Materials Science Forum Vols. 575-578

Abstract: Al-Mg based alloys have special attention due to the lightness of the material and certain mechanical properties and reciclability. Normally classified as non-heat-treatable these alloys obtain higher strength either by strain-hardening or by solid solution. The P/M process in the Al-Mg-Zr alloys in study leading to fine grain structure after the thermal treatment. The understanding of the observed phenomena depends of the fact that materials produced by powder metallurgy present complex interface reactions in a great amount of nucleation sites and a subtle change in the structure of the material causes an important variation in your properties. Alloys in study presented interesting values of properties, with evident technological potential.

Abstract: The corrosion behaviors, including the immersion corrosion, electro-chemical corrosion, stress-corrosion fracture, of heat-treated SAE 8620 steels have been investigated. Experimental results show that the 400°C􀊳 tempered specimen is only susceptible to local attack of pitting corrosion and can exhibit an excellent corrosion resistance during the static immersion and electro-chemical tests in a 3.5% NaCl solution. The tensile strength and elongation of the normalized and 300~500°C tempered specimens will be reduced when tested in NaCl solutions, especially at a higher testing temperature. The normalized specimen can inhibit effectively the crack-growth under constant loading and the 300~500°C tempered specimens have a sequence of crack-growth rate as 300°C > 400°C > 500°C.

Abstract: The numerical simulation calculation of longitudinal seam TIG welding of thin-wall aluminium cylinder was conducted by the FEM software, Marc. Based on the generating of analysis model, displacement field was quantitatively described. Circular profile of aluminium alloy cylinder after welding was predicted by the radial displacement. The simulation results showed that the post-weld deformation for the longitudinal seam of aluminium alloy cylinder was mainly destabilizing deformation.

Abstract: The temperature at specific positions was measured by multi-channel data acquisition system in order to understand the solidification and feeding process of the sample. The Olympus metallurgical microscope was used to observe the macrostructure of the casting and analyze the freezing mechanism. The mold filling and solidification processes of the Al-alloy sample were studied by using the commercialized simulation software Z-Cast. And the simulated result was compared with the results of practical pouring test. When preheat temperature of mold is low, the pouring temperature should be higher in order to ensure completely filling of mold. As a result the solidification of sample could be feeding effectively, and the shrinkage on the upper end of sample could be eliminated. It is shown that the casting simulation software Z-CAST can be used to simulate the filling and solidification process of gravity cast Al alloy and can provide exact flow fields and temperature fields thus can predict cast defects and their positions.

Abstract: In this paper, taking elastic and plastic characteristics of rock into account, the authors have studied the relationship between different constitutive models. By transforming material parameters merely, on the basis of Equivalent Mohr-Coulomb Yield Criterion, the researchers achieved the application of these relationship in the computer program-Ansys5.7. They also have discussed the magnitude relationship between the transformed parameters and the original ones. By analyzing the cases of rock slope with obvious sliding surface, the researchers proved that it is liable to replace Mohr-Coulomb Yield Criterion with Equivalent Mohr-Coulomb Yield Criterion. We can use Equivalent Mohr-Coulomb Yield Criterion to simulate rock material, the results are smaller and more conservative than the standard ones. Meanwhile, the authors indicate that it is beneficial to apply Equivalent Mohr-Coulomb Yield Criterion to simulate rock material in rock slope projects with obvious sliding surface which have accurate standard requirements about displacement.

Abstract: The object of this paper concerns with the research of 8-electrode oil-water two-phase flow electrical capacitance tomography system. The distribution models of sensor’s field are established by the finite element method for the influence of the parameters of sensor’s structure on the performance of sensor. The analyses of simulation and experiment and the sensor’s optimization design are done, and the measure function of sensor’s optimization design is proposed based on sensor parameters that are listed as follows: length of electrodes, stretch angle of electrodes, thickness of pipeline, permittivity, thickness of stuff filled between screen and electrodes, radial electrodes and so on. In conclusion, the final parameters and materials adopted are proved better than those adopted before. Consequently the sensitivity and uniformity of the sensitive field is improved and the design of the measurement circuit is easier, and the data precision of sensitive field is enough for image reconstruction.

