Advanced Materials Research Vols. 284-286

Abstract: Silicon carbide whiskers were prepared by carbothermal reduction. Materials are silica fume and carbon black, Si, Fe₂O₃, Si-Fe as catalyst, the phase composition and microstructure of compound products were investigated by XRD and SEM, effect of synthesized temperature, kind of catalysts, amount of catalyst were discussed. The results showed that: Silicon carbide whiskers were synthesized by silica fume and black carbon, add catalyst, synthesis temperature is 1550°C. Synthesis effect of silicon carbide whiskers with Si is better than Si-Fe and Fe₂O₃. Adding amount of Si is 2%, synthesized rate of silicon carbide whiskers is high, it is straight, length is 10~15μm, diameter is 0.1~0.3μm.

Abstract: The effects of different amounts of rare earth Gd added into AZ61 on the microstructure and mechanical properties of magnesium alloys were studied in this paper. And it adopts T6 heat treatment. When 2% Gd has been added, the microstructure of the alloy becomes uniform. The grains are refining. Gd is prior to reacting with Al for forming Al₂Gd phase with high melting point. It is in the form of dot-like and globosity along the grain boundary. And β-Mg₁₇A1₁₂ phase is reduced and its shape is thinner. The Al₂Gd phase hinders dislocation movement. It markedly improves the mechanical properties of the alloy at room temperature and high temperature.

Abstract: An analysis process for break impact loadings to tower, conductors and unfaulted insulators is proposed when one of the composite multi- insulators tension string comes to rupture. A finite element method is used to simulate the break impact process in order to consider the whole structural model of transmission lines and geometric nonlinearity. And a two-step calculation process, form-finding analysis and break impact analysis, is performed. The calculation results are verified by testing data. And an impact influence coefficient is defined to characterize the influence of maximum impact loading to tower, unfaulted insulators, conductors and fittings. A typical example with the structure of three-composite-insulators string and two/three suspension points is presented. The impact loading characteristics are obtained with different fracture locations. The obtained results are beneficial to design composite multi-insulators tension string structure.

Abstract: This article studies the mechanical properties of PA6 reinforced polymer blends comprised of a soft PMMA matrix. These composites are designed as a model system to investigate the impact of the content of the two phases on the composite mechanical properties. The addition of the PA6 phase to the matrix PMMA increases the strength of the blend, but lowers its toughness as it decreases the elongation at break. When PA6 particles are added the blends become relatively brittle. The composites containing moderate content of PA6 particles show enhanced tensile modulus and strength. This enhancement is associated with the formation of a network within the polymeric matrix comprised of PA6 particles welded together by the minor component.

Abstract: PA66 nanocomposites with various contents of TiO2 were prepared by twin-screw extruder in order to study the influence of inorganic nanoparticles on tribological properties of PA66melt-intercalation method. The effects of content of nanoparticles and load on friction coefficient and wear volume loss were investigated, respectively. The tensile properties of PA66/TiO2 nanocomposites were greatly improved. The tribological behaviors of the PA66/TiO₂ nanocomposites against steel ring were evaluated on a block-on-ring type (M-2000) wear tester. Nano TiO2 at 1vol.% was effective for improving the tribological properties of neat PA66, because the nano TiO2 at the low content may act as the reinforcing element to bore load and thus decrease the plastic deformation.

Abstract: Wind loads are key considerations in the structural design of steel roof structures, especially for large span ones. The analysis of wind loads on large span steel roof structure (LSSRS) requires large amounts of calculations. Due to combined effects of horizontal and vertical winds, the wind induced vibrations of LSSRS are analyzed with the frequency domain method as the first application of the method for the analysis of wind responses of LSSRS. A program is developed to analyze the wind-induced vibrations due to a combination of wind vibration modes. The program, which predicts the wind vibration coefficient and wind pressure acting on the LSSRS, is designed with input and output interfaces to other finite element software, resulting in preferably solving the wind load analytical problem in the design of LSSRS. The effectiveness and accuracy of the proposed method and the program are verified by numerical analyses of practical projects.

Abstract: The stress-absorbing interlayer of modified asphalt mixture studied in this report is a special asphalt pavement mixture. Capable of delaying the occurrence of reflection cracks, the asphalt mixture is mainly composed of aggregate passing through a 9.5 mm sieve, machine-made or natural sand, and modified asphalt binder. Because the adopted modified asphalt binder can form the highly elastic network structure in the mixture with good fatigue resistance, the stress-absorbing interlayer of modified asphalt mixture can effectively delay reflection cracks of semi-rigid base pavement.

Abstract: The effect of microstructure and its distribution of pyrolytic carbon in different deposition stage in carbon-carbon composites infiltrated by multi-factor physical fields chemical vapor infiltration (CVI) on the mechanical has been studied by polarized -light microscopy, Raman spectra, scanning electron microscope and three-point bending tests. The temperature and the change of the [A_S/V_R]-ratio with progressive infiltration are key parameters for the formation of microstructure and its distribution of pyrolytic carbon around the same fiber. SL pyrolytic carbon corresponds to brittle failure mode and smooth two-step fracture surface due to its low and uniform texture，although the abnormal graphitization occurs in the carbon fiber near the fiber/matrix interface. In contrast, RL matrix can function for achievement of nonbrittle fracture behavior with a zig-zag-like fracture surface and a relatively high value of flexural strength due to high and nonuniform texture.

Abstract: Mixtures of WC-Co containing 6% and 9%wt cobalt and having variable particles size of 8nm, 50nm and 3.5mm were selected for sintering by spark plasma sintering (SPS). The starting powder of WC with a particle size of ~3.5mm was ball milled for intervals of 3 hours for up to 72 hours yielding WC with 8nm average crystallite size. Later, pre-milled WC powders were ball mixed for 18 hours with cobalt. All sizes of powders, 8nm, 50nm and 3.5mm were sintered in SPS at the temperature of 1150°C and 1250°C for 10 minutes by applying uniaxial pressures of 50 and 75 MPa. Sintering parameters were optimized by examining densification and microstructural observations. Sintered samples were studied by XRD, SEM, and hardness testing. It was observed that optimizing the parameters of SPS has a crucial role in increasing the densification percentage of the final product and slightly affects the hardness values.

Abstract: Mo-9Si-8B-3Hf alloy consisting of a Mo solid solution and intermetallic phases Mo₃Si and Mo₅SiB₂ was fabricated by hot pressing sintering to yield a fine microstructure with all three phases being in the size range of micrometer. The tensile properties of this alloy at elevated temperature were evaluated in vacuum at elevated temperatures. This alloy displayed extensive plasticity or superplasticity at temperatures ranging from 1400 °C to 1560 °C with strain rate of 3×10^-4 s^-1. The tensile elongation of 410% is measured at 1560 °C. Grain boundary sliding is the main mechanism of plastic deformation for this alloy.