Sharif Digital Repository

Researchers have examined different approaches to improve damage tolerance of discontinuously reinforced aluminum (DRA). In this study, three-layer DRA laminates containing two exterior layers of Al6061-15 vol.% SiCp and an interlayer of Al1050 were fabricated by hot roll bonding. Interfacial adhesion between the layers was controlled by means of rolling stain. The results of shear test revealed that, the bonding strength of laminates was influenced by number of rolling passes. Considering this effect, the role of interfacial bonding on the toughness of laminates was studied under three-point bending in the crack divider orientation. The quasi-static toughness of the laminates was greater... 

Steel shear panels in combination with bracing are a novel form of steel shear walls that eliminate large distributed loads to impose on primary beams along with columns. This paper presents the results of a comparative experimental program on two types of steel shear panels with and without stiffeners. For this purpose, the proposed quasi-static cyclic loading history of Federal Emergency Management Agency(FEMA) 461 was applied on two full-scale specimens. Structural steel was selected as the material of the panels, which were welded to the surrounding boundary elements. In addition, using finite element models, performed tests were simulated and scaling effects were investigated. This... 

In this paper, we have proposed a quasi-static model of a multi-agent system as police agents with and without non-holonomic constraints for agents' motion. We also consider an active thief agent which has stochastic dynamic equation of motion. Our control purpose is that these police agents pursue the thief agent and the geometrical center of them aims the thief agent current position. Also in the motion of the police agents for surrounding the thief, the unity of the swarm should be preserved and collision between them should be avoided. Police agents do not have all of the dynamic states of the thief agent's motion andalso those that are available and observable for the police agents are... 

Although manual crack inspection has been widely used for structural health monitoring over the last decades, the development of computer vision methods allows continuous monitoring and compensates the human judgment inaccuracy. In this study, an image-based method entitled Arc Length method is introduced for extracting crack pattern characteristics, including crack width and crack length. The method contains two major steps; in the first step, the crack zones are estimated in the whole image. Afterwards, the algorithm finds the start point, follows the crack pattern, and measures the crack features, such as crack width, crack length, and crack pattern angle. The efficiency of the method is... 

This paper presents a new reduced-order modeling approach based on boundary element method. In this approach the eigenvalue problem of the unsteady flows is defined based on the unknown wake singularities. By constructing this reduced-order model, the body quasi-static eigenmodes are removed from the eigensystem and it is possible to obtain satisfactory results without static correction technique when enough eigenmodes are used. In addition to the conventional method, Eigenanalysis and reduced-order modeling of unsteady flows over a NACA 0012 airfoil and a wing with NACA 0012 section are performed using this new ROM method. Numerical examples are presented that demonstrate the accuracy and... 

Abutments of concrete arch dams are usually crossed by several joints, which may create some rock wedges. Abutment stability analysis and controlling the probable wedge movements is one of the main concerns in the design procedure of arch dams that should be investigated. For decades, the quasi-static method, due to its simple approach, has been used by most of dam designers. In this study, the dynamic method is presented and the obtained time history of sliding safety factors is compared with the quasi-static results. For this purpose, all three components of Kobe (1979) and Imperial Valley (1940) earthquakes are applied to the wedge, simultaneously, and the magnitude and direction of wedge... 

The robots that can move on rough terrains are very important especially in Rescue operation, exploration, etc. In this research, a mechanism is introduced for a ring-like robot with a flexible body. This robot is moved by arms which are placed radially and have Reciprocating motion in this direction. By controlling the contraction and the extension of the arms which contact lhe ground, the robot will be forced to move which is called rolling-creeping motion. The robot is stable in stationary state.; also the maximum angle which it can be stable is determined. Considering the speed of contracted arm is the input parameter, the speed of the extended arm for locomotion of the robot has been... 

At present, corrugated plates have numerous applications such as web of plate girders and aerospace applications. Higher out-of-plane stiffness and initial elastic strength of the corrugated plates compared with flat plates are reasons for consideration. This study investigates the behavior of trapezoidally corrugated steel plate shear walls (TCSPSWs) under monotonic and cyclic loadings. Finite element analyses that include both material and geometric nonlinearities are employed for the examination. The results from finite element analysis are verified through tested specimen findings. Moreover, the behavior of the steel shear walls with the flat infill panels and the corrugated plate infill... 

