A local isotropic damage coupled hyperelastic-plastic framework is formulated in principal axes where thermo-mechanical extensions are also addressed. It is shown that, in a functional setting, treatment of many damage growth models, including ones originated from phenomenological models (with formal thermodynamical derivations), micro-mechanical models or fracture criteria, proposed in the literature, is possible. Quasi-unilateral damage evolutionary forms are given with special emphasis on the feasibility of formulations in principal axes. Local integration procedures are summarized starting from a full set of seven equations which are simplified step by step initially to two and finally to one where different operator split methodologies such as elastic predictor-plastic/damage corrector (simultaneous plastic-damage solution scheme) and elastic predictor-plastic corrector-damage deteriorator (staggered plasticdamage solution scheme) are given. For regularization of the post peak response with softening due to damage and temperature, Perzyna type viscosity is devised. Analytical forms accompanied with algorithmic expressions including the consistent material tangents are derived and the models are implemented as UMAT and UMATHT subroutines for ABAQUS/Standard, VUMAT subroutines for ABAQUS/Explicit and UFINITE subroutines for MSC.Marc. The subroutines are used in certain application problems including numerical modeling of discrete internal cracks, namely chevron cracks, in direct forward extrusion process where comparison with the experimental facts show the predicting capability of the model, isoerror map production for accuracy assessment of the local integration methods, and development two novel necking triggering methods in the context of a damage coupled environment.

Coins and medallions are manufactured by using coining process which is a metal forming process. In coining of medallions, there is a strong need to shorten the production time and reduce the production cost and waste of material in conventional coining method. An alternative coining method may be considered in order to reduce the production time and the manufacturing cost. In this study, a new method has been proposed. In the proposed method, design of the medallion is performed by utilizing computer aided engineering (CAE) environment and the master die is manufactured by means of NC codes. The modular designs of blanking and coining die sets for medallions with a diameter in the range of 30-90 mm have been realized. Coining and blanking processes for production of the medallion have been simulated by using a commercial finite volume program. Moreover, a commemorative medallion for the opening ceremony of METU-BILTIR Center Forging Research and Application Laboratory has been designed. After die sets have been manufactured, the real-life experiments have been conducted by using 1000 tones mechanical forging press and 200 tones eccentric press available in Forging Research and Application Laboratory of the METU-BILTIR Center. The results have been compared with the computer simulations. After the real-life experiments, it has been observed that medallions have successfully been obtained by employing the new proposed method. Therefore, the new proposed method for coining has been verified.

In this dissertation, the mapping of outdoor environments and localization of a mobile robot in that setting is considered. It is well known that in the absence of a map or precise pose estimates, localization and mapping is a coupled problem. However, in this dissertation this problem is decoupled in to two disjoint steps / mapping and localization on the acquired map. First the images of the outdoor environment is downloaded from a website such as Google Earth and then these images are processed by utilizing several artificial neural network topologies to create maps. Once these maps are obtained, the localization is done by using Monte Carlo localization. This dissertation addresses a solution for the information which is most of the time taken for granted in most studies / a prior map of environment. Mapping is solved by using a novel approach / the map of the environment is created by processing satellite images. Several global localization techniques are developed and evaluated to be used with these map so as to localize a mobile robot globally. The outcome of this novel approach presented here may serve as a virtual GPS. Mobile phone applications can localize a user within a circle of uncertainty without GPS. This crude localization may be used to download relevant satellite images of the local environment. Once the mobile robot is localized on the map created from the satellite images by using available techniques in the literature i.e. Monte Carlo localization, it may be claimed that it is localized on Earth.

Rolling element bearings are the one of the most widely used machine elements in the industry. The most important criterion in bearing selection is the endurance life. The first attempts on the prediction of the endurance life of rolling elements bearings are done by Lundberg and Palmgren in 1950s (Harris, 1999). Their work adopted as an ANSI, ABMA and ISO standard which is widely used in industry today. The basic assumption of Lundberg-Palmgren formulation is that no matter how small the load applied on rolling element bearing, all material in the stressed volume is subject to fatigue failure. In this study, four main life theories / Weibull, Lundberg-Palmgren, Ioannides-Harris, and Zaretsky on rolling element bearings have been investigated. Three-dimensional finite element models of a bearing&rsquo / s inner ring and rolling element have been prepared. The stress fields within the inner ring and the ball with respect to the applied load are obtained numerically. The fatigue life of the inner ring has been predicted by two methods that are widely used for fatigue analysis / Total Life Analysis (S-N method) and Crack Initiation Analysis (&amp / #56256 / &amp / #56624 / -N method). Obtained results are compared with ISO formulation. As a result of the investigation, S-N and &amp / #56256 / &amp / #56624 / -N methods are determined to give more conservative results than ISO method for higher loads that cause stresses above the fatigue limit of the material. The used methods for bearing life prediction recognize the existence of the fatigue limit stress. Hence as the stresses within an operating bearing do not exceed the limit stress, the bearing can achieve infinite life. It is also observed that load variation has a direct influence on the bearing life. When the load significantly changes from the levels which create stress above the fatigue limit to the levels that result stress is below the fatigue limit, the bearing would have higher endurance life than predicted by ISO method.

