JOURNAL OF FACULTY OF ENGINEERING (UNIVERSITY OF TABRIZ)
Year:2008 | Volume:36 | Issue:2 (54) MECHANICAL ENGINEERING|Papers Count:10

In the present research, the microstructural evolution and ferrite grain refinement at the deformation temperature of 845oC (i.e. between Ae3 Ar3) with different strain rates were investigated using single pass isothermal hot compression experiments for a low carbon Nb-Ti microalloyed steel. The physical processes that occurred during deformation were discussed by observing the optical microstructure and analyzing the true stress-true strain responses. At strain rates of 0.001 and 0.01s-1 , there is no evidence of work hardening behavior during hot deformation and strain-induced dynamic transformation (SIDT) leads to dynamic flow softening in flow curves. Optical microscopy observation shows that ultrafine and equiaxed ferrite with grain sizes of 2mm can be obtained by applying deformation with strain rate of 0.1s-1 due to SIDT just after deformation.Furthermore, increasing the strain rate from 0.001 to 0.1s-1 reduces both the grain size of the equiaxed ferrite and the amount of deformed ferrite. As high strain rates reduce the extent of dynamic softening events, DRC/DRX, occurring during deformation and in turn increases the driving force for SIDT just at the end of deformation. It was realized that high strain rates is considered to be favorable conditions to produce ultrafine ferrite.

In this paper, the possibility of forming the metallic bellows in closed-die, and also in open-die, tube hydroforming process has been studied by numerical simulation and experiment. The results obtained illustrated that forming the tube in the closed-die process is only possible for a single-convolution bellows. when the tube is fed from one end; if the feeding is performed from both the ends, then the process is also possible for a double convolution bellows. If the number of convolutions is more than two, then it is impossible to form the bellows in the closed-die process. But, in forming the bellows in the open-die tube hydroforming, there is no limitation on the number of convolutions.

Analysis of mechanical systems usually leads to the solution of a set of simultaneous equations. Very often these equations can be classified as a combination of a group of linear equations in terms of some selected variables and a group of nonlinear equations. This paper presents a new method for the solution of these equations. The method uses any non-iteration technique suitable for the solution of linear group. The nonlinear group, however, is solved by a new formula for the nonlinear variable increments in consecutive iterations. This is based on Taylor series expansion. It is shown that the method is effective with good rate of convergence and needs less number of initialapproximationscomparedwiththoseneededinNewton-Raphsonmethod. The paper also presents a method for removing errors from measured data. The method creates a matrix filter based on the available information about the system involved. These two methods have been described in a simple case study of a simple beam under pure bending. The results of simultaneous identification of modulus of elasticity and removing of errors from measured lateral deflections of the beam prove the effectiveness and accuracy of the proposed methods.

Water-gas shift reaction is an important step for production of syngas from natural gas or naphtha to produce valuable chemicals such as ammonia, methanol, hydrogen and gasoline. In this work high temperature water-gas shift catalysts were prepared by coprecipitation method using analytical grade chemicals. They were charcterized using different techniques and then their activities were investigated. The results showed that the calcined catalysts have higher degree of crystallinity. Catalysts prepared by sodium carbonate as precipitant presented higher activity. The effect of chromium oxide content of the catalysts on the activity were also studied. The suitable temperature of calcination were shown to be 350oC.

Low volume and high product mix characterize a job shop manufacturing. The CAM software in generating NC programs needs to reduce dependence on human judgment in operation planning in order to be used in low repetitive and high product mix production environments. In this paper a procedure for extracting machining methods for automated operation planning is proposed. Furthermore an optimum operation sequencing and tool selection algorithm is developed in CAM system. Numerical example has been provided and comparisons made with a known algorithm. Results indicate that the algorithms proposed in this research establish automated operation planning with reduced dependence on human judgment. It is also achieved considerable flexibility and adaptability, allowing the users to implement particular manufacturing knowledge of their own and resources available at individual shop sites.

