High Pressure Die Casting (HPDC) is low-cost technique for the mass production of complex, non-ferrous parts. Despite its benefits such as dimensional accuracy, surface quality and high production rate / some mechanical drawbacks limit use of HPDC in production of critical parts especially under dynamical loads. This study aims to improve impact resistance and surface hardness of die cast parts by means of tool steel inserts. These inserts act as a barrier between the impactor and die casting alloy, in order to avoid surface deformation and reduce stress localization which leads crack formation. Except the impact surface, whole insert is embedded into the die casting alloy by placing them on specially machined die casting molds prior to the metal injection. The mentioned method was evaluated by mechanical test and micro-examinations which were applied on AISI D2 tool steel inserted A518.0, A413.2 and Zamak5 alloy samples. To see the effect of inserts on energy absorbance under single destructive loads, both monolithic (conventional) and inserted (produced by mentioned technique) samples were subjected to Charpy impact test. In order to observe its behavior under non-destructive, cyclic, low velocity impacts / a dedicated real rifle part was produced by this method and tested in the real service loads. Explicit Finite Elemental Analysis was also carried out to understand how the inserts increases the energy absorbance and protect the die cast body by simulating both destructive and non-destructive impact loads. In addition to these, micro-examinations were also conducted especially on insert-die casting alloy interface for chemical and physical interactions, defects and stability. In regards of experimental findings, mechanical feasibility of the method was achieved. It was proved that steel inserts improve energy absorbance, stress distribution and impact-surface hardness of die cast products.

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Micro-scale self assembly is an attractive method for manufacturing sub-millimeter sized thermoelectric device parts. Challenges controlling assembly yield rates, however, have caused research to find novel ways to implement the process while still resulting in a working device. While a typical system uses single n-type and p-type material elements in series, one method used to increase the probability of a working device involves adding redundant parallel elements in clusters. The drawback to this technique is that thermal performance is affected in clusters which have missing elements. While one-dimensional modeling sufficiently describes overall performance in terms of average junction temperatures and net heat flux, it fails when a detailed thermal profile is needed for a non-homogeneous system. For this reason, a three-dimensional model was created to describe thermal performance using Ansys v12.1. From the results, local and net performance can be described to help in designing an acceptable self-assembled device. In addition, a haptic thermal display was designed using thermoelectric elements with the intention of testing the thermal grill illusion. The display consists of 5 electrically independent rows of thermoelectric elements which are controlled using pulse width modulating direct current motor controllers.

Thin films that are functionally gradient improve the mechanical properties of film-substrate layered materials. Mechanical properties of such materials are found by using indentation tests. In this study, finite element models are developed to simulate the indentation test. The models are based on an axisymmetric half space of a specimen subjected to spherical indentation. The film layer through the thickness is modeled to have either homogeneous material properties or nonhomogeneous material properties that vary linearly. Maximum indenter displacement, and maximum normal and shear stresses at the interface are compared between the homogeneous model and the nonhomogeneous model for pragmatic contact length to film thickness ratios of 0.2 to 0.4, and film to substrate moduli ratios of 1 to 200 to 1. Additionally, a coefficient is derived from regression of the stress data produced by these models and compared to that used to define the pressure field in the axisymmetric Hertzian contact model. The results of this study suggest that a displacement boundary condition to an indenter produces the same results as a pressure distribution boundary condition. The critical normal stresses that occur between modeling a film as a nonhomogeneous and as a homogeneous material vary from 19% for a modulus ratio of 2.5:1 to as high as 66% for a modulus ratio of 200:1 indicating that the modeling techniques produced very different maximum normal stresses. The difference in the maximum shear stress between the nonhomogeneous and the homogeneous models varied from 19% for a 2.5:1 modulus ratio to 57% for the 200:1 modulus ratio but reached values as low as 6% for the 50:1 modulus ratio. The maximum contact depth between the nonhomogeneous and the homogeneous models varied from 14% for the 2.5:1 case to as much as 75% in the 200:1 case. The results from the reapplication of the pressure field derived from the regression coefficients and the R2 values from these regression models indicate the correctness of the regression model used as well as its ability to replicate the normal stresses in the contact area and maximum indenter displacements in a FEA model for both the homogeneous and the nonhomogeneous models for modulus ratios ranging from 2.5:1 to 200:1. The agreement between the regression based coefficients and the force based coefficients suggests the validity for the use of the theoretical axisymmetric Hertzian contact model for defining the pressure field in the contact area and displacements for both the homogeneous case and the nonhomogeneous case for the considered film to substrate moduli ratios and contact length to film thickness ratios.

The objective of this dissertation is to study the switched reluctance machine (SRM) electromagnetic design and optimization. The research of electric machines is mostly driven by the motivation for higher efficiency and lower cost. The demands for high-performance electric machines also come from the development of emerging industries, such as electric vehicles (EV), hybrid electric vehicles (HEV), renewable energy conversion, energy storage and precision manufacturing. The additional requirements for those applications include volume, weight, speed, torque, reliability, fault tolerance capability, etc. The focus of the research effort is on the high speed and high torque applications, where the SRM stands out compared to other types of machines. The conventional design method significantly depends on the designer’s experience, which uses equivalent magnetic circuit models, and therefore the SRM design is not well developed. A novel SRM electromagnetic design and optimization method is developed, which uses the current-fed FEA simulation as the SRM performance estimation tool. This method serves as the main innovation of this research work. First, the proposed method is applicable to any SRM topologies and dimension, and no detailed modeling of a specific SRM configuration is required in advance. Therefore, an automated SRM design and optimization approach is developed. Secondly, great accuracy of the SRM electromagnetic analysis, e.g. flux density, torque, and current calculation, is achieved by using FEA simulation instead of simplified magnetic circuit approximations. This contribution is particularly significant when considering the poor accuracy of conventional SRM analytical analysis methods, where several assumptions and approximations are used. Lastly, the proposed design method takes the typical SRM control strategy into account, where the excitation current profile is characterized as a trapezoid. This method adapts the flux linkage of the first FEA simulation result to specify the excitation current profile for the second FEA simulation, so the calculated SRM performance in FEA simulation agrees with the measurement on a practical machine. The proposed SRM design and optimization method is used for a 12/8 SRM rotor design and for a complete 4/2 SRM design. These design examples validate the applicability of the proposed method to different SRM configurations and dimensions. Detailed design steps are presented for both design cases, and the selection of the parametric design variables are also discussed. The optimization results are demonstrated using multi-dimension diagrams, where the optimal design with the highest torque can be easily identified. The FEA simulation results are compared to the experimental results of a fabricated SRM prototype, and good agreement is found. In addition, a new rotor configuration with a flux bridge is proposed for an ultra high speed SRM design. The primary motivation of this rotor topology is to reduce the windgae losses and the acoustic noise at a high speed of 50,000 rpm. However, care must be taken for the flux bridge design, and the impact of different flux bridge thicknesses to the SRM performance is studied. Meanwhile, the manufacturing difficulties and the mechanical stresses should also be considered when fabricating the flux-bridge rotor. As a result, two SRM prototypes are built, and the two rotors are one without a flux bridge and one with a flux bridge. The prototypes are tested at different speeds (10,000 rpm, 20,000 rpm and 50,000 rpm) respectively, and the experimental results show good agreement with the FEA simulation results.

