Sharif Digital Repository

The inhibition of mild steel corrosion in 0.5 M sulphuric acid by the symmetrical acetylenic alcohol 2- butyne-1,4-diol is investigated. Weight loss and electrochemical impedance data consistently indicate inhibition efficiencies up to 98%. Short-term impedance measurements reveal that the interfacial inhibition is a function of the exposure time, and that full performance is achieved faster as inhibitor concentration and temperature are higher. An infrared study of the surface film provides evidence that the film does not achieve its final state but after several hours. Atomic force Microscopy has been used for investigation the surface topography of metallic electrode. © 2009 by ESG  

Most seismic design codes accept heavy damages to buildings in case of large earthquakes, provided that they are prevented against collapse. However, this leads to unacceptable consequences, such as very large volume of the required reconstruction works, in large populated cities. One way to get rid of these adverse consequences is using the idea of combining rocking/seesaw motion of the building's structure and energy dissipation at base level to create buildings easily repairable even after a large earthquake. In the present study, this idea has been employed for designing steel buildings with seesaw motion capability by using a central massive column at ground floor, with elastic behavior... 

A new model on the evolution of dislocation structure of cell forming metals and alloys through severe plastic deformation is presented. Following previous approaches, the model considers a cellular dislocation structure consisted of two phases: cell interiors and cell walls. The model distinguishes edge and screw dislocations in terms of three categories: mobile dislocations, immobile dislocations in cell interiors and immobile dislocations in cell walls. Then considering physical and geometrical assumptions for each dislocation category, an evolutional law is derived, based on some dislocation interaction mechanisms such as dislocation generation, annihilation, locking and migration. The... 

Since the constitutive information is one of the most important aspects of material deformation analysis, here a new constitutive model is proposed that can investigate the behavior of material during intense deformation better than existent models. The model that is completely based on physical mechanisms can predict all stages of flow stress evolution and also can elucidate the effects of strain and strain rate on flow stress evolution of material during intense plastic deformation. Here as an application, implementation of the constitutive model in finite element method (FEM) is used to compare two methods of sever plastic deformation (SPD) processes of copper sheet; repetitive... 

In this study, a dislocation-based model is presented for investigating the evolution of micro structure and mechanical properties of thin films during a wide range of straining. The model is applied to the High Pressure Torsion (HPT) process of thin nickel disks that provides valuable information on the evolution of material parameters during deformation. The model considers a free surface theory for thin films and can explain the size effect phenomenon in agreement with previous reported trends in literature  

In this paper, an integration approach consists of implementation of true internal state variables constitutive model to finite element (FE) analysis is presented. From the approach, the deformation homogeneity during severe plastic deformation of sheet (SPD) is investigated. Since there is not any constitutive model for large deformation that based on appropriated physical assumptions, here a new constitutive model is proposed that is entirely based on metallurgical mechanisms. Also, in order to achieve accurate results with low computation time, a new approach for integration of the constitutive model to FE analysis is presented. By coupling the constitutive model and FE analysis, the... 

Commercial purity aluminum sheets are subjected to a severe plastic deformation technique called constrained groove pressing. In this study for the first time by using some technical optimizations, a strain magnitude of 6.9 is imposed to the sheets. The grain size evolution during severe plastic deformation is studied using Williamson-Hall analysis on X-ray diffraction pattern of the deformed samples. These results and transmission electron microscopy observations show that constrained groove pressing process can effectively refine the coarse-grained structure to an ultrafine grain range. The results of mechanical tests show that imposing strain in range of 0-5.75 causes to strengthening of... 

A hybrid model based on the flow function and dislocation cell structure model by considering the Taylor assumption is utilized to model the dislocation structure evolution, cell size and mechanical properties of OFHC in severe plastic deformation. Here, the ECAP is chosen as a process of severe plastic deformation. In this study, the model is modified by taking the value of cell size coefficient as a function of strain and considering two different values of dynamic recovery coefficients of cell walls and cell interiors. These modifications lead to achieve the more accurate modeling results. From the flow function the strain rate distribution are achieved and then using the model the... 

A general flow line model is developed to investigate the deformation behavior of Cu and Al through Bc route of Equal Channel Angular Pressing process at curved and sharp dies. Considering the Taylor theory, the obtained strain and strain rate from the flow line model and also using a modified version of ETMB model, the evolutions of nano-structure in the processed Cu and Al are predicted. Comparison between the modeling results and experimental data is carried out and a reasonable agreement is achieved. The results show that the deformation in the sharp die occurs in a narrow zone with higher strain rate than that in the curved die. Also, the cell size of the processed Cu is smaller than... 

