Sharif Digital Repository

Nanopositioning is the technology to control position of the objects with precision of the scale of nanometers. Nowdays, This technology emerged as one of the components of research and production in the micro and nanometer dimensions, helping researches and producers to carry out many state of the art projects. A nanopositioning device, consists of a support to path guidance, an actuator to apply force and motion, a driving circuit for communication with the actuator, a sensor for measuring displacement, a circuit for reading sensor’s data, a controlling algorithm to reach the desired precision, a controlling hardware to enforce controlling logic, a power supply and a graphical user... 

Measurements of magnitude and direction of thrust generated by a propulsion engine is important for verification of design, fabrication, assembely and or repare procedure used for a engine. Due to possible simplification in design calculations, human and machine errors in manufacturing process, the resulted thrust generated may be different from those values expected. Also, It is important to determine the dependency of magnitude and direction of thrust forces relative to tolerances and manufacturing processes. It is necessary to have thrust measuring stand with high accuracy with capability to measure the forces in different directions. A new digital engine test stand has been designed,... 

In recent years, the world has seen a great progress in micro electro-mechanical systems (MEMS). Small size, low weight, high accuracy and low energy consumption have made these devices applicable in a variety of usages. In MEMS devices, mechanical components are used for specific purposes among which one of the most widely used are micro plates. Microplates are used in the structure of many devices such as microswitchs and atomic force microscopes. Therefore, studying of static and dynamic behavior of microplates is important. As the object gets smaller (to the scale of micro and nano meters), the classic theory of mechanics of continuous media cannot predict the behavior due to its... 

In this study, multi directional forging as a severe plastic deformation method is applied on pure aluminum at the different strain of 0.5, 1.5, 2.5, and 3.5. Annealing has been applied to samples at 150 C, 250 C, 350 C, and 450 C for one hour. In the next step, compressive test is carried out on MDFed and annealed MFDed pure aluminum through strain rate of 0.01 1/s, 0.001 1/s, and 0.0001 1/s. Based on experimental data, when the number of MDF is passes increased, because of increasing the dislocation density and grain boundary area, yield stress is increased. As an example, the yield stress of 7 passed MDFed aluminum is 2.25 times of that of 1 passes MDFed aluminum. Annealing would... 

Considering the importance of studying dynamic characteristics of soils in the analysis of wave propagation and the design of earth constructions or soil-related structures, as well as the role of Resonant Column-Torsional Shear in determining the dynamic parameters, including shear modulus, damping ratio and wave velocity in soil, this device was designed and developed in this research. The apparatus developed is able to conduct both resonant column and torsional shear tests and also measure dynamic parameters in large ranges of strain. The unsaturated pressure panel built alongside this device and the especial design of the device components have made the above-mentioned experiments... 

FE simulations have been widely used to investigate the response of the brain tissue in various circumstances. The accuracy of the material models critically affects the results of the numerical simulation. However, despite the numerous studies aiming for the material modeling of the brain, there is still divergence between the results reported in the literature. A part of this discrepancy is due to the inherent difference between samples. Nonetheless, another part of it is resulted from the differences between testing protocols used by researchers. In some protocols multiple mechanical tests are performed on each sample. Enough recovery time should be considered between consecutive test... 

The present study looks into the fracture of perforated steel plates and their sensitivity in ductile fracture. It also examines the effects of strain rise phenomenon in these specimens. The main employed fracture model is VGM, which was first introduced by Rice and Tracey, and later enhanced by Kanvinde et al.. The general methodology includes finite element simulation and lab experiments on perforated plates, to determine ductility, strain concentration in hole periphery and model sensitivity. Fot thid purpose 86 steel sheet specimen with different holes and cuts were manufactured and tested. With the acquired data, the impact of strain concentration on the load carrying capabilities 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... 

The purpose of this work is to introduce an inverse finite element tool for prediction of the blank geometry and forming severity in stamping of 3D sheet metal parts. To achieve this goal total deformation theory of plasticity has been employed. In this method the final 3D part is unfolded on the flat surface and therefore the problem is reduced to two dimensional computations. Some tooling effects including blank holder force, bending and unbending and effect of draw bead are also considered. To investigate the capability of this work, predictions of the blank shape and strain distribution and forming severity have been performed on two circular and square parts. The results have been... 

Shear modulus and damping ratio are of the most important parameters for geotechnical structures during dynamic and seismic loading. Secant shear modulus is the slope of hysteresis shear stress-shear strain loop, and damping ratio is indicative of dissipation of waves energy during propagation in the soil. These parameters mainly depend on void ratio, stress state, and shear strain of the soil. Climate changes cause some drying and wetting process which changes the soil state from saturated to unsaturated form. Previous researches indicated that the shear modulus and damping ratio change with the amount of matric suction. During the drying process, the matric suction increases,therefore,... 

Small strain shear modulus, Gmax, is one of the most important parameters for characterization of the behavior of earth structures subjected to static or dynamic loading conditions. This research presents an experimental laboratory study on the effect of non-plastic fines content and hydraulic hysteresis on the maximum shear modulus of unsaturated sand-silt mixtures. In this regard, clean Firoozkuh No. 161 silica sand which is classified as poorly graded uniform sand was mixed with different percentages of silica non-plastic silt. A set of bender element tests were planned to carry out implementing two modified triaxial devices. The modifications on these two apparatus were to add HAV... 