Seeking to quench airliners’ unending thirst for lightweight, reliable and more comfortable seating solutions, designers are developing a new generation of slim economy – class seats. Challenge in front of the designers is to carve out additional “living space”, as well as to give a “lie – flat” experience to air travellers with strict adherence to safety regulations. Present research tries to address all these industry needs through an innovative and novel “Sleep Seat”. A generous angle of recline (40 degree), movement of “Seat Pan” along the gradient, fixed outer shell of backrest, and unique single “Forward Beam” design distinguishes “Sleep Seat” form current generation seats. It is an ultralightweight design weighing 8kg (typical seat weight is 11kg). It satisfies “Generic Requirements (GR2)” which ensures “Comfort in Air”. It will be a “16g” seat, means it can sustain the “Emergency landing” loads as specified by “Certification Specifications (CS 25.561 and CS 25.562)”. For present research, only CS 25.561 has been considered. Since, the design of “Sleep Seat” is still in its conceptual phase, it is not possible to build the prototypes and their physical testing, due to costs and time involved. “Finite Element Analysis (FEA)” is a useful tool to predict the response of the structure when subjected to real life loads. Hence, the aim of research being undertaken is to develop a detailed FE model of the complete seat structure, which will help designers to identify potential weak areas and to compare different design concepts virtually, thereby reducing the development cycle time. In order to avoid handling of large number of design variables; major load carrying members (called Primary Load Path) i.e. Forward beam and leg; are designed for the most critical “Forward 9g” loads; using FEA results as a basis. A robust framework to verify the FEA results is developed. “Sequential Model Development Approach”; which builds the final, detailed FE model starting from preliminary model (by continuously updating the FE model by addition of details that are backed up by pilot studies); resulted in a FE model which could predict the stress induced in each of the components for applied CS 25.561 loads along with “Seat Interface Loads”. The “Interface Load” is the force exerted by the seat design on the floor and is one of the main contributing factors in seat design. “Optistruct” is used as a solver for linear static FEA, whereas “Abaqus / Standard” is used for non-linear FEA. Stepwise methodologies for mesh sensitivity study, modelling of bolt-preload, representing bolted joint in FEA, preventing rigid body motion, and obtaining a converged solution for non-linear FEA are developed during this research. Free-Shape Optimisation is used to arrive at a final design of Seat-leg. All the findings and steps taken during this are well documented in this report. Finally, a detailed FE model (involving all the three non-linearities : Contact, material and geometric) of the complete seat structure was analysed for the loads taken from CS 25.561, and it was found that design of “Forward beam” and leg are safe against CS 25.561. Therefore, all the aims and objectives outlined for this research were accomplished. For future work, first area to look for, would be validation of present FEA results by experimental testing. FE model to simulate dynamic loads CS 25.562 can be developed followed by design improvements and optimisation.

Infrared (IR) imaging is a key technology in a variety of military and civilian applications, especially for night vision and remote sensing. Compared with cryogenically cooled IR sensors, uncooled infrared imaging devices have the advantages of being low cost, light weight, and superior reliability. The electro-thermal analysis of a microbolometer pixel is critical to determine both device performance and reliability. To date, most microbolometer analysis research has focused on performance optimization and computation of thermal conductance directly from the geometry. However, modeling of the thermal distribution across the microbolometer pixel is critical for the comprehensive analysis of system performance and reliability. Therefore, this thesis investigates the electro-thermo-mechanical characteristics of a microbolometer pixel considering the effects of joule heating and incoming IR energy. The contributions of the present research include the electro-thermal models for microbolometer and methods of validating thermal distribution using experimental results. The electro-thermal models explain the effect of microbolometer material properties and geometry on device performance and reliability. The research also contributes methods of estimating the thermal conductivity of microbolometer, which take into account different heat transfer mechanisms, including radiation and convection. Previous approaches for estimating the thermal conductance of uncooled microbolometer consider heat conduction via legs from the geometry of the pixel structure and material properties [2]. This approach assumes linear temperature distribution in the pixel legs structure. It also leaves out the various electro-thermal effects existing for multilayer structures. In the present research, a different approach is used to develop the thermal conductance of microbolometer pixel structure. The temperature distribution in the pixel is computed from an electro-thermal model. Then, the average temperature in the pixel microplate and the total heat energy generated by joule heating is utilized to compute the thermal conductance of the structure. The thesis discusses electro-thermal and thermo-mechanical modeling, simulation and testing of Polysilicon Multi-User MEMS Process (PolyMUMPs®) test devices as the groundwork for the investigation of microbolometer performance and reliability in space applications. An electro-thermal analytical and numerical model was developed to predict the temperature distribution across the microbolometer pixel by solving the second order differential heat equation. To provide a qualitative insight of the effect of different parameters in the thermal distribution, including material properties and device geometry, first an explicit formulation for the solution of the electro-thermal coupling is obtained using the analytical method. In addition, the electro-thermal model, which accounts for the effect of IR energy and radiation heat transfer, spreading resistance and transient conditions, was studied using numerical methods. In addition, an analytical model has been developed to compute the IR absorption coefficient of a Thin Single Stage (TSS) microbolometer pixel. The simulation result of this model was used to compute absorbed IR energy for the numerical model. Subsequently, the temperature distribution calculated from the analytical model is used to obtain the deflections that the structure undergoes, which will be fundamental for the reliability analysis of the device. Finite element analysis (FEA) has been simulated for the selected device using commercial software, ANSYS® multiphysics. Finite element simulation shows that the electro-thermal models predict the temperature distribution across a microbolometer pixel at steady-state conditions within 2.3% difference from the analytical model. The analytical and numerical models are also simulated and results for a temperature distribution within 1.6% difference. In addition, to validate the analytical and numerical electro-thermal and thermo-mechanical models, a PolyMUMPs® test device has been used. The test results showed a close agreement with the FEM simulation deflection of the test device.

