Journal Of Mechanical Research And Application (پژوهش و کاربرد در مکانیک)
سال:1390 | دوره: | شماره: |تعداد مقالات:8

In recent years the aluminum matrix composites are gaining wide spread applications in automotive, aerospace, defense, sport and other industries. The reason for this is their exciting properties like high specific strength, stiffness, hardness, wear resistance, dimensional stability and designer flexibility. The present work reports on mechanical properties and microstructure analysis of Al-SiC particulate composites with different wt. % of SiCp. Al-SiCp composite specimens with different weight % of SiC (viz.5, 10, 15, 20, 25 and 30 wt. % of SiC) were fabricated through casting process. The induction furnace and open furnace were used for melting of Al-SiC particulate composites. The induction furnace gives the advantage of self stirring action on the introduction of SiC particles. Grinding and fine polishing was done using diamond paste to prepare different samples for microscopic study. The microstructure examination of the polished and carefully etched Al-SiCp composite specimens showed that the structure consists of a network of silicon particles, which were formed in inter-dendritic aluminum silicon eutectic composition. These SEM micrographs clearly indicate that the SiC particulates are dispersed uniformly in the Al matrix even at higher percentage such as 20 weight % SiCp. The SiC particulates were observed to be in irregular shape.

In this paper, exergy of conditioned air, exergy efficiency, irreversibility, and entropy generation of common models of evaporative cooling have been investigated in five cities of Iran. Direct evaporative cooling (DEC), indirect evaporative cooling (IEC), and two stage IEC/DEC as the most popular methods of cooling have been modeled. Atmospheric conditions are considered as the dead state of each city. Exergy analyses of conditioned air are based on the output results of the theoretical modeling of evaporative cooling. Moreover, exergy balances of three cooling methods are derived. Thus, exergy destruction, reversible work, and entropy generation are calculated according to the exergy balances. The results obtained reveal that Bam, which is a hot city with medium relative humidity (24%RH), has the best exergy efficiency of direct evaporative cooling. The highest exergy efficiency of two stage indirect/direct evaporative cooling belongs to Kerman. Kerman with the lowest dry-bulb temperature has medium relative humidity (24%RH). In addition, total output exergy of air in Yazd is more than other cities. Yazd is a hot-dried city with rather low relative humidity (19.5%RH).

In this paper, penetration of high velocity impact of 4340 steel and tungsten carbide projectiles with specific shapes in to ceramic armor that includes 10 mm alumina (95%) is considered analytically and simulated with Ls-Dyna software. Bernoulli equation used to consider the penetration velocity in ceramics, shows that the penetration is better and easier by increasing projectile density. The simulations showed the same results as well. Using the numerical solution, ballistic limit velocity (BLV) of ceramic armor is calculated and the results showed that the increase in projectile density decreased BLV and so the tungsten carbide projectile which is heavier than steel, penetrates alumina target easier and better and with lower velocity (about 100 m/s) with respect to steel projectile in which BLV is about 170 m/s. Also, comparison between the analytical and the numerical method reveals that the compatibility of these solutions are better at higher range of velocity.

Basalt fibers enjoy the best potential to be turned into a serious contender in fiber composite market due to its good mechanical properties and favorable costs. The creep behavior of basalt fiber reinforced epoxy (BFRE) and glass fiber reinforced epoxy (GFRE) composites was studied through tensile testing at a high temperature. To study the effect of reinforcing epoxy, the micro glass powder (MGP) was added at various volume percentage into the epoxy resin in BFRE composites. The initial strain for all the specimens were evaluated and compared with each other. No creep rupture failures were observed in short term (less than 10000 seconds) high temperature (T=150 and 200 oC) tensile creep tests at the loads up to 15% of the ultimate tensile strength of the specimen. It was also found that the creep resistance of BFRE was higher than that of GFRE and the materials are generally behaved as non-linear for all stresses and temperatures. Adding MGP decreased the initial strain of BFRE, but had no significant effect on the overall life time of BFRE.

Since knowledge on hydrodynamic torque of a butterfly valve is very important for butterfly valve design, its hydrodynamic torque is investigated in this paper. In reality, the investigation of the loss coefficient and torque from some experiments will take a long time and a lot of money. This paper presents a statistical study of the flow past the butterfly valve in a static analysis using commercial fluid dynamics software fluent. The simulation was done for 16 different positions of the valve disk including 0o, 5o, 10o, 15o, 20o, 30o, 35o, 45o, 50o, 55o, 65o, 70o, 75o and 80o. The value of pressure in the pressure inlet was set to be 16 bars. The study focuses on the investigation of the characteristics of loss coefficient, torque behavior and flow field of the 262 mm butterfly valve. The results show that the loss coefficient is directly dependent on the position of the valve disk and by increasing the angle of the valve disk the value of loss coefficient increases and the value of torque increases until about 10o -20o and then decreases. By comparing between the experimental and statistical data, acceptable relationships were observed.

Design models of multi-stage, axial flow compressor are developed for gas turbine engines. Axial flow compressor is one of the most important parts of gas turbine units.Therefore, its design and performance prediction are very important. One-dimensional modeling is a simple, fast and accurate method for performance prediction of any type of compressors with different geometries. In this approach, inlet flow conditions and compressor geometry are identified and by considering various compressor losses, velocity triangles at rotor, and stator inlets and outlets are determined, and then compressor performance characteristics are predicted.Numerous models have been developed theoretically and experimentally for estimating various types of compressor losses. In the present work, performance characteristics of the axial-flow compressor are predicted based on one-dimensional modeling approach. Firstly, the proposed algorithm for modeling and then the losses model for calculation of pressure loss coefficient in the blades cascade have been represented. In this study, models of Lieblein, Koch-Smith, Aungier, Hawell are implemented to consider the compressor losses. Finally, the model results are compared with experimental data to validate the model.

The growth of the electrical energy consumption form one side and the bounded available fossil fuel and other limitations from the other side, makes the thermal power plants upgrading as a main demand in the world. Decreasing the internal energy consumption, increasing the performance and the output power with the minimum costs are the important targets of the power plants retrofitting. Nowadays power plant repowering with the help of gas turbine that includes two manners (Full Repowering and Para-Repowering) is one of the best methods for the power plants progress. Different repowering methods according to their costs, amount of the output power increase and the power plant situation could be various solutions for the retrofitting. Choosing each of these methods can be done just by analyzing the related parameters. Technical and economic comparisons between different repowering methods needs an investigation of several technical and economic parameters and the characteristics of the electrical networks development as well. Combined cycling/cycles as a repowering method usually is used for low capacity units and for the bigger units para repowering could be more suitable. Feasibility study for repowering a power plant and choosing the best method should be done through a case study for that specific power plant. In this paper using different para repowering methods has been studied for the Low shan power plant. The results show that feed water heating repowering is the best method based on the cost of electrical energy generation in this case.

In this paper, free vibration of functionally graded (FG) rectangular simply supported thick plates based on two variable-refined plate theory is presented. According to a power-law distribution, the mass density and elasticity modulus of the plate are considered to vary while Poisson's ratio is constant. In order to extract the five constitutive equations of motion, Hamilton principle is employed. The high accuracy of this theory is investigated by comparing the exact results reported by higher order shear deformation theory. Furthermore, parametric study of non-dimensional natural frequencies is carried out and the influences of geometrical parameters such as aspect ratios of the plate on these frequencies are studied.