In today&#039 / s technology severe working conditions increase demands on structural materials. A class of materials which are developed to meet these increased demands is Functionally Graded Materials (FGMs). These are inhomogeneous structural materials which are able to withstand large temperature gradients and corrosive environment. Application areas of FGMs are in aerospace industry, nuclear reactors, chemical plants and turbine systems. FGMs have gradual compositional variation from metal to ceramic which give them mechanical strength, toughness and heat resistance. However under high temperature gradients, cracking problems may arise due to thermal stresses. In layered structures the final stage of failure may be delamination due to crack extension. The objective of this study is to model a particular type of crack problem in a layered structure consisting of a substrate, a bond coat and an orthotropic FGM coating. There is an internal crack in the orthotropic layer and it is perpendicular to material gradation of coating. The position of the crack inside the coating is kept as a variable. The steady-state temperature distribution between the substrate and the coating causes a buckled shape along crack face. The critical temperature change, temperature distribution, mixed mode stress intensity values and energy release rates are calculated by using Displacement Correlation Technique. Results of this study present the effects of geometric parameters such as crack length, crack position, etc as well as the effects of the type of gradation on buckling behavior and mixed mode stress intensity factors.

In cold forming operations, tool geometry has a direct influence on the product quality, forming force, load acting on dies and tool life. Finite element method provides a means to analyse these parameters to predict forming defects and die failures. In this study, shrink fitting the components of a bolt forming die is modelled and the finite element results are compared with the analytical solutions and experiments. In order to perform die stress analyses, deformable die models are implemented in the forging simulations. Furthermore, effect of using rigid and deformable dies on the stress distributions in the tools, forming force and product dimensions are examined. Some applications of tool geometry improvements and optimization of prestressing are presented in the case studies. In the second part of the study, the appropriate friction model for the cold forming operation of bolts is investigated. For this purpose, ring compression and forward rod extrusion tests are conducted. Dimensional variations and deformation forces are compared with the finite element simulations performed for different friction models and constants. The results of shrink fit analyses of die prestressing are in good agreement with the elasticity formulations and real applications. In the studied bolt production cases, after improving the die stress distributions by using FE simulations, longer tool lives are achieved. Finally, for more accurate results, Coulomb friction model is determined as an appropiate model for bolt forming analyses.

In this study, cooling of small form factor computer is numerically investigated. The numerical model is analyzed using a commercial computational fluid dynamics software Icepak&trade / . The effects of grid selection, discretization schemes and turbulence models are discussed and presented. In addition, physical phenomena like recirculation and relaminarization are addressed briefly. For a comparison with the computational fluid dynamics results, an experiment is conducted and some temperature measurements are obtained from critical locations inside the chassis.The computational results were found to be in good agreement with the experimental ones.

Assembling of the compliant parts used in aviation industry is a challenging process. Assembly fixtures are quite important tools in this effort and widely used in industry. In fixturing of easily deformable sheet metal parts, besides restraining the rigid body motion of the parts, the possible deformations that may occur during the assembly process and the spring-back effect on the final product need to be taken in to consideration. In order to guarantee a successful assembling, in other words, to obtain the final product within specified tolerances, a systematic approach to the fixture design problem is required. The designer should predict the correlation between the input variations and the final assembly variation, especially, for the complex assemblies. This study proposes a design and analysis approach in fixturing of sheet metal assemblies for helicopter components. The design of an assembly fixture for a particular tail cone has been completed convenient to the existing locating principles. Finite Element Analysis (FEA) has been realized in simulating the assembling process in order to predict the possible variation of the interested feature on a complex assembly due to deformations.

The task of a drill bit in percussive drilling is to transport the initial kinetic energy of the hammer to the workpiece in terms of stress waves. The efficiency of this transportation and the stresses that the drill bit is exposed to during the process is dependent on the nature of the stress waves. In hand-type hammer drilling, changing dimensions of the bit means changing conditions for the propagation and interaction of the stress waves. In this study, using finite element method, wave propagation and interaction in hand-type hammer drill bits is investigated with respect to drill bit dimensions. The main aim is to assess the effect of length and thickness on the efficiency and stress history of a hand-type drill bit. The results are evaluated in regard to workpiece hardness, which is a factor changing the effect of dimensions. In addition, chiseling test, which is used to prove bits under percussive loading, is carried out to detect differences between thin and thick drill bits, and the results are explained with the help of finite element simulations. Conclusions are drawn revealing the efficiency and stress history of drill bits under percussive loading with respect to thickness, length and workpiece hardness. Finally, it is seen that the real-life results of chiseling test are in agreement with the simulation results.

In this thesis, two types of geared linkages are studied in detail. One of the mechanisms is the geared five link mechanism for which the input and output shafts are collinear. The other is a two degree-of-freedom nine-link mechanism which is called the &quot / geared adjustable stroke mechanism&quot / . The geared adjustable stroke mechanism uses the geared five link mechanism in its structure. The geared adjustable stroke mechanism has been used in practice, but neither of these mechanisms have been studied in the literature. Analysis procedures are developed and expressions for the transmission angles of the mechanisms are derived. A synthesis procedure is proposed and charts are prepared for the design of such mechanisms.

