فهرست مطالب مصطفی حبیب نیا

The contact resistance between polymer exchange membrane fuel cell (PEMFC) components has a crucial effect on cell performance. The geometry of the endplate, on the other hand, plays an essential role in the contact pressure distribution on the membrane electrode assembly (MEA) and the amount of contact resistance between plates. In this paper, the effect of endplate geometry on the contact pressure distribution over the MEA is simulated using ABAQUS software. In addition, a new geometry endplate is provided and the obtained results are compared with flat endplates. Geometrical parameters of an endplate with curvature (bomb-shaped endplate) are considered, and the effects of these parameters on the contact pressure distribution over the MEA are investigated. In this simulation, a 3D model of the fuel cell is developed. Our simulation results show good performances for the designed endplate and uniform contact pressure distribution on the fuel cell active area. Finally, a single fuel cell was manufactured and assembled using the simulation parameters, and experimental tests are conducted using pressure measurement films to validate the design.

Nowadays, by technology progression (CAD), controlling tools movement in Incremental forming process, caused improvement of forming function mechanism-manufacturing symmetrical and asymmetrical pieces, as by determination of an ideal direction pattern and the way of contacting tools with pieces, Caused improvement of forming behavior in sheet metals and geometry firming of complicated forms, was used in airspace and auto-making industries. In present research two-point incremental forming of sheet metal was studied experimentally by investigating priority of tool movement in negative and positive limit of geometrical profile in central cavity die. Moving pattern of tools rotationally and spindle axis constant of system (Z) around die geometrical profile, was investigated for positive and negative forming. Used sheet metal in this research is 1050 Aluminum with 15mm thickness. The results of die geometrical profile showed that critical area with maximum thinning led to tearing of all samples of sheet metals in negative forming limit while moving pattern of rotator caused decrease of tearing rate and thinning relative to constant tools in sheet metal. Maximum rate of deep, formed in negative critical area of die geometrical profile, occurrence time of tearing in sheet metal Z= -25.2mm in rotational case of tools with first negative and second positive forming pattern, is the most ideal two-point forming case in central cavity pieces.

One of the major parameters which affects fuel cell performance is the ohmic loss due to electrical resistance among fuel cell components. Assembly and design parameters affect the pressure distribution on gas diffusion layer. In this study, the influence of effective parameters such as the amount of clamping force, sealant groove depth and the thickness of end plate on the uniform pressure distribution over gas diffusion layer were investigated. By decreasing clamping force, the amount of end plate deformation decreases and uniform pressure distribution on gas diffusion layer increases. By reducing pressure on the gas diffusion layer, the possibility of leakage increases. By using an experimental sealing test, the minimum compression stress over washer for no leakage condition was achieved to be 2 MPa. According to the gas diffusion layer manufacturer, the most efficiency was achieved in 1 MPa compressive stress. Furthermore, the influence of effective parameters on the uniform pressure distribution over gas diffusion layer was examined and discussed. Finally, optimum parameters were obtained using radial basis function neural network and Bee algorithm.

Grinding is one of the final processes on the ground part that improves surface quality. Grinding wheel must be sharpened before surface quality damaged. Dressing parameters must be well adjusted in order to achieve the best conditions of grinding wheel surface. In the present research an experimental study has been performed to analyze effect of dressing parameters on surface quality of chrome-molybdenum rolls. Firstly, dressing was performed on grinding wheel and topography of wheel, wheel surface quality and surface quality of ground part were compared before and after grinding process. Further, a parameters study was carried out to determine the effects of dressing speed, feed rate and dressing depth on the surface roughness of the ground part. Here, 20 experiments were designed by use of central composite design and response surface methodology to determine effects of parameters on the final surface roughness and also identify optimal parameters. In the parameters study obtained results indicated that in minimum dressing feed rate and in minimum dressing depth and in maximum dressing speed are the most effective parameters among process parameters. Finally, the desirability approach function has been used to optimize surface roughness simultaneously.

