtained under different processing conditions were characterized in terms of physical and mechanical properties. Mechanical properties comparable with those obtained by compression molding and vacuum bagging were obtained. The maximum values obtained are 12.1 GPa and 290 MPa for the flexural modulus and the flexural strength, respectively. Furthermore, the results obtained show that mechanical properties improve with increasing the pressure during the cycle and with the maximum temperature used in the process. © 2007 Wiley Periodicals, Inc. Adv Polym Techn 26:21,32, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20085 [source] Chemical modification and surface reactions on carbon fibers studied by SERSJOURNAL OF RAMAN SPECTROSCOPY, Issue 12 2006Bing Xu Abstract Carbon fibers were modified by reacting with maleic anhydride (MA) and oxidation in nitric acid to alter their inert nature. Bismaleimide, acting as a model compound of polyimide, was chosen to react with the surface-active carbon fibers. Surface-enhanced Raman scattering was performed by chemically depositing Ag colloids on different carbon fiber samples, including raw, modified and post-reaction materials. The obtained enhanced Raman spectra explained the surface chemistry of the different carbon fiber samples and their further interaction with bismaleimide. The results could serve as a guide for the design of functional groups on carbon fibers and the manufacture of the carbon-fiber-reinforced polyimide matrix composites. Moreover, the effect of different laser powers and laser irradiation times on the carbon fiber surface was studied and is discussed. Copyright © 2006 John Wiley & Sons, Ltd. [source] Interpreting Impedance Response of Silicon Carbide Whisker/Alumina Composites Through Microstructural SimulationJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2006David S. Mebane A three-dimensional, object-defined Monte Carlo simulation is applied to alumina-silicon carbide whisker ceramic matrix composites. The simulation takes whisker orientation and size distributions into account simultaneously, and calculates a connectivity factor that relates whisker conductivity to macroscopic conductivity. Simulation results are compared with electrical measurements taken on real samples via impedance spectroscopy. Results show that the effect of whisker clumping can be seen in the impedance response as a decrease in the overall measured conductivity. Results also show that interfacial resistance influences the overall resistivity strongly relative to connectivity at volume fractions far above the percolation threshold. The possible mechanisms for interfacial resistance in the composite and their effect on the impedance response are discussed. [source] Spark-Plasma Sintering of Silicon Carbide Whiskers (SiCw) Reinforced Nanocrystalline AluminaJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2004Guo-Dong Zhan The combined effect of rapid sintering by spark-plasma-sintering (SPS) technique and mechanical milling of ,-Al2O3 nanopowder via high-energy ball milling (HEBM) on the microstructural development and mechanical properties of nanocrystalline alumina matrix composites toughened by 20 vol% silicon carbide whiskers was investigated. SiCw/,-Al2O3 nanopowders processed by HEBM can be successfully consolidated to full density by SPS at a temperature as low as 1125°C and still retain a near-nanocrystalline matrix grain size (,118 nm). However, to densify the same nanopowder mixture to full density without the benefit of HEBM procedure, the required temperature for sintering was higher than 1200°C, where one encountered excessive grain growth. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results indicated that HEBM did not lead to the transformation of ,-Al2O3 to ,-Al2O3 of the starting powder but rather induced possible residual stress that enhances the densification at lower temperatures. The SiCw/HEBM,-Al2O3 nanocomposite with grain size of 118 nm has attractive mechanical properties, i.e., Vickers hardness of 26.1 GPa and fracture toughness of 6.2 MPa·m1/2. [source] Processing and Properties of a Porous Oxide Matrix Composite Reinforced with Continuous Oxide FibersJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2003Magnus G. Holmquist A process to manufacture porous oxide matrix/polycrystalline oxide fiber composites was developed and evaluated. The method uses infiltration of fiber cloths with an aqueous slurry of mullite/alumina powders to make prepregs. By careful manipulation of the interparticle pair potential in the slurry, a consolidated slurry with a high particle density is produced with a sufficiently low viscosity to allow efficient infiltration of the fiber tows. Vibration-assisted infiltration of stacked, cloth prepregs in combination with a simple vacuum bag technique produced composites with homogeneous microstructures. The method has the additional advantage of allowing complex shapes to be made. Subsequent infiltration of the powder mixture with an alumina precursor was made to strengthen the matrix. The porous matrix, without fibers, possessed good thermal stability and showed linear shrinkage of 0.9% on heat treatment at 1200°C. Mechanical properties were evaluated in flexural testing in a manner that precluded interlaminar shear failure before failure via the tensile stresses. It was shown that the composite produced by this method was comparable to porous oxide matrix composites manufactured by other processes using the same fibers (N610 and N720). The ratio of notch strength to unnotch strength for a crack to width ratio of 0.5 was 0.7,0.9, indicating moderate notch sensitivity. Interlaminar shear strength, which is dominated by matrix strength, changed from 7 to 12 MPa for matrix porosity ranging from 38% to 43%, respectively. The porous microstructure did not change after aging at 1200°C for 100 h. Heat treatment at 1300°C for 100 h reduced the strength for the N610 and N720 composites by 35% and 20%, respectively, and increased their brittle nature. [source] Evaluation of different sealing methods for anodized aluminum-silicon carbide (Al/SiC) composites using EIS and SEM techniquesMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 11 2007H. Herrera-Hernandez Electrochemical impedance spectroscopy (EIS) and the scanning electron microscope (SEM) have been used in an investigation of the effectiveness of various sealing methods that can be used to improve the corrosion resistance of an anodized aluminum-silicon carbide (Al/SiC) composite. Anodic oxide films were grown on Al7075-T6 and the Al/SiC composite by sulfuric acid anodizing and sealing in a cold saturated solution of nickel acetate. Other samples were sealed using the traditional method of boiling water or hot nickel acetate for comparison. The results revealed a uniform anodized layer on Al7075-T6 that resisted pitting corrosion for more than 2,weeks exposure to NaCl, whereas a cracked oxide film with variations in thickness was observed on the composite material. Pit initiation occurred in less than 5,days on the anodized Al/SiC that was sealed in the hot solutions. This study suggests that the traditional hot sealing methods did not provide sufficient corrosion protection for aluminum metal,matrix composites (MMCs) because the reinforcing SiC particles deteriorated the surface film structure. However, this defective film can be repaired by nickel hydrate precipitation during cold sealing or by applying a thick polyurethane coating. [source] | |||||||||||||||||||||||||||||||