Roll-forming is an efficient sheet forming process that is used in manufacturing long parts with constant cross-section. The theoretical, experimental and numerical analyses of the process are limited since the sheet takes a complex 3D shape during the process. In this study proper finite element method models to simulate the roll-forming process are examined both numerically and experimentally. In addition, the applicability of 2D plane strain models to the simulation of the process is investigated. To reveal the deformation of the sheet, important geometrical parameters of the sheet and the rollers are introduced. The effect of these parameters on the strain hardening and deformation of the sheet is analyzed at distinct parts of the sheet that undergoes different types of deformations. Having revealed the deformation mechanisms, the assumptions behind the theoretical knowledge is criticized. The mentioned studies are verified with a case study in which a roll-formed product is analyzed under service loads. The manufacturing of the product and service load application are simulated and the results are compared with the experiments. In addition, effects of cold forming on the behaviour of the product under service loads are examined. It is concluded that under some conditions, 2D plane strain simulations can be used to predict the strain hardening in the material that occurs during roll-forming and this hardening has a considerable effect on the response of the material under loading.

In this study analysis and design procedures of partially compliant mechanisms using two degree of freedom mechanism model are developed. The flexible segments are modeled as revolute joints with torsional springs. While one freedom is controlled by the input to the mechanism, the motion of the parts are governed both by the kinematics and the force balance. The procedure developed for the analysis of such mechanisms is shown on two different mechanisms: a five link mechanism with crank input and slider output (five-bar mechanism) / a five link mechanism with crank input and rocker output. Design charts are prepared according to output-link oscillation and dimensionless design parameters

Highly effective and power efficient biological mechanisms are common in nature. The use of biological design principles in engineering domain requires adequate training in both engineering and biological domains. This requires cooperation between biologists and engineers that leads to a new discipline of biomimetic science and engineering. Biomimetic is the abstraction of good design from nature. Because of the fact that biomimetic design has an important place in mechatronic applications, this study is directed towards biomimetic design of grasshopper-like jumping mechanism. A biomimetic design procedure is developed and steps of the procedure have followed through all the study. A literature survey on jumping mechanisms of grasshoppers and jumping robots and bio-robots are done and specifically apteral types of grasshoppers are observed. After the inspections, 2D and 3D mathematical models are developed representing the kinematics and dynamics of the hind leg movements. Body-femur, femur-tibia and tibia-ground angles until take-off are obtained from the mathematical leg models. The force analysis of the leg models with artificial muscles and biological muscles are derived from the torque analysis. A simulation program is used with a simple model for verification. The horizontal displacement of jumping is compared with the data obtained from the simulation program and equation of motion solutions with and without air resistance. Actuators are the muscles of robots that lead robots to move and have an important place in robotics. In this scope, artificial muscles are studied as a fourth step of biomimetic design. A few ready-made artificial muscles were selected as an actuator of the grasshopper-like jumping mechanism at the beginning of the study. Because of their disadvantages, a new artificial muscle is designed and manufactured for mini bio-robot applications. An artificial muscle is designed to be driven by an explosion obtained due to the voltage applied in a piston and cylinder system filled with dielectric fluid. A 3.78-mm diameter Teflon piston is fitted with a clearance into a Teflon cylinder filled with a 25.7- mm fluid height and maximum 225 V is applied to the electrodes by using an electrical discharge machine (EDM) circuit. The force on the piston is measured by using a set-up of Kistler piezoelectric low level force sensor. The data obtained from the sensor is captured by using an oscilloscope, a charge meter, and a GPIB connecting card with software, Agilent. From the experiments, the new artificial muscle force is about 300 mN giving a 38:1 force to weight ratio and percentage elongation is expected to be higher than that of the natural muscles and the other artificial muscles. From the force analysis of the leg model, it is shown that the measured force is not enough alone for jumping of an about 500 mgr body. An additional artificial muscle or a single muscle designed with the same operating principle giving higher force to weight ratio is recommended as a future study.

With the advances in computer technology and the changing needs of people&rsquo / s daily lives, robots start to offer alternative solutions. As one of these solutions, the branch of humanoid robots emerged as advanced robots that can interact with people. Robot faces are one of the most effective means of interacting with people / since they can express their emotions and reactions through facial mimics. However, the development of realistic robot faces necessitates the knowledge of the trajectories and displacements of actual face mimics. In this study, a setup (both hardware and software), that can be used for tracking critical points on human face while exhibiting mimics, is developed. From the outputs of this setup, the mimic trajectories are going to be extracted. The setup is designed and manufactured to be durable to external effects so that with a single camera calibration procedure the 3D reconstruction can be carried out several times. The setup consists of two webcams that are specially oriented for mimic tracking. The images taken from the cameras are corrected / their features are extracted using image processing algorithms / the centroids of the features are found / correspondence is carried out and the reconstruction is made. This system can also be used for any special point tracking or volumetric measurement purposes.