The electrical resistance between the different components of fuel cell¡ related to the compressive stress between the various components is the fuel cell. In this study¡ two important goals pursued: first obtain the least stress on the gaskets for leakage will not happen and additional investigated the effect of stress distribution on gas diffusion layer on the amount of electrical resistance. To reach this goal¡ first designed experimental setup and achieved 2MPa minimum compressive stress on the gasket to prevent leakage. Then by another experimental setup effect of compressive stress on resistance value between the different parts have been investigated. Then according to experimental data¡ effect of clamping force on electrical resistance in simulation was investigated. Moreover effective parameters on pressure distribution on gas diffusion layer and electrical resistance was investigated. It was observed that the electrical resistance decreases by increasing clamping force. also observed pressure distribution in 4 bolt not uniform. By increasing bolt up to 8 the pressure uniformity was better than 4 bolt. But by increasing the number of bolt 8 to 12 significant changes not occurred.

Development of research on aluminum light joints is one of the most effective ways to reduce fuel consumption¡ increase strength and development of aerial structures. In this study¡ the feasibility of Tjoint AA7075 aluminum alloy with using friction stir welding process was studied. For this purpose the AA7075 aluminum joint with different tool offset¡ plunge depth¡ linear and rotational speeds were studied. In order to better understanding the production and distribution of heat¡ welding process was simulated using commercial fluent package software. Depending on the selected parameters in the process¡ the strongest connection was produced in the 1.5mm tool offset on advancing side¡ the 0.4 mm plunge depth¡ 2o tool tilt angle¡ and 1325 rpm rotational speed and 69 mm/min linear velocity¡ respectively. The failure position of all tensile samples was located on the T appendage. Tunnel void was the major defect in the joints which disappeared with increased heat input and cooling rate. The strongest connection which produced in these experiments had 181 MPa strength that nearly 80% of the aluminum base metal. The connection elongation after the tensile test was close to 11 mm.

In this research, successfully joint of dissimilar 5050 Al alloy to 304stainless steel by friction Stir Welding (FSW) has been studied. In FSW many parameters on the microstructure and mechanical properties is effective. Therefore, to achieve the highest strength possible, the important process parameters such as tool rotational speed, feedrate tool offset and pin profile have been investigated. Considering the results of the mechanical properties, the best condition to obtain the highest strength in weld nugget was 80mm/min feedrate, 500rpm tool rotational speed, with a conical pin profile and 1.8mm tool offset respectivly. In this case the strength of the 94/203MPa is obtained that this value is equal to 97% strength aluminum alloy base metal.

In this article, effects of Friction stir welding tool rotational and traverse speeds were studied on the temperature distribution, material flow and formation of defects in the welding zone. Computational fluid dynamics method was used to simulate the process with commercial CFD Fluent 6.4 package. To enhance the accuracy of simulation in this Study, the welding line that is located between two workpieces, defined with pseudo melt behavior around the FSW pin tool. Simulation results showed that with increase of FSW tool rotational speed to linear speed, the material flow in front of tool became more and dimensions of the stir zone will be bigger. The calculation result also shows that the maximum temperature and stir of the material was occurred on the advancing side. The computed results showed that with incompetent heat generation, insufficient material flow caused around the pin and defects formed in weld root. The computed results were in good agreement with the experimental results of other researchers. Based on the welding parameters that used in this simulation, the maximum strain rate is predicted between -4(S-1) to +4(S-1) in the stir zone.

Friction Stir Welding (FSW) is a solid state welding method. Now، for joining the variety of materials، especially dissimilar metals، has many applications. This method has no restrictions on the fusion welding. In addition to its many advantages، including the joining of metals with different melting points. In this paper، a successfully joint between Al5050Aluminum alloys to AISI304 stainless steel was reported. Friction Stir Welding (FSW) process was used for joining these dissimilar materials. In friction stir welding many parameters such as tool rotational speed، feedrate، offset and pin profile were effective on microstructure and mechanical properties of weld nugget by. This paper is focused on the effect of tool rotational speed، feedrate and offset on tensile strength and micro-hardness. In addition، effect of annealing operations was investigated on microstructure and mechanical properties of the weld nugget. The elongation and tensile strength of the weld nugget were increased 100 and 9 percent respectively by the annealing process.

In this research, sheets of aluminum alloys 6082 and 5050 were joined to stainless steel 304 by friction stir welding. The corrosion behavior of parent metal, heat affected zone and boundary line of joints in each side of the sheets was studied in 3.5% NaCl media by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Results showed that maximum current density belonged to the galvanic cell of the boundary lines of the joints. For the aluminum sheets, the corrosion resistance of HAZ was lower than parent metals. On the other hand the corrosion resistance of stainless steel 304 was the same in all regions.