Main objective of this study is to design a compliant mechanism with high frequency and high mechanical amplification ratio to be used for amplifying the stroke of a piezostack actuator. In this thesis, first of all, related literature is investigated and then alternative conceptual designs are established utilizing the mechanisms found in literature survey. Once best conceptual design is selected, detailed design of this mechanism is done. For detailed design of the compliant mechanism, topology optimization method is used in this study. To design the mechanism, first a design domain is defined and then a finite element model of the design domain is prepared to be used in topology optimization runs. After running the topology optimization model by using TOSCA with ANSYS, results are imported to ANSYS, where final performance of the mechanism design is checked. After finalizing design of the mechanism, it is produced and its performance is tested through experiments.

Main objective of this study is to design a compliant mechanism with high frequency and high mechanical amplification ratio to be used for amplifying the stroke of a piezostack actuator. In this thesis, first of all, related literature is investigated and then alternative conceptual designs are established utilizing the mechanisms found in literature survey. Once best conceptual design is selected, detailed design of this mechanism is done. For detailed design of the compliant mechanism, topology optimization method is used in this study. To design the mechanism, first a design domain is defined and then a finite element model of the design domain is prepared to be used in topology optimization runs. After running the topology optimization model by using TOSCA with ANSYS, results are imported to ANSYS, where final performance of the mechanism design is checked. After finalizing design of the mechanism, it is produced and its performance is tested through experiments.

In this study, application of computational fluid dynamics to ground vehicle aerodynamics was investigated. Two types of vehicle models namely, Ahmed Body and MIRA Notchback Body and their scaled models were used. A commercial software &quot / Fluent&quot / was used and the effects of implementing different turbulence models with wall functions were observed. As a result, an appropriate turbulence model was selected to use in the study. The drag forces, surface pressure distributions and wake formations were investigated in simulation of various test cases available in the literature. The study was extended to simulate the aerodynamics of the vehicles in close-following situation. The results were then compared with available wind tunnel test data.

In this thesis, design of a car door window regulator is presented. This design comprises a mechanism in order that the car door window makes a specified translational motion. First, conceptual design is carried out to obtain the best suitable concept for the design and best suitable concept comes out to be a scissor mechanism. Afterwards, detailed design of the chosen concept is given. In the detail design stage, kinematic synthesis of the mechanism is performed basically using the Cardan motion. Lastly, implementation of the design on a car door is described.

Recent investigations in nanotechnology show that carbon nanotubes (CNT) have one of the most significant mechanical, electrical and optical properties. Interactions between those areas like electrical, optical and mechanical properties are also very promising in both research and industrial fields. Those unique characteristics are built by mainly the atomistic structure of the carbon nanotubes. In this thesis, the effects of vacant atoms on single walled carbon nanotubes (SWCNT) are investigated using matrix stiffness method. In order to use this technique a linkage between structural mechanics and molecular mechanics is established. A code has been developed to construct the SWCNT with the desired chirality, extracting the vacant atoms with the corresponding atomic bonds between the neighbor nodes and calculating the effect of those vacancies on its vibrational properties. A finite element software is also utilized for validation of the code and results. In order to investigate the convergence of the effect of those vacant nodes a numerous number of analyses have been carried out with randomly positioned vacant atoms. Also consecutive vacant nodes have been positioned in order to investigate the effect on the structural properties through the length of a CNT. In addition to those, as a case study, the reduction in Young&#039 / s modulus property because of the vacancies has also been investigated and the effects are tabulated in the report. It is concluded in this study that the any amount of vacant atoms have substantial effect on modal frequencies and Young&#039 / s modulus. Chirality and the position of the vacancies are the main parameters determining the structural properties of a CNT.

This thesis study addresses the problem of overconstraint via introduction of conformal polyhedral linkages comprising revolute joints only and investigation of special geometric properties for the mobility of such overconstrained linkages. These linkages are of particular interest as deployable structures. First, planar case is issued and conditions for assembling irregular conformal polygonal linkages composed of regular and angulated scissor elements are derived. These planar assemblies are implemented into faces of polyhedral shapes and radially intersecting planes to obtain two different kind of polyhedral linkages. Rest of the thesis work relates to spatial linkages. Identical isosceles Bennett loops are assembled to obtain regular polygonal linkages and many such linkages are assembled to form polyhedral linkages. Then, Fulleroid-like linkages are presented. After these seemingly independent linkage types, Jitterbug-like linkages are introduced. Based on some observations on present linkages in the literature a definition for Jitterbug-like linkages is given first, and then a set of critical properties of these linkages are revealed. This special type of polyhedral linkages is further classified as being homothetic and non-homothetic, and geometric conditions to obtain mobile homothetic Jitterbug-like polyhedral linkages are investigated. Homohedral linkages, linkages with polyhedral supports with 3- and 4-valent vertices only, tangential polyhedral linkages are detailed as special cases and the degenerate case where all faces are coplanar is discussed. Two types of modifications on Jitterbug-like linkages are presented by addition of links on the faces and radial planes of Jitterbug-like linkages. Finally, a special class of Jitterbug-like linkages - modified Wren platforms are introduced as potential deployable structures.

