Sharif Digital Repository

A simplified efficient finite element method called the inverse approach (IA) has been developed to estimate initial blank and strain distribution in sheet metal forming. This algorithm is an inverse method since the position of points in final shape is known and their corresponding position in the initial blank should be determined. This approach deals with the geometric compatibility of finite elements, plastic deformation theory, and virtual work principle. This method often based on implicit static algorithms, sometimes causes convergence problems because of strong nonlinearities. This paper introduces an initial guess to speed up the convergence of Newton- Raphson solution. The... 

Recent investigations show that ceramic/ceramic joints have high potential for applications in industry. Cost and difficulty in manufacturing complex components, either in one step or by joining of ceramic-metal and ceramic-ceramic, have inhibited more widespread use. It is important to know how to join components without problems and to understand the role of the interface as the main factor controlling the properties in these joints. The purpose of this paper was to investigate the joining of two ceramics with metal fillers (SiC to SiC and Al2O3 to Al2O3) and to investigate the interface of SiC/SiC and Al2O3/Al 2O3 with the same metal interlayer (Ag-Cu-Ti) and the effects on the... 

The accuracy of multi dimensional simulation of vehicle dynamics has been significantly increased for both passive and active vehicles which are equipped with advanced electronic components. Recently, one of the subjects that has been considered is increasing the car safety in design. Therefore, many efforts have been done to increase vehicle stability especially during the turn. It is also very important in three wheel car. One of the most important efforts is adjusting the camber angle in the car suspension system. Camber angle as well as the vehicle stability has major effects on the wheel slip, reducing rubber abrasion, acceleration and braking. Since the increase or decrease in the... 

Peripheral milling is extensively used in manufacturing industry. To achieve more material removal rate, high precision and surface quality and increase tool life, chatter vibration must be suppressed. In this paper, an extended dynamic model of the peripheral milling process including both the structural nonlinearity and nonlinear cutting forces is presented. Using the multiple-scale approach, as a perturbation technique, internal resonance of the milling process is investigated. Transfer of the energy between the coupled x-y modes is studied. According to results obtained, it is possible to adjust the rate at which the x-mode (or y-mode) decays by implementation of the internal resonance... 

We consider a two-echelon inventory system with a manufacturer operating from a warehouse supplying multiple distribution centers (DCs) that satisfy the demand originating from multiple sources. The manufacturer has a finite production capacity and production times are stochastic. Demand from each source follows an independent Poisson process. We assume that the transportation times between the warehouse and DCs may be positive which may require keeping inventory at both the warehouse and DCs. Inventory in both echelons is managed using the base-stock policy. Each demand source can procure the product from one or more DCs, each incurring a different fulfilment cost. The objective is to... 

Success in forecasting and analyzing sales for given goods or services can mean the difference between profit and loss for an accounting period and, ultimately, the success or failure of the business itself. Therefore, reliable prediction of sales becomes a very important task. This article presents a novel sales forecasting approach by the integration of genetic fuzzy systems (GFS) and data clustering to construct a sales forecasting expert system. At first, all records of data are categorized into k clusters by using the K-means model. Then, all clusters will be fed into independent GFS models with the ability of rule base extraction and data base tuning. In order to evaluate our K-means... 

This paper investigates the problem of assembly line balancing problem, in which the products in the production line may undergo to be reworked on the current task. Since the real manufacturing systems deal with the stochastic nature of the items in production lines, this paper considers the simple assembly line balancing problem type 2 (SALBP-II) under the conditions of stochastic processing time of tasks and the element of reworking system. Exposing to the stochastic conditions encouraged us to handle the problem via simulation optimization procedure, which uses the well known genetic algorithm as an optimization tool. Results show the adaptation and effectiveness of GA to considered... 

High-temperature (1200-1350°C) corrosion of fused-cast ZrO2-Al2O3-SiO2 (ZAS) refractory contacting lead silicate glass melt (LSG) containing 68.5wt% PbO was investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), differential scanning calorimetry (DSC), x-ray diffraction (XRD), thickness measurement and Archimedes density measurement. ZAS durability was improved by baddeliyete content and deteriorated with open porosity proportion, corundum percentage and eutectic mixture presence. Diffusion of lead resulted in fusion-temperature lowering of the glassy layers embedded within the ZAS particles. Heating caused viscosity drop across the interface, loosening the... 

In this paper, a design of the supply chain distributer-retailer network for a seasonal multiple-product location allocation-inventory control problem in a planning horizon consisting of multiple periods is modeled. The distance between the distributers and retailers are assumed to be Euclidean and square Euclidean while retailers purchase the products from the distributers under all-unit and incremental quantity discount policies. Furthermore, the products are delivered in packets of known size of items and in case of shortage, a fraction of demand is considered backorder and a fraction lost sale. Besides, the distributers store the manufactured products in their warehouses before... 

In this paper a new model is proposed for the integrated problem of supply chain network designing and assembly line balancing under demand uncertainty. In this problem there are three types of entities: manufacturers, assemblers and customers. Manufacturers provide assemblers with components and assemblers use these components to produce the final products and satisfy the demand of the customers. This problem involves determining the location of manufacturers and assemblers in the network, balancing the assembly lines, and transportation of materials and products throughout the network. A mixed integer nonlinear programming formulation based on two stage stochastic programming method is... 

Bi-objective optimization of a multi-product multi-period three-echelon supply-chain-network problem is aimed in this paper. The network consists of manufacturing plants, distribution centers (DCs), and customer nodes. To bring the problem closer to reality, the majority of the parameters in this network including fixed and variable costs, customer demand, available production time, set-up and production times, all are considered stochastic. The goal is to determine the quantities of the products produced by the manufacturing plants in different periods, the number and locations of the warehouses, the quantities of products transported between the supply chain entities, the inventory of... 

We develop a replacement-repair model to study a renewing free replacement warranty (RFRW) for a class of multi-state deteriorating repairable products. Each product may experience N different working states with different hazard functions, before the warranty contract expires. Once the item enters working state j(j = 1, 2, . . . , N), it can either fail or move t any of the subsequent states. In the former case, the best rectification action, replacement or minimal repair, regarding the failure status, should be done to put the item into operation. In each working state there is a determined probability for transition to each of the subsequent working states. After a replacement the product... 

Peripheral milling is extensively used in manufacturing processes, especially in aerospace industry where end mills are used for milling of wing parts and engine components. Knowledge of the cutting forces is the first necessary stage in analysis of the milling process. In this paper, cutting forces are presented for both two and three dimensional models. Instead of the common linear dependency of cutting forces to the cut chip thickness, two nonlinear models are presented. In the first model, cutting forces are considered as a function of chip thickness with a complete third order polynomial. In the second one, the quadratic and constant terms of the third order polynomial are set to zero.... 

In mechanical assemblies, the performance, quality, cost and assemblability of the product are significantly affected by the geometric errors of the parts. This paper develops the statistical error analysis approach for dimensional control in automotive body multi-station assembly process. In this method, the homogeneous transformation matrices are used to describe the location and orientation of part and assembly features and the small homogeneous transformation matrices are used to model the errors. In this approach, the effective errors in automotive body assembly process are classified in three categories: manufacturing errors (dimensional and geometric tolerances), locating errors... 

This paper presents a new architecture for a DLL based frequency synthesizer for wireless transceivers. Owing to its DLL based nature, the synthesizer generates the target frequencies with minimum phase noise. The proposed architecture takes the advantage of a combination of a frequency divider and an edge combiner to create the desired frequencies. As an example, the synthesizer is adopted to create the channel frequencies of French DVB-H/T standard. The circuit level design guidelines and power consumption trade-offs are presented. It was shown that for the mentioned standard a mere 6 stage delay line is sufficient. Simulation results confirm the analytical predictions  

Thermo mechanical processing and controlled rolling of microalloyed steel sheets are affected by several factors. In this investigation, finishing temperature of rolling which is considered as the most effective parameters on the final mechanical properties of hot rolled products has been studied. For this purpose, three different finishing temperatures of 950, 900 and 850 °C below the non-recrystallization temperature and one temperature of 800 °C in the intercritical range were chosen. It is observed that decreasing the finishing temperature causes increase of strength and decrease of total elongation. This is accompanied by more grain refinement of microstructure and the morphology was... 

Grinding is widely used for manufacturing of components that require fine surface finish and good dimensional accuracy. In this study a thermo-mechanical finite element analysis is conducted to find out how grinding parameters can affect temperature and residual stress distribution in the workpiece. Results of parametric study presented in this work indicate, by carefully selecting the grinding parameters, minimum thermal and mechanical damage can be achieved. Higher workpiece velocities produce higher surface residual stress. By increasing depths of cut, depth of tensile residual stresses increases. Convection heat coefficient does not have any considerable effect on surface residual stress... 

In aerospace applications structures weight is considered as a major performance parameter. One of the most effective manufacturing methods for weight reduction is superplastic forming. By this technique, not only the weight, but also the stress concentration, the cost, and the manufacturing time are noticeably reduced. Additionally, the components with complicated shapes could be formed in a single manufacturing step. Due to the wide demand for whiskers reinforced metal matrix composites (MMCs) in aerospace industries, many research works have been designed to extend the borders of superplastic forming to MMCs materials. In the present study, a 3-D symmetric micromechanical finite element... 

This paper represents a systematic procedure of simulating charge pump based delay locked loops (DLLs). The presented procedure is based on the systematic modelling of the DLL components in Matlab simulink simulator. The system has been designed for 1Hz input clock signal that by changing the whole system scale, it can be used for every other input frequencies. The simulation results in Matlab and design considerations for DLL based frequency multiplier are presented  

In this paper, a new compact, low power and low voltage structure for CMOS analog multiplier is proposed. All of them are implemented using a compact circuit. The circuit is designed and analyzed in 0.18μm CMOS process model. Simulation results for the circuit with a 1.2V single supply show that it consumes only 25μw quiescent power with 2GHz bandwidth and 1.5% THD