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Autonomous vehicle technology has been evolving for years since the Automated Highway System Project. However, this technology has been under increased scrutiny ever since an autonomous vehicle killed Elaine Herzberg, who was crossing the street in Tempe, Arizona in March 2018. Recent tests of autonomous vehicles on public roads

Autonomous vehicle technology has been evolving for years since the Automated Highway System Project. However, this technology has been under increased scrutiny ever since an autonomous vehicle killed Elaine Herzberg, who was crossing the street in Tempe, Arizona in March 2018. Recent tests of autonomous vehicles on public roads have faced opposition from nearby residents. Before these vehicles are widely deployed, it is imperative that the general public trusts them. For this, the vehicles must be able to identify objects in their surroundings and demonstrate the ability to follow traffic rules while making decisions with human-like moral integrity when confronted with an ethical dilemma, such as an unavoidable crash that will injure either a pedestrian or the passenger.

Testing autonomous vehicles in real-world scenarios would pose a threat to people and property alike. A safe alternative is to simulate these scenarios and test to ensure that the resulting programs can work in real-world scenarios. Moreover, in order to detect a moral dilemma situation quickly, the vehicle should be able to identify objects in real-time while driving. Toward this end, this thesis investigates the use of cross-platform training for neural networks that perform visual identification of common objects in driving scenarios. Here, the object detection algorithm Faster R-CNN is used. The hypothesis is that it is possible to train a neural network model to detect objects from two different domains, simulated or physical, using transfer learning. As a proof of concept, an object detection model is trained on image datasets extracted from CARLA, a virtual driving environment, via transfer learning. After bringing the total loss factor to 0.4, the model is evaluated with an IoU metric. It is determined that the model has a precision of 100% and 75% for vehicles and traffic lights respectively. The recall is found to be 84.62% and 75% for the same. It is also shown that this model can detect the same classes of objects from other virtual environments and real-world images. Further modifications to the algorithm that may be required to improve performance are discussed as future work.
ContributorsSankaramangalam Ulhas, Sangeet (Author) / Berman, Spring (Thesis advisor) / Johnson, Kathryn (Committee member) / Yong, Sze Zheng (Committee member) / Arizona State University (Publisher)
Created2019
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Description
Essential knowledge of Co-continuous composite material properties are explored in this thesis. Mechanical characterization of these materials gives a detailed outlook to use them in design, manufacture and tailor make the products.

Soft and hard polymer materials have extensive properties individually, but when combined to make a single structure, they

Essential knowledge of Co-continuous composite material properties are explored in this thesis. Mechanical characterization of these materials gives a detailed outlook to use them in design, manufacture and tailor make the products.

Soft and hard polymer materials have extensive properties individually, but when combined to make a single structure, they give an exceptional combination of properties. In this study, Polymer materials used are in the form of Co-Continuous structures (i.e., both soft and hard polymers are continuous throughout the microstructure) fabricated into several microstructures namely, Simple Cubic (SC), Body-Centered Cubic (BCC) and Face Centered Cubic (FCC) shapes. An experimental process is designed and fine-tuned from existing methods to understand and record the mechanical response of these co-continuous polymers. Experimental testing is used to gather detailed information about several constituencies namely stress behavior and damage progression. A 3D imaging technique, Microtomography is used to visualize damage initiation and progression in the sample. Variations in energy absorption, fracture initiation and damage propagation in samples are observed and correlated analysis is performed to provide a logical explanation. Comparative studies are performed as well for different structures.

Based on the Knowledge gained from the above study on co-continuous polymer composites, several conclusions are drawn, and future work directions are suggested.
ContributorsVARAKANTHAM, MADHAVA REDDY (Author) / Yongming, Liu (Thesis advisor) / Patel, Jay (Committee member) / Hanqing, Jiang (Committee member) / Arizona State University (Publisher)
Created2019
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Description
Demand for green energy alternatives to provide stable and reliable energy

solutions has increased over the years which has led to the rapid expansion of global

markets in renewable energy sources such as solar photovoltaic (PV) technology. Newest

amongst these technologies is the Bifacial PV modules, which harvests incident radiation

from both sides of

Demand for green energy alternatives to provide stable and reliable energy

solutions has increased over the years which has led to the rapid expansion of global

markets in renewable energy sources such as solar photovoltaic (PV) technology. Newest

amongst these technologies is the Bifacial PV modules, which harvests incident radiation

from both sides of the module. The overall power generation can be significantly increased

by using these bifacial modules. The purpose of this research is to investigate and maximize

the effect of back reflectors, designed to increase the efficiency of the module by utilizing

the intercell light passing through the module to increase the incident irradiance, on the

energy output using different profiles placed at varied distances from the plane of the array

(POA). The optimum reflector profile and displacement of the reflector from the module

are determined experimentally.

Theoretically, a 60-cell bifacial module can produce 26% additional energy in

comparison to a 48-cell bifacial module due to the 12 excess cells found in the 60-cell

module. It was determined that bifacial modules have the capacity to produce additional

energy when optimized back reflectors are utilized. The inverted U reflector produced

higher energy gain when placed at farther distances from the module, indicating direct

dependent proportionality between the placement distance of the reflector from the module

and the output energy gain. It performed the best out of all current construction geometries

with reflective coatings, generating more than half of the additional energy produced by a

densely-spaced 60-cell benchmark module compared to a sparsely-spaced 48-cