[en] This work presents the development and the characterization of Ce O₂-stabilized tetragonal Zr O₂ polycrystals (Ce-TZP ceramics), since it is considered candidate material for applications as structural high performance ceramics, an as substitute of some metallic materials. Ce-TZP ceramics attain remarkable increasing in strength and fracture toughness. Sintered ceramics were fabricated from mixtures of powders containing different Ce O₂ content prepared by conventional mechanical technique. It were adopted the bending strength, Vickers hardness and fracture toughness techniques to the determination of the mechanical parameters. These results were discussed and compared to those published in international literature. (author)

[en] This paper summarizes recent progress in developing Cr₂Nb/Cr(Nb) alloys for structural use in advanced fossil energy conversion systems. Alloy additions were added to control the microstructure and mechanical properties. Two beneficial elements have been identified among all alloying additions added to the alloys. One element is effective in refining the coarse eutectic structure and thus substantially improves the compressive strength and ductility of the alloys. The other element enhances oxidation resistance without sacrificing the ductility. The tensile properties are sensitive to cast defects, which can not be effectively reduced by HIPping at 1450-1590 degrees C and/or directionally solidifying via a floating zone remelting method

[en] A comparison of the finite element method (FEM) simulation using the three types of elements (three, four and eight noded isoparametric) for the plane stress condition is presented. (author). 3 refs., 2 figs

[en] One of the major future applications of titanium matrix composites is as a material for airplane turbine components, e.g., in the compressor. Service temperatures of up to 800 C will be involved. This application objective will only be reached when it will be possible to solve two major material problems: first, a matrix with sufficient ductility at room temperature and sufficient strength at service temperatures has to be found; and second, the problem of fiber/matrix reaction at application temperatures has to be solved. In composites with the high ductility IMI834 alloy (Ti-5.8Al-4.0Sn-3.5Zr-0.7Nb-0.5Mo-0.35Si-0.06C in wt. pct) as matrix, the optimal tensile properties can be exploited: the ultimate tensile strength and Young's modulus values are in accordance with the prediction of the rule of mixtures, and an elongation at fracture of nearly 1.3 pct, typical of SiC fibers, is measured. It was shown that in SiC-SCS-6 fiber-reinforced IMI834 composites, these properties are achieved up to temperatures of 1,000 C. In the present study, results of the thermal stability of the SiC-SCS-6 fiber-reinforced IMI834 alloys are presented

[en] Differences in the chemical compositions and mechanical properties of fibers and different schemes of layer reinforcement of composite shells pose the problem of their optimal choice to ensure high specific strength under dynamic loading (such as for protective constructions of a single action)

[en] Different SiAlON composites based on α'-SiAlON are investigated, with respect to the phase relationships, densification behavior, and mechanical properties. The compositions are located on a phase-diagram line parallel to the Si₃N₄-Y₂O₃·9AlN compound in the Si₃N₄-SiO₂-AlN-Al₂O₃-Y₂O₃-YN system. Analysis of the reaction sequences shows that the formation of the composites is associated with the transient appearance of Y₄Al₂O₉ (YAM), yttrium-aluminum-garnet (YAG), melilite, and a nitrogen-rich liquid phase. The small shift of compositions on the Si₃N₄-Y₂O₃·9AlN compound phase-diagram line toward the Al₂O₃-rich side offers the advantage of a higher sinterability and the removal of the melilite phase from a wide range of compositions containing α'-SiAlON and polytypes. The α'/β'-SiAlON composites show better mechanical properties in comparison to pure α'-SiAlON and composites of α'-SiAlON and polytypes. A post-heat-treatment causes the crystallization of YAG as a grain-boundary phase and leads to excellent strength retention up to temperatures of 1,350 C

[en] The limit flow stresses for transverse loading of metal matrix composites reinforced with continuous fibers and for uniaxial loading of spherical particle reinforced metal matrix composites are investigated by recently developed embedded cell models in conjunction with the finite element method. A fiber of circular cross section or a spherical particle is surrounded by a metal matrix, which is again embedded in the composite material with the mechanical behavior to be determined iteratively in a self-consistent manner. Stress-strain curves have been calculated for a number of metal matrix composites with the embedded cell method and compared with literature data of a particle reinforced Ag-58vol.%Ni composite and for a transversely loaded uniaxially fiber reinforced Al-46vol.%B composite. Good agreement has been obtained between experiment and calculation and the embedded cell model is thus found to represent well metal matrix composites with randomly arranged inclusions. Systematic studies of the mechanical behavior of fiber and particle reinforced composites with plane strain and axisymmetric embedded cell models are carried out to determine the influence of fiber or particle volume fraction and matrix strain-hardening ability on composite strengthening levels. Finally, closed-form expressions are derived to predict composite strengthening levels for regular and random fiber or particle arrangements as a function of matrix hardening and particle volume fraction. The impact of the results on effectively designing technically relevant metal matrix composites reinforced by randomly arranged strong inclusions is emphasized

[en] Thermodynamics of the Bi₂Te₃ monocrystals deflections is studied. The sample reinforcement with thin steel rods, positiond perpendicularly to the cleavage plane, was used for changing the cleavage form. It is found that reinforcement increases the samples strength limits for bending δ more than by two times. It is shown that transition from one type of bending to another leads to essential change of the energy dissipation spectra in the sample by deformation. Certain aspects of practical application of the observed effects are considered

[en] While short compressive stresses can readily be produced by laser ablation, the generation of pure tensile stresses is more difficult. We demonstrate that a 90 degree prism made of polyethylene can serve to produce short and pure tensile stresses. A compressive wave is generated by ablating a thin layer of strongly absorbing ink on one surface of the prism with a Q-switched frequency-doubled Nd:YAG laser. The compressive wave driven into the prism is reflected as a tensile wave by the polyethylene-air interface at its long surface. The low acoustic impedance of polyethylene makes it ideal for coupling tensile stresses into liquids. In water, tensile stresses up to -200bars with a rise time of the order of 20 ns and a duration of 100 ns are achieved. The tensile strength of water is determined for pure tensile stresses lasting for 100 ns only. The technique has potential application in studying the initiation of cavitation in liquids and in comparing the effect of compressive and tensile stress transients on biological media. copyright 1997 American Institute of Physics

[en] The purpose of this study is to evaluate the effects of burn-off on thermal shock resistance and thermal shock fracture toughness of a carbon fiber reinforced carbon composite (C/C composite) and three fine-grained isotropic graphites. The thermal shock resistance and thermal shock fracture toughness was degraded slightly by air oxidation at 500^oC. The extent of degradations of the thermal shock parameters were less than those of the mechanical and fracture mechanics properties, however, they were larger than that of the thermal diffusivity. In observations of the microstructures of the fracture surfaces after oxidation of the graphites, the size and the number of pores were increased and the fracture surfaces were rough due to oxidation of boundaries of graphite particles. After oxidation of the C/C composite, there were preferential removal of the boundary layer between carbon fiber and pyrolytic carbon matrix and pull out of carbon fiber. (author)