Performance of a refrigerator can be characterized with its ability to maintain a preset low temperature by spending the least amount of electricity. It is important to understand natural convection inside a refrigerator for optimizing its design for performance. Computational Fluid Dynamics (CFD) together with experiments is a very powerful tool for visualizing flow and temperature fields that are essential for understanding a phenomenon that involves both fluid and heat flow. In this aspect, simulations are performed for compartment and total refrigerator models using the package program Fluent which is based on finite volume method. An experimental study is performed to determine the constant wall temperature boundary conditions for the numerical models. Effect of radiation is also investigated by comparing the numerical study of a different full refrigerator model with a similar one in literature. While evaluating the radiation effect, convection boundary condition is selected by defining overall heat transfer coefficient between the ambient room air at a constant temperature and the inner surfaces of the walls. Based on assumptions, related heat transfer analyses are done using compartment and total refrigerator model analyses. Performing CFD simulations of a refrigerator cabinet for visualizing the flow and temperature fields which is the aim of the study is achieved and some observations that can be useful in design optimization are made.

Two different Statistical Energy Analysis (SEA) models of a single turbo-prop engine propeller aircraft have been developed to predict the interior and exterior noise levels. The commercial software VA One is used for the analysis. First model is a pure SEA model developed with ribbed plates on the aircraft exterior. Second model is a hybrid model which employs finite element (FE) modeling of aircraft components with low modal density. These models have been analyzed for three different flight conditions, namely, take-off, cruise and climb for three different damping loss factors in each condition. Wind tunnel measurements are used to estimate the turbulent boundary layer (TBL) information on the surface of the aircraft. Propeller noise together with TBL loading are then used as the excitation for the models. Flow paths of energy are identified and cabin interior noise levels are predicted for the developed models. Results of analyses are comparatively evaluated.

Understanding and manipulating nanosized particles is crucial for the advancement of nanotechnology research. Dependent light scattering of noble metals can be used to achieve new material responses that can be used in different applications. Dependent light scattering of nanoparticles allows the understanding of orientation and location of closely positioned particles. Besides, dependently scattering metallic particles create significantly enhanced near fields and high absorption rates when excited at their plasmon resonance. It is used for spectrally selective heating and melting of nanosized particles as a nanomanufacturing method. With numerical methods dependent scattering properties of particles can be obtained. In this study, the dependent optical absorption efficiencies of metallic nanoparticles are obtained with the newly developed Integrated Poynting Vector Approach (IPVA). This is used in conjunction with a numerical light scattering solution tool DDSCAT. Results indicate that IPVA and DDSCAT together can be used for the estimation of scattering and absorption of nanoparticles affected by the near field of other particles in their close vicinity. The method is suggested to be suitable for the understanding of physical mechanisms behind dependent scattering prior to experiments that require lots of effort and resources.

This study aims to simulate a vapor compression refrigeration cycle, working with either butane (R-600) or isobutane (R-600a). For this purpose a computer program is written to design a household refrigerator, by modeling a steady-state, vapor compression cycle, with user defined input data. Each refrigerator component can be designed separately, as well as parts of a single refrigeration system in the program. In order to determine the refrigerant thermophysical properties at different states, least squares polynomial equations for different properties of R-600 and R-600a have been developed. Computer program is used for refrigeration cycle analysis, variable speed compressor design and calculating coefficient of performance (COP) and irreversibility of the cycle. Sample-preliminary designs have been carried out for different refrigeration loads, room and cold space temperatures with the program, to compare the performance characteristics of the refrigerants. Designs have been performed at different refrigeration loads, room and cold space temperatures. It is observed that for the same conditions R-600 has slightly better performance characteristics than those of R-600a.

The steady-state natural convection from vertically placed rectangular fins is investigated numerically by means of a commercial CFD program called ICEPAK. The effects of geometric parameters of fin arrays on the performance of heat dissipation from fin arrays are examined. In order to simulate the different fin configurations and compare the results with literature, two experimental studies from literature are selected. Optimum fin spacing for both studies are found numerically and compared with experimental studies. The models are first verified by simulating natural convection on vertically placed flat plate and comparing the results with literature. After verification 30 different fin array configurations for the first experimental case study and 15 different fin array configurations for the second experimental case study from literature are analyzed. It is observed that the present results agree very well with the optimum fin spacing results of the experimental studies. It is also observed that the empirical correlations in the literature are conservative and the numerically obtained correlations predict higher heat transfer rates.

In today&amp / #8217 / s market conditions, higher tool life and durable cutting tools which can stand high cutting speeds are required in chip removal process. In order to improve the performance of cutting tools, coatings are employed extensively. Cubic boron nitride (cBN) is a new kind of coating material for cutting tools due to its outstanding properties and testing of cBN as a hard coating for machining have been increasing in recent years. However, there are some challenges such as compressive residual stress, poor adhesion and limiting coating thickness during the deposition of cBN on substrates. In this study, cubic boron nitride (cBN) coatings are formed on cutting tools from hexagonal boron nitride (hBN) target plates. For this purpose, a physical vapor deposition (PVD) system is utilized. PVD system works on magnetron sputtering technique in which material transfer takes place from target plate to substrate surface. Firstly, cBN coatings are deposited on steel and silicon wafer substrates for measurements and analyses. Compositional, structural and mechanical measurements and analysis are performed for the characterization of coatings. Next, several types of cutting tools are coated by cBN and the effects of cBN coatings on cutting performance are investigated. Finally, it can be said that cubic boron nitride coatings are successfully formed on substrates and the improvement of wear resistance and machining performance of cBN coated cutting tools are observed.