جستجوی مقالات مرتبط با کلیدواژه « روش رویه پاسخ » در نشریات گروه « مکانیک »

In this research, the parameters of brazing temperature, time, and joint seam have been optimized in brazing joints of 420 stainless steel with BNi-2 filler metal on the shear strength of lap joint samples using response surface methodology. The parameters of brazing temperature, time, and joint seam were determined by the design of the experiment using the Benken box method. The thickness of BNi-2 filler metal was considered to be 0.04, 0.07, and 0.1 mm in this research. After preparing the samples, they were placed in a vacuum furnace at temperatures of 1000°C, 1070°C, and 1140°C for 10, 30, and 50 minutes. The mechanical tensile test was performed to determine the shear strength. It was observed that increasing the joint seam from 0.04 to 0.1 mm caused a 14% decrease in shear strength. Also, increasing the brazing temperature from 1000°C to 1140°C has increased the shear strength by 21%, and increasing the brazing time from 10 to 50 minutes has increased the shear strength by 27%. In the end, it was optimized that the maximum shear strength is 164.429 MPa in the joint seam of 0.04 mm, the temperature is 1109.84 °C and the time is 46.58 minutes.

In this research, the effect of various operating conditions on the performance of an Unmanned Aerial Vehicle (UAV) with a PEMFC propulsion system is surveyed using a statistical approach, namely the Design of Experiment technique (DOE). This process starts by designing a thermodynamic cycle for UAV based on the literature review. Then, a zero-dimensional model is established to simulate the PEMFC’s performance. After validating the developed model for PEMFC, mass and energy balance equations are employed for all components of the thermodynamic cycle to calculate the efficiency of PEMFC and the system simultaneously. Afterward, the Response Surface Method (RSM) is used to design appropriate tests to study the influence of independent variables, i.e., altitude, operating pressure, and cathode stoichiometry, on the efficiency of PEMFC and system. Results indicate that increasing operating pressure improves the efficiency parameter for both the PEMFC and the system 3.5% and 14.5% respectively. Although increasing cathode stoichiometry augments the PEMFC efficiency, it plummets the system efficiency up to 30.6%. In addition, the influence of operating altitude on the PEMFC efficiency is negligible, while it causes a substantial decline in the system efficiency (more than 30%). As proved, at any desired operating altitude, maximum efficiency for the system obtains when the operating pressure and cathode stoichiometry are set at their maximum and minimum bound, respectively.

Electrochemical polishing is a nontraditional finishing process by which the surface roughness of the metallic workpiece is reduced due to anodic dissolution. In this process, an electrochemical cell is formed using the workpiece as the anode, a tool as the cathode, and a power supply.  Different parameters like inter electrode gap, the chemical composition of the electrolyte, and its temperature along with the electric potential affect the finishing performance. The important performance parameters are surface roughness, material removal rate, and the dimensional tolerance of the workpiece. In this article, the effect of inter electrode gap, cathode geometry, tool feed rate, and electric potential on the process outputs are evaluated experimentally. Due to the high number of input and output variables and possible interactions between the input variables, Box-Behnken design in response surface methodology is selected for designing the experiments. The experimental models are evaluated by analysis of variance. Using the response surface methodology, the effect of input parameters on process outputs and the possible interactions between the input variables are extracted. Also, multi-objective optimization is performed for determining the input variables which are adequate for maximizing the material removal rate along with achieving a predetermined amount for surface smoothness and geometric tolerance.

The thermal cycles involved in friction stir welding process cause softening in the joint of heat-treatable aluminum alloys. To overcome this limitation, submerged friction stir welding process has been developed. In this study, firstly, the butt joints were produced from Al7075-T6 alloy using friction stir welding process. To this end, the response surface methodology was selected as the experiment design technique. So, the factors such as tool rotational speed, tool feed rate, tool shoulder diameter, and tool tilt angle were identified as the input variables. Then, a statistical analysis of variables affecting the tensile strength of joints was performed. Afterward, the butt joints were produced using submerged friction stir welding process based on the optimal values of tool feed rate and tool tilt angle. The obtained results from analysis of variance and regression analysis of experimental data confirmed the accuracy of regression equations. Furthermore, it is shown that the linear, interactional and quadratic terms of the tool rotational speed and tool shoulder diameter are effective on the ultimate tensile strength of the underwater welded joints. Also, the optimal condition of input variables was determined using the desirability method. In addition, the optimal condition has been confirmed by implementing the verification test.

