Rapid prototyping methods embrace a family of manufacturing methods that are developed to speed up the prototyping stage of product design. The sole needed input for production being the solid model of the part, mold/tool-free production characteristics and the geometric part complexity that can be achieved due to layer-by-layer production have extended the applicability/research areas of these methods beyond prototyping. Local pore formation in part that occurs as a result of the discrete manufacturing nature of rapid prototyping methods can be viewed as an opportunity for material development. In this thesis, the manufacturing-internal (porous) structure-mechanical property relations of porous materials are investigated. These porous parts are produced via Selective Laser Sintering (SLS) which is a rapid prototyping method. The elastic modulus, tensile strength, rupture strength and Poisson&rsquo / s ratio of uniform porous specimens with known porosities are determined through standardized mechanical tests for polymeric materials. The mechanical property variation profiles in graded materials are determined using the mechanical properties of uniform parts. The mechanical behavior of uniform and graded materials under applied loads are modeled using finite element method and simulation results are compared to the results of mechanical tests performed on graded materials. In addition, feasibility of producing resin filled composite parts from these uniform and graded porous parts are sought. Porous parts (both uniformly and graded) that are infiltrated with epoxy resin have been characterized mechanically and the results have been compared with the uninfiltrated porous parts.

In today&rsquo / s world, buried structures are used for a variety of purposes in many areas such as transportation, underground depot areas, metro stations and water transportation. The serviceability of these structures is crucial in many cases following an earthquake / that is, the earthquake should not impose such damage leading to the loss of serviceability of the structure. The seismic design methodology utilized for these structures differs in many ways from the above ground structures. The most commonly utilized approach in dynamic analysis of underground structures is to neglect the inertial forces of the substructures since these forces are relatively insignificant contrary to the case of surface structures. In seismic design of these underground structures, different approaches are utilized like free-field deformation approach and soil-structure interaction approach. Within the confines of this thesis, seismic response of highway tunnels is considered through a case study on Bolu Tunnels, which are well documented and subjected to D&uuml / zce earthquake. In the analyses, the seismic response of a section of the Bolu tunnels is examined with 2-D finite element models and results are compared with the recorded data to evaluate the capability of the available analysis methods. In general, the results of analyses did not show any distinct difference from the recorded data regarding the seismic performance of the analyzed section and that the liner capacities were sufficient, which is consistent with the post earthquake condition of the Bolu Tunnels.

Potential applications such as high intensity focused ultrasound in medical therapeutics require larger output pressures. To offer unprecedented acoustic output pressure in transmit without the limitations, Capacitive Micromachined Ultrasonic Transducer operation modes of collapse and collapse-snapback are introduced in literature. Both operation modes require the membrane to contact the substrate surface, which poses a problem on the durability of the membrane in terms of structural integrity and tribological property. Based on the additional requirements of these modes, diamond is proposed as the ultimate solution to be used as the membrane material. Mechanical, thermal, and electrical properties of diamond are all in favor of its use in the microfabrication of CMUTs. This thesis introduces the design and test results of the first diamond-based CMUTs as an alternative to silicon and silicon nitride based CMUTs. Simulations are performed using Finite Element Methods (FEM) using a commercially available software package, ANSYS. The diamond-based CMUT is operated successfully both in air and immersion for the first time. Fully customizable in-house software is developed to command and control the test setup equipments for current dissertation and future work. Fresnel and Fraunhofer regions of the CMUT are characterized in sunflower oil using a combination of advanced hardware and software. The experimental results of radiation and diffraction for the diamond-based circular CMUT are verified by the theoretical calculations for a circular piston transducer. The results obtained from the first generation diamond-based CMUTs presented the diamond as a promising material for membranes in CMUTs.

Launchers are military systems that are responsible for communication with munitions, safe seperation and aiming of rockets and missiles to the target. Since they are military equipments, they are used in harsh environments. One of the most important design considerations for military equipment is its maintability and one of the most important parameter which affects the maintability is wear in launchers. Therefore, for predicting the life-time of a launcher, wear should be investigated beside other parameters such as fatigue etc. This thesis study includes experimental and modeling study about dry sliding wear in some mechanical parts of a typical rail launcher that is used in helicopters. Firstly, measurements about the material loss, which is generated during firing of missiles, were made on launcher components which have interfaces with missile. Then, these results were used to simulate the wear phenomenon by using a commercial finite element program, ANSYS. By the help of finite element model, crack initiation period depending on wear is tried to be evaluated without making additional firing tests.

Dental implant is an artificial dental root that is used to construct dental restorations, similar to the original teeth, in order to regain the function of missing teeth of patients experiencing tooth loss. At the interface between the jawbone and the roots of natural teeth, a thin, elastic, shock absorbing tissue, called the periodontal ligament (PDL), forms a cushion which provides certain mobility to the natural teeth. The restorations supported by dental implants, however, involve completely rigid structures. This causes overloading of the implant while bearing functional loading together with neighboring natural teeth, which leads to high local stresses within the implant system and in the jawbone. The aim of this thesis study was to develop a novel dental implant model involving resilient components in the upper structure (abutment) in order to mimic the mechanical behavior of the PDL. Within the scope of the study, a complete mechanical design of a new dental implant model was made. The proposed model was optimized based on the design objectives by using Finite Element Method. The optimal design was verified to overcome the problem of loosening of the abutment screw (a common complication in previous designs), yield very similar axial mobility behavior as that of a natural tooth and withstand biomechanical loads without failure. In addition, as a support of a dental bridge in combination with a natural tooth, the proposed design was demonstrated to provide uniform load sharing with the natural tooth and substantially reduced magnitude of peak stresses within the construction, compared to a rigid counterpart.

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The purpose of this study is to integrate the efficiency of the computer-aided design software Pro Engineer and the finite element analysis software LS-DYNA on the structural design of the golf club head. By means of the parametric design characteristics of Pro Engineer, various thickness and different shapes of the golf club head have been studied. The impact model will extract the ball velocities and spins for a given hit location on the club face which is analyzed by the software LS-DYNA. After that, the factors for influencing the dynamic analysis, such as the thickness and the shape of the hitting face, the off-center hitting, the ball velocity and spin, the stress distribution, and stress propagation in the head are further identified and measured. Finally, the effects of the factors described above have been analyzed quantitatively to investigate the maximum velocity of the ball and the sweet spot of the golf club head.

Modern engineering design tends to use computer simulations such as Finite Element Analysis (FEA) to replace physical experiments when evaluating a quality response, e.g., the stress level in a phone packaging process. The use of computer models has certain advantages over running physical experiments, such as being cost effective, easy to try out different design alternatives, and having greater impact on product design. However, due to the complexity of FEA codes, it could be computationally expensive to calculate the quality response function over a large number of combinations of design and environmental factors. Traditional experimental design and response surface methodology, which were developed for physical experiments with the presence of random errors, are not very effective in dealing with deterministic FEA simulation outputs. In this thesis, we will utilize a spatial statistical method (i.e., Kriging model) for analyzing deterministic computer simulation-based experiments. Subsequently, we will devise a sequential strategy, which allows us to explore the whole response surface in an efficient way. The overall number of computer experiments will be remarkably reduced compared with the traditional response surface methodology. The proposed methodology is illustrated using an electronic packaging example.

Textile composites can be tailored to meet specific thermo-mechanical requirements for structural applications. The focus of this research is on 2x2 biaxial braided composites since they have good stiffness and strength properties. Moreover, they have potentially better impact and fatigue resistance than laminated composites. Along with good properties, they have a reduced manufacturing cost because much of the fabrication can be automated. In order to exploit these benefits, thorough understanding of the effect of various factors on their material behavior is necessary. Obtaining effective mechanical properties is the first order of concern in any structural analysis. This work presents an investigation of the effect of various parameters like braid angle, waviness ratio, stacking sequence and material properties on the effective engineering properties of the 2x2 braids. To achieve this goal, three dimensional finite element micromechanics models were developed first. Extensive parametric studies were conducted for two material systems: 1). Glass (S2) fiber / epoxy (SC-15) matrix and 2). Carbon (AS4) fiber / Vinyl Ester (411-350) matrix. Equivalent laminated materials with angle plies and a resin layer were also analyzed to compare the difference in predictions from the full three dimensional finite element analysis of the 2x2 braided composites. A full three-dimensional stress state exists in braids even for very simple loading. In order to locate the potential damage spots, the stress distributions in both the matrix and the tows were predicted. The effect of braid angle on location and magnitude of peak stresses was determined.

Theoretical formulations, analytical solutions, and finite element solutions for laminated composite plate and shell structures with smart material laminae are presented in the study. A unified third-order shear deformation theory is formulated and used to study vibration/deflection suppression characteristics of plate and shell structures. The von K??rm??n type geometric nonlinearity is included in the formulation. Third-order shear deformation theory based on Donnell and Sanders nonlinear shell theories is chosen for the shell formulation. The smart material used in this study to achieve damping of transverse deflection is the Terfenol-D magnetostrictive material. A negative velocity feedback control is used to control the structural system with the constant control gain. The Navier solutions of laminated composite plates and shells of rectangular planeform are obtained for the simply supported boundary conditions using the linear theories. Displacement finite element models that account for the geometric nonlinearity and dynamic response are developed. The conforming element which has eight degrees of freedom per node is used to develop the finite element model. Newmark's time integration scheme is used to reduce the ordinary differential equations in time to algebraic equations. Newton-Raphson iteration scheme is used to solve the resulting nonlinear finite element equations. A number of parametric studies are carried out to understand the damping characteristics of laminated composites with embedded smart material layers.