Applied Mechanics and Materials Vols. 341-342

Abstract: In this paper, the axisymmetric general steady-state solution for porous media is presented. And the completeness of the P-Ns representation for the axisymmetric displacement field equation is proved directly from the equations governing the displacement field, which can be applied to homogeneous and isotropic poroelastic materials. At last, the Boussinesq general solution and Timpe general solution are obtained from P-N General Solution.

Abstract: Uniform spherical alumina powders have been synthesized via homogeneous precipitation method from aluminum nitrate using urea as the precipitant. The amount of ammonium sulfate has a significant effect on morphology and particle size of the precursor powders. It was found that spherical particles can be obtained when the molar ratio of ammonium sulfate to aluminum nitrate is about 0.72 and the concentration of the aluminum nitrate is 0.005M. Spherical alumina particles with 400 nm in diameter were obtained by calcining the precursors at 1100°C for 4 hrs.

Abstract: The gradual damage progress of unidirectional laminate T700/ epoxy 6808 is investigated by acoustic emission test, and impact rate, impact amplitude, cumulative impact and impact energy in different test stages are measured. The results indicate that the sample suffers from diverse damage models in different loading stages. In the initial stage, damage mode is matrix crack, while other modes like matrix crack/ crack propagation, interface fracture and fiber breakage can be successively detected in the test.

Abstract: Aiming at electrical contact degradation behavior of beryllium bronze in storage, electrical contact accelerated degradation test was made. Choosing contact resistance as the performance degradation sensitive parameter, studied its degradation behavior by testing contact resistance of beryllium bronze under different temperature after different oxidized times. The result shows that the relationship between contact resistance and oxidized time is exponential and the lifetime of beryllium bronze samples at normal stress is 24.4 years when failure threshold is 100 mΩ and confidence is 95%, which is predicted by Arrhenius model related to temperature.

Abstract: The Y₃Al_5-xFe_xO₁₂ (0x5, YAIG) powders have been prepared by co-precipitation technique in which NH₄HCO₃ or (NH₄)₂CO₃ is used as a precipitant and Y(NO₃)₃·6H₂O, Al (NO₃)₃·9H₂O and Fe (NO₃)₃·9H₂O as raw materials. The composition of YAIG precursor, the phase formation process of YAIG and the properties of the powders were investigated by means of XRD, SEM, TEM and EDS. The results indicated that the precipitant effects the preparation of pure-phase YAIG powders. AC as precipitant could produce a hydroxide precursor, which transformed to a mixture. AHC as precipitant could produce a loosely agglomerated carbonate precursor. The resultant YAIG powders showed good dispersity and excellent sinterability.

Abstract: An environmental, biodegradable breeding container made from rice hull and starch adhesive was produced by a hot-press machine. The heat treatment was introduced to improve the properties of breeding container. The dry and wet strength, water absorption, FTIR, biodegradation, and thermal stability were tested and discussed. The results showed that curing temperature played a great influence of on the dry and wet strength of breeding container. The dry and wet strength was increased with the temperature rise. The water absorption decreased from 89.1% to 50.9%. Pattern of the peak at 3400 cm^-1, 2900 cm^-1, 1640 cm ^-1, 1500 cm^-1 and 1050 cm^-1 has changed after the heat treatment of specimens. The hydrogen bond was likely produced between straw and adhesive during the heat treatment process. The degradation rate of specimens after heat treatment was lower because the high temperature led to deeper cross-linked reaction. The TGA showed that heat treatment can improve the thermal stability, while the degradability was not changed.

Abstract: The ceramic-resin composite structure is generally used as the investment casting pattern. Due to the coefficient of thermal expansion (CTE) of resin is higher than that of ceramic, the thermal expansion of the resin pattern will lead to the crack of the ceramic shell during the burnout procedure. Simultaneously, the stiffness of the whole structure should be maintained at a certain level. In this paper, topology optimizations with respect to the cavity configuration of the resin pattern were developed to find out the optimal designs. A method involves the assist element was also introduced to control the rigid displacement of the ceramic shell during the heating procedure. Several optimal designs were presented and the comparison of the objectives respectively before and after the optimization investigated these designs could avoid the crack problem of the ceramic shell effectively.

Abstract: TiCoSb-based half-Heusler compounds, which are narrow band gap semiconductors with a high Seebeck coefficient, have been intensively studied in bulk form but rarely in thin films. In this article TiFe_xCo_1-xSb (x=0, 0.17) thin films were synthesized on n-type single crystal Si (100) and MgO (100) substrates by DC magnetron sputtering followed by rapid thermal annealing. The X-ray diffraction patterns show that Fe doping does not affect the crystallization temperature of TiCoSb phase, but seem to induce the formation of binary phases like TiSb. Hall measurements reveal that the undoped TiCoSb thin films are n-type semiconducting, while TiFe_0.2Co_0.8Sb turns to p-type with half-order higher carrier concentration of 1.5×10²¹ cm^-3. The vibrating sample magnetometer spectrum indicate that the TiCoSb thin film is non-magnetic and TiFe_xCo_1-xSb (x=0.17) is weak magnetic.

Abstract: Based on taking combustion synthesis into high-gravity field to fabricate high-hardness bulk solidified TiC-TiB₂ composite, layered composite of solidified TiC-TiB₂ ceramic to Ti-6Al-4V alloy was obtained by the introduction of Ti-6Al-4V alloy plates at the bottom of graphite crucible. XRD, FESEM and EDS results showed that the layered composite was achieved in multi-scale (micron/submicron/micro-nanometer) and multi-level (TiC_1-x-TiB-TiB₂ + TiB₂-Ti-TiC_1-x-TiB + TiB₂-TiC_1-x-TiB-Ti + TiB-TiC_1-x-Ti + TiC_1-x-Ti + Ti) graded microstructure between the ceramic and Ti alloy, which was characterized by size and distribution of TiB₂ and TiB, thereby paving a new way for developing light-weight materials for special engineering.

Abstract: Based on increasing the acceleration of high-gravity field from 500 g to 2500 g, a series of TiC-TiB₂ composites are prepared by combustion synthesis in high-gravity field, and microstructure modification, microstructure homogeneity and mechanical properties of TiC-TiB₂ composites are discussed in terms of liquid-liquid separation of TiC-TiB₂ and Al₂O₃ in high gravity field. XRD, FESEM and EDS results showed that by increasing the acceleration of high gravity field, Al₂O₃ inclusions in the ceramic decreased both in volume fraction and size due to the enhanced separation of TiC-TiB₂ liquid and Al₂O₃ liquid, while the enhanced Stokes flow induced by the enhanced liquid-liquid separation also promoted the constitutional homogeneity of TiC-TiB₂ melt, thereby bringing about the refinement of the solidified microstructures, finally, making Vickers hardness and fracture toughness of the composites increase with the acceleration of high gravity field.