The thermal cycles involved in friction stir welding (FSW) cause softening in the joint. This phenomenon generally occurs in heat-treatable aluminum alloys leading to decrease in mechanical properties. Submerged friction stir welding (SFSW) has been developed to overcome this limitation. In this study, firstly, the butt joints were produced from Al7075-T6 alloy using FSW process. To this end, the RSM was selected as the experiment design technique. So, the factors such as: tool rotational speed, tool feed rate, tool shoulder diameter, and tool tilt angle were identified as the input variables. Then, statistical analysis and optimization of variables affecting the hardness of cross-sections was performed. In attention to the high value of desirability function (0.976), it could be found that the procedure of optimization has well fulfilled the pre-determined target. In addition, the optimal condition has been confirmed by implementing the verification test. Afterward, the butt joints were produced using SFSW based on the optimal values of tool feed rate and tool tilt angle. The obtained results from analysis of experimental data, confirmed the accuracy of regression equation. Furthermore, it is shown that the final model can predict the MHD parameter with an error less than 5%. Also, the linear terms of the tool shoulder diameter and tool rotational speed are effective on the hardness of cross-sections of the underwater welded joints.

In this study, E-glass/epoxy laminated composites with [0]12 stacking sequence manufactured by hand lay-up method. Afterwards, by considering the most important input parameters of the micro-drilling process including tool rotational speed, feed rate and tool diameter, the statistical mathematical modeling is performed to accurately investigate the thrust force response behavior versus the mentioned variables. For this purpose, using full factorial experimental design and response surface methodology and performing 54 experimental tests and considering repeatability of experiments in order to improve modeling accuracy, a second-order linear regression equation has been obtained. Also, by using the Sobel sensitivity analysis method, the quantitative effect of force behavior sensitivity versus input parameters is investigated. Moreover, the Derringer optimization algorithm is used to achieve the minimum amount of thrust force in micro-drilling process of laminated composites. The results of the statistical analysis show that the lowest feed rate, maximum tool rotational speed and smaller diameter lead to produce lowest thrust force of laminated composites. The Sobol sensitivity analysis shows that the diameter of the tool (57.8%), the feed rate (24.4%), and the rotational speed (17.8%) will have the greatest effect on thrust force in micro-drilling process, respectively. Finally, the optimization analysis show that, the lowest thrust force was obtained at a rotational speed of 2515 rpm, a feed rate of 10 mm / min and a tool diameter of 0.5 mm.

In this research, the effect of anode stoichiometry, cathode stoichiometry and temperature of inlet gases on water management and performance of a PEM fuel cell is studied by means of DOE (Design of Experiments) and direct visualization. In order to visualize the liquid water accumulation in cathode flow channels, a transparent PEM fuel cell is designed and manufactured in fuel cell research laboratory of Amirkabir University of Technology. Design of experiments is based on response surface method and central composite design. Cell’s performance is recorded over the test time and a video is simultaneously captured from its transparent cathode flow channels. Then, a digital image processing technique is used to detect and quantify channel areas that are occupied by liquid water. Area of regions containing liquid water is divided by total area of flow channels to calculate a parameter called water coverage ratio (WCR) which is then used to study flooding phenomenon. Results show that increase in cathode stoichiometry, anode stoichiometry and gas inlet temperature leads to a decrease in WCR. Also, WCR lies between 1.8 and 4.3 when an optimized produced power is reached. It is also proved that anode and cathode stoichiometry has to be minimized to reach the maximum produced power at a high inlet gas temperature.

Magnetic Abrasive Finishing (MAF) is a nano-machining process; due to low machining temperature, this process is categorized as a cold forming process. Therefore, the machined surface is free from thermal damages such as micro cracks, phase changes, burnt area and etc. In this paper, the effects of machining parameters (machining gap, work piece rotational speed and abrasive particles’ type) on work piece surface roughness have been experimentally studied. To achieve this goal a series of experimental tests were conducted on a newly developed setup and workpiece surface roughness was measured. The results of experimental studies were then used to develop a mathematical model for work piece surface roughness using Response Surface Method (RSM). The results show that there is a good agreement between experimental results and model predictions. This model was then used to minimize workipece surface roughness. In the selected range of machining parameters the minimum value of surface roughness is achieved by workpiece rotational speed of 373.73 rpm, machining gap of 2 mm and using diamond particles as abrasive. In addition, it was shown that abrasive particles’ type is the most affecting parameter on workpiece surface roughness. Furthermore, Microscopic results of surface tissue specimens, Shows that magnetic abrasive finishing process the direction and grooves resulting from the grinding process have significantly eliminated and as well as a super-polishing and uniformity surface finish like a mirror to a range of 0.207 µm is obtained.

In this study, mechanical properties including impact strength, elastic modulus and elongation at break of nanocomposites based on polypropylene/ Carboxylated Nitrile Rubber (PP/XNBR) were optimized by using response surface methodology (RSM). The samples were produced using a co-rotating twin screw extruder including 0,2,4 Wt.% of nano particles, 0, 5, 10 Wt.% of XNBR and 0,3,6 Wt.% of Polypropylene-g-glycidyl Methacrylate (PP-gMA) as compatibilizer. Impact and tensile tests were carried out to obtain impact strength, elastic modulus and elongation at break of nano composites. The results of analysis of variance showed that all three major factors silica nanoparticles, Carboxylated Nitrile Rubber and PP-gMA as compatibilizer effect on the mechanical properties with a higher probability of 90%. Also, Fisher's probable quantity values showed that silica nanoparticles had the greatest effect on the elastic modulus and XNBR had the greatest effect on impact strength and elongation at break. On the other hand, for each mechanical property, a regression model with a desirability of over 85% was obtained. Finally, the optimal values of the nano-composites were predicted to be 1.6162 wt% for silica nano powder, 10 wt% for XNBR, and 4.9697 wt% for PP-gMA.

In order to improve the properties of aluminum and its alloys, various solutions have been considered, such as: reduction of grain size, addition of alloying elements and composite manufacturing. In this regard, the use of solid-state processes such as friction stir processing (FSP) to create surface composite at temperatures below the melting point is very suitable. Hence, considering the FSP ability as a thermo-mechanical process and its advantages in the production of surface composite, in the present study, the Al7075 surface composites with the use of reinforcing particles (Al2O3) were produced using this process in accordance with the DOE principles. To this end, the response surface methodology (RSM) was selected as the experiment design technique. So, the factors such as: tool rotational speed, tool feed rate, tool shoulder diameter, and reinforcing particle size were identified as the input variables. Then, statistical analysis of variables affecting the mechanical properties of surface composite Al7075/Al2O3 was performed. The obtained results from analysis of variance (ANOVA) and regression analysis of experimental data, confirmed the accuracy of regression equations. Furthermore, it is shown that the linear, interactional and quadratic terms of the input variables are effective on the yield strength and hardness of the composite samples. Also, the tool feed rate and the reinforcing particle size were introduced as the most effective linear factors on the yield strength and hardness of the composite components, respectively.

Polymeric foams are one of the best candidates for thermal insulation. Accordingly, to investigate the thermal insulation properties of polymeric foams has attracted the attention of scientific communities in recent years. In this study, optimization of thermal insulation properties of polymeric foams is performed from solid and radiation thermal conductivities points of view. In this regard, a theoretical model based on cell size and foam density is developed. The results of the developed theoretical model are verified in comparison to various experimental results. Based on the results, the error of the theoretical model is lesser than 5%. Decreasing the foam density increases and decreases the solid and radiation thermal conductivity, respectively. Also, the radiation thermal conductivity is decreased by reducing the cell size. Response surface method (RSM) is applied in order to optimize the solid and radiation thermal conductivities. The results illuminate that the foam density of 23.5 kg.m-3 and cell size of 53 μm are the optimum conditions. At the optimum conditions, both of the solid and radiation thermal conductivities are lesser than 3 mW/mK. According to the results, the data obtained from developed theoretical model and RSM are in a good agreement. The total thermal conductivity is 30 mW/mK at optimum conditions which is a desirable value at aforementioned cell size range.

