Sharif Digital Repository

In this study, the effect of protection methods regarding the corrosion decrement of steel in concrete was simulated by artificial neural networks (ANNs) and fuzzy logic (FL) approaches. Hot dip galvanizing as a protective coating, Ferrogard 901 corrosion inhibitor, a pozzolanic component, such as fly ash (FA) and micro-silica (MS), and eventually rebar AISI-304 were employed in concrete. Reinforced concrete samples were held under impressed voltage of 30 V in 3.5 % NaCl electrolyte for 350 hours toward a stainless-steel auxiliary electrode. Corrosion currents have been modelled using feed forward back propagation ANNs and FL methods. The results demonstrate good consistency between... 

In recent years, there has been a growing interest in the simulation and analysis of piezoelectric transducers with the he help of equivalent electrical circuit simulations (EECS). This paper has been devoted to study of such approach for two designed and fabricated ultrasonic sandwich transducers. By using analytical analysis, the dimensions of components of the two piezoelectric transducers were determined for the assumed resonance frequencies of 30 kHz and 40 kHz. Then, by using a two dimensional finite element model, and regarding two different modeling techniques for the transducers and by application of a current source which was connected directly to the piezoelectric pieces of the... 

In this research, we simulate the corrosive behavior of steel reinforcements on 5 different mixtures to investigate the effect of two powerful protective methods, including pozzolanic additives and corrosion inhibitor on concrete, by artificial neural networks (ANNs). Related to this model, fly ash (FA), micro silica (MS), and slag were used as pozzolanic materials at an optimum 25%, 10%, and 25% of cement weight, respectively. Moreover, Ferrogard 901 as an inhibitor was also utilized. The producer recommends using12 kg/m3 to get the best possible results. The non-linear corrosion of concrete into a marine solution (3.5% NaCl) was simulated by the feed forward back propagation (FFBP)... 

In this research, we simulate the corrosive behavior of steel reinforcements on 5 different mixtures to investigate the effect of two powerful protective methods, including pozzolanic additives and corrosion inhibitor on concrete, by artificial neural networks (ANNs). Related to this model, fly ash (FA), micro silica (MS), and slag were used as pozzolanic materials at an optimum 25%, 10%, and 25% of cement weight, respectively. Moreover, Ferrogard 901 as an inhibitor was also utilized. The producer recommends using12 kg/m3 to get the best possible results. The non-linear corrosion of concrete into a marine solution (3.5% NaCl) was simulated by the feed forward back propagation (FFBP)... 

Constant volume transparent test combustion chambers are extensively used for investigating injection and fuel burning properties of various combustion engines. Their configuration depends on the engine type and the research purpose. Material of components, shape and dimensions of the chamber and its parts, ease of use, accessibility, sealing and safety of the assembly are the parameters needed to be considered in designing the test cell. This paper explains, structural design of a test combustion chamber and its optical windows using finite element analysis of ANSYS 12.0 software for bearing high pressure variations and thermal shocks of combustion. It was designed for conducting CNG direct... 

Porous PZT-PCN ceramics were fabricated with this formula, “0.8 Pb(Zr1/2Ti1/2)O3-0.2 Pb(Co1/3Nb2/3)O3”, abbreviated as “PZTPCN” by introducing Polyvinyl chloride(PVC) and stearic acid (SA) as pore forming agents (PFA) with varied percentages (5, 10 and 15 wt%). The optimum sintering procedure was designed according to the thermogravimetric analysis of pore formers. XRD and FESEM were applied to study the formed phase and the microstructure of the system. Electrical Characterization was conducted using Piezo meter. A decrease in density reduced longitudinal piezoelectric coefficient (d33) and relative dielectric constant (ε) and enhanced hydrostatic figure of merit (dhgh) of PZTPCN ceramics.... 

Abstract Porous lead zirconate titanate-lead cobalt niobate 0.8Pb(Zr1/2Ti1/2)O3-0.2Pb(Co1/3Nb2/3)O3 (PZT-PCN) piezoelectric ceramics were fabricated by introducing pore-forming agent polymethyl methacrylate (PMMA), and the effect of sintering behavior on their microstructure, dielectric, and piezoelectric properties were investigated. The optimum sintering procedure was designed according to the thermogravimetric analysis of pore former. Finally the electrical properties were measured. The porosity of PZT-PCN ceramics decreased and the grain size increased with an increase in the sintering temperature at a fixed PMMA addition. "An increase in density with sintering temperature from 1050 to... 

Corrosion of steel rebars in concrete can reduce the durability of concrete structures in coastal environments. The corrosion rate of these concrete structures can be reduced by using suitable concrete additives and coating on rebars. This paper investigates the corrosion resistance of steel rebars by the addition of pozzolanic materials including fly ash, silica fume, polypropylene fibers, and industrial 2-dimethylaminoethanol (FerroGard 901) inhibitors to the concrete mixture. Three different types of rebars including mild steel rebar st37, and two stainless steel reinforcements, AISI 304 and AISI 316, were used. Various types of primer and coating including alkyd based primer, hot-dip... 

The grain size dependence of flow stress in Cu-2.7 vol.%Al2O3 (15 nm) composite with a bimodal structure was studied. It is shown that the yield strength obeys the Hall-Petch equation when an appropriate value of average grain size based on the "rule of mixture" is employed. The Hall-Petch constants (σ0ε and kε) are proportional to strain as ε0.5. An equation for flow stress as a function of true strain and average grain size is proposed. The effect of alumina nanoparticles on the yield strength is shown to be related to large amounts of dislocations density. © 2009 Elsevier B.V. All rights reserved  

Operational modal analysis based on power spectral density transmissibility (PSDT) functions is a useful tool to identify the modal parameters with low sensitivity to excitations. For pole extraction from the PSDT function, a proper parametric identification method such as the polyreference least squares complex frequency-domain method or poly-Max method can be used. Then, the poles are selected from a stabilization diagram (SD) with overestimating the system model order. Therefore, spurious modes can be identified that must be distinguished and removed from the system poles. To reach this aim, many techniques have been proposed and applied. In this paper, a new algorithm is proposed to... 

Cu-2.7 vol.% Al2O3 (15 nm) composite was synthesized by an internal oxidation and hot extrusion process. The grain growth at elevated temperatures was studied and compared with extruded copper powder. Abnormal grain growth via a mechanism analogous to that of site-saturated phase transformation was observed. The critical grain size for the abnormal growth was determined to be 1.1 ± 0.2 μm. The growth rate decreased with time until the grain size approaching a final value ranging from 7.9 to 13.3 μm depending on the temperature. © 2008 Acta Materialia Inc  

Fifteen years after introduction of Business Process Reengineering (BPR) and a series of successful and not-so-successful BPR implementation, a revised methodology is needed to incorporate cases of major and sudden organizational or environmental changes with BPR. The new methodology can also be particularly applicable to project oriented businesses. September 11, Tsunami, and other major world events show that nothing is constant but change. A reengineered process may only stay as the environment factors stay the same. Therefore, the processes can no longer be the central focus of reengineering, but the output needs. Technology has enabled us to refocus and apply reengineering constantly to...