Sharif Digital Repository

In this investigation, a neural network model was used to predict mechanical properties of dual phase (DP) steels and sensivity analysis was performed to investigate the importance of the effects of pre-strain, deformation temperature, volume fraction and morphology of martensite on room temperature mechanical behavior of these steels. In order to train the neural network, dual-phase (DP) steels with different morphology and volume fractions of martensite were deformed between 2 and 8%, at high temperature range of 150-450 °C. The results of this investigation show that there is a good agreement between experimental and predicted values and the well-trained neural network has a great... 

In the present study a laboratory flat rolling machine is utilized to assess the deformation behavior of low and high carbon steel wires in wire flat rolling process. The effects of friction coefficient, rolling reduction and roll speed on rolling force and deformation behavior of the wires are experimentally investigated. It is found that the roll speed affects considerably the rolling force but a negligible effect on deformation behavior. It is noted that by increasing the roll speed, the rolling force may decrease or increase depending on the magnitude of the roll speed. Also, the deformation behavior of the wires in flat rolling is formulated. A relationship is developed for calculating... 

The wear properties of low modulus polymer-based friction materials were studied. The wear equation W = K Pa Vb tc was used to correlate the wear of polymer-based friction material sliding against cast iron with the wear coefficient (K), load (P), speed (V), and time (f). The parameters were determined experimentally by varying only one variable at a time and keeping the other two variables constant. The wear rate of selected polymer-based friction material was compared with cast iron friction material. © 2005 Wiley Periodicals, Inc  

We have applied Rosenbrock's optimization algorithm to obtain the optimized efficiency of a solar cell and its structural parameters. To obtain these parameters, we have developed a computer program for simultaneous optimization and simulation of the solar cell. We have used experimental data on the electrical and optical properties of a-Si1-xCx layers, put them into the written code and obtained the optimized parameters of this solar cell. The maximum efficiency is 6.32% which is close to one experimental result. © 2004 Elsevier B.V. All rights reserved  

Phenolic compounds and carboxylic acids are methylated with dimethyl carbonate in the presence of a catalytic amount of BF3· OEt2, DBU, or KOH, in good to excellent yields under microwave irradiation and solvent-free conditions  

A carbon-paste electrode (CPE) chemically modified with the cobalt(II)-4-methylsalophen (CoMSal) as a Schiff base complex was used as a highly sensitive and fairly selective electrochemical sensor for simultaneous, determination of minor mounts of ascorbic acid (AA) and cysteine. This modified electrode shows very efficient electrocatalytic activity for anodic oxidation of both AA and cysteine via substantially decreasing of anodic overpotentials for both compounds. The. mechanism of electrochemical oxidation of both AA and cysteine using CoMSal-modified electrode was thoroughly investigated by cyclic voltammetry and polarization studies. Results of cyclic voltammetry (CV) and differential... 

In this study, the kinetics of dynamic recrystallization is predicted under hot rolling conditions employing a first-order rate equation. The proposed model considers the effects of temperature and strain rate variations on recrystallization kinetics by simultaneously modelling heat transfer and plastic deformation phenomena. To do so, a two-dimensional finite element method is coupled with the transformation equation to calculate the temperature distribution and the strain rate field as well as the kinetics of dynamic recrystallization within the metal, concurrently, The model developed was examined for a low carbon steel. A series of hot compression tests were carried out at different... 

Voltammetric behavior of two mercaptopyrimidine derivatives (2-thiouracil and 2-thiobarbituric acid) has been studied by cyclic voltammetry at a cobalt phthalocyanine (CoPc)-modified carbon-paste electrode. The results of voltammetric determinations showed that the CoPc in the matrix of modified electrode acts as catalyst for electrooxidation of these thiols (RSH), lowering the overpotential of the reaction and significantly increasing the sensitivity for detection of thiols in neutral conditions. The results of voltammetric and polarization measurements in solutions with various pHs were used for prediction of the mechanism of electrocatalytic oxidation at the surface of modified electrode.... 

Dynamic strain ageing may occur during warm working of low carbon steels and causes significant changes in flow behaviour and microstructure of the deformed material. Therefore, for a proper designing of an industrial forming process performing under warm deformation conditions, the effect of dynamic strain aging should be taken into account. The aim of this investigation is to predict the velocity and the temperature fields within the rolling metal with regard to the dynamic strain aging. For this purpose, compression tests at various temperatures and strain rates have been conducted to evaluate dynamic strain aging in a low carbon steel. Then, by coupling the experimental results with a... 

In the present paper, employing compression experiments for three grades of low carbon steel, the effects of deformation condition and chemical composition on the occurrence of dynamic strain ageing are studied. Also, based on the achieved results, the flow behavior of steels under warm deformation conditions is predicted for the employed steels. The results show that both chromium and niobium postpone the happening of serrated flow and shifts the serrated flow region to lower temperatures in comparison with low carbon steel, while the activation energy for commencing dynamic strain ageing increases. © 2003 Elsevier Science B.V. All rights reserved  

Cobalt hydroxide modified glassy carbon electrodes (CHM/GC) prepared by the anodic deposition in presence of tartrate ions have been used for the electro-catalytic oxidation of methanol in alkaline solutions where the methods of cyclic voltammetery (CV), chronoamperometry (CA) and impedance spectroscopy (IS) have been employed. In CV studies, in the presence of methanol the peak current of the oxidation of cobalt hydroxide increase is followed by a decrease in the corresponding cathodic current. This suggests that the oxidation of methanol is being catalysed through the mediated electron transfer across the cobalt hydroxide layer comprising of cobalt ions of various valence states. A... 

Tough, optically clear simultaneous interpenetrating polymer networks (SINs) of polyurethane (PU) and poly(allyl diglycol carbonate) (ADC) at different compositions were synthesized. The effects of the molecular weight of PU soft segment on the morphology, mechanical properties, and thermal transition behavior of the SINs at two levels of crosslinking agent were studied. The miscibility of PU/ADC SINs, studied by TEM and DMA, was greatly influenced by the SIN composition and the molecular weight of poly(caprolactone) diol (PCL) as the PU soft segment. A single-phase morphology at a PU concentration of 10% changed to a very fine microheterogeneous morphology as the molecular weight of PCL... 

A study has been made to determine the influence of the carbon content on the kinetics of dynamic recrystallization and recovery as well as flow stress during hot deformation of carbon steels. For this purpose, single hit hot compression experiments at various strain rates and temperatures on two grades of carbon steel together with the Avrami-type kinetics equation and Bergstrom approach have been utilized. The results show that the apparent hot deformation activation energy decreases with increasing carbon content and this phenomenon results in a faster dynamic recrystallization and recovery and a lower flow stress at high temperatures and/or low strain rates in high carbon steels, while... 

This paper presents a mathematical model for predicting the temperature distribution and austenite microstructural changes during hot rolling of steel bars and rod. The model is based on the finite element method for evaluating the temperature distribution and Wusatowski approach to determine the strain field within the deformation zone. Also, by employing double and single hit hot compression experiments, the kinetics of dynamic and static recrystallization of a low carbon steel are determined to predict the flow stress as well as the phase changes in austenite range during and after the hot rolling process. To deal with the correlation between the metal flow and thermal behaviour and...