Matching Items (11)
Filtering by
- Genre: Masters Thesis
Description
This study focuses on implementing probabilistic nature of material properties (Kevlar® 49) to the existing deterministic finite element analysis (FEA) of fabric based engine containment system through Monte Carlo simulations (MCS) and implementation of probabilistic analysis in engineering designs through Reliability Based Design Optimization (RBDO). First, the emphasis is on experimental data analysis focusing on probabilistic distribution models which characterize the randomness associated with the experimental data. The material properties of Kevlar® 49 are modeled using experimental data analysis and implemented along with an existing spiral modeling scheme (SMS) and user defined constitutive model (UMAT) for fabric based engine containment simulations in LS-DYNA. MCS of the model are performed to observe the failure pattern and exit velocities of the models. Then the solutions are compared with NASA experimental tests and deterministic results. MCS with probabilistic material data give a good prospective on results rather than a single deterministic simulation results. The next part of research is to implement the probabilistic material properties in engineering designs. The main aim of structural design is to obtain optimal solutions. In any case, in a deterministic optimization problem even though the structures are cost effective, it becomes highly unreliable if the uncertainty that may be associated with the system (material properties, loading etc.) is not represented or considered in the solution process. Reliable and optimal solution can be obtained by performing reliability optimization along with the deterministic optimization, which is RBDO. In RBDO problem formulation, in addition to structural performance constraints, reliability constraints are also considered. This part of research starts with introduction to reliability analysis such as first order reliability analysis, second order reliability analysis followed by simulation technique that are performed to obtain probability of failure and reliability of structures. Next, decoupled RBDO procedure is proposed with a new reliability analysis formulation with sensitivity analysis, which is performed to remove the highly reliable constraints in the RBDO, thereby reducing the computational time and function evaluations. Followed by implementation of the reliability analysis concepts and RBDO in finite element 2D truss problems and a planar beam problem are presented and discussed.
ContributorsDeivanayagam, Arumugam (Author) / Rajan, Subramaniam D. (Thesis advisor) / Mobasher, Barzin (Committee member) / Neithalath, Narayanan (Committee member) / Arizona State University (Publisher)
Created2012
Description
Origami is an art transforming a flat sheet of paper into a sculpture. Among various types of origami, the focus is on a particular class called the `Rigid Origami' ("RO"). A Rigid Origami, unlike other forms, is not intended to be folded into fancy shapes. On the contrary, an RO has a simple and a geometrically well-defined crease pattern and does not have curved/smudged faces. The folds can be carried out by a continuous motion in which, at each step, each face of the origami is completely flat. As a result, these planar faces experience very minimal strain due to loading. This property allows it to be used to fold surfaces made of rigid materials. Tapping into the geometrical properties of RO will open a new field of research with great practical utility. Analyzing each new RO pattern will require generating numerous prototypes; this is practically impossible to do, as it consumes a lot of time and material. The advantages of Finite Element Analysis
umerical modeling become very clear in this scenario. A new design concept may be modeled to determine its real world behavior under various load environments and may, therefore, be refined prior to the creation of drawings, when changes are inexpensive. Since an RO undergoes a non-local deformation when subjected to a disturbance, the usage of conventional FEA will not produce accurate results. A non-local element model was developed which can be used in conjunction with the finite element package ABAQUS, via its user-defined element (UEL). This model was tested on two RO patterns, namely Miura-Ori and Ron Resch, by carrying out basic simulations. There are many other interesting origami patterns, exhibiting different meta-material properties, yet to be explored. This Finite Element Approach equips researchers with necessary tools to study those options in great detail.
umerical modeling become very clear in this scenario. A new design concept may be modeled to determine its real world behavior under various load environments and may, therefore, be refined prior to the creation of drawings, when changes are inexpensive. Since an RO undergoes a non-local deformation when subjected to a disturbance, the usage of conventional FEA will not produce accurate results. A non-local element model was developed which can be used in conjunction with the finite element package ABAQUS, via its user-defined element (UEL). This model was tested on two RO patterns, namely Miura-Ori and Ron Resch, by carrying out basic simulations. There are many other interesting origami patterns, exhibiting different meta-material properties, yet to be explored. This Finite Element Approach equips researchers with necessary tools to study those options in great detail.
ContributorsKrishnaraju, Deepakshyam (Author) / Jiang, Dr. Hanqing (Thesis advisor) / Yu, Dr. Honyu (Committee member) / Mignolet, Dr. Marc (Committee member) / Arizona State University (Publisher)
Created2014
Description
Skin electronics is one of the most promising applications of stretchable electronics. The versatility of skin electronics can only be guaranteed when it has conformal contact with human skin. While both analytical and numerical solutions for contact between serpentine interconnects and soft substrate remain unreported, the motivation of this thesis is to render a novel method to numerically study the conformability of the serpentine interconnects. This thesis explained thoroughly how to conduct finite element analysis for the conformability of skin electronics, including modeling, meshing method and step setup etc.. User-defined elements were implemented to the finite element commercial package ABAQUS for the analysis of conformability. With thorough investigation into the conformability of Fermat’s spiral, it has been found that the kirigami based pattern exhibits high conformability. Since thickness is a key factor to design skin electronics, the thesis also talked about how the change of thickness of the skin electronics impacts on the conformability.
