General design of Sutong Bridge

The main span of Sutong Bridge is a double-pylon, double-plane cable-stayed bridge with steel box girder, which has the world＇ s longest central span of 1 088 m within cable-stayed bridges. To overcome problems caused by severe meteorological conditions, perplexing hydrological conditions, deep buried bedrock and higher navigation level, many new technics and methods were created. Keys including structural system, steel box girder, stayed cable, tower, pier, tower foundation, collision avoidance system, wind-resistance, seismic-resistance, structural nonlinear response and structural static stability were presented individually in this paper.     

Effects of welding wire composition and welding process on the weld metal toughness of submerged arc welded pipeline steel

The effects of alloying elements in welding wires and submerged arc welding process on the microstructures and low-temperature impact toughness of weld metals have been investigated. The results indicate that the optimal contents of alloying elements in welding wires can improve the low-temperature impact toughness of weld metals because the proeutectoid ferrite and bainite formations can be suppressed, and the fraction of acicular ferrite increases. However, the contents of alloying elements need to vary along with the welding heat input. With the increase in welding heat input, the contents of alloying elements in welding wires need to be increased accordingly. The microstructures mainly consisting of acicular ferrite can be obtained in weld metals after four-wire submerged arc welding using the wires with a low carbon content and appropriate contents of Mn, Mo, Ti-B, Cu, Ni, and RE, resulting in the high low-temperature impact toughness of weld metals.     

Computer simulation on the controlled cooling of 82B high-speed rod

A modified temperature-phase transformation field coupled nonlinear mathematical model was made and used in computer simulation on the controlled cooling of 82B high-speed rods. The surface temperature history and volume fraction of pearlite as well as the phase transformation history were simulated by using the finite element software Marc/Mentat. The simulated results were compared with the actual measurement and the agreement is good which can validate the presented computational models.     

Microstructure and magnetic properties of FePt/MgO multilayers deposited by RF magnetron sputtering

FePt (50 nm) and [FePt(a nm)/MgO(b nm)₅/glass (a=1, 2, 3; b=1, 2, 3) films were prepared by radio frequency (RF) magnetron sputtering technique, and then were annealed at 600℃ for 30 min. The effect of MgO layer thickness on the structures and magnetic properties of the FePt/MgO multilayers was investigated. The coercivities and inter-grain interactions of the FePt/MgO films were decreased, yet the degree of (001) texturing drastically increased with the increase in MgO layer thickness when the FePt layer thickness was fixed. Thus, the FePt/MgO films with appropriate coercivities, high perpendicular anisotropy, and weak intergrain interactions were obtained by controlling the MgO layer thickness. Overall, these results indicate that the FePt/MgO nanostructured films are promising candidates for future high-density perpendicular recording media.     

Mechanism of low thermal conductivity of xonotlite-silica aerogel nanoporous super insulation material

In an effort to incorporate the low thermal conductivity of the silica aerogel and the superior structure strength of the xonotlite,a composite material of these two was produced. It was synthesized under vacuum condition and dried by supercritical drying technique. The thermal conductivity of the new material,which is at 298K with the gas pressure ranging from 1.01×105 to 1×10-2 Pa,was measured using the transient hot-strip method. The mechanism of the low thermal conductivity was studied. The results indicate that the low thermal conductivity mainly results from the significant decrease of gaseous thermal conductivity of the new material due to the restriction of the motion of gas molecules in its fine structures. The formation of the fine structures is because the new material takes the pore structure of the silica aerogel which consists of mainly nanometer-sized pores.     

Design,preparation,and structure of particle preforms for Si3N4(P)/Si3N4 radome composites prepared using chemical vapor infiltration process

A particle preform was designed and prepared by conglomerating and cold-pressed process, which was condensed by chemical vapor infiltration (CVI) process to fabricate silicon nitride particles reinforced silicon nitride composites. The conglomerations are of almost sphericity after conglomerated. There are large pores among the conglomerations and small pores within themselves in the preform according to the design and the test of pore size distribution. The pore size of the preform is characterized by a double-peak distribution. The pore size distribution is influenced by conglomeration size. Large pores among the conglomerations still exist after infiltrated Si₃N₄ matrix. The conglomerations, however, are very compact. The CVI Si₃N₄ looks like cauliflowershaped structure.     