This study includes examination of the machinability characteristics of two medium carbon steel types (SAE 1040 and SAE 1050) as a result of spherodizing treatment. Both steel types were handled into four categories according to their spherodizing treatment parameters (temperature and time). Microstructural investigation, hardness and ultrasonic sound velocity measurement (with both longitudinal and transverse waves) of these steels were performed, and effect of applied heat treatments on microstructure, hardness and ultrasonic sound velocity was investigated. Pulse-echo method has been used for ultrasonic sound velocity measurements, and measurements were performed with 5 and 10 MHz longitudinal and 5 MHz transverse wave probes. Tool life criterion was used for determining the machinability characteristics of the steels. For this purpose, flank wear land measurements were performed on the cutting tools. Results have showed that, by appliying heat treatment it is possible to change the microstructure, hardness, ultrasonic sound velocity and machinability characteristics of a steel.

The aim of this study is to present a design approach for compliant bistable four-link mechanisms. The design constraints are the two positions of the mechanism, the force required to snap between the positions and the fatigue life of the designed mechanism. The theory presented here will be applied to the door lock mechanism used in commercial dishwashers, which is originally designed as a rigid inverted slider crank mechanism snapping between two positions with the force applied by a spring. The mechanism is re-designed as a compliant bistable four-link mechanism and a prototype has been manufactured.

WEAR ANALYSIS OF HOT FORGING DIES ABACHI, Siamak M. S., Department of Mechanical Engineering Supervisor: Prof. Dr. Metin AKK&Ouml / K Co-Supervisor: Prof. Dr. Mustafa lhan G&Ouml / KLER December 2004, 94 pages The service lives of dies in forging processes are to a large extent limited by wear, fatigue fracture and plastic deformation, etc. In hot forging processes, wear is the predominant factor in the operating lives of dies. In this study, the wear analysis of a closed die at the final stage of a hot forging process has been realized. The preform geometry of the part to be forged was measured by Coordinate Measuring Machine (CMM), and the CAD model of the die and the worn die were provided by the particular forging company. The hot forging operation was carried out at a workpiece temperature of 1100&deg / C and die temperature of 300&deg / C for a batch of 678 on a 1600-ton mechanical press. The die and the workpiece materials were AISI L6 tool steel and DIN 1.4021, respectively. The simulation of forging process for the die and the workpiece was carried out by Finite Volume Method using MSC.SuperForge. The flow of the material in the die, die filling, contact pressure distribution, sliding velocities and temperature distribution of the die have been investigated. In a single stroke, the depth of wear was evaluated using Archard&rsquo / s wear equation with a constant wear coefficient of 1&yen / 10-12 Pa-1 as an initial value. The depth of wear on the die surface in every step has been evaluated using the Finite Volume simulation results and then the total depth of wear was determined. To be able to compare the wear analysis results with the experimental worn die, the surface measurement of the worn die has been done on CMM. By comparing the numerical results of the die wear analysis with the worn die measurement, the dimensional wear coefficient has been evaluated for different points of the die surface and finally a value of dimensional wear coefficient is suggested. As a result, the wear coefficient was evaluated as 6.5&yen / 10-13 Pa-1 and considered as a good approximation to obtain the wear depth and the die life in hot forging processes under similar conditions.

This study is conducted for the design and analysis of pressure vessels and associated pressurized equipment using various codes and methods. A computer software is developed as the main outcome of this study, which provides a quick and comprehensive analysis by using various methods utilized in codes and standards together with theoretical and empirical methods which are widely accepted throughout the world. Pressure vessels are analyzed using ASME Boiler and Pressure Vessel Code, whereas auxiliary codes, especially ASCE and AISC codes are utilized for structural analyses of these equipment. Effect of wind, seismic, and other types of loadings are also taken into consideration in detail, with dynamic analyses. Support structures and their auxiliary components are also items of analysis. Apart from pressure vessels, many pressurized process equipments that are commonly used in the industy are also included in the scope of the study. They include safety valves which are an integral part of those kinds of pressurized or enclosed systems, two of the heat exchanger components with great importance -tubesheets and expansion joints-, and API 650 tanks for oil or water storage. The computer software called as VESSELAID is written in Microsoft Visual Basic 6.0 using SI units. Design and analysis methods of VESSELAID are based on various code rules, recommended design practices and alternative approaches.