In this paper, a simple approach is presented to determine the Muskhelishvili potential function in a generic quasi-static contact problem between two elastically similar half planes. As an example, this approach is applied to the symmetric indentation of a flat surface by a bi-quadratic punch to obtain the interior elastic stress field of the indented lower half plane  

Large signal behavior of the Laser Diode is analyzed with the aim of finding a qualitative relationship between modulation amplitude and the change in the shape of its transfer function. It is found that, at quasi-static conditions, increasing the amplitude of the modulating signal smoothes out the original piecewise-linear transfer function of the diode. It further shifts the now smoothed knee point to lower DC currents. As the frequency increases, however, these effects become less and less pronounced. In addition, the transfer function becomes rather wavy due to the failure of current density to reach the saturation level necessary for adequate stimulated emission. At even higher... 

In this study, scaling effects on fiber metal laminates under tensile and three-point bending tests were investigated numerically and experimentally. The fiber metal laminate specimens were made of aluminum 1050 and unidirectional glass-epoxy. Two scaled sizes of specimens were prepared based on A1n, 0n=90n s. Some specified mechanical properties of these samples were investigated and results showed that fiber metal laminates obey scaling law under quasi-static loading. Explicit finite element code LS-DYNA was utilized for numerical simulation. After validating numerical simulation with experiments, scaling law was studied numerically for four different... 

The biomechanical behavior of brain tissue is needed for predicting the traumatic brain injury (TBI). Each year over 1.5 million people sustain a TBI in the United States. The appropriate coefficients for modeling the injury prediction can be evaluated using experimental data. In the present paper, using an experimental setup on bovine brain tissue, unconfined compression tests at quasi-static strain rates of ϵ 0.0004s-1, 0.008s-1 and 0.4s-1 combined with a stress relaxation test under unconfined uniaxial compression with ϵ 0.67s-1 ramp rate are performed. The fitted viscohyperelastic parameters were utilized by using obtained stressstrain curves. The finite element analysis (FEA) is... 

The shape memory alloys (SMAs) and smart composites have a large use in high and low level industry, while a lot of research is being done in this field. The existence of smart composite structures is because of the advance mechanical benefits of the above materials. This work refers to dynamic and quasi static nonlinear explanation of these materials. After mathematical model consideration on the rate of strain, a model which is about martensite ratio of NiTi has been presented. This work has been done because of the high sensitivity of these materials to strain rate and use of visual and measurable engineering criteria to access other variables. As the martensite ratio is not engineering... 

This paper theoretically finds the different parameters of shape memory alloys via strain rate. Finite element formulation for temperature rate, and produced latent heat due to phase transition have been derived. Moreover, the equivalent viscous damp coefficient is provided. In addition, the Devonshire coefficient has been theoretically found by simplifications. This method helps to predict the heat and temperature change in quasi-static and dynamic studies in NiTi. Furthermore, they could be used in high nonlinear and low elastic deflection of NiTi. Then, the nonlinear vibration of smart composite involved with NiTi from any kind and percent of Ni and Ti could be handled by results.... 

The quasi-static and strain-controlled fatigue characteristics of ZK60 extrusion have been investigated along three different directions: the extrusion direction (ED), the radial direction (RD), and 45° to the extrusion direction (45°). The quasi-static response showed symmetric behavior for the samples tested along RD and 45° whereas the ED samples manifested completely asymmetric behavior. Although the ED samples exhibited longer fatigue lives than the RD and 45° in the high cycle fatigue, the fatigue lives in the low cycle fatigue regime were similar. The texture measurement indicated a sharp basal texture along ED, explaining its asymmetric behavior. Higher tensile mean stress and less... 

In this article, the ribbed bracing system is proposed and evaluated through experimental and numerical studies. Ribbed bracing system is composed of a supplemental part with ribbed interfaces that is attached to a brace member and allows for its free length reduction to prevent the development of compressional forces responsible for buckling of the brace. Ribbed bracing system provides two different mechanisms: completely closed ribbed bracing system and improved-centering ribbed bracing system which are validated, in this study, through design, fabrication, and testing of small-scale specimens subjected to cyclic quasi-static loading. As verified by the test results, in improved-centering...