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- All Subjects: Mechanical Engineering
- Genre: Masters Thesis
Description
The presented work in this report is about Real time Estimation of wind and analyzing current wind correction algorithm in commercial off the shelf Autopilot board. The open source ArduPilot Mega 2.5 (APM 2.5) board manufactured by 3D Robotics is used. Currently there is lot of development being done in the field of Unmanned Aerial Systems (UAVs), various aerial platforms and corresponding; autonomous systems for them. This technology has advanced to such a stage that UAVs can be used for specific designed missions and deployed with reliability. But in some areas like missions requiring high maneuverability with greater efficiency is still under research area. This would help in increasing reliability and augmenting range of UAVs significantly. One of the problems addressed through this thesis work is, current autopilot systems have algorithm that handles wind by attitude correction with appropriate Crab angle. But the real time wind vector (direction) and its calculated velocity is based on geometrical and algebraic transformation between ground speed and air speed vectors. This method of wind estimation and prediction, many a times leads to inaccuracy in attitude correction. The same has been proved in the following report with simulation and actual field testing. In later part, new ways to tackle while flying windy conditions have been proposed.
ContributorsBiradar, Anandrao Shesherao (Author) / Saripalli, Srikanth (Thesis advisor) / Berman, Spring (Thesis advisor) / Thanga, Jekan (Committee member) / Arizona State University (Publisher)
Created2014
Description
The United States Department of Energy (DOE) has always held the safety and reliability of the nation's nuclear reactor fleet as a top priority. Continual improvements and advancements in nuclear fuels have been instrumental in maximizing energy generation from nuclear power plants and minimizing waste. One aspect of the DOE Fuel Cycle Research and Development Advanced Fuels Campaign is to improve the mechanical properties of uranium dioxide (UO2) for nuclear fuel applications.
In an effort to improve the performance of UO2, by increasing the fracture toughness and ductility, small quantities of oxide materials have been added to samples to act as dopants. The different dopants used in this study are: titanium dioxide, yttrium oxide, aluminum oxide, silicon dioxide, and chromium oxide. The effects of the individual dopants and some dopant combinations on the microstructure and mechanical properties are determined using indentation fracture experiments in tandem with scanning electron microscopy. Indentation fracture experiments are carried out at room temperature and at temperatures between 450 °C and 1160 °C.
The results of this work find that doping with aluminosilicate produces the largest favorable change in the mechanical properties of UO2. This sample exhibits an increase in fracture toughness at room temperature without showing a change in yield strength at elevated temperatures. The results also show that doping with Al2O3 and TiO2 produce stronger samples and it is hypothesized that this is a result of the sample containing dopant-rich secondary phase particles.
In an effort to improve the performance of UO2, by increasing the fracture toughness and ductility, small quantities of oxide materials have been added to samples to act as dopants. The different dopants used in this study are: titanium dioxide, yttrium oxide, aluminum oxide, silicon dioxide, and chromium oxide. The effects of the individual dopants and some dopant combinations on the microstructure and mechanical properties are determined using indentation fracture experiments in tandem with scanning electron microscopy. Indentation fracture experiments are carried out at room temperature and at temperatures between 450 °C and 1160 °C.
The results of this work find that doping with aluminosilicate produces the largest favorable change in the mechanical properties of UO2. This sample exhibits an increase in fracture toughness at room temperature without showing a change in yield strength at elevated temperatures. The results also show that doping with Al2O3 and TiO2 produce stronger samples and it is hypothesized that this is a result of the sample containing dopant-rich secondary phase particles.