ContributorsFan, Yiling (Author) / Jiang, Hanqing (Thesis advisor) / Hildreth, Owen (Committee member) / Yu, Hongbin (Committee member) / Arizona State University (Publisher)
Created2015
Description
In order to verify the dispersive nature of transverse displacement in a beam, a deep understanding of the governing partial differential equation is developed. Using the finite element method and Newmark’s method, along with Fourier transforms and other methods, the aim is to obtain consistent results across each numerical technique. An analytical solution is also analyzed for the Euler-Bernoulli beam in order to gain confidence in the numerical techniques when used for more advance beam theories that do not have a known analytical solution. Three different beam theories are analyzed in this report: The Euler-Bernoulli beam theory, Rayleigh beam theory and Timoshenko beam theory. A comparison of the results show the difference between each theory and the advantages of using a more advanced beam theory for higher frequency vibrations.
ContributorsTschetter, Ryan William (Author) / Hjelmstad, Keith D. (Thesis advisor) / Rajan, Subramaniam D. (Committee member) / Mobasher, Barzin (Committee member) / Arizona State University (Publisher)
Created2016
Description
Mechanical behavior of metallic thin films at room temperature (RT) is relatively well characterized. However, measuring the high temperature mechanical properties of thin films poses several challenges. These include ensuring uniformity in sample temperature and minimizing temporal fluctuations due to ambient heat loss, in addition to difficulties involved in mechanical testing of microscale samples. To address these issues, we designed and analyzed a MEMS-based high temperature tensile testing stage made from single crystal silicon. The freestanding thin film specimens were co-fabricated with the stage to ensure uniaxial loading. Multi-physics simulations of Joule heating, incorporating both radiation and convection heat transfer, were carried out using COMSOL to map the temperature distribution across the stage and the specimen. The simulations were validated using temperature measurements from a thermoreflectance microscope.
ContributorsEswarappa Prameela, Suhas (Author) / Rajagopalan, Jagannathan (Thesis advisor) / Wang, Liping (Committee member) / Jiao, Yang (Committee member) / Arizona State University (Publisher)
Created2016
Description
A previously developed small time scale fatigue crack growth model is improved, modified and extended with an emphasis on creating the simplest models that maintain the desired level of accuracy for a variety of materials. The model provides a means of estimating load sequence effects by continuously updating the crack opening stress every cycle, in a simplified manner. One of the significant phenomena of the crack opening stress under negative stress ratio is the residual tensile stress induced by the applied compressive stress. A modified coefficient is introduced to determine the extent to which residual stress impact the crack closure and is observed to vary for different materials. Several other literature models for crack closure under constant loading are also reviewed and compared with the proposed model. The modified model is then shown to predict several sets of published test results under constant loading for a variety of materials.
The crack opening stress is formalized as a function of the plastic zone sizes at the crack tip and the current crack length, which provided a means of approximation, accounting for both acceleration and retardation effects in a simplified manner. A sensitivity parameter is introduced to modify the enlarged plastic zone due to overload, to better fit the delay cycles with the test data and is observed to vary for different materials. Furthermore, the interaction effect induced by the combination of overload and underload sequence is modeled by depleting the compressive plastic zone due to an overload with the tensile plastic zone due to an underload. A qualitative analysis showed the simulation capacity of the small time scale model under different load types. A good agreement between prediction and test data for several irregular load types proved the applicability of the small time scale model under variable amplitude loading.
The crack opening stress is formalized as a function of the plastic zone sizes at the crack tip and the current crack length, which provided a means of approximation, accounting for both acceleration and retardation effects in a simplified manner. A sensitivity parameter is introduced to modify the enlarged plastic zone due to overload, to better fit the delay cycles with the test data and is observed to vary for different materials. Furthermore, the interaction effect induced by the combination of overload and underload sequence is modeled by depleting the compressive plastic zone due to an overload with the tensile plastic zone due to an underload. A qualitative analysis showed the simulation capacity of the small time scale model under different load types. A good agreement between prediction and test data for several irregular load types proved the applicability of the small time scale model under variable amplitude loading.