In this paper, the simulation of fiber-laser drilling process of Inconel 718 superalloy with the thickness of 1mm is investigated through the Finite Element Method. The influence of process parameters i.e. laser pulse frequency (150 to 550 Hz), laser power (200 to 500 watts), laser focal plane position (-0.5 to +0.5 mm) and the duty cycle (30 to 70%) were investigated in 5 levels and two external parameters i.e. the hole's entrance diameter and hole taper angle, were observed to be the process output responses. By performing the statistical analysis, the input and output parameters were found to have a direct relation with each other. By an increase in each of the input variables, the hole's entrance diameter and the hole taper angel increase. Verification of model was performed by experimental results. The results of the conducted simulations and statistical analyses having been used, the laser drilling process were optimized by means of the desire ability approach. Finally, residual stress simulation of this process was carried out at optimum setting. The residual stress value on the surface of sheet is maximum (0.14 MPa) and this value decreases with increasing distance from the surface of the sample.

Laser percussion drilling is one of the advanced drilling processes that its numerous advantages have extended the applications of this process. This study focuses on experimental investigation of laser percussion drilling using Nd:YAG laser on titanium alloy Ti6Al4V sheets with various thickness which is widely used in industry. In this paper the effects of the input parameters peak power, pulse width, frequency, assist gas type, gas pressure and sheet thickness on the most important process outputs include hole entrance diameter, hole exit diameter, hole taper angle, hole entrance circularity and hole exit circularity were studied. Statistical analysis was employed to analyze the experimental data and significant parameters in each response are presented. For conducting the experiments “Design of Experiments” method and for modelling “Response Surface Methodology” were used. The results obtained show that sheet thickness affects all outputs. After that frequency and pulse width, peak power and assist gas type respectively are the most significant parameters influence process outputs. Gas pressure only affects the hole entrance circularity. For this alloy to achieve a hole with high quality, it is recommended to work at lower peak power and frequency, shorter pulse width and higher assist gas pressure with Nitrogen as assist gas.

Performance of cutting fluids in machining of different materials is critical importance in order to improve the efficiency of any machining process. The objective of this research is investigation the effects of cryogenic cooling on tool wear and power consumption in the turning process of AISI 304 austenitic stainless steel. Cutting speed and cutting time each at three levels were selected as cutting variables. Response surface methodology (RSM), employing a face-centered central composite design scheme, has been used to plan and analyze the experiments. The relationships between machining parameters and output variables were modeled using RSM. Analysis of variance (ANOVA) was performed to check the adequacy of the mathematical model and its respective variables. The results showed a good agreement between the measured tool wear and power consumption and predicted values obtained by developed models. Suitable mathematical models for the response outputs were obtained using the ANOVA technique, in which significant terms were chosen according to their p values less than 0.05 (95% of confidence interval). When experiments and analysis of results were done, it is observed that tool wear was decreased till 67.5% and power consumption was decreased till 24% in cryogenic cooling method when compared with dry machining.

In the present study, the effect of parameters of autogenous pulsed Nd: YAG laser welding process on the lap joint of a 316L stainless steel foil with a thickness of 100 µm to be used as bipolar plates of polymeric fuel cell was investigated. For this purpose, the statistical tools, the analysis of variance and the various diagrams were used to analyze the data by response surface methodology. The peak power (130 to 650 W), pulse durability (1.5 to 3.5 ms), and welding frequency (14 to 18 Hz) were considered as input parameters. The mentioned statistical method was able to predict the effect of welding parameters by developing second-order polynomials, so that the total error including the repeatability error and the lack of fit error for shear strength model, weld undercut model, and weld underfill model obtained 2, 8 and 3, respectively. The defects of weld undercut and lack of penetration were identified as most important factors affecting the shear strength. The laser power is as the main parameter in this process and the impact of it on the shear strength of the weld, the weld undercut and the weld underfill is calculated 64, 62 and 66%, respectively. Finally, the maximum shear strength with the value of 522 MPa is achieved at a peak power of 260 W, pulsed duration of 3 ms and welding frequency of 17 Hz. In this case, the weld undercut is determined as 3 micrometers.