A unified model composed of the flow function model, dislocation model and Taylor theory is used to investigate the evolution of dislocation density, cell size, and strength of tantalum during ECAP process. From the flow function model, strain and strain rate distributions are achieved and then using a modified version of three-dimensional ETMB model, the dislocation density, cell size, and strength are predicted. The predicted dislocation density, cell size, and strength are compared with the experimental data and a remarkable agreement is obtained. In addition, the effect of dynamic recovery on the strength of the processed tantalum is modeled and compared with other materials. © 2008... 

In this study, the flow softening of FCC materials through severe plastic deformation (SPD) is investigated using ETMB (Y. Estrin, L.S. Toth, A. Molinari, Y. Brechet) model. To do so, using the model, the equal channel angular pressing (ECAP) processes of two FCC materials, aluminum and copper, are investigated. The correlation between the recovery parameters of ETMB model (the dynamic recovery exponents and coefficients) and the intrinsic characteristics of the materials (the stacking fault energy (SFE) and melting point) is described and compared with the previous claims. © 2009 Elsevier B.V. All rights reserved  

Natural and synthetic anion receptors are extensively employed, but the structures of their bound complexes are difficult to determine in the liquid phase. Infrared spectroscopy is used in this work to characterize the solution structures of bound anion receptors for the first time, and surprisingly only two of three hydroxyl groups of the neutral aliphatic triols are found to directly interact with Cl-. The binding constants of these triols with zero to three CF3 groups were measured in a polar environment, and KCD3CN(Cl-) = 1.1 × 106 M-1 for the tris(trifluoromethyl) derivative. This is a remarkably large value, and high selectivity with respect to interfering anions such as, Br-, NO3 -... 

The debate over innovativeness of large firms and SMEs, which was bolded by Schumpeter, still continues under mixed empirical evidences. There are several implications for this debate including policy orientation in support of large firms or SMEs. But there is a scarce of studies in developing countries and no such study in Iran yet. The present study has explored the proportionality of increase of innovation activity versus firm size within 522 Iranian knowledge-based firms categorized in 9 industries. Innovation activity was measured by R&D expenditure while firm size stood for number of employees. Using log-log regression in the first phase, it was found that R&D expenditure confirms a... 

The debate over innovativeness of large firms and SMEs, which was bolded by Schumpeter, still continues under mixed empirical evidences. There are several implications for this debate including policy orientation in support of large firms or SMEs. But there is a scarce of studies in developing countries and no such study in Iran yet. The present study has explored the proportionality of increase of innovation activity versus firm size within 522 Iranian knowledge-based firms categorized in 9 industries. Innovation activity was measured by R&D expenditure while firm size stood for number of employees. Using log–log regression in the first phase, it was found that R&D expenditure confirms a... 

With the stricter limitations on both fuel consumption and air pollution, the advantages of a hybrid electric vehicle are becoming more evident than ever. In the present study, an energy management system for a hybrid electric vehicle is developed. Because the plant under consideration is nonlinear, multi-domain, time-varying, has multiple uncertainties and, in addition, the designed control strategy must be able to obey the driver's commands and achieve the par-internship for a new generation of vehicle regulations, the fuzzy logic approach is chosen. A feed-forward hybrid vehicle simulation model is used to demonstrate the validity and the convenience of the current approach and its... 

In this paper, an incompressible smoothed particle hydrodynamics (SPH) method is presented to solve unsteady free-surface flows. Both Newtonian and viscoelastic fluids are considered. In the case of viscoelastic fluids, both the Maxwell and Oldroyd-B models are investigated. The proposed SPH method uses a Poisson pressure equation to satisfy the incompressibility constraints. The solution algorithm is an explicit predictor-corrector scheme and employs an adaptive smoothing length based on density variations. To alleviate the numerical difficulties encountered when fluid is highly stretched, an artificial stress term is incorporated into the momentum equation which reduces the risk of... 

In this paper, a decentralized controller for trajectory tracking of modular and reconfigurable robot manipulators is developed. The proposed control scheme uses joint-torque sensory feedback; also sliding mode control is employed to make both position and velocity tracking errors of robot manipulators globally converging to zero. Proposed scheme also guarantees that all signals in closed-loop systems will be bounded. In contrast to some of prior works in this scheme, each controller uses a smooth law to achieve its purposes. In this method, each controller uses only local information for producing control law hence separated controller can be used to control each module of manipulator and...