Šiame darbe nagrinėjama standžių sujungimo mazgų įrengimo įtaka iš anksto įtemptų surenkamų gelžbetoninių sijų laikomajai galiai ir įlinkiams. Laikomosios galios analizės metu nagrinėjama sijų ribinės apkrovos ir tempiamos zonos armatūros kiekio priklausomybė nuo standžiai jungčiai įrengti naudojamos jungiamosios armatūros skerspjūvio ploto ir betono klasės. Sijų įlinkių analizės metu nagrinėjama, kiek galima sumažinti sijų įlinkius, skerspjūvio aukštį ar padidinti tarpatramio ilgį įrengus standžias jungtis. Taip pat atliekama standaus mazgo apspaudimo įtakos sijų įlinkiams analizė. Remiantis moksliniais straipsniais ir mokomosiomis knygomis nagrinėjami įvairūs standaus mazgo įrengimo konstrukciniai sprendiniai bei kontinualių sijų įrąžų ir įlinkių skaičiavimo metodai. Standžios jungties įtempių ir deformacijų būvis tiriamas baigtinių elementų metodu naudojant kompiuterinę statybinių konstrukcijų skaičiavimo programą LUSAS Analyst. Atlikus iš anksto įtemptų surenkamųjų gelžbetoninių sijų, sujungtų tarpusavyje standžiu mazgu, darbo analizę pateikiamos baigiamojo magistro darbo išvados ir pasiūlymai. Darbą sudaro 8 dalys: įvadas, standžių mazgų įrengimo ypatumai ir konstrukcinai sprendiniai, kontinualių sijų įrąžų ir įlinkių skaičiavimo metodai, standžių mazgų įrengimo įtakos sijų laikomajai galiai analizė, standžių mazgų įrengimo įtakos sijų įlinkiams analizė, standaus mazgo analizė baigtinių elementų metodu, išvados ir pasiūlymai, literatūros sąrašas. Darbo apimtis –... [toliau žr. visą tekstą] / The paper investigates precast prestressed beams and increase of their carrying capacity and decrease of deflections by providing rigid connections between adjascent spans. The analysis of carrying capacity includes relations between load capacity (herewith the sectional area of tensile reinforcement) and material properties of rigid connection, such as sectional area of continuity reinforcement and concrete grade. The analaysis of deflections investigates the reduction of beam height and increase of span length by providing moment continuity between adjascent spans. The effects of prestressing rigid connection is also discussed. Various moment continuity provision methods are reviewed. The stress-strain state of rigid connection is analysed by using finite element method. The conclutions and suggestions are made at the end of the thesis. The master thesis includes these parts: introduction, analysis of moment continuity provision methods, review of moment redistribution and deflection calculation methods, analysis of increased load carrying capacity after provision of moment continuity, analysis of decreased deflections after provision of moment continuity, rigid connection analysis using finite element method, conclusions and suggestions, references. Master thesis consists of – 77 p. text without appendixes, 24 pictures, 16 tables, 15 bibliographical entries.

Baigiamajame magistro darbe nagrinėjamas ekscentriškai gniuždomas elipsinis tuščiaviduris skerspjūvis (angl. EHS) bei sudaromas šio skerspjūvio projektavimo algoritmas. Darbą sudaro penki skyriai, išvados ir priedai. Pirmajame skyriuje pateiktas bendras EHS apibūdinimas, nurodyti šio skerspjūvio privalumai bei panaudojimo sritys. Antrajame skyriuje pateikta atliktų EHS tyrimų apžvalga, aptariami galimi metodai skerspjūvio klasei nustatyti. Trečiajame skyriuje sudaromas ekscentriškai gniuždomo EHS elemento projektavimo algoritmas, programiniu paketu Mathcad sukuriama šio skerspjūvio skaičiavimo programa bei atliekami analitiniai skaičiavimai. Ketvirtajame skyriuje pateiktas baigtinių elementų modelio sudarymas naudojant programinį paketą SolidWorks Simulation 2012, atliekama baigtinių elementų (BE) analizė, atkartojanti analitinius skaičiavimus. Penktajame skyriuje palyginami analitinių skaičiavimų ir BE analizės rezultatai. Darbo gale pateiktas rezultatų apibendrinimas, suformuluojamos darbo išvados. / The final postgraduate work consists of analysis of elliptical hollow section (EHS) under eccentric compression. Design algorithm is developed. There are five chapters, conclusions and appendixes presented. First chapter gives a background to EHS including applications and advantages. Second chapter gives a literature review of EHS related work, investigates methods for the cross-section class determination. Third chapter includes developing of the design algorithm of EHS. Analytical calculations are made using the software package Mathcad. In the fourth chapter the finite element model is generated using the software package SolidWorks Simulation 2012. The analytical calculations are replicated with the finite element analysis. The results are compared in the fifth chapter. In the end of the final paper the results are summarized and the final conclusions are made.

