Workpieces during cold forging fail basically due to ductile fracture. Ductile fracture can be predicted by damage models. In this study, various damage models such as Cockcroft &amp / Latham, McClintock, Freudenthal, Rice &amp / Tracy, Oyane, Ayada, Brozzo are investigated for their applicability to three workpiece materials: bearing steel (100Cr6), stainless steel (X5CrNiMo1810) and brass (CuZn39). The damage material parameters have been obtained by various tests such as tensile, standard compression, ring compression, compression with flanges and conical compression tests. The characterization has been assisted by finite element simulation of the various tests. It has been shown that the available damage models can predict the location of failure satisfactorily but are no able to predict the onset of failure quantitatively. Keywords: Formability Limit, Failure Criteria, Cold Forming, Surface Cracks, Finite Element Analysis

This thesis investigates the effect of hydrophilic polymers as novel solid couplants in ultrasonic inspection. These polymers can absorb large quantities of water, thus become soft and flexible, and also adapt themselves very well to applications. In this study, experiments were carried out by preparing three different types of polymer membranes namely [Poly(HEMA), Poly(HEMA-co-GMA), Poly(HEMA-NN&amp / #8242 / -dH2O)] with different thicknesses and monomer contents. Swelling ratios were determined in deionized water using 9mm diameter samples, cut from each polymer. Ultrasonic velocity and sound attenuation measurements were performed with pulse-echo and immersion techniques. These results were analyzed and compared with water, typical plastics and rubbers. In order to evaluate the coupling performance of hydrophilic polymers, weights of 50g, 200g, 500g and 1 kg were used as loading conditions to change the pressure applied to the transducer. Results obtained with this study showed that hydrophilic polymers offer low attenuation at high frequencies and couple effectively while eliminating the risk of test piece contamination. The study also revealed that velocities of polymers decrease by increasing the water content. This research can be used as a guideline for an alternative choice of couplant while testing water sensitive materials in safety critical structures or where the test piece is avoided from contamination and also can be used for rough surfaces.

The objective of this thesis is to predict shape change due to ablation and to find temperature distribution of the thermal protection system of a supersonic vehicle under aerodynamic heating by using finite element method. A subliming ablative is used as thermal protection material. Required material properties for the ablation analyses are found by using DSC (Differential Scanning Calorimetry) and TGA (Thermogravimetric Analysis) thermal analysis techniques. DSC is a thermal analysis technique that looks at how a material&#039 / s specific heat capacity is changed by temperature and TGA is a technique in which the mass of a substance is monitored as a function of temperature. Moreover, oxyacetylene ablation tests are conducted for the subliming ablative specimens and measured recession values are compared with the analytically calculated values. Maximum difference between experimental results and analytical results is observed as 3% as seen in Table 7. For the finite element analyses, ANSYS Software is used. A numerical algorithm is developed by using programming language APDL (ANSYS Parametric Design Language) and element kill feature of ANSYS is used for simulation of ablation process. To see the effect of mesh size and time step on the solution of analyses, oxyacetylene test results are used. Numerical algorithm is also applied to the blunt-nosed section of a supersonic rocket which is made from subliming ablative material. Ablation analyses are performed for the nose section because nose recession is very important for a rocket to follow the desired trajectory and nose temperature is very important for the avionics in the inner side of the nose. By using the developed algorithm, under aerodynamic heating, shape change and temperature distribution of the nose section at the end of the flight are obtained. Moreover, effects of ablation on the trajectory of the rocket and on the flow around the rocket are examined by Missile DATCOM and CFD (computational fluid dynamics) analysis tools.

Increasing insensitivity demands on designing and producing munitions necessitates utilizing primarily insensitive initiation trains specifically in missile systems. Exploding Foil Initiator (EFI) is a high voltage detonator that is used as the initiation elementof rocket motor and warhead initiation trains of modern insensitive missile systems. In this thesis, EFI prototypes are designed and manufactured with the knowledge gained from detailed literature studies. An experimental setup is constructed including firing and testing means for EFI prototypes. That experimental setup is capable of firing EFI prototypes from 500 volts to 3000 volts voltage range. Besides, it allows measuring electrical characteristics like current and voltage traces and average velocity of the flyer plates of these prototypes.Using EFI prototypes,detonation tests of HNS &ndash / IV and PBXN &ndash / 5 explosive pellets are carried out.Function times and detonation outputs of the prototypesare measured with the same experimental setup. A numerical study which predicts electrical performance of EFI prototypes and impact characteristics of flyer plates are carried out. Numerical code is validated with the experimental results.

In this study, a calibration setup for laser beam positioning systems used in visual inspection applications in industry is designed and manufactured. The laser positioning systems generate movable parallel laser lines on the projection surface. There are several translational and angular error sources affecting the positioning accuracy of the laser lines on the projection surface. Especially, since the laser line positioning error caused by angular error sources increases with the distance between the laser system and the projection surface, angular parameters of the laser sources should be measured and adjusted precisely. The calibration setup developed in this study detects the laser line positions at two different projection distances by means of laser sensing cameras which are positioned precisely along the laser lines and laser positioning axis which is perpendicular to these lines. Cameras detect the positions of the laser lines which are directed to the camera sensors with micrometer repeatability by means of some special imaging algorithms. The precise positioning of the cameras requires a special camera positioning system. For this reason, the disturbances like temperature changes and vibration should be minimized. In order to provide a suitable environment for the calibration system, special tests are conducted and a special calibration room is constituted. Construction inside the room is also made by considering the required ambient parameters. Finally, several verification tests of the calibration system are conducted.

In this study a methodology is developed for the fatigue and fracture analysis of helicopter fuselage structures, which are considered as the stiffened panels. The damage tolerance behavior of the stiffened panels multiaxially loaded is investigated by implementing virtual crack closure technique (VCCT). Validation of VCCT is done through comparison between numerical analysis and the studies from literature, which consists of stiffened panels uniaxially loaded and the panel with an inclined crack. A program based on Fortran programming language is developed to automate the crack growth analysis under mixed mode conditions. The program integrates the prediction of the change in crack propagation direction by maximum circumferential stress criterion and the computation of energy release rate by VCCT. It allows reducing the computation time for damage tolerance evaluation for mixed mode cases through finite element analysis and runs the procedure file of MSC.Marc/Mentat for numerical analysis and the program generated by Patran Command Language (PCL) of MSC.Patran for remeshing. The developed code is verified by comparing the crack growth trajectories obtained by numerical analysis with the experimental studies from literature. A submodeling technique is utilized to analyze a particular fuselage portion of helicopter tail boom. Effects of different skin/stringer configurations of the helicopter fuselage structure on stress intensity factor are studied by means of the developed program. Fatigue crack growth analysis is performed by using stress intensity factors obtained from numerical analysis and fatigue propagation models proposed in literature.

The main goal of this thesis study is the optimization of the basic design parameters of hybrid electric vehicle drivetrain components to minimize fuel consumption and emission objectives, together with constraints derived from performance requirements. In order to generate a user friendly and flexible platform to model, select drivetrain components, simulate performance, and optimize parameters of series and parallel hybrid electric vehicles, a MATLAB based graphical user interface is designed. A basic sizing procedure for the internal combustion engine, electric motor, and battery is developed. Pre-defined control strategies are implemented for both types of hybrid configurations. To achieve better fuel consumption and emission values, while satisfying nonlinear performance constraints, multi-objective gradient based optimization procedure is carried out with user defined upper and lower bounds of optimization parameters. The optimization process is applied to a number of case studies and the results are evaluated by comparison with similar cases found in literature.

To teleoperate an unmanned vehicle a rich set of information should be gathered from surroundings.These systems use sensors which sends high amounts of data and processing the data in CPUs can be time consuming. Similarly, the algorithms that use the data may work slow because of the amount of the data. The solution is, preprocessing the data taken from the sensors on the vehicle and transmitting only the necessary parts or the results of the preprocessing. In this thesis a 180 degree laser scanner at the front end of an unmanned ground vehicle (UGV) tilted up and down on a horizontal axis and point clouds constructed from the surroundings. Instead of transmitting this data directly to the path planning or obstacle avoidance algorithms, a preprocessing stage has been run. In this preprocess rst, the points belonging to the ground plane have been detected and a simplied version of ground has been constructed then the obstacles have been detected. At last, a simplied ground plane as ground and simple primitive geometric shapes as obstacles have been sent to the path planning algorithms instead of sending the whole point cloud.

To be competitive in the market, it is very important to design cost effective and reliable products. For this purpose, it is necessary to consider reliability as an integral part of the design procedure. Therefore, reliability which is a design parameter that affects cost and safety of a system should be taken into consideration in early phases since it is very difficult to change design at the later phases. Reliability of a rocket motor can be evaluated by reliability testing but these tests are very expensive and difficult since the tests are destructive and test sample size is determined by the binomial law. Because of the difficulties in reliability testing, in early design phases reliability can be evaluated by using reliability prediction results. This thesis report includes application of probabilistic approach for a solid rocket motor design to evaluate its reliability in preliminary design phase. In this study, it is aimed to assess the solid rocket motor ballistic performance reliability and casing structural reliability, determine important parameters affective on the solid rocket motor reliability and find a new design point to improve the reliability. Variations in dimensions and material properties are considered as the sources of failures and the limit states for acceleration, total impulse and maximum stress in the casing are approximated with response surface method by considering these variations. With the response surface functions, Monte Carlo simulation is used to assess failure probability and distributions of the rocket motor performance. Besides the assessment of the reliability, capability of the response surface functions to estimate the rocket motor performance and effects of the input parameters on the rocket motor performance and performance variation are also examined. By considering the effect of the input parameters, a new design point is proposed to decrease the total probability of failure.

Oxidation filters are used to decrease particulate emissions commonly. In this study, design of a particulate trap to produce an alternative, low cost filter has been aimed. An experimental setup has been installed according to standards to carry out tests of these designed filters. Electronic measurement and control systems have been attached to this setup to increase efficiency of experiments. Two filter designs have been used in the experiments. First design consists of aluminum wire cloth. Second design is sheet metal structure, which includes three longitudinal cells. Metal chip is used as filter material. Empty filter tests have been performed firstly, and then experiments have been repeated with aluminum, iron, and copper chip addition in filter. Copper chip test results are better than other metal chip for first experiments. Afterwards, experiments have been repeated with varying copper chip amount. Suitable copper chip amount was determined based on fuel consumption rate of the engine. As a result, designed filter reduce the particulate emissions with high efficiency. Although, carbon monoxide, and carbon dioxide gaseous emissions increase with designed filter, hydro carbon emissions decrease.