In dual fuel engines, pilot fuel quantity has significant effects on performance and emissions. To investigate combustion. performance and emissions of these engines at different loads, experimental studies have been carried out on a dual fuel engine.In this work. ignition delay, combustion process and pollutant formation were analyzed in two ways. In the first method, amount of the pilot fuel was kept constant. while gaseous fuel quantity and the engine load were increasing. In the second method, for 25% load by decreasing pilot fuel, more gaseous fuel was substituted. The results indicate that at full load condition, increasing gaseous fuel and decreasing pilot fuel quantities. decrease combustion duration and concentration of CO, TUHC pollutants. But at part load (25%), increasing gaseous fuel and decreasing pilot fuel, increase combustion process duration, concentration of CO, TUHC pollutants increase and at last, performance parameters deteriorate.

Vanadium-phosphorus oxides (VPO) are the most widely used catalysts for the selective oxidation of butane and n-butane to maleic anhydride.In the present study the vanadium-Phosphorus-Oxide (VPO) catalysts with different p/v atomic ratio and different reflux time were prepared using alcohol based preparation procedures.The effect of reduction agents (benzyl alcohol or allyl alcohol) and calcinations atmosphere (air or pure oxygen) were investigated. A comparative study has been conducted between promoted VPO catalysts (with molybdenum) and un-promoted VPO catalysts. Effects of PN atomic ratio, reflux time and calcinations atmosphere on crystalline structure were studied. In addition effects of PN atomic ratio, reflux time, reduction agent and presence of promoter on surface area, reduction temperature and active sites were interpreted. The catalysts have been characterized by X-Ray diffraction (XRD) spectroscopy, Fourier Infrared Spectroscopy (FTIR), BET, SEM and ammonia TPD study.Prepared catalysts were found to be effective for the oxidation of n-butane to maleic anhydride (MA). With the addition of Mo promoter, high n-butane selectivity to maleic anhydride (98%) was observed at 425oC.

In this study the effect of pipe diameter of the high pressure fuel injection system (FIS) on the performance and emissions of an off-road internal combustion diesel engine has been studied. Numerical simulation of the fuel pipe shows that the injection chamber pressure, rate of fuel injection and fuel pipe pressure decrease with increasing the pipe diameter. In order to investigate the effect of fuel pipe diameter on exhaust emissions, an off road diesel engine has been tested according to an eight-mode steady-state test cycle based on the United Nations standard ECER96. Results show that an increase in the pipe diameter decreases the nitrogen oxides (NOx) emissions, but it increases the unburned hydrocarbons (UHC) and carbon monoxide (CO) emissions.

Artificial Neural Networks (ANNs) with advantages such as learning and estimation capabilities are widely used in various fields of chemical engineering such as process simulation and control. They are suitable for modeling, simulation, and solution of highly nonlinear problems. One of these problems is Nonlinear Dynamic Data Reconciliation. In this paper a new method, namely NetDDR, which uses ANNs, is described. NDDR of a distillation column is used to illustrate different aspects and advantages of the new method.

Using thermal reactive diffusion (TRD) process in order to produce a carbide or nitride layer (such as chromium carbide) onto metals and alloys is one of the techniques for increasing surface hardness and enhancing oxidation, corrosion and wear resistance. In this research, kinetics of chromium carbide coating formation onto AISI 1020 steel by salt bath method at 950, 1000.1050oC for 3- 9 h has been studied. The presence of (Cr, Fe)7C3 on steel surface was shown by XRD analysis. Observations using optical and SEM microscopes from sample cross sections show a rather smooth and compact layer of chromium carbide onto samples surface.Surface micro hardness of coated steel, measured by Vickers method, is equal to 1350 HV0050KKg. kinetic study of carbide coating, formed by this process, shows firstly a parabolic relationship between carbide thickness and treated time, secondly the activation energy for chromium carbide formation on 1020 steel in borax salt bath is equal to 225.6 KJ/mol. In addition, for predicting carbide layer thickness, contour diagrams are suggested. Yet the possibility of using a series of mathematical equations for predicting carbide thickness from treated time and bath temperature has been discussed.