Microelectromechanical systems (MEMS) devices have been increasing in popularity for radio frequency (RF) and microwave communication systems due to the ability of MEMS devices to improve the performance of these circuits and systems. This interdisciplinary field combines the aspects of lithographic fabrication, mechanics, materials science, and RF/microwave circuit technology to produce moving structures with feature dimensions on the micron scale (micro-structures). MEMS technology has been used to improve switches, varactors, and inductors to name a few specific examples. Most MEMS devices have been fabricated using planar micro fabrication techniques that are similar to current integrated circuit (IC) fabrication techniques. These techniques limit the thickness of individual layers to a few microns, and restrict the structures to have planar and not vertical features. One micro fabrication technology that has not seen much application to microwave MEMS devices is LIGA, a German acronym for X-ray lithography, electroforming, and moulding. LIGA uses X-ray lithography to produce very tall structures (hundreds of microns) with excellent structural quality, and with lateral feature sizes smaller than a micron. These unique properties have led to an increased interest in LIGA for the development of high performance microwave devices, particularly as operating frequencies increase and physical device size decreases. Existing work using LIGA for microwave devices has concentrated on statically operating structures such as transmission lines, filters, couplers, and antennas. This research uses these unique fabrication capabilities to develop dynamically operating microwave devices with high frequency performance. This thesis documents the design, fabrication and testing of LIGA-MEMS variable capacitors that exploit the vertical dimension. Also included are methods to improve both the reliable fabrication and operation of these devices as well as material property characterization. Variable capacitors can be found in systems such as voltage-controlled oscillators, filters, impedance matching networks and phase shifters. Important figures-of-merit for these devices include the quality factor (Q), tuning range and tuning voltage. Two different types of variable capacitors are presented, a pull-away design and a design based on the principle of leveraged bending. The pull-away style variable capacitors were found to have high Q-factors, especially the devices fabricated using a thick gold device layer. As an example, the small gold half capacitance electrode design features a Q-factor of 95 at an operating frequency of 5.6 GHz and a tuning ratio of 1.36:1 with a tuning voltage range of 0 to 7.8 V. The design based on leveraged bending significantly improves the tuning ratio to a value of 1.9:1 while still maintaining a high Q-factor similar to those found in the pull-away style designs. A further increase in tuning ratio to a value of approximately 2.7:1 would be possible, based on simulated results, by simply changing the angle of the capacitance electrode in the layout. To improve device performance and fabrication reliability, modifications were made to both the fabrication process and the device layout. In the fabrication process the exposure step, electroplating step, and the etching process were modified to improve the quality of the resulting devices. In the layout, anti-stiction measures were introduced that reduce the contact area during collapse. To improve device characterization as well as the feedback link between simulation and fabrication, a set of test structures called VM-TEST was developed to accurately determine the important mechanical material properties of thick electroplated layers. These structures utilize the measurement of the pull-in voltage in cantilever and fixed-fixed beams, along with measured structure dimensions, to accurately extract the mechanical properties. Both nickel and gold test structures were analyzed with extracted Young’s modulus values of 186.2 and 60.8 GPa respectively. Also presented is a study of the gap shape in cantilever and fixed-fixed beams that significantly reduces the pull-in voltage while still maintaining a required maximum actuator displacement. It was shown that in the case of cantilever beam actuators, an approximately 40% reduction in pull-in voltage is possible, and in the case of fixed-fixed beam actuators, an approximately 30% reduction is possible by simply varying the shape of the gap between the beam and actuator electrode. These results can be used to significantly reduce the pull-in voltage of future designs. These promising results show that the LIGA fabrication process is capable of producing high performance dynamically operating RF MEMS devices, by exploiting the vertical dimension, not typically performed in most existing RF MEMS designs.

