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Lu Z.,Beihang University | Liu Q.,Beihang University | Han H.,Beihang University | Zhang D.,National Key Laboratory of Advanced Functional Composite Materials Technology
Materials Science and Engineering A | Year: 2013

Two types of porous Si 3N 4 ceramics with different porosity are fabricated by gel casting technique, where the high pure Al 2O 3 and Y 2O 3 are selected as sintering additive. The effective Young's modulus and compression strength are tested by compressive experiments, respectively. The present emphasis is placed on the mechanical characterization of porous Si 3N 4 ceramics by employing finite element (FE) method. Extracting the primary features of bonded networks, the microstructure of real material is reconstructed in the numerical model. For the obtained materials with different porosity, their compressive behaviors are modeled by FE simulation, respectively. Afterwards, the effective Young's modulus and compression strength are calculated from the numerical results. Compared with experiment data, the calculated results provide a sufficient accordance. Moreover, the modeled failure mechanism in microstructure is also verified by experimental observation. Utilizing the present FE model, the influences of grain aspect ratio and properties of grain boundaries on the effective Young's modulus and compression strength are also investigated, which provides an insight into the relationship between microstructure and macro-mechanical properties for porous Si 3N 4 ceramics. © 2012 Elsevier B.V. Source


Geng X.,Beihang University | Zhang Y.,Beihang University | Li Y.,Beihang University | Li S.,National Key Laboratory of Advanced Functional Composite Materials Technology | Shi X.,Beihang University
Materials Science Forum | Year: 2010

Precursor derived Si-B-C-N ceramic is a kind of amorphous materials with high hardness, low density, durability at extremely high temperature. The materials show a great potential to be used in the field of the Thermal Protective System (TPS). The physical states and chemical properties of the amorphous materials greatly depend on the starting materials. The effect of degree of polymerization (DP) of the precursor on the pyrolysis process and the characteristics of the amorphous Si-B-C-N materials are studied. The SiBCN-based preceramic polymer synthesized by dichloromethylvinylsilane, ammonia and BH3·SMe2. Dichloromethylvinylsilane reacted with ammonia and BH3·SMe2 in toluene or tetrahydrofuran (THF) as solvent in the presence of catalytic amounts of pyridine. The polymeric precursors were cured at low temperature to obtain solid-state precursors. Pyrolysis process of the solid-state precursors under various temperatures and carried out in nitrogen atmosphere. The results showed that DP of the precursor influences the pyrolysis process and the high temperature stability of the Si-B-C-N amorphous ceramics. © (2010) Trans Tech Publications. Source


Gao D.,Beihang University | Zhang Y.,Beihang University | Xu C.,National Key Laboratory of Advanced Functional Composite Materials Technology | Song Y.,National Key Laboratory of Advanced Functional Composite Materials Technology | Shi X.,National Key Laboratory of Advanced Functional Composite Materials Technology
Corrosion Science | Year: 2011

Ceramics of ZrB2-20vol.% SiC were prepared by hot pressing method, and ozone (O3) was adsorbed on the surface of the ceramics. Then the as-adsorbed ceramics were oxidized in air and the effect of ozone adsorption on the oxidation behaviour of the ceramic composites was analyzed. The experimental results indicate that adsorption of ozone promotes the oxidation of the ceramic composites, especially for the SiC. In addition, more silica glass formed promotes the formation and crystal growth of zircon. © 2010 Elsevier Ltd. Source


Gao D.,Beihang University | Gao D.,AVIC Commercial Aircraft Engine Co. | Zhang Y.,Beihang University | Xu C.,National Key Laboratory of Advanced Functional Composite Materials Technology | And 2 more authors.
Ceramics International | Year: 2013

The isothermal oxidation of ZrB2 ceramics with different content of SiC was carried out in air up to 1700 °C, and the effect of chemical composition on the oxidation kinetics of ZrB2-SiC ceramics was analyzed. As indicated by the experimental results, both ceramics with 20 vol% and 30 vol% SiC particles followed near parabolic oxidation kinetics. And higher concentration of SiC led to better oxidation resistance performance due to the formation of more silica glass on the surface of the specimens and formation of zircon phase ZrSiO4. In addition, the oxidation of the ceramic composites is diffusion controlled and the activation energies for the diffusion of oxygen in the oxide scale of the ceramics oxidized at temperatures below 1500 °C were 5134 J/mol and 5960 J/mol for ZS2 and ZS3, respectively. Then the oxidation of the ceramics transformed to reaction controlled under elevated temperature due to evaporation of the protective silica glass. Furthermore, the evolution process of the surface morphology and oxide scale of the ceramic during initial oxidation stage was given detailed investigation. © 2012 Elsevier Ltd and Techna Group S.r.l. Source


Lu Z.,Beihang University | Zhou Y.,Beihang University | Feng Z.,National Key Laboratory of Advanced Functional Composite Materials Technology | Yang Y.,National Key Laboratory of Advanced Functional Composite Materials Technology | Ji G.,National Key Laboratory of Advanced Functional Composite Materials Technology
Fuhe Cailiao Xuebao/Acta Materiae Compositae Sinica | Year: 2015

To investigate the damage and failure mechanisms of 2.5D woven fabric composites under compression, and verify the effectiveness of the finite element numerical simulation method with a two-scale, progressive damage model, quasi-static compression experiments were conducted on both warp and weft directional specimens to obtain the corresponding stress-strain curves. And the initial elastic modulus and ultimate strength of materials were measured. On this basis, the compressive stress-strain responses and the damage evolution behavior were simulated using the two-scale, progressive damage finite element numerical method. The results from both experiment and simulation show good agreements, and indicate that the main failure mode of 2.5D woven fabric composites in weft directional compression is the axial crush and fracture of weft yarns, from which relatively higher strength is obtained. Meanwhile, additional bending moment is added to the warp yarn under warp directional compression due to bending, which causes extrusion on surrounding matrix. Therefore, matrix fracture and delamination cracking between neighboring warp yarns easily occur before the axial fracture of warp yarns, which are not conducive to utilize the advantage of fibers in bearing load, and result in relatively lower strength. ©, 2015, Beijing University of Aeronautics and Astronautics (BUAA). All right reserved. Source

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