In the present study, a novel integrated system containing biomass gasifier, sodium high-temperature heat pipes, and solid oxide fuel cells is introduced. The integrated system is taken into consideration due to its high efficiency and power in order to simultaneous producing electrical power and heat. The modeling of system is performed using equilibrium constants, mass and energy conservation law and the analysis of codes is done in EES software. The effect of gasifier STBR, current density, fuel utilization factor, and outlet fuel cell’s temperature as variable parameters is investigated on the power and total energy efficiency of integrated system using response surface method; after validation of modeling in comparison to the experimental results. The analysis of variance results indicate that fuel utilization factor (with 53% contribution) and current density (with 33% contribution) are the most effective parameter on the power and total efficiency, respectively. The power of integrated system is increased by increasing of temperature while power has an increasing behavior follows by decreasing behavior by increasing fuel utilization factor. The total efficiency is increased by increasing temperature and STBR while it is decreased by increasing current density and fuel utilization factor. The results revealed that the power and total efficiency is obtained at optimum states as high as 300 kW and 90%, respectively.

In this study, mechanical and thermal properties of nanocomposites based on polypropylene/ linear low density polyethylene/ nano titanium dioxide (PP/LLDPE/TiO2) were studied. Experiments were designed according to Box-Behnken response surface methodology (RSM) to screen out significant factors from linear low density polyethylene (LLDPE), styrene-ethylene-butylenestyrene (SEBS) and titanium dioxidenano particles (TiO2). The samples were produced using a co rotating twin screw extruder including 0,2,4 Wt.% of nano particles, 20,40,60 Wt.% of LLDPE and 0,3,6 Wt.% styrene-ethylene-butylene-styrene(SEBS) as comptabilizer. Tensile properties (modulus, tensile strength and elongation at break) and impact resistance were evaluated. The results showed that modulus was increased by 7% with addition of nano particles in comparison to PP/LLDPE. In addition, impact resistance was increased by 5% and tensile strength and elongation at break were decreased.Some models also presented using the response syrface for predicting the mechanical properties.

In this study, using design of experiments, the effect of the total weight percentage of graphene nanosheets and nano clay and their weight ratio and weight percentage of compatibilizer (PPg-MA) on the tensile properties of polypropylene/ graphene/ nano clay/ PP-g-MA nanocomposites were investigated. Design of experiments and analysis of experimental data with Minitab 16 software and response surface methodology were carried out. Making nanocomposites, based on the melt mixing was performed. All combinations and pure states materials were mixed together in a co-rotating twin-screw extruder and then injection molded into standard tensile test samples. The tensile properties of all samples including tensile strength, Young's modulus and elongation at break was studied experimentally. Statistical models provided by response surface methodology had good agreement with experimental findings. Statistical analysis showed that with increasing the percentage of nanoparticles, tensile strength and elongation at break of nanocomposites reduced. Also increasing the percentage of nanoparticles increase the stiffness of nanocomposites without compatibilizer, however, with the increasing amount of compatibilizer, reduced modulus. Compounds morphology by Scanning Electron Microscopy (SEM) was performed. Micrographes showed better dispersion of the particles in lower percentages.

Because of vast applications of Liquid fuel engines in rockets and importance of their functional parameters such as trust, specific impulse and fuel consumption in engine performance, it is needed to be tested in different functional conditions before operation in actual missions. The analysis of test data used to improve the design, engine troubleshooting and to expand the production program for future rockets. Selecting the suitable injector(s) is the key parameter for improving combustion parameters. With respect to finding the effective ways to analyzing the engine hardware performance without neglecting from their main characteristics, one of the alternatives is doing the hot-fire tests by using a sub scaled engine instead of the full-scale engine. In this research, the design process and manufacturing details of a 300N trust (nominal) micro engine with single swirl Injector is presented. Initial firings using the actual fuel and oxide were not successful. Low fuel flow, low mixing area of the fuel and oxide, and contamination in the self ignition fuel (TR-1) were considered to be the reasons. Overcoming to these problems resulted in successful firing of the subscale engine.