ContributorsMcDonald, Robert (Author) / Peralta, Pedro (Thesis advisor) / Rajagopalan, Jagannathan (Committee member) / Solanki, Kiran (Committee member) / Arizona State University (Publisher)
Created2014
Description
Uranium Dioxide (UO2) is a significant nuclear fission fuel, which is widely used
in nuclear reactors. Understanding the influence of microstructure on thermo-mechanical behavior of UO2 is extremely important to predict its performance. In particular, evaluating mechanical properties, such as elasticity, plasticity and creep at sub-grain length scales is key to developing this understanding as well as building multi-scale models of fuel behavior with predicting capabilities. In this work, modeling techniques were developed to study effects of microstructure on Young’s modulus, which was selected as a key representative property that affects overall mechanical behavior, using experimental data obtained from micro-cantilever bending testing as benchmarks. Beam theory was firstly introduced to calculate Young's modulus of UO2 from the experimental data and then three-dimensional finite element models of the micro-cantilever beams were constructed to simulate bending tests in UO2 at room temperature. The influence of the pore distribution was studied to explain the discrepancy between predicted values and experimental results. Results indicate that results of tests are significantly affected by porosity given that both pore size and spacing in the samples are of the order of the micro-beam dimensions. Microstructure reconstruction was conducted with images collected from three-dimensional serial sectioning using focused ion beam (FIB) and electron backscattering diffraction (EBSD) and pore clusters were placed at different locations along the length of the beam. Results indicate that the presence of pore clusters close to the substrate, i.e., the clamp of the micro-cantilever beam, has the strongest effect on load-deflection behavior, leading to a reduction of stiffness that is the largest for any location of the pore cluster. Furthermore, it was also found from both numerical and i
analytical models that pore clusters located towards the middle of the span and close to the end of the beam only have a very small effect on the load-deflection behavior, and it is concluded that better estimates of Young's modulus can be obtained from micro- cantilever experiments by using microstructurally explicit models that account for porosity in about one half of the beam length close to the clamp. This, in turn, provides an avenue to simplify micro-scale experiments and their analysis.
in nuclear reactors. Understanding the influence of microstructure on thermo-mechanical behavior of UO2 is extremely important to predict its performance. In particular, evaluating mechanical properties, such as elasticity, plasticity and creep at sub-grain length scales is key to developing this understanding as well as building multi-scale models of fuel behavior with predicting capabilities. In this work, modeling techniques were developed to study effects of microstructure on Young’s modulus, which was selected as a key representative property that affects overall mechanical behavior, using experimental data obtained from micro-cantilever bending testing as benchmarks. Beam theory was firstly introduced to calculate Young's modulus of UO2 from the experimental data and then three-dimensional finite element models of the micro-cantilever beams were constructed to simulate bending tests in UO2 at room temperature. The influence of the pore distribution was studied to explain the discrepancy between predicted values and experimental results. Results indicate that results of tests are significantly affected by porosity given that both pore size and spacing in the samples are of the order of the micro-beam dimensions. Microstructure reconstruction was conducted with images collected from three-dimensional serial sectioning using focused ion beam (FIB) and electron backscattering diffraction (EBSD) and pore clusters were placed at different locations along the length of the beam. Results indicate that the presence of pore clusters close to the substrate, i.e., the clamp of the micro-cantilever beam, has the strongest effect on load-deflection behavior, leading to a reduction of stiffness that is the largest for any location of the pore cluster. Furthermore, it was also found from both numerical and i
analytical models that pore clusters located towards the middle of the span and close to the end of the beam only have a very small effect on the load-deflection behavior, and it is concluded that better estimates of Young's modulus can be obtained from micro- cantilever experiments by using microstructurally explicit models that account for porosity in about one half of the beam length close to the clamp. This, in turn, provides an avenue to simplify micro-scale experiments and their analysis.