Abstract: Chemical mechanical polishing (CMP) is a widely adopted technique to achieve high level of global and local planarity required in modern integrate circuit (IC) industries, wherein the pad properties weigh heavily on the final performance. A preliminary two-dimensional wafer-scale flow model for CMP is presented considering the roughness, the elasticity, as well as the porosity of the pad. Numerical simulations were conducted to show the slurry flow features’ variations due to pad parameters change. The results show that the porosity of the pad is conducive to slurry delivering, and small porous parameter will lead to prominent increase of load capability, accounting for larger material removal rate (MRR) whilst the elasticity of the pad has a more complex influence. The rough surface carries additional fluid in the valleys of the polishing pad thereby provide some chemical reactions. The model will shed lights on the mechanism of CMP process, which is for a long time considered as a difficult circle to square.

Abstract: Being as a functional material, piezoelectric ceramics is applied to drive a micropump when it is composed to be a thin membrane on a brass film to form a diaphragm. According to the properties of the piezoelectric material, the stiffness of the diaphragm influences the vibration displacement and therefore the supply flow rate of the micropump. This paper focuses on the dynamic characteristic study of the micropump and the stiffness influence of the diaphragm on the characteristics. The mathematical model of the valve-less micropump considering the diaphragm stiffness is developed in order to predict the dynamic characteristics of the piezoelectric valve-less micropump. Using the 3-D finite element analysis (FEA) method, the static and vibration mode of the diaphragm are analyzed to obtain the diaphragm stiffness and natural frequency. The method using Matlab is to predict the pressure and flow rate characteristics of the micropump when the diaphragm stiffness is considered or not. Comparison of the simulation results shows the stiffness of the diaphragm influences the dynamic characteristics of micropumps. It also shows that the method combining FEA software with Matlab provides a possible and effective tool to take the diaphragm stiffness into account when the pressure and flow rate characteristics of micropumps are studied.

Abstract: Precalciner, in which endothermic raw meal calcination and exothermic fuel combustion proceed simultaneously, is a key equipment in dry process of cement production. To increase the precalcination degree and reduce the energy consumption, more and more attentions have been paid on modeling gas-solid flow field in precalciners. However, most of them aimed at just qualitative studies lacking in necessary further quantitative analysis of precalciner performance parameters. In this paper, combining qualitative studies and quantitative analysis, the gas-solid flow field was carried out aiming at an actual precalciner under operational-based boundary conditions. In Euler coordinate system the gas phase is expressed with k-ε model, in Lagrange coordinate system the solid phase is expressed with Discrete Phase Model(DPM), and the random effects of turbulence on the particle dispersion is accounted for with Discrete Random Walk (DRW) model. The predicted gas velocity field agrees well with the measured result, and the calculated raw meal concentration distribution is consistent with the actul condition. The results predicted that there is a simple spraying-liked flow field in the precalciner, with not only a non-uniform particle dispersion condition but also a low solid residence-time and residence-time ratio between solid and gas.

Abstract: A spool type high temperature control valve is developed to control the flow rate of high temperature fuel supply for scramjet engines in this paper. The clearance between the friction pairs of the spool and sleeve is crucial for the proper performance of the valve working at the temperature as high as 700 K. The high temperature environment may cause problems to the valve, for instance the thermal deformation of the valve materials, the failure of the friction pairs inside the valve and even the damage of the operating proportional electromagnet. Therefore the thermodynamic analyses of the valve are carried out using 2D finite element analysis method. The heat transfer and fluid dynamic models, as well as the boundary conditions are introduced. The heat flux through the fluid/solid interface is calculated to connect the heat transfer models inside the solid domain and the fluid domain. By solving both the heat transfer and turbulent flow models in the solid and fluid domains, the flow field distribution inside the flow channel and the thermal field distribution inside all the parts of the valve are shown. Suggestions on the design of the valve are given according to the thermodynamic analysis results.