Book reviewsComposite materials: fatigue and fracture: Edited by: H.T. Hahn ASTM STP 907, 1986 (£64.00)

The effect of Si 3 N 4 , Ta 5 Si 3 , and TaSi 2 additions on the oxidation behavior of ZrB 2 was characterized at 1200°-1500°C and compared with both ZrB 2 and ZrB 2 /SiC. Significantly improved oxidation resistance of all Si-containing compositions relative to ZrB 2 was a result of the formation of a protective layer of borosilicate glass during exposure to the oxidizing environment. Oxidation resistance of the Si 3 N 4 -modified ceramics increased with increasing Si 3 N 4 content and was further improved by the addition of Cr and Ta diborides. Chromium and tantalum oxides induced phase separation in the borosilicate glass, which lead to an increase in liquidus temperature and viscosity and to a decrease in oxygen diffusivity and of boria evaporation from the glass. All tantalum silicide-containing compositions demonstrated phase separation in the borosilicate glass and higher oxidation resistance than pure ZrB 2 , with the effect increasing with temperature. The most oxidation-resistant ceramics contained 15 vol% Ta 5 Si 3 , 30 vol% TaSi 2 , 35 vol% Si 3 N 4 , or 20 vol% Si 3 N 4 with 10 mol% CrB 2 . These materials exceeded the oxidation resistance of the ZrB 2 /SiC ceramics below 1300°-1400°C. However, the ZrB 2 /SiC ceramics showed slightly superior oxidation resistance at 1500°C.

High‐Temperature Chemistry and Oxidation of ZrB2 Ceramics Containing SiC, Si3N4, Ta5Si3, and TaSi2

Ceramic/polymer composites have been considered as third-generation orthopedic biomaterials due to their ability to closely match properties (such as surface, chemistry, biological, and mechanical) of natural bone. It has already been shown that the addition of nanophase compared with conventional (or micron-scale) ceramics to polymers enhances bone cell functions. However, in order to fully take advantage of the promising nanometer size effects that nanoceramics can provide when added to polymers, it is critical to uniformly disperse them in a polymer matrix. This is critical since ceramic nanoparticles inherently have a strong tendency to form larger agglomerates in a polymer matrix which may compromise their properties. Therefore, in this study, model ceramic nanoparticles, specifically titania and hydroxyapatite (HA), were dispersed in a model polymer (PLGA, poly-lactic-co-glycolic acid) using high-power ultrasonic energy. The mechanical properties of the resulting PLGA composites with well-dispersed ceramic (either titania or HA) nanoparticles were investigated and compared with composites with agglomerated ceramic nanoparticles. Results demonstrated that well-dispersed ceramic nanoparticles (titania or HA) in PLGA improved mechanical properties compared with agglomerated ceramic nanoparticles even though the weight percentage of the ceramics was the same. Specifically, well-dispersed nanoceramics in PLGA enhanced the tensile modulus, tensile strength at yield, ultimate tensile strength, and compressive modulus compared with the more agglomerated nanoceramics in PLGA. In summary, supplemented by previous studies that demonstrated greater osteoblast (bone-forming cell) functions on well-dispersed nanophase ceramics in polymers, the present study demonstrated that the combination of PLGA with well-dispersed nanoceramics enhanced mechanical properties necessary for load-bearing orthopedic/dental applications.

/pdf/mechanical-properties-of-dispersed-ceramic-nanoparticles-in-a82uht2l3o.pdf

Mechanical properties of dispersed ceramic nanoparticles in polymer composites for orthopedic applications.

