Sharif Digital Repository

In this research two stage deep drawing has been analyzed by the upper bound method. During this study, the deep drawings of cylindrical parts have been analyzed. In this method, for the first stage the whole deformation region is divided into five zones including punch bottom, punch radius, between punch and die, die radius and flange. Then, the geometric equations of each zones is generated by sweeping the section curves defined on the boundary of each zone. The velocity fields are expressed in a similar manner by sweeping the boundary velocity functions. At each stage, with the change of height between punch and die, the point location is changed and movement and tension in the sheet are... 

This work presents a quick method in estimation of spring back effect in sheet metal forming. In this method, the so called Inverse Finite Element Method (IFEM) has been adopted for compution of strains and also blank shape. Although the of element used is membrane, the effect of bending/ unbendiing is considered by addition of some extra forces as the bending forces to the nodal forces. The results of strain distribution obtained by IFEM are applied to another algorithm developed for computation of the spring back . this algorithm has been developed for the sections with plane starin assumption. Therefore, spring back of longitudinal parts, can be estimated by this method in a short time.... 

In designing sheet forming processes, finding out the value of the maximum strain before necking in sheets is extremely important. Therefore, many experimental and theoretical efforts have been carried out in order to answer this question. One of the most well-known and useful theoretical methods in this regard is the Marciniak - Kuczynski method which was introduced in 1967 and is still the topic of many researches. In this model, it is assumed that a groove as a defect primarily exists in the sheet and due to the weakness of this region, necking will initiate. Furthermore, the effects of various parameters such as sensitivity to strain rate, strain path, thickness, three dimensional... 

In the rolling process some parameters may cause the rolling process to be asymmetric, the most important of this parameters are unequal radii, friction and rotational speed of upper and lower rolls. The mentioned asymmetry factors change the symmetric rolling process to the new process called asymmetrical rolling process. Asymmerical roling process that caused from various asymmetry factor have been studeid for many years by various researchers from different directions with different methods.Among the most important of which was raised by many researchers, slab method was the most accuracy and acceptable method. Using the slab method researchers were able to calculate the force, torque and... 

In recent decades, the importance of theoretical and experimental researches on sheet metal forming has been revealed due to its wide-spreading applications. The purpose of these researches is to optimize the forming processes and minimize the existing imperfections. Since classical theories don’t include parameters for describing the dependence of metals behavior on size effects or inhomogeneous plastic deformation effects, gradient theories are considered in many researches. In gradient theories, this dependence is considered by changing the constitutive equations and the existence of higher order of strain gradient in zones with inhomogeneous deformation. By considering the localized and... 

In this project, by using the image processing method, the strain rate in the deformed sheets is measured, and then compared with experimental results. Scratches are first drawn on the surface of the sheet. After the deformation, photographs of the surface are taken, by using image processing method as well as the use of special techniques, the strain is obtained fast with accurately. By determining the strain, tension will also be achieved through Levy Mises relations. In this project, by using this method, the strain is calculated on surfaces with simple geometry, such as sphere (spherical surface of the sheet in the FLD test), as well as surfaces whose surface geometry is unknown and... 

Sheet metal forming is widely being used in the production fields. Improve of quality, production rate and efficiency of this process are important. Temperature and strain rate are the most effective parameters on the formability of sheet metals. Utilizing forming limit diagram is the most common method of determining the formability. In this study, forming limit diagram of AA3003 aluminum alloy is extracted in different temperatures and velocities using simulation of Nakazima test with Abaqus finite element software. The simulation results, indicate that at 250°C formability is about 3 times more than that at room temperature. increasing the velocity of the punch in low strain rates causes... 

Using thick plates is common in different industries including ship and pressure vessel manufacturing.In this research a plate forming method called line heating is examined. This method requires basic equipment and is very economical.Heat transfer between gas torch and plate is studied in more detail. Impingement jet model is used to simulate the effect of torch on plate. Velocity and temperature fields of exiting air are calculated in Fluent, a commercial software. Then heat is transferred between hot air and plate, which is related to velocity field and both temperature distribution of air and plate. In this method torch moves along the plate. In order to simulate this movement, a moving... 

Sheet Metals are widely used in different industries such as ship building and pressure vessels. One important subject in these industries is to create the desired sheets through line heating process. Designing the heating lines in order to get the desired shape with the sufficient accuracy has always been a concern for the engineers in this process. In this thesis, the Strain-Based Method in designing the heat lines for creating special surfaces is discussed. Two sets of surfaces were considered. The first one is 2D surfaces set such as cylindrical surfaces. The second set is 3D surfaces set. The examples of such surfaces are double-curved surfaces such as a pillow and a saddle shape. The... 

In recent years, two-layer sheets have been used in various industries. In this research, the formability of a two-layer sheet which is made of 1.35 mm steel and 0.45 mm copper sheets has been studied. The two-layer sheet used in this study was made by explosive welding method. In order to investigate the formability of the sheet, forming limit diagram was determined. First, Marciniak-Kuczynski (M-K) model was used. In order to determine forming limit diagram using this method, the two-layer sheet was equated with a single-layer sheet and MATLAB software was used. The two-layer sheet was also modeled in finite element software ABAQUS. In order to determine the forming limit diagram, Nakazima... 

One of the most useful methods in metal forming is Sheet Metal Forming. Use of Forming limit diagrams (FLD) in designing is a conventional method. Therefore many experimental and theoretical efforts have been carried out in order to investigate the FLDs. Many ways to obtain this FLDs and their effective parameters have been studied. But the stress state at these studies is planar which lead to an untrue model for several metal forming process such as incremental sheet forming. With this technique, the forming limit curve (FLC) appears in a different pattern, revealing an enhanced formability, compared to conventional forming techniques. Therefore, in this study, the effect of through... 

This world’s commercial and competitive space force’s designers and manufactures to produce and supply products with high quality and low price at desirable level of reliability. On the other hand, during the design and production process, Engineers are always faced with uncertainty. Essentially, uncertainties can be divided into two categories: aleatory and epistemic. Aleatory uncertainties are due to changes in design conditions, material properties, physical dimensions of components and operating conditions. This kind of uncertainty will not be reduced during the life.on the otherhand, Epistemic uncertainties that are due to lack of knowledge about physical nature of systems can be... 

The Tilor welded blank (TWB) two or more sheets with different thickness or strength which are welded together. The automobile designer are searching for new methods to reduce the cars’ weight and producing cost in order to diminish fuel consumption so they can survive in the competitive market. One way to achieve to this seemingly Contradictory demands, is using TWB in cars’ body. One of the most applicable methods to investigate the formability of metals sheets, is Forming Limit Diagrams (FLD). Three ways to determine the FLD are: Analytical Method, Experimental Methods, and Numerical Method. The experimental method to determine FLD, require metal sheets to undergo in different strain... 

In hydraulic autoferttage, the tube is subjected to high internal pressure and the resulting residual stresses increase the pressure capacity and fatigue lifetime of the tube. High strength steels are used for construction of such tubes. Material behavior of these steels is very complicated due to pronounced Bauschinger effect. DIN1.6959 steel is frequently used for construction of autofrettaged tubes in some countries such as Germany, Switzerland and Iran. In this work, the material behavior of this steel was modeled accurately using uniaxial tension-compression tests and mechanical properties and material behavior of this steel also were compared with A723 and HB7 steels. As a general... 

Cancer is the second leading cause of death in the world, with a high annual cost of treatment. As the cancer progresses, the cancer cells in the bloodstream metastasize to other parts of the body, causing the disease to spread throughout the patient's body and disrupt organ functions. sepration of cancer cells in the bloodstream inhibits the growth of cancer. Cancer cells differ from healthy cells in some features, such as size, electrical charge and polarization. These features can be used to seprate cancer cells from healthy cells.In this study, cell surface electrical charge was used as a biomarker to seprate cancer cells. By passing blood flow through a chanal and applying an electrical... 

The tolerance stack-up in mechanical assemblies is closely related to the quality of finished products and to the costs of production. In practice, choosing a large tolerance range will result in performance reduction. On the other hand, with small tolerances considered, production costs will increase. Tolerance allocation is a useful tool to control the dimensional and geometric variables of the product, so design engineers can control the final product quality level, production cost, and other variables. The proposed method for tolerance design considers the effects of degradation and quality loss over time and allocates tolerances so that, the functional key characteristic satisfies, as... 

Resonantly actuated microstructures known as microresoantors, are the basic parts of many of MEMS devices such as highly sensitive pressure sensors, mass sensors, biosensors, RF filters, AFMs , ... . Vibration analysis of microresonators specially that of the coupled in-plane and out-f-plane motions has draught many attentions, during recent years. The purpose of the present thesis was to analyze the vibration and dynamics of an FGM microresonator consisted of a clamped-clamped beam with a relative massive pedal attached to the middle of the beam. By modeling the system initially, linear natural in-plane and out-of-plane frequencies and associated mode shapes are obtained. Results are... 

Smart heat-sensitive polymers play a unique role in drug delivery systems due to reversible behavior in response to environmental changes, especially temperature changes. Among the heat-sensitive polymers, UCST polymers due to their specific behavior and very little-known polymers with this feature are the subject of many new researches. In the present study, New designed temperature-sensitive polymers with UCST capability based on acrylamide and vinyl acetate were synthesized. These copolymers were synthesized in different percentages of acrylamide by free radical polymerization in solution conditions. All polymers compounds were characterized by H-NMR, FT-IR, DSC and GPC measurements. The...