In this thesis, adsorption of Carbon monoxide and Hydrogen on graphene, by DFT calculation has been studied. Also effect of strain on some electrical properties, such as band structure, electrical conductivity and Density of states, for pristine graphene and adsorption CO and H2 on it has been probed. This results show that with strain up to 12% on pristine graphene , we won’t have any band gap on Fermi surface and energy adsorption for Carbon monoxide on strained graphene (up 12%) increase up 400 per cent. Also for strained graphene (12%) on Carbon monoxide adsorption condition we will have energy band gap almost a few electron volt on Fermi surface. In general this results express... 

Today, Stability review of existing structures is one of the most important problems that have underperformed in our country. Base of doing this important project is Instruction for Seismic Rehabilitation of Existing Buildings No.360. In these Criteria, Nonlinear Static Procedure (NSP) is the most popular analytical method. In this procedure, a building shall be modeled, analyzed, and evaluated as an assembly of elements and components. For modeling of components, in lieu of relationships derived from experiment or analysis, the generalized load-deformation with parameters a, b, c, shall be used for members of structure. These parameters were defined in Tables 5-6 and 5-7 for steel moment... 

Wide applications of elastomeric (rubber-like) materials have led to significant interest of researchers to these materials. Elastomers as a great category of polymeric materials,posses specific properties such as large elastic deformations and energy absorption which make them suitable for aerospace and automotive applications as well as shock and vibration absorbers.In this thesis, an exponential strain energy function (SEF) has been proposed for elastomers which well reproduces the mechanical behavior of these materials and also the material parameters are related to the physical parameters of the material molecular network. This SEF has been concluded from a relation proposed for the... 

The orientations which predominate in a final orientation distribution resulted from a specific deformation mode are the ideal orientations. There is a set of ideal orientations for each of crystal structures under a predefined mode of deformation. Ideal orientations are one of the material characteristics in the applied mode of deformation. The material texture strongly influences its final properties and affects the material behaviour in the subsequent forming processes.
In this project, final texture of 1010 steel sheet resulted from simple tension mode of deformation is investigated computationally and experimentally. The calculated texture based on the simulation procedure is... 

Strain rate dependence of plastic yield and failure properties displayed by most metals affects energies, forces and forming limits involved in high speed forming processes. This paper investigates the influence of the strain rate on the forming properties of some industrial sheet metals used in Automotive and Aerospace industries. First, Split Hopkinson Tensile Bar (SHTB) experiments are carried out to determine the influence of the strain rate on the materials’ stress-strain curves. Then, the SHTB results are used to model the constitutive behaviour of the metal sheets using the phenomenological Johnson-Cook (JC) and Voce models. Finally, forming limit diagrams (FLDs) are calculated using... 

Porous shape memory alloys (SMAs) were fabricated by many researchers in the last decade and have been initially utilized as bone implants. Also, due to hysteresis in superelastic behavior, and the porous structure, porous SMAs can be used in energy absorbing applications. Such applications call for efficient constitutive modeling of porous SMAs. Moreover, porous SMAs with a wide range of porosity ratios and mechanical properties have been produced in the recent years; therefore, it is necessary to improve the available models and carefully study porous SMA behavior. Different approaches have been utilized for modeling porous SMA behavior. Most of the researchers used homogenization approach... 

Results of previous studies on silt and clay indicated that variations in the small strain shear modulus, Gmax, during drying had a non-linear increasing trend with matric suction with greater values upon wetting. However, due to different material properties and inter-particle forces, different behaviour in Gmax is expected for sand. Although considerable research has been devoted in recent years to characterize the behaviour of Gmax of sand during drying, rather less attention has been paid to the effect of hydraulic hysteresis on Gmax and its variations during wetting. In the study presented herein, an effort was made to characterize the variation of Gmax for specimens of sand during... 

Austenite in the 300 stainless steels is not a table phase in deformation processing during which martensite phase forms. This causes significant changes in the microstructures as well as the mechanical properties of deformed steel. In this work, the effects of rolling speed, reduction, temperature and strain pass on the strain-induced martensite during strip rolling operation of stainless steel 304L are studied. Cold rolling experiments under different speeds, reduction and temperature are conducted and then, the microstructural events and mechanical properties of the rolled steel are evaluated. For doing so, different testing techniques including tensile test, hardness measurement, optical... 

In this thesis, experimental and numerical investigations are performed on dynamic behavior of fiber reinforced concrete (FRC) by split Hopkinson pressure bar (SHPB) and penetration tests. In the experimental part, effects of parameters such as quasi-static compressive strength of matrix (36 and 48 MPa), strain rate (3*10-5 up to 100 s-1), type of fibers (crimped steel, hooked-end steel, micro polypropylene and micro polypropylene) and volume fraction of the fibers (0%, 1% and 2%) are studied by employing SHPB apparatus on testing more than 150 specimens. Also, different types of FRC panels with 5 cm thickness were casted to perform 20 penetration tests with compressed gas gun apparatus. The...