ContributorsGong, Bowen (Author) / Peralta, Pedro (Thesis advisor) / Rajagopalan, Jagannathan (Committee member) / Solanki, Kiran (Committee member) / Arizona State University (Publisher)
Created2015
Description
Characterization and modeling of deformation and failure in metallic materials under extreme conditions, such as the high loads and strain rates found under shock loading due to explosive detonation and high velocity-impacts, are extremely important for a wide variety of military and industrial applications. When a shock wave causes stress in a material that exceeds the elastic limit, plasticity and eventually spallation occur in the material. The process of spall fracture, which in ductile materials stems from strain localization, void nucleation, growth and coalescence, can be caused by microstructural heterogeneity. The analysis of void nucleation performed from a microstructurally explicit simulation of a spall damage evolution in a multicrystalline copper indicated triple junctions as the preferred sites for incipient damage nucleation revealing 75% of them with at least two grain boundaries with misorientation angle between 20-55°. The analysis suggested the nature of the boundaries connecting at a triple junction is an indicator of their tendency to localize spall damage. The results also showed that damage propagated preferentially into one of the high angle boundaries after voids nucleate at triple junctions. Recently the Rayleigh-Taylor Instability (RTI) and the Richtmyer-Meshkov Instability (RMI) have been used to deduce dynamic material strength at very high pressures and strain rates. The RMI is used in this work since it allows using precise diagnostics such as Transient Imaging Displacement Interferometry (TIDI) due to its slower linear growth rate. The Preston-Tonks-Wallace (PTW) model is used to study the effects of dynamic strength on the behavior of samples with a fed-thru RMI, induced via direct laser drive on a perturbed surface, on stability of the shock front and the dynamic evolution of the amplitudes and velocities of the perturbation imprinted on the back (flat) surface by the perturbed shock front. Simulation results clearly showed that the amplitude of the hydrodynamic instability increases with a decrease in strength and vice versa and that the amplitude of the perturbed shock front produced by the fed-thru RMI is also affected by strength in the same way, which provides an alternative to amplitude measurements to study strength effects under dynamic conditions. Simulation results also indicate the presence of second harmonics in the surface perturbation after a certain time, which were also affected by the material strength.
ContributorsGautam, Sudrishti (Author) / Peralta, Pedro (Thesis advisor) / Oswald, Jay (Committee member) / Solanki, Kiran (Committee member) / Arizona State University (Publisher)
Created2016
Description
The study of response of various materials to intense dynamic loading events,
such as shock loading due to high-velocity impacts, is extremely important in a wide
variety of military and industrial applications. Shock loading triggers extreme states,
leading to high pressures and strain rates, and neglecting strength is a typical
approximation under such conditions. However, recent results have shown that strength
effects are larger than expected, so they must be taken into account. Recently,
hydrodynamic instabilities, the most common being the Rayleigh-Taylor (RTI) and
Richtmyer-Meshkov (RMI) instabilities, have been used to infer the dynamic strength of
materials at high pressure conditions. In our experiments and simulations, a novel RMI
approach is used, in which periodic surface perturbations are made on high purity
aluminium target, which was laser ablated to create a rippled shock front. Due to the
slow linear growth rate of RMI, the evolution of the perturbations on the back surface of
the sample as a result of the rippled shock can be measured via Transient Imaging
Displacement Interferometry (TIDI). The velocity history at the free surface was
recorded by spatially resolved laser velocimetry. These measurements were compared
with the results from the simulations, which were implemented using rate independent
and rate dependent material models, to characterize the dynamic strength of the
material. Simulations using the elastic-perfectly plastic model, which is rate
independent, failed to provide a value of dynamic yield strength that would match
experimental measurements of perturbation amplitudes. The Preston-Tonks-Wallace
(PTW) model, which is rate dependent model, worked well for aluminium. This model
was, in turn, used as a reference for calibrating the rate dependent Steinberg-Lund
model and the results from simulations using the calibration models were also compared
to experimental measurements.
such as shock loading due to high-velocity impacts, is extremely important in a wide
variety of military and industrial applications. Shock loading triggers extreme states,
leading to high pressures and strain rates, and neglecting strength is a typical
approximation under such conditions. However, recent results have shown that strength
effects are larger than expected, so they must be taken into account. Recently,
hydrodynamic instabilities, the most common being the Rayleigh-Taylor (RTI) and
Richtmyer-Meshkov (RMI) instabilities, have been used to infer the dynamic strength of
materials at high pressure conditions. In our experiments and simulations, a novel RMI
approach is used, in which periodic surface perturbations are made on high purity
aluminium target, which was laser ablated to create a rippled shock front. Due to the
slow linear growth rate of RMI, the evolution of the perturbations on the back surface of
the sample as a result of the rippled shock can be measured via Transient Imaging
Displacement Interferometry (TIDI). The velocity history at the free surface was
recorded by spatially resolved laser velocimetry. These measurements were compared
with the results from the simulations, which were implemented using rate independent
and rate dependent material models, to characterize the dynamic strength of the
material. Simulations using the elastic-perfectly plastic model, which is rate
independent, failed to provide a value of dynamic yield strength that would match
experimental measurements of perturbation amplitudes. The Preston-Tonks-Wallace
(PTW) model, which is rate dependent model, worked well for aluminium. This model
was, in turn, used as a reference for calibrating the rate dependent Steinberg-Lund
model and the results from simulations using the calibration models were also compared
to experimental measurements.
