Advanced Materials Research Vols. 328-330

Abstract: Molecular dynamics (MD) simulations have been carried out to investigate the defect’s effect on the mechanical properties of copper nanowire with different crystallographic orientations, under tensile deformation. Three different crystallographic orientations have been considered. The deformation mechanism has been carefully discussed. It is found that the Young’s modulus is insensitive to the defect, even when the nanowire’s crystallographic orientation is different. However, due to the defect’s effect, the yield strength and yield strain appear a large decrease. The defects have played a role of dislocation sources, the slips or stacking faults are first generated around the locations of the defects. The necking locations have also been affected by different defects. Due to the surface defect, the plastic deformation has received a large influence for the and orientated nanowires, and a relative small influence is seen for the nanowire.

Abstract: In order to obtain high-speed and large-drive-current during operation, this paper proposed two structure-advanced BiCMOS analog switches. On the key parts of the circuit, a few Bipolar Junction Transistors (BJTs) were used while for the main parts, the Complementary Metal Oxide Semiconductor (CMOS) devices were configured. The component parameters were optimized and the measures for accelerating the operation and raising the drive-current were taken. The performance of the proposed two analog switches was tested through simulation and experiments of hardware circuits. The results indicated that the Delay-Power Product (DP) of the BiCMOS operating in the voltage range of 2.5V~3.5V is reduced by an average of 26.1pJ and the driving current is more than 1.38mA as compared with those of the conventional CMOS analog switches. These advantages show the great potential of the proposed two BiCMOS analog switches in the digital communication systems which require low-voltage, high-speed and large-drive-current.

Abstract: Flow equalization is one of the key technologies in the parallel control of inversion module. This paper presents the multi-inversion module parallel flow equalization system with TMS320LF2407A as the main control chip, which adopts the control strategy of “synchronous control of seizure and coincidence”, gains the data communication in the multi-module parallel connection and the multi-inversion module parallel flow equalization control with CAN controller embedded in TMS320LF2407A. It can be seen from the experimental data and experimental wave that it can effectively restrain the ring current and achieve the equipartition of load in the condition of resistive load and inductive load or capacitive load to achieve the data communication among the parallel inversion modules.

Abstract: This paper analyzed thermodynamic principle of preparation VC,VN and V(C,N) with V₂O₅ and C by carbon-heat reduction. The results show that synthesizing process includes phase change and the vanadium oxide is reduced gradually. And because of the reaction kinetics, there are no obvious boundaries between each reaction. There are two principles for V₂O₅ reducing by carbon thermal method. One reaction depends mainly on CO/CO₂ gas-solid transmitted and another reaction depends mainly on the solid-solid reaction between carbon and vanadium oxide. But no matter what kind of mixing method, two kinds of reaction mechanism are also present in different degree. The reacting principle which is primary is depended on original mixed condition between V₂O₅ and C. It is propitious to reducing process by increasing temperature. The preparation of VC should be done at the condition with CO or vacuum.

Abstract: Silicone resin is the mainly adhesive in mica insulation industry, and this sort of adhesive is easy to produce toxic and harmful volatile organic compounds and causing the environment pollution. Under the premise of no decrease in insulation performance of the mica composite insulation material, the environmental friendly modified starch adhesive is chosen. In order to obtain the high performance composite materials, the improvement of its flexural strength is necessary, and the method of modification is introduced. Four kinds of modified starch, such as: maize soluble starch, oxidized starch, β-dextrin and cationic starch are discussed. The cationic starch is avaliable as the bond medium and the silicone coupling agent KH-550 is used for modified enhancement. When the dosage of the cationic starch is 10% and modified 30mins by silicone coupling agent KH-550 with the concentration of 1%, the flexural strength and dielectric strength of the mica composite insulation material can reach 248.5 N/mm² and 23.16 KV/mm respectively.