ContributorsVenkatesan, Karthik Rajan (Author) / Liu, Yongming (Thesis advisor) / Oswald, Jay (Committee member) / Jiang, Hanqing (Committee member) / Arizona State University (Publisher)
Created2016
Description
Ordered buckling of stiff films on elastomeric substrates has many applications in the field of stretchable electronics. Mechanics plays a very important role in such systems. A full three dimensional finite element analysis studying the pattern of wrinkles formed on a stiff film bonded to a compliant substrate under the action of a compressive force has been widely studied. For thin films, this wrinkling pattern is usually sinusoidal, and for wide films the pattern depends on loading conditions. The present study establishes a relationship between the effect of the load applied at an angle to the stiff film. A systematic experimental and analytical study of these systems has been presented in the present study. The study is performed for two different loading conditions, one with the compressive force applied parallel to the film and the other with an angle included between the application of the force and the alignment of the stiff film. A geometric model closely resembling the experimental specimen studied is created and a three dimensional finite element analysis is carried out using ABAQUS (Version 6.7). The objective of the finite element simulations is to validate the results of the experimental study to be corresponding to the minimum total energy of the system. It also helps to establish a relation between the parameters of the buckling profile and the parameters (elastic and dimensional parameters) of the system. Two methods of non-linear analysis namely, the Newton-Raphson method and Arc-Length method are used. It is found that the Arc-Length method is the most cost effective in terms of total simulation time for large models (higher number of elements).The convergence of the results is affected by a variety of factors like the dimensional parameters of the substrate, mesh density of the model, length of the substrate and the film, the angle included. For narrow silicon films the buckling profile is observed to be sinusoidal and perpendicular to the direction of the silicon film. As the angle increases in wider stiff films the buckling profile is seen to transit from being perpendicular to the direction of the film to being perpendicular to the direction of the application of the pre-stress. This study improves and expands the application of the stiff film buckling to an angled loading condition.
ContributorsKondagari, Swathi Sri (Author) / Jiang, Hanqing (Thesis advisor) / Yu, Hongyu (Committee member) / Rajan, Subramaniam D. (Committee member) / Arizona State University (Publisher)
Created2010
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
The study aims to develop and evaluate failure prediction models that accurately predict crack initiation sites, fatigue life in additively manufactured Ti-6Al-4V, and burst pressure in relevant applications.The first part proposes a classification model to identify crack initiation sites in AM-built Ti-6Al-4V alloy. The model utilizes surface and pore-related parameters and achieves high accuracy (0.97) and robustness (F1 score of 0.98). Leveraging CT images for characterization and data extraction from the CT-images built STL files, the model effectively detects crack initiation sites while minimizing false positives and negatives. Data augmentation techniques, including SMOTE+Tomek Links, are employed to address imbalanced data distributions and improve model performance.
This study proposes the Probabilistic Physics-guided Neural Network 2.0 (PPgNN) for probabilistic fatigue life estimation. The presented approach overcomes the limitations of classical regression machine models commonly used to analyze fatigue data. One key advantage of the proposed method is incorporating known physics constraints, resulting in accurate and physically consistent predictions.
The efficacy of the model is demonstrated by training the model with multiple fatigue S-N curve data sets from open literature with relevant morphological data and tested using the data extracted from CT-built STL files. The results illustrate that PPgNN 2.0 is a flexible and robust model for predicting fatigue life and quantifying uncertainties by estimating the mean and standard deviation of the fatigue life. The loss function that trains the proposed model can capture the underlying distribution and reduce the prediction error.
A comparison study between the performance of neural network models highlights the benefits of physics-guided learning for fatigue data analysis. The proposed model demonstrates satisfactory learning capacity and generalization, providing accurate fatigue life predictions to unseen examples.
An elastic-plastic Finite Element Model (FEM) is developed in the second part to assess pipeline integrity, focusing on burst pressure estimation in high-pressure gas pipelines with interactive corrosion defects. The FEM accurately predicts burst pressure and evaluates the remaining useful life by considering the interaction between corrosion defects and neighboring pits. The FEM outperforms the well-known ASME-B31G method in handling interactive corrosion threats.
ContributorsBalamurugan, Rakesh (Author) / Liu, Yongming (Thesis advisor) / Zhuang, Houlong (Committee member) / Bhate, Dhruv (Committee member) / Arizona State University (Publisher)
Created2023
Description
In nature, it is commonly observed that animals and birds perform movement-based thermoregulation activities to regulate their body temperatures. For example, flapping of elephant ears or plumage fluffing in birds. Taking inspiration from nature and to explore the possibilities of such heat transfer enhancements, augmentation of heat transfer rates induced by the vibration of solid and well as novel flexible pinned heatsinks were studied in this research project. Enhancement of natural convection has always been very important in improving the performance of the cooling mechanisms. In this research, flexible heatsinks were developed and they were characterized based on natural convection cooling with moderately vibrating conditions. The vibration of heated surfaces such as motor surfaces, condenser surfaces, robotic arms and exoskeletons led to the motivation of the development of heat sinks having flexible fins with an improved heat transfer capacity. The performance of an inflexible, solid copper pin fin heat sink was considered as the baseline, current industry standard for the thermal performance. It is expected to obtain maximum convective heat transfer at the resonance frequency of the flexible pin fins. Current experimental results with fixed input frequency and varying amplitudes indicate that the vibration provides a moderate improvement in convective heat transfer, however, the flexibility of fins had negligible effects.
ContributorsPrabhu, Saurabh (Author) / Rykaczewski, Konrad (Thesis advisor) / Phelan, Patrick (Committee member) / Wang, Robert (Committee member) / Arizona State University (Publisher)
Created2019