This thesis is devoted to the numerical and experimental investigation of residual stress and deformation in polycrystalline metallic alloys at different scales. The emphasis in the current study is placed on establishing the connection between the simulation of deformation by the Finite Element (FE) method and experimental characterisation by synchrotron X-Ray Diffraction (XRD). Of particular importance is the interpretation of modelling results and their validation by careful comparison with experimental data. The concept of eigenstrain was used extensively throughout the report to study the residual elastic strain distributions and their sources. A pseudo-thermal strain FE procedure was used systematically to simulate the residual stress states in samples and engineering components of different shape and dimensionality. The case of 1-D strain variation was considered using the example of a plastically bent bar. The direct and inverse problems of eigenstrain analysis were solved, and validated experimentally by the use of XRD and EDM slitting methods. A novel 2-D discrete inverse eigenstrain algorithm was proposed and implemented to reconstruct the residual stress distribution in a worn rail head. The link between the residual stress and deformation history was studied via thermo-mechanical modelling of the Linear Friction Welding (LFW) process. To advance the understanding of polycrystalline deformation behaviour across the scales, a crystal plasticity model was employed to simulate the elastic-plastic deformation behaviour of Ti-6Al-4V alloy. A post-processor was developed to extract the average elastic strains for orientation-specific grain groups and to compare them with XRD data. A “peak constructor” post-processor was developed that utilised the knowledge of both the elastic strain and dislocation density. In a further development step, a strain gradient crystal plasticity formulation was adopted to account for the local dislocation evolution. Intra-granular deformation analysis was carried out and micro-beam Laue experimental diffraction technique was used for validation. Thus, local lattice arrangement was studied at the microscopic, intragranular scale. Special attention was paid to the phenomenon of Laue spot “streaking”, indicative of the local lattice misorientation caused by dislocation activity during deformation. The results presented in this thesis contributed to the fundamental understanding of the residual stress and deformation in polycrystalline metallic alloys and lead to more than 20 publications in peer-reviewed journals and conference proceedings, which are listed in the Appendix.

Deep excavations have been used worldwide for underground construction, but they also alter the ground conditions and induce ground movements which might cause risks to adjacent infrastructure. Field measurements are normally carried out during excavations to ensure their safety, and also provide valuable data to calibrate the results from the numerical analysis which is an effective way to investigate the performance of deep excavations. This thesis is concerned with evaluating the capability of advanced finite element analysis in reproducing various aspects of observed deep excavation behaviour in the field through back analysis of case histories. The finite element model developed considers both geotechnical and structural aspects such as (i) detailed geometry of the excavation and retaining structures, (ii) realistic material models for the soil, structures and the soil-structure interface, and (iii) correct construction sequences. Parametric studies are conducted first based on a simplified square excavation to understand the effect of several important aspects, e.g. (i) the merit of shell or solid elements to model the retaining wall, (ii) the effect of construction joints in the retaining wall, (iii) the effect of the operational stiffness of concrete structural components due to cracks, (iv) the thermal effect of concrete beams and floor slabs during curing process and due to variation of ambient temperature, (v) the effect of soil-structure interface behaviour, and (vi) the effect of stiffness and strength properties of the soil. Two more complex case histories are then investigated through fully 3D analyses to explore the influence of various factors such as (i) neglecting the small-strain stiffness nonlinearity in the soil model, (ii) the selected K_0 value to represent the initial stress state in the ground, (iii) the appropriate anisotropic wall properties to consider the joints in the diaphragm wall, (iv) the parameters governing the settlements of adjacent buildings and buried pipelines, (v) the effectiveness of ground improvement on reducing the building settlement, (vi) the variation of construction sequences, (vii) the effectiveness of earth berms, and (viii) ignoring the openings in the floor slabs. This research has strong practical implications, but cautions should also be taken in applications, e.g. element types and parameter selection.