Abstract: Room temperature vulcanizing (RTV) silicone rubber coating with superhydrophobicity for anti-pollution flashover is prepared by filling silica-encapsulated calcium carbonate particles (CaCO3/SiO2 composite particles) into polydimethylsiloxane (PDMS) rubber. Two-step spraying technology is applied for fabricating the superhydrophobic RTV coating film on outdoor insulators. The primary spray coating provides basically the strong adhesion and certain hydrophobicity, and the second one produces the appropriate roughness structure and further enhances the superhydrophobicity. The water contact angle on the prepared RTV coating film is 165°and the sliding (rolling) angle of water droplet is about 5°, allowing water droplets to move easily on the coating surface and give self-cleaning function of the RTV coated insulator surface. The flashover voltage of insulators with superhydrophobic RTV coating is 29.95 kV, quite higher than that of insulators with common RTV coating (23.29) and that without RTV coating (11.34 kV).

Abstract: Use Cr15 high chrome steel as base, WC particles as reinforcing particles, and adopting casting-infiltration method, a kind of quite steel-base surface wear-resistant material was prepared. The effect of Alloy powder for WC/steel base surface composite structure and interface was tested by OM, SEM and EDS. The results showed that after adding nickel powder into the composite layer, martensite, austenite, pearlite and eutectic carbide distributed in the matrix; after adding tungsten iron powder into the composite layer, more martensite distributed in the matrix; after adding molybdenum iron powder into the composite layer, martensite, austenite, pearlite and carbide distributed in the matrix. If the base material was high chrome (Cr15) and adds molybdenum iron powder in the composite layer, composite layer interface transition is good, more WC particles and irregular small carbide particles in composite layer.

Abstract: According to BS7448 fracture toughness test standard, crack tip opening displacement (CTOD) for ASTM A333 Gr.6 low temperature steel which is used in offshore platform were carried out in low temperature (0°C, -29°C). Three point bending tests were conducted on the specimens, the dimension of which is B×2B (B is the thickness) and notch direction is NP. The final value of CTOD was calculated by P-V curves of both the welds and HAZ (heat affected zone). And the experimental results were analyzed and discussed in the paper. The low temperature steel welded joints show good low temperature toughness, the selected welding procedure is applied to construction of pipelines.The CTOD value of HAZ is larger than weld metal and weld is the weakest position in the whole structure. The experiment results provide an important basis for the choice of welding method and welding process parameters, ECA assessment and construction of offshore platform.

Abstract: The Poly-crystal alumina short fiber reinforcing 2024 matrix composites was produced by the gas pressure infiltration, and a new apparatus has been developed for the infiltration of MMCs by the gas pressure infiltration technique. The reasonable sintering parameter for the preform were determined.The preform was heated at 450°C to remove the organic binder and pore-forming material, and then heated at 1050°C for 2.5h to obtain the comprehensive properties.Scanning electron microscope was used to observe the tensile fracture of Aluminum matrix composites, and the fracture feature of composites produced in different temperature was analyzed. The melting temperature of 2024Al was 800°C and holding time was 20mins; the infiltration gas pressure was 0.5Mpa and holding time was 20s.And then interface reaction is appropriate between the fiber and matrix ,a good performance of composites was produced.

Abstract: As the loading conditions for the railway vehicles are becoming more and more complex, nominal stress has been unable to fully satisfy the requirements for assessing fatigue strength for weld structures. Hot spots stress is much more closer to the actual stress of a weld structure, it can suit the demand of high speed trains’ fatigue evaluation better. In this paper, on the basis of UIC615-4 standard, the nominal stress of the welded bogie frame was calculated and its fatigue strength was assessed using FEA method. Also, set the joint section between drawbar seat and the transom bottom flange as the object of the study, succeeded in evaluating the hot spot stress of the welded bogie frame. Compared the hot spot stress calculation result with the nominal stress from shell elements, the result shows that hot spot stress is higher than the nominal stress. Using the hot spot stress to assess fatigue has the higher reliability