Effect of particle size on the optically transparent nano meter-order glass particle-dispersed epoxy matrix composites

Effect of nanoparticle content on the microstructural and mechanical properties of nano-SiC dispersed bulk ultrafine-grained Cu matrix composites

Effect of particle size on light transmittance of glass particle dispersed epoxy matrix optical composites

Optically transparent polymers are required for the packaging of advanced optoelectric devices; if such materials are available, the communication between the outside and inside devices at near IR light (λ≈ 800 nm) becomes possible. The minimum of the required material properties for the packaging materials are (i) optical transparency at near IR wavelength region and (ii) thermal expansion coefficient close to optoelectronic devices. An epoxy material is one of the strong candidates because the material possesses good optical properties and easy to apply conventional packaging processes. However, the thermal expansion coefficients of epoxy materials are one order larger than those of optoelectronic devices and this thermal expansion mismatch induces severe damage under service condition. Thus, the pure epoxy material could not be used as the packaging material even though its light transmittance is in the required range. The incorporation of glass particles is one of the solutions to reduce the apparent thermal expansion coefficient of epoxy materials, however. The light transmittance after the incorporation is usually lost by the difference between the refractive index of the particle and that of epoxy matrix. Recently, a composite material, which has both an optical transparency and a low thermal expansion coefficient, was reported [1, 2]. The report proved that when the refractive index difference was reduced to the order of 10−3, optical transparency appears in the composite. Theoretical consideration also demonstrates a procedure for the selection of fiber and matrix to achieve optical transparency after the incorporation of a glass fiber into an epoxy matrix [3]. Reports also demonstrated the effect of refractive index difference on the light transmittance [4] and particle size on the light transmittance [5]. However, the relation between the light transmittance and thermal expansion coefficient of the glass particle-dispersed optically transparent epoxy matrix composites is not yet reported. The purpose of this paper is to show the guideline for the property design in light transmittance and thermal expansion coefficient of glass particledispersed epoxy matrix composites. Two different size glass particles were used. The particle had an average diameter of dp= 26 and 85μm. It should be noted that the size of the glass particles was much larger than the wavelength of light in the visible wavelength region. The chemical composition of the glass particle was SiO2 (60 wt %), Al2O3 (17.4 wt %),

Optothermal properties of glass particle-dispersed epoxy matrix composite

The effect of surface-modified SiTiCO (Tyranno®) fiber on the tensile behavior of SiC-matrix minicomposites has been examined. Standard SiTiCO fiber and two kinds of surface-modified fibers were used and the composites were fabricated by a polymer infiltration pyrolysis process. The strengths of the surface-modified-fiber-reinforced minicomposites were significantly improved compared to that of the standard fiber minicomposite. The scattering of tensile strength also decreased with the use of surface-modified fibers. The results demonstrate the achievement of SiTiCO-fiber-reinforced SiC-matrix composite by modifying the surface chemistry of the fiber.

Tensile Fracture Behavior and Strength of Surface-Modified SiTiCO Fiber SiC-Matrix Minicomposites Fabricated by the PIP Process

The energy release rate for an interfacial debond crack in a fiber pull-out model

Unnotched SiC (SCS-6) fiber-reinforced Ti-15-3 alloy composite is subjected to a tension-tension fatigue test in a vacuum of 2×10−3 Pa at 293 and 823 K with a frequency of 2 Hz and R=0.1. Direct observation of the damage evolution process during the test is carried out by scanning electron microscopy (SEM). Test temperature dependent and independent fatigue damage behaviors are observed. The early stage fiber fractures observed at the polished surface are not influenced by the test temperature; however, matrix crack initiation and propagation behaviors differ greatly with temperature. The evolution of interface wear damage also differs with temperature, becoming more severe at 823 K, and the interface wear damage zone increases with the increase of the number of fatigue cycles. The macroscopic fatigue damage appears as a modulus reduction associated with interface sliding, matrix crack propagation, and plastic deformation of the matrix. The deformation zone of the composite tested at 823 K spreads more than that at 293 K. The fatigue life of the composite tested at 823 K is longer than that at 293 K. This behavior is related to the difference in spread of the damage zone in the matrix.

Observation of fatigue damage process in SiC fiber-reinforced Ti-15-3 composite at high temperature

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