Sharif Digital Repository

A high-quality butt joint of aluminum to copper (Al/Cu) can rarely be achieved by conventional fusion and solid-state welding processes. In this research, the appropriateness of friction stir welding (FSW) for making high-quality Al/Cu welds was studied. A sound Al/Cu butt joint was achieved with relatively high strength in uni-axial tensile tests. Mechanical properties and microstructure of the sound friction stir welds were examined. The ultimate tensile strength of the joints reached about 75 percent of the aluminum base metal, with the fracture occurring at aluminum side. The metallurgical study of the welds before and after their failure in tensile tests showed that the heat affected... 

A multilayer back propagation learning algorithm was used as an artificial neural network tool to predict the mechanical properties of porous NiTi shape memory alloys fabricated by press/sintering of the mixed powders. Effects of green porosity, sintering time and the ratio of the average Ti to Ni particle sizes on properties of the product were investigated. Hardness and tensile strength of the compacts were determined by hardness Rockwell B method and shear punch test. Three-fourths of 36 pairs of experimental data were used for training the network within the toolbox of the MATLAB software. Porosity, sintering time and particle size ratios were defined as the input variables of the model.... 

A method for joining metals in the semisolid state is presented. A model alloy Sn-15%Pb was used to demonstrate the concept. By presented process, dendritic microstructure of the weld zone can be avoided. Moreover, near-weld zone of the cold worked substrates which is affected by heat would have a globular structure due to a thermomechanical treatment. The two substrates were heated up locally in the joint line to the semisolid temperature range. At this point a stirrer was introduced into the weld seam in order to mix the two sides into a single uniform joint. Localized mechanical properties of different zones were examined using Shear Punch Test (SPT), showing a good strength in the weld... 

The influence of different parameters such as welding pressure, rotational speed, and traverse speed on the weld properties has been evaluated earlier but there are some important parameters yet to be thoroughly investigated. In this study, an effort has been made to determine the influence of different ratios of rotational speed/traverse speed on mechanical properties of different zones of friction stir welded AZ31 magnesium alloy. Mechanical properties of different zones were determined by a shear punch test. It was found out that increasing the aforementioned ratio leads to a slight decrease in yield and ultimate strength of the stir zone and the transitional zone. It was also observed... 

Numerous advantages of application of tailor welded blanks (TWBs) in automobile industry, namely reduction of weight, fuel consumption and air pollution, have made the manufacturers eager to investigate in this field. On the other hand, while experiments generally provide valuable information in regard with mechanical behaviors, but utilization of simulation methods has extended vastly due to time and cost saving issues. One challenging issue in numerically analyzing the forming behavior of transversely welded TWBs, welded by laser welding methods, has been the presence of weld zone. While some researchers believe that during simulation, the weld zone can be neglected due to its minority and... 

Forming limit diagrams (FLDs) are extensively used in industries, particularly the auto industry. The establishment of these diagrams using a predictive approach can lead to reduction in both cost and time. In the present work, Gurson-Tvergaard-Needleman (GTN), a porosity-based model, was used to predict the FLD of an interstitial-free steel via finite element simulation. Optimum values of the GTN model were obtained by applying a response surface methodology (RSM) based on central composite design. Results show that RSM is a good method for an appropriate determination of the GTN model parameters, such as initial void volume fraction, effective void volume fraction, critical void volume... 

Friction Stir Welding (FSW) is a novel solid state welding process for joining materials. In this process a high speed tool is introduced into the weld seam and due to localized frictional heat, plastic deformation and transverse movement along the weld seam, joining is accomplished. In this study aluminum matrix composite A356 + 15%SiCp is chosen for friction stir welding. Fragmentation of SiC particles and silicon needles existing in eutectic phase as well as their homogenous distribution as a result of stirring with high plastic strains, improve mechanical properties such as modulus of elasticity, yield and ultimate strength, elongation and hardness in the weld zone compared to that of... 

A method for joining metals in the semisolid state is presented. A model alloy Sn-15%Pb was used to demonstrate the concept. By presented process, dendritic microstructure of the weld zone can be avoided. Moreover, near-weld zone of the cold worked substrates which is affected by heat would have a globular structure due to a thermomechanical treatment. The two substrates were heated up locally in the joint line to the semisolid temperature range. At this point a stirrer was introduced into the weld seam in order to mix the two sides into a single uniform joint. Localized mechanical properties of different zones were examined using Shear Punch Test (SPT), showing a good strength in the weld... 

To stay competitive in the new dynamic market having large fluctuations in product demand, manufacturing companies must use systems that not only produce their goods with high productivity but also allow for rapid response to market changes. Reconfigurable manufacturing system (RMS) is a new paradigm that enables manufacturing systems to respond quickly and cost effectively to market demand. In other words, RMS is a system designed from the outset, for rapid changes in both hardware and software components, in order to quickly adjust its production capacity to fluctuations in market demand and adapt its functionality to new products. The effectiveness of an RMS depends on implementing its... 

In the new competitive dynamic market, manufacturing success and survival are becoming more and more difficult to ensure. In other words, getting the right product with low cost and high quality is not the only key to success. New requirements such as production responsiveness and flexibility should be considered. Reconfigurable Manufacturing System. (RMS) is a new paradigm that enables manufacturing systems to achieve rapid response to market demand. The effectiveness of an RMS depends on implementing key characteristics and capabilities of RMS in system design stage and benefiting from them in utilisation stage. In this paper, we introduced a methodology to adjust rapidly and productively... 

This article introduces a methodology to integrate fuzzy multiattribute decision making (FMADM) and fuzzy simulation. According to this method, a fuzzy simulation method is applied to study the effect of different alternative on system's performance and decision criteria taking into account fuzzy inputs. Using a fuzzy analytical hierarchy process (FAHP) and the results of fuzzy simulation, a FMADM is conducted to select the best alternative. This article introduces how to incorporate fuzzy set theory with discrete-event simulation in order to model uncertain activity duration in simulating a realworld system, especially when insufficient or no sample data are available. A case study is... 

This paper introduces how to incorporate fuzzy set theory with discrete-event simulation in order to model uncertain activity duration in simulating a real-world system, especially when insufficient or no sample data are available. A case study is developed to apply this method to select a scenario to implement the maintenance program in a constant work in process (CONWIP) system. The maintenance activities directly or indirectly affect on production system performance such as response time production costs and etc. so we used the fuzzy simulation to determine the maintenance affects on the system performance. Finally we used the fuzzy simulation result to develop a fuzzy multi attribute... 

In naturally fractured reservoirs, modeling of mass transfer between matrix blocks and fractures is an important subject during gas injection or contaminant transport. This study focuses on developing an exact analytical solution to transient tracer transport problem along a discrete fracture in a porous rock matrix. Using Gauss-Legendre quadrature, an expression was obtained in the form of a double integral which is considered as the general transient solution. This solution has the ability to account the following phenomena: advective transport in fractures and molecular diffusion from the fracture to the matrix block. Certain assumptions are made which allow the problem to be formulated... 

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the Editors. Some parts of this paper are similar to the following previously-published paper, but do not include appropriate citation: Amin Sharifi Haddad, Hassan Hassanzadeh, Jalal Abedi; Advective-diffuse mass tranfer in fractured porous media with variable rock matrix block size; Journal of Contaminant Hydrology, Volume 133, 15 May 2012, Pages 94–107. DOI: 10.1016/j.jconhyd.2012.02.008. The Authors apologise unreservedly for this violation of publishing policies, and for any... 

Over the past few years, due to increasing population, limited water resources, and other pressures on the urban water systems (UWS), urban water management has become a major concern for urban policymakers to develop efficient management solutions. In this study, a new hybrid model called sustainable dynamic urban water metabolism management (SDUWMM) is presented, based on urban water metabolism and system dynamics. Isfahan's UWS has been modeled by SDUWMM and its conditions have been simulated until 2041. SDUWMM considers effective internal relationships of the UWS components such as population, climate change, water supply and demand, infrastructures condition, water price, costs and... 

In this paper, we introduce a technique for improving power distribution characteristics of space time block codes (STBCs) which include peak to average power ratio (PAPR), average to minimum power ratio (Ave/min), and probability of transmitting “zero” by antenna. We consider STBCs in multiple input multiple output (MIMO) and multiple input single output (MISO) systems that achieve full diversity for linear or maximum likelihood (ML) receivers. It is proved that by multiplying a specific non-singular square matrix by the code matrix, a new code is obtained that achieves full diversity and the power distribution characteristics are improved. The proposed technique is general can be applied... 

Improving power distribution characteristics of space time block codes (STBCs), namely peak to average power ratio (PAPR), average to minimum power ratio (Ave/min), and probability of transmitting 'zero' by antenna, makes easier their practical implementation. To this end, this study proposes to multiply full diversity STBC with a non-singular matrix in multiple input multiple output (MIMO) or multiple input single output (MISO) systems with linear or maximum likelihood (ML) receivers. It is proved that the obtained code achieves full diversity and the order of detection complexity does not change. The proposed method is applied to different types of STBCs. The bit error rate (BER) and power... 

In this paper, design and exergy method optimization of a 5 kW power output polymer electrolyte fuel cell (PEFC) fuel cell with cogeneration application has been investigated. It is assumed that cooling water is passed through the fuel cell cooling channel, warmed up and supplied for space heating applications. The performance of the proposed system has been optimized by the second law based on exergy analysis. Results show that for maximum system efficiency and minimum entropy generation, fuel cell temperature and voltage should be as high as possible in the range of application. Also, the fuel cell pressure and stoichiometric air:fuel ratio should be as low as possible in the range of... 

In this study; a Sugeno type ANFI model which describes the relationship between the bio surfactant concentration as a model output and the critical medium components as its inputs has been constructed. The critical medium components are glucose, urea,SrCl2 and MgSo4 .The experimental data for training and testing capability of the model obtained by a statistical experimental design which have been captured from literatures. Six generalized bell shaped membership function have been selected for each of input variables and based on the training data ANFI model has been trained using the hybrid learning algorithm. The yielded biosurfactant concentration values from the model prediction shows... 

In this investigation, application of the least square support vector machine (LSSVM) for modeling of the electrical resistivity of the magnetic Zn-Mn-S nanocrystalline semiconductor films has been described. The model has been trained based on the experimental data obtained from a published work by Sreekantha Reddy et al. The model inputs are temperature and variations in the concentrations of Zn, Mn. The results indicate that LSSVM is able to be used for accurate prediction of the electrical resistivity of the Zn-Mn-S nanocrystalline semiconductor films