ContributorsGopalakrishnan, Ashish (Author) / Peralta, Pedro (Thesis advisor) / Rajagopalan, Jagannathan (Committee member) / Solanki, Kiran (Committee member) / Arizona State University (Publisher)
Created2017
Finite element analysis of silicon thin films on soft substrates as anodes for lithium ion batteries
Description
The wide-scale use of green technologies such as electric vehicles has been slowed due to insufficient means of storing enough portable energy. Therefore it is critical that efficient storage mediums be developed in order to transform abundant renewable energy into an on-demand source of power. Lithium (Li) ion batteries are seeing a stream of improvements as they are introduced into many consumer electronics, electric vehicles and aircraft, and medical devices. Li-ion batteries are well suited for portable applications because of their high energy-to-weight ratios, high energy densities, and reasonable life cycles. Current research into Li-ion batteries is focused on enhancing its energy density, and by changing the electrode materials, greater energy capacities can be realized. Silicon (Si) is a very attractive option because it has the highest known theoretical charge capacity. Current Si anodes, however, suffer from early capacity fading caused by pulverization from the stresses induced by large volumetric changes that occur during charging and discharging. An innovative system aimed at resolving this issue is being developed. This system incorporates a thin Si film bonded to an elastomeric substrate which is intended to provide the desired stress relief. Non-linear finite element simulations have shown that a significant amount of deformation can be accommodated until a critical threshold of Li concentration is reached; beyond which buckling is induced and a wavy structure appears. When compared to a similar system using rigid substrates where no buckling occurs, the stress is reduced by an order of magnitude, significantly prolonging the life of the Si anode. Thus the stress can be released at high Li-ion diffusion induced strains by buckling the Si thin film. Several aspects of this anode system have been analyzed including studying the effects of charge rate and thin film plasticity, and the results are compared with preliminary empirical measurements to show great promise. This study serves as the basis for a radical resolution to one of the few remaining barriers left in the development of high performing Si based electrodes for Li-ion batteries.
ContributorsShaffer, Joseph (Author) / Jiang, Hanqing (Thesis advisor) / Rajan, Subramaniam D. (Committee member) / Peralta, Pedro (Committee member) / Arizona State University (Publisher)
Created2011
Description
This thesis presents a study of the microstructure and mechanical properties of Yttrium-Zinc (YZn) thin films. Rare-earth intermetallic compounds have gained significant attention in recent years due to their unique structural and mechanical properties, making them suitable for various applications. However, studies on the Y-Zn system are scarce and there are very few published reports on YZn thin films. The main objective of this study is to investigate the microstructure and mechanical properties of YZn thin films using various experimental techniques.In this study, YZn films of various thicknesses were synthesized via magnetron co-sputtering: 200 nm, 500 nm, 1 µm, 2 µm and 11.5 µm. Then these samples were annealed at 250°C, 300°C, 350°C and 400°C to investigate their microstructural evolution and mechanical properties. X-ray diffraction (XRD) and scanning electron microscopy (SEM) based techniques have been used to analyze the microstructure and chemical composition of these compounds. The mechanical properties such as hardness and elastic modulus have been measured using nanoindentation.
The results show that the microstructure of YZn thin films is dependent on the annealing conditions. The microstructure of samples deposited at room temperature and those annealed at 250°C and 300°C were found to be amorphous except for the 200 nm YZn film. Annealing at higher temperatures leads to crystallization of the films. Moreover, the results demonstrate that YZn intermetallic thin films have high hardness, which varies with the film thickness and annealing treatment.
This work represents an initial effort to understand the microstructural evolution and mechanical properties of YZn thin films as a function of film thickness and annealing temperatures. The results of this study can be used to guide the design and development of YZn thin films with tailored microstructures and mechanical properties for various applications.
ContributorsAkkarakaduppil, Riju Philip James (Author) / Rajagopalan, Jagannathan (Thesis advisor, Committee member) / Peralta, Pedro (Committee member) / Solanki, Kiran (Committee member) / Arizona State University (Publisher)
Created2023