Carbon Capture and Storage (CCS) is recognised as having a significant role to play in tackling climate change and reducing carbon dioxide (CO2) emissions. In CCS schemes, CO2 is captured from anthropogenic sources, and transported to suitable sites either for EOR (Enhanced Oil Recovery) or storage. The transport of such huge amount of CO2 causes new challenges. The main concern is in the difference between natural gas and CO2 transportation pipelines. CO2 phase behaviour during decompression, existence of different impurities and very high operating pressure are some of the new challenges for pipeline designer and operators. This PhD study has taken a systematic approach to understand the mechanics involved in the fracture of pipes containing high pressure flue-gas CO2. The work involved the development of a novel weight function stress intensity factor solution that can be used with complex stress fields induced by residual and/or thermal stresses in addition to applied pressure. In addition, the thesis reports a substantial experimented test programme which involved low temperature fracture toughness tests linked to a detailed finite element based stress analysis. Overall, the thesis presents an integrated engineering criticality means to assess the suitability or otherwise of a pipeline system to transport high pressure flue-gas CO2.

Introduction: As fractures of the supraorbital region are far less common than midfacial or orbital fractures, a study was initiated to investigate whether fist blows could lead to fractures similar to those often seen in the midface. Methods: A detailed skull model and an impactor resembling a fist were created and a fist blow to the supraorbital region was simulated. A transient finite element analysis was carried out to calculate von Mises stresses, peak force, and impact time. Results: Within the contact zone of skull and impactor critical stress values could be seen which lay at the lower yield border for potential fractures. A second much lower stress zone was depicted in the anterior-medial orbital roof. Conclusions: In this simulation a fist punch, which could generate distinct fractures in the midface and naso-ethmoid-orbital region, would only reach the limits of a small fracture in the supraorbital region. The reason is seen in the strong bony architecture. Much higher forces are needed to create severe trauma in the upper face which is supported by clinical findings. Finite element analysis is the method of choice to investigate the impact of trauma on the human skeleton.

This work describes the implementation of the eXtended Finite Element Method (XFEM) in the Abaqus software package. A user-defined element was developed containing the analytical functions relating to homogeneous and interface fracture mechanics. The long-term goal of such work is to increase the ability to analyze fractures and other imperfections in multimaterial systems containing large elastic mismatches, such as flexible electronics. A review of XFEM-related literature is presented, as well as an overview of fracture mechanics for both homogeneous and interface systems. The theoretical basis of the XFEM is then covered, including the concepts of Partition of Unity and stress intensity factor evaluation. Finally, numerical results of the implementation are compared to several benchmark cases, along with conclusions and suggestions for future work.