Anticorrosion performance of the coating/metal system by electrochemical impedance spectra

In order to investigate the anticorrosion performance of the organic coating/metal system, electrochemical impedance spectra (EIS) were measured in the 3.5wt% NaCl solution, the chemical component and the formation of corrosion products scale were analyzed by laser Raman microspectroscopy, and the pattern of the organic coating/metal system was observed by scanning electron microscopy (SEM). The characteristics and the delamination process of the organic coating/metal system were investigated systematically, and the emphases were on the transportation of the corrosive medium and the changes of the coating/metal interface. The results show that the impedance decreases at the initial immersion, then increases at the middle-immersion, and again decreases at last, which is related to the corrosion products scale. The concentration of Cl in the coating, which destroys the corrosion products scale, increases with the immersion time.     

Numerical simulation of dense particle-gas two-phase flow using the minimal potential energy principle

A simulation method of dense particle-gas two-phase flow has been developed. The binding force is introduced to present the impact of particle clustering and its expression is deduced according to the principle of minimal potential energy. The cluster collision, break-up and coalescence models are proposed based on the assumption that the particle cluster are treated as one discrete phase. These models are used to numerically study the two-phase flow field in a circulating fluidized bed (CFB). Detailed results of the cluster structure, cluster size, particle volume fraction, gas velocity, and particle velocity are obtained. The correlation between the simulation results and experimental data justifies that these models and algorithm are reasonable, and can be used to efficiently study the dense particle-gas two-phase flow.     

Effects of Ca(Y)-Si modifier on interface morphology and solute segregation during directional solidification of an austenite medium Mn steel

The austenite medium Mn steel modified with controlled additions of Ca, Y, Si were directionally solidified using the vertical Bridgman method to study the effects of Ca(Y)-Si modifier on the solid-liquid (S-L) interface morphology and solute segregation. The interface morphology and the C and Mn segregation of the steel directionally solidified at 6.9 μm/s were investigated with an image analysis and a scanning electron microscope equipped with energy dispersive X-ray analysis. The 0.5wt% Ca-Si modified steel is solidified with a planar S-L interface. The interface of the 1.0wt% Ca-Si modified steel is similar to that of the 0.5wt% Ca-Si modified steel, but with larger nodes. The 1.5wt% Ca-Si modified steel displays a cellular growth parttern. The S-L interface morphology of the 0.5wt% Ca-Si+1.0wt% Y-Si modified Mn steel appears as dendritic interface, and primary austenite dendrites reveal developed lateral branching at the quenched liquid. In the meantime, the independent austenite colonies are formed ahead of the S-L interface. A mechanism involving constitutional supercooling explains the S-L interface evolution. It depends mainly on the difference in the contents of Ca, Y, and Si ahead of the S-L interface. The segregation of C and Mn ahead of the S-L interface enhanced by the modifiers is observed.     

Alloying elements characterization in a Ti-5.6Al-4.8Sn-2Zr-1Mo-0.35Si-1Nd titanium alloy by carbon addition

The effects of carbon addition (0.01wt%-0.43wt%) on a Ti-5.6Al-4.8Sn-2Zr-1Mo-0.35Si-1Nd (wt%) alloy with a bimodal microstructure were investigated. Electron probe microanalysis was carried out to examine the partitioning behavior of carbon and the relation of carbon content to the distributions of Al and Mo in the primary α phase (α_p) and β transformed structure (β). It was found that interstitial carbon is enriched in the α_p phase and its content slightly reduces with the increase of the volume fraction of α_p.The measurements of carbon content in the present alloy with an α_p of 15vol% showed that the carbon content in the α_p phase increases with the increment of carbon addition until a maximum but keeps almost constant in the β phase. The addition of carbon reduces the solubility of Al and Mo in the α_p phase and leads to the increment of Mo partitioning to the β phase. When the carbon content is over 0.17wt% (0.67at%), carbide precipitation occurs in the matrix and its volume fraction is related to the volume fraction of α_p which can be explained in term of the difference of carbon solubility in the α_p and β phases.