Sharif Digital Repository

Wind and ocean waves highly influence the performance and functionality of structures, requiring an efficient control element. The structural behavior of one of the most recent structural control elements, namely shape memory alloys (SMA)-based control element, under cyclic loadings of oceans waves, has been investigated. Shape memory alloys are one of the attractive smart materials with the ability to return to the initial shape after experiencing large deformation. Experimental tests have been conducted to study the effects of cyclic loads on several specimens of the SMA wires. The SMA wires are being used in the SMA-based structural control system to dissipate the energy of external... 

Dynamic environmental loads, such as winds and waves, make the stability of offshore structures at high risk, requiring reliable yet efficient control elements to ensure the stability of such structures under lateral loads. Among the variety of control elements that have been developed to enhance the stability of a structure, shape memory alloy (SMA)-based control elements are promising as they are low-cost, easy to embed into the main control element, and do not need an external power supply. However, cyclic loads may highly influence the performance and functionality of SMA-based elements. The present work investigates the effects of pre-straining SMA components in energy dissipation... 

Laminated composite beams incorporated with magneto-rheological fluid are being used in variety of critical applications. An N-layer magneto-rheological-laminated beam based on layerwise theory has been developed to study the dynamic characteristics. For simulation purpose, an MR-laminated beam with five layers is considered in which two layers filled with magneto-rheological and three layers are made of composite materials. The results of simulations are compared with existing layerwise, first-order shear-deformation theory and experimental tests where it shows the accuracy and functionality of the present model. The complex shear modulus of magneto-rheological fluid has been determined... 

Laminated composite beams with variable thickness are being widely used in many engineering applications. To enhance the dynamic behavior of structures subject to random loading, tapered laminated beams incorporated with magnetorheological (MR) fluids (MR-tapered beam) are proposed. A finite element model has been developed for random vibration analysis of MR-tapered beam based on layerwise displacement theory. The effects of thickness ratios of tapered beam, magnetic fields, statistical properties, correlation and autocorrelation on dynamic behaviors of structures have been investigated. The proposed structural element significantly enhances the dynamic response of MR-tapered beam under... 

Vibration characteristics of laminated composite beams with magnetorheological (MR) layer are investigated using layerwise theory. In most studies, shear strain across the thickness of MR layer has been considered as a constant value, which does not precisely describe the shear strain. In this study, layerwise theory is employed to develop a finite element formulation to investigate MR-laminated beams. Experimental tests under different magnetic fields are carried out to verify the numerical results. Layerwise numerical results are compared with the experimental results and other theories. An empirical expression for complex shear modulus is presented. The effects of MR layer thickness on... 

Laminated composite beams with variable thickness are being widely used in many engineering applications. To enhance the dynamic behavior of structures subject to random loading, tapered laminated beams incorporated with magnetorheological (MR) fluids (MR-tapered beam) are proposed. A finite element model has been developed for random vibration analysis of MR-tapered beam based on layerwise displacement theory. The effects of thickness ratios of tapered beam, magnetic fields, statistical properties, correlation and autocorrelation on dynamic behaviors of structures have been investigated. The proposed structural element significantly enhances the dynamic response of MR-tapered beam under... 

Titanium matrix composites (TMCs) have wide application prospects in the field of aerospace, automobile and other industries because of their good properties, such as high specific strength, good ductility, and excellent fatigue properties. However, in order to improve their fatigue strength and life, crack initiation and growth at the surface layers must be suppressed using surface treatments. Shot peening (SP) is an effective surface mechanical treatment method widely used in industry which can improve the mechanical properties of a surface. However, artificial neural networks (ANNs) have been used as an efficient approach to predict and optimize the science and engineering problems. In... 

This paper deals with vibrational behaviors of blades with cracks which are key components in rotating machines. However, since modelling and analysis of real blade is a complex problem, a simplified cantilever beam with both chordwise (in X-Y plane) and flapwise (in X-Z plane) motion are modeled instead. Finite Element Method (FEM) is used to model beam and to investigate its natural frequencies with a crack. Finally a limit function using modal data is developed and reliability analysis of beam model is performed. © 2017 IEEE  

Marine structures, as key elements in the global energy network, constantly are subjected to harsh environmental loading conditions. Therefore, reliable yet efficient structural control mechanisms are required to ensure their safe functionality and structural stability. In the present work, a novel hybrid structural control element for marine structures has been designed in which the superelasticity effect of shape memory alloy (SMA) and damping controllability of magnetorheological fluid (MRF), as smart materials, have been combined. The novel system does not require huge external energy for activation and in addition, the system has the ability to be tuned for variable loading conditions.... 

Shape Memory Alloys (SMAs) are a new generation of smart materials with the capability of recovering their predefined shape after experiencing a large strain. This is mainly due to the shape memory effects and the superelasticity of SMA. These properties make SMA an excellent alternative to be used in passive, semi-active, and active control systems in civil engineering applications. This paper presents a comprehensive review of the recent developments in the applications of SMA in civil infrastructures, including, steel, concrete, and timber structures. This review reveals the significance of SMA in civil infrastructures particularly, the enhancement of structural behavior and energy... 

The stability and integrity of structures under indeterminant external loadings, particularly earthquakes, is a vital issue for the design and safe operation of marine and offshore structures. Over the past decades, many structural control systems, such as viscous-based systems, have been developed and embedded in marine and offshore structures, particularly oil platforms to maintain the stability and mitigate the seismic hazards. Rapid improvement in intelligent materials, including shape memory alloys (SMAs) and Magnetorheological fluid (MRF), have led to the design and development of efficient structural control elements. The present work aims to establish a framework for the structural... 

Structural integrity and ensuring the stability of steel frame structures, including marine and coastal structures, are the main challenges for designers in civil infrastructures, particularly in oil platforms, subjected to tough periodic and non-periodic environmental loading conditions. Variable loadings with different amplitudes and frequencies may lead to the stability of steel structures loss. In order to keep the stability of the steel structures and prevent possible damages, reliable yet efficient structural control systems are in demand. Conventional structural control systems need significant activation energy and/or in-depth users knowledge to be effective. Most recently, smart... 

Civil infrastructures are vulnerable to catastrophic failures when exceeding the limit loading, requiring a reliable structural control mechanism, such as bracing systems, to enhance the integrity and stability of the structure. Bracing systems improve the performance of the structures by increasing the stiffness/strength of structures, the damping coefficient, and/or the energy absorption capacity. However, the functionality of these bracing systems is not controllable and may be altered after strong seismic events. Recently, the smart bracing systems based on multifunctional materials, particularly the shape memory alloy (SMA) and the magnetorheological fluid (MRF) have been developed. The... 

In recent years, structures integrated with magnetorheological (MR) fluid have been considered for their tunable dynamic characteristics. Shear modulus of MR layer in composite structure is dramatically lower than the elastic layers, leading to high shear deformation inside the MR layer, thus classical theories are not accurate enough to predict the dynamic behavior of such structures. In present study a layerwise displacement theory has been utilized to predict a more accurate deformation for MR-composite beam and equation of motions derived using finite element model (FEM). ASTM E756-98 was employed to evaluate the complex shear modulus of MR fluid. By experimental test a practical... 

Vibration behavior of adaptive laminated composite beams integrated with magnetorheological (MR) fluid layer has been investigated using layerwise displacement theory. In most of the existing studies on the adaptive laminated beams with MR fluids, shear strain across the thickness of magnetorheological (MR) layer has been assumed a constant value, resulting in a constant shear stress in MR layer. However, due to the high shear deformation pattern inside MR layer, this assumption is not adequate to accurately describe the shear strain and stress in MR fluid layer. In this work a modified layerwise theory is employed to develop a Finite Element Model (FEM) formulation to simulate the laminated... 

Vibration behavior of adaptive laminated composite beams integrated with magnetorheological (MR) fluid layer has been investigated using layerwise displacement theory. In most of the existing studies on the adaptive laminated beams with MR fluids, shear strain across the thickness of magnetorheological (MR) layer has been assumed a constant value, resulting in a constant shear stress in MR layer. However, due to the high shear deformation pattern inside MR layer, this assumption is not adequate to accurately describe the shear strain and stress in MR fluid layer. In this work a modified layerwise theory is employed to develop a Finite Element Model (FEM) formulation to simulate the laminated... 

Laminated composite structures are widely being used in modern industries particularly robot arms, aerospace and wind turbine blades where the structures mainly exposed to harsh random vibration and in turn, leads to unpredicted failure. Adding Magneto-rheological (MR) fluids in such structures may significantly improve their dynamic response. In the present work, the vibration response of laminated composite beams filled with MR fluids (MR laminated beam) under random loading has been investigated using experimental as well as simulation approaches. Finite Element Model (FEM) has been utilized to simulate the vibration response under random loading. An in-house set-up has been designed to... 

This research presents an application of transparent lanthanum-modified lead zirconate titanate (PLZT) materials in micro light source tracking device, which is designed to function as a result of irradiation, having neither lead wires nor electric circuits. The focus of the paper is on the analytical and finite element investigation into ultraviolet photo-induced multi-physics responses of PLZT photocantilever and a comparison of the measured bending displacement to check the feasibility of these materials in design of micro light source tracking device. The finite element formulation of the transverse deflection for multi-physics analysis of PLZT ceramics by including the photovoltaic and... 

Micro grippers are essential tools for manipulation of objects in micron size. An electrostatic micro stepper-motor is used for actuating a proposed gripper mechanism and performance of this gripper is compared with the previous ones. The characteristic of the proposed mechanism is analyzed by simulation and it is shown that the designed gripper has the capability of doing manipulation in micron dimension with an acceptable performance  

Minimally Invasive Surgery (MIS) is getting common these days. MIS robots using special tools can perform surgery precisely as humans. This is only possible with dexterous end-effectors and a well-controlled system. Local, lightweight and powerful actuators positioned at end-effectors provide the ability to decrease the degrees of freedom and simplify the design. This paper discusses a grasper design actuated by Shape Memory Alloy (SMA) wires that can be used in MIS robotics. The properties of a commercially available shape memory alloy are explored and analytical formulations for the actuation procedure are developed. The grasper actuated by SMA wires is studied and the procedure of...