فهرست مطالب

  • Volume:4 Issue: 1, 2010
  • تاریخ انتشار: 1389/09/20
  • تعداد عناوین: 7
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  • Mahmood Mehrdad Shokrieh, Saeed Niakan Page 1
    Carbon nanotube (CNT), due to extraordinary mechanical properties, is an effective Stiffener as reinforcement in resin for fabricating of nanocomposites. It is demonstrated by adding a small amount of CNT to the matrix, the elastic modulus of matrix increases remarkably. In this paper, the elastic modulus of CNT reinforced nanocomposites is obtained two-dimensionally using a finite element method (FEM), averaging approach and micromechanical. The obtained results are compared with experimental results that had already been reached by other researchers. It is shown that the experimental results are in acceptable agreement with the results presented in the present paper. Since the utilization of Micromechanics approach is an easier method, this method as used in the present paper can be used to calculate the elastic modulus of CNT reinforced nanocomposites
  • Rahmatollah Ghajar, Javad Alizadeh Page 11

    In the last decade, decrease of the wear rate, increase in the axel load, and the velocity of the trains have changed the main damage mechanism of railway wheels from wear to rolling contact fatigue (RCF). RCF may lead to surface and subsurface cracks. The interaction between wear and RCF, removes the surface cracks, but the subsurface crack propagate gradually, and may lead to deeper and more dangerous fractures. In this study, by considering an elliptical subsurface crack, the lifetime of an Iranian railway system wheel has been predicted using FEM, and under RCF condition. To this end, a 3D model of a cracked R7T wheel with 920mm diameter in contact with UIC60 rail has been prepared and analyzed in Abaqus FEM software. The histories of the stress intensity factors of the subsurface crack have been extracted in one cycle wheel rolling. Then, equivalent stress intensity factors have been calculated using Tanaka and Liu-Mahadevan models. Finally, wheel lifetime has been predicted by Walker relation. This paper provides a local criterion of critical crack length and crack growth lifetime that is essential for frequent inspections of railroad wheel.

  • Mehdi Ghanavati, Afshin Ghanbarzadeh Page 25
    In this project guidance and control of underwater robot, including three engines and propeller attached to it, by Fuzzy control has been investigated. Fuzzy control is done based on human experience and requiered laws. The robot can also be controlled and guided by the user. This robot may be used in sea or swimming pool environment for finding goal point and locate in desired direction. In addition, this robot is able to follow a definite path and to do searching operation in that path. This robot is also able to overtake barriers on the surface or under the surface and forward toward target and path the barriers using fuzzy rules. In other words, while facing any barriers using fuzzy rules. In other words, while facing any barrier, robot decides necessary decision in such a way not to collide with it and path it. For simulation of the required system, webot's software which is strong software for mobile robot simulation and Maple's material software is used. This robot is capable to distance any obstacle in 3D and move towards the goal. Obstacle avoidance is done by fuzzy rules. Means when face any obstacle, the underwater robot decide for not collision and passes it. For the simulation system, Webots that is strong software for mobile robot simulation and mathematical software Maple is used.
  • Ahmad Sedaghat, Saeed Jafari, Iman Rouholamin Page 33
    In industry, flow instabilities are important in journal bearings at high rotational speeds. For inviscid flows between two rotating coaxial cylinders, an instability criterion was introduced by Taylor-Couette. However, viscosity may play as stabilizer or destabilize in such flows. In this work, stability theories were reviewed for two coaxial rotating cylinders. Then, flow instability patterns, velocity, pressure, and vorticity fields were simulated using Fluent. In this method, the fluid flow was assumed laminar and by gradually increasing the relative rotational speeds between two coaxial cylinders, the critical Taylor number was calculated and compared with Taylor analytical solution. By increasing Taylor number, it is observed that vortices become stronger and instabilities appear in the form of cellular square patterns. The characteristics of these cellular square patterns were examined.
  • Mohamadhosein Mirghasemi, Mohamadreza Salmani Page 43
    In recent years, more attention is paid to stainless Steel 316L as fracture plate and fixation in human's body. Present studies are focused on surface and metallurgical properties of this material. Biocompatibelity of this material and its superior mechanical properties has made it the most demanded biomaterial. In this research, four different implants are investigated in three stages. Four commercial brands of implants from Germany, Switzerland, India and Iran are selected. Mechanical tests such as impact, hardness and fatigue are done on this implant, according to their corresponding standard. Scanning electronic microscope (SCM) is used to investigate surface fracture, and optical microscope for microstructure, to determine kind of fracture. Corrosion test is simulated in the body using hank solution to determine implant corrosion. Aim of this research is quality evaluation with respect to mechanical properties and failure resistance. Moreover, regardless of brand it is aimed to investigate medical/metallurgical methods to present implant failure inside the body. Iranian brand is more or less similar to Sweden and German brand, however, Indian brand is not compatible to medical standards in term of microstructure, chemical composition and mechanical properties.
  • Rouhollah Hoseini, Hamzeh Salehipour Page 55
    In this work an improved method for designing a linear vibrational absorber, excited by random vibrations is presented and analyzed. First, analytical expressions, for non-stationary white noise accelerations, are derived. The criterion is different from the conventional criteria, used for structural design under random vibration, and it is based on minimum displacement or acceleration response of the main structure, without considering required performance against failure. In this study, in order to control the structural vibrations induced on a mechanical structure excited by non-stationary based acceleration random process, the Multi-objective optimum (MOO) design of a vibration absorber has been developed. This has been performed using the bees optimization algorithm. The analysis is developed by considering a case study of a multi degree of freedom system with uncertain parameters, subject to random vibrations and equipped with a vibration absorber. Results demonstrate the importance of performing a pre-design procedure and show that the multi-objective pre-design methodology is economical and leads to time reduction and raw data accumulation. This method is particularly well performed for structures with higher degrees of freedom (DOF.
  • Saeed Daneshmand Page 63
    Nowadays, we live in a world which quality, speed, accuracy and cost are the most important parameters in part's design and manufacturing. Due to the complexity of part manufacturing, traditional and nontraditional manufacturing techniques are used. Aerodynamic tests usually requires one or several models for testing in wind tunnels and these models typically have particular complexities in which necessitates different techniques such as machining, casting or rapid prototyping in order to manufacture them; However, these techniques imply certain advantages and disadvantages. Selection of an optimal method affects the results and quality of manufacturing. In this study, the surface roughness experimental effect of a projectile on its aerodynamic coefficients is investigated. For this purpose, three projectiles with three levels of high, medium and rough surface quality were built and analyzed in different angles of attack and velocities, the aerodynamic coefficients and the ratio of lift to drag. The results indicated that at high velocities and high angles of attack, it is better to use a model with the highest surface quality because it reduces the drag and increases the ratio of lift to drag, thus has influence on the aerodynamic coefficients and with increasing roughness, critical Reynolds number is also reduced.