The present work details the creation and analysis of a finite element model of the foot, wherein the plantar fascia was modeled as a viscohyperelastic solid. The objective of this work was to develop a fully functional CAD and Finite Element Model of the foot and plantar fascia for analysis by examining the transient stresses on the plantar fascia through the use of a viscohyperelastic material model. The model’s geometry was developed through the use of image processing techniques with anatomical images provided by the National Institutes of Health. The finite element method was used to analyze the transient response of the plantar fascia during loading. As a first step towards modeling the transient response of the mechanical behavior of the plantar fascia under dynamic loadings, standing conditions were used to analyze the relaxation of the plantar fascia over a time period of 120 seconds (which is the steady-state relaxation time of the plantar fascia). This study resulted in a fully functional model with transient stress data on the behavior of the plantar fascia during loading, along with stress and deformation data for the bones and soft tissue of the foot. The results obtained were similar to that recorded in literature. This model is the first step towards fully characterizing the mechanics of the plantar fascia so as to develop novel treatment methods for plantar fasciitis, and can be applied to future studies to develop novel orthotic devices and surgical techniques for the treatment of and prevention of plantar fasciitis.

This dissertation is concerned with a type of energy absorption device made of thin-walled tubes. The tubes will undergo plastic deformation when subjected to an impact loading, and therefore absorb kinetic energy. It has been found that, if the surface of a tube is pre-folded according to an origami pattern, the failure mode of the tube can be altered, leading to a noticeable increase in energy absorption while at the same time, reducing the force needed to initiate plastic deformation within the tube. The main work is presented in four parts. First of all, an experimental study of a type of previously reported thin-walled square tube with pre-manufactured pyramid patterns on the surface has been conducted. Quasi-static axial crushing tests show that the octagonal mode, although numerically proven to be efficient in terms of energy absorption, cannot be consistently triggered. Secondly, a new type of thin-walled tubular energy absorption device, known as the origami tube, which has origami pattern pre-fabricated on the surface, has been studied. A family of origami patterns has been designed for tubes with different profiles. The performances of a series of origami tubes with various configurations subjected to quasi-static axial crushing have been investigated numerically. It is found that a new failure mode, referred to as the complete diamond mode, can be triggered, and both over 50% increase in the mean crushing force and about 30% reduction in the peak force can be achieved in a single tube design in comparison with those of a conventional square tube with identical surface area and wall thickness. A theoretical study of the axial crushing of square origami tubes has been conducted and a mathematical formula has been derived to calculate the mean crushing force. Comparison between theoretical prediction and numerical results shows a good agreement. Quasi-static axial crushing experiments on several square origami tube samples have been carried out. The results show that the complete diamond mode is formed in the samples and both peak force reduction and mean crushing force increase are attained. Thirdly, a new type of curved thin-walled beam with pre-manufactured origami pattern on the surface, known as the origami beam, has been designed and analyzed. A numerical study of a series of origami beams with a variety of configurations subjected to quasi-static lateral bending has been conducted. The results show that two new failure modes, namely, the longitudinal folding mode and the mixed mode, can be induced, and both reduced peak force and increased energy absorption are achieved. Finally, a number of automobile frontal bumpers, which have the origami tube and the origami beam as key components, have been designed and analyzed. Three impact tests have been conducted on each bumper. The numerical results show that both types of origami structures can perform well in realistic loading scenarios, leading to improved energy absorption of the bumpers.

Elastomer seals are used in a variety of industries that require flow isolation. The characterization of the behavior of these seals remains largely unexplored and hence, this study is focused on simulating and validating the axial-compressive behavior of an annular rubber seal constrained concentrically in a pipe. The elastomer material composing the seal, was experimentally characterized for its mechanical, frictional, and viscoelastic properties and modelled using models developed by Yeoh, Thirion, and Prony respectively. A 2D axisymmetric finite-element model was developed using ANSYS 16 and used alongside the material models to simulate an axial load versus displacement curve, a contact pressure distribution, and a pipe hoop strain gradient. The results for quasi-static loading and viscoelastic effects agreed within 7% and 18% of the experimental results, respectively. It was observed that pipe geometry, rubber chemistry, frictional properties, and viscoelastic effects have significant effect on the compressive behavior of the seal. / October 2016

Approved for public release; distribution in unlimited. / MEMS technology is rapidly taking an important role in today's and future military systems. MEMS are able to lower the device size from millimeter to micrometer and maintain and sometimes surpass the performance of conventional devices. This thesis encompasses the knowledge acquired throughout the MEMS courses to design a two-axis capacitive accelerometer. The required acceleration and operating temperature range were Š50g in each axis and -40ʻC to +80 ʻC, respectively. The accelerometer was also needed to survive within a dynamic shocking environment with accelerations of up to 225g. The parameters of the accelerometer to achieve above specifications were calculated using lumped element approximation and the results were used for initial layout of it. A finite element analysis code (ANSYS) was used to perform simulations of the accelerometer under various operating conditions and to determine the optimum configuration. The simulated results were found to be within about 5% of the calculations indicating the validity of lumped element approach. The response of the designed accelerometer was 7 mV/g and with sensitivity of 1.3g at 3dB. It was also found that the accelerometer was stable in the desired range of operation including under the shock. Two axes sensing can be achieved using two identical accelerometers having their sensing axes perpendicular to each other. / Major, Taiwan Army

Le stockage des céréales se fait en milieu rural au nord du Bénin dans des greniers (silo) en terre qui ont une contenance limitée. Les nombreuses tentatives d’introduction de magasins modernes ont essuyé le rejet des populations. Le présent travail a pour but d’étudier la possibilité d’augmenter le volume de stockage du grenier de type Yom sans changer ni sa forme architecturale, ni le composite argile-paille-décoction de néré. La caractérisation expérimentale du comportement mécanique du banco, matériau de construction de ces greniers a permis de définir le meilleur dosage pour des caractéristiques maximales. En faisant varier la proportion de paille et de décoction de néré, l’influence sur la terre crue de la paille et de la décoction est mise en évidence. La simulation de l’action des grains, à la vidange et au remplissage sur la paroi du grenier et l’analyse des déformations induites montrent qu’il y a possibilité de construire des greniers de plus grande taille. Une optimisation paramétrique des dimensions a été faite. L'effet des échauffements successifs sur la paroi du grenier a été pris en compte à travers la modélisation des transferts thermiques. La modélisation des profils de température dans diverses coupes orientées du silo montre que le flux est bien amorti et les conditions d'ambiance dans le grenier garantissent une bonne conservation. Il est donc possible de construire des greniers de grande capacité de stockage qui serviraient de greniers communautaires ou banques de céréales à disposition des coopératives villageoises. Cette solution règlerait le problème de l’insécurité alimentaire au niveau du monde rural / The storage of cereals is done in rural areas in northern Benin in earth silo that have a limited capacity. The numerous attempts to introduce modern shops have been rejected by the population. This work aims to study the possibility of increasing the storage volume of Yom type silo without changing its architectural form, nor the clay-straw-nere composite. The experimental characterization of the mechanical behaviour of the banco, the construction material of these silo made it possible to define the best dosage for maximum characteristics. By varying the proportion of straw and decoction of nere, the influence on the raw earth of the straw and the decoction is highlighted. The simulation of grain action (filling and discharging) on the silo wall and the analysis of the induced deformations shows that there is a possibility of building larger earth silo. A parametric optimization of the dimensions was made. The effect of successive heating on the silo wall has been considered by modelling heat transfer. The modelling of the temperature profiles in various silo-oriented sections shows that the flow is well damped and the ambient conditions in the attic guarantee good conservation. It is therefore possible to build earth silo with large storage capacity that could be used as community silo or cereal banks for village cooperatives. This solution would solve the problem of food insecurity in rural areas