Sharif Digital Repository

In recent years, Total Knee Replacement is a highly common surgery. Other than the injuries caused by trauma in accidents among different ages, a need for Total Knee Replacement can arise due to diseases such as Knee Osteoporosis among the elderly which leads to loss of balance in the physiologic properties of knee joint and a failure in load transfer from distal femur to proximal tibia. Currently, the practice of Total Knee Replacement is performed by implanting a mechanical knee between femoral and tibial shafts. Increase in life expectancy of the people with replaced knee, causes the failure of some prostheses due to various factors. Following the failure, a second operation is required... 

Smart materials are able to change their physical properties under various environmental conditions. Shape memory alloys (SMA) are relatively new smart materials that can respond to environmental stimuli e.g., heat, electricity, etc. Unique behaviors of SMAs, called shape memory effect and superelasticity, have motivated many applications in various fields of study (aerospace, medical, civil engineering, etc.). Although the behavior of SMAs is complicated, modeling and utilizing these materials have been receiving much attention in the past 20 years. Since a cable tolerate more tension than a wire or rod, the shape memory alloy cables could have a broad range of potential applications.... 

Smart materials and structures are among the research fields that have been expanded significantly in recent years. At a glance, a smart structure consists of sensors and actuators in which the recorded data are used to control the structural response against the applied lateral loadings, utilizing a specific control algorithm. In this regard, the Piezo-electric materials are widely used both as sensors and actuators in smart structures. In this thesis, the dynamic behavior of a simply supported Euler-Bernoulli beam that beside the effect of moving load or mass is subjected to support excitation is evaluated and the dynamic response of its mid-span is determined. Then, an extensive... 

Magnetic elastomers are smart materials that consist of a combination of elastomeric matrix and magnetic particles. The mechanical and magnetic properties of this materials are changed by Applying an external magnetic field. The presence of an external magnetic field can cause these elastomers deform largely.Significant deformations of the magnetic elastomers, has made them suitable for a wide range of applications. The aim of this project is to solve the governing equations of magnetic elastomers with finite element method. Since there are no suitable models for the behavior of these elastomers in the commercial softwares, magnetic field module and solid mechanics module should be coupled... 

Laparoscopy is a minimally invasive surgical (MIS) procedure specific to the surgical sites within the abdomen. For this surgical method a laparoscope, a camera (endoscope), and a grasping instrument is needed. They all inserted in to the abdomen through openings (5 - 10 mm diameter side port). Currently used grasper heads are small and often with steel material. With respect to these two properties applying large forces that cause damage in the organs is inevitable. The aim of this project is to design a new large laparoscopic grasper head that applies pressure along the length of the lever arms and can take up tissues of large sizes. Based on surveys and estimations SMA, artificial muscles... 

The actuation mechanism of the tip of the laparoscopic instrument is the main problem in designing the process of miniature scale motorized instruments especially when high level of functionality and multi degrees of freedom (DOF) are concerned. Previous studies suggest local actuation as the best design for this kind of end effectors. In the present study, different actuation methods of needle holders were reviewed, related capabilities and drawbacks were evaluated and a hybrid local actuated design was appointed. The hybrid design included a micro DC motor and a PZT actuator. The main idea behind it was to combine the advantages of DC motors and piezoelectric (PZT) actuators in providing... 

The present study investigates the effect of MR materials on the vibrations of three-layer pretwisted rotating beams. For this purpose, by considering MR material as the core of the rotating beam and using Hamilton's principle, the equations governing the three-layer rotating beam are extracted. After solving the desired equation, we optimize the dynamic behavior of the three-layer beam at different rotational speeds. Using the Genetic Algorithm optimization tool, the desired beam weight will be minimized and maximum damping will be applied to the desired system. The goal is to find the optimum magnetic field strength for maximum damping in the system at any rotational speed, in addition to... 

Ionic polymer metal nanocomposites (IPMNCs) are among the advance materials which have been widely used recently as smart materials. These nanocomposites, which are made of polymeric layers (Nafion) plated by metallic or non-metallic conductive electrodes, show large deformations under low applied voltages. The advance materials like these nanocomposites have resolved the problems of the conventional actuators and helped in producing accurate systems.
Several methods have been used to predict the behavior of IPMNCs which any of them consider some simplifying assumptions. In these materials physical phenomena happen at the molecular scale and deformations observed at the large scale.... 

As the aeronautical design evolves, the optimal solutions tend to employ slenderer and aeroelastic wings. These slender wings could help to increase the flight endurance, by decreasing the fuel consumption. However, as a wing becomes slenderer its structural stiffness decreases. The decrease in the stiffness highlights the structural vibrations and aeroelastic behavior in these wings. Atmospheric turbulences induce vibrations that can cause fatigue and structural failures. A possible solution to decrease these oscillations is to use active vibration control and flutter suppression. Conventional control surfaces on a wing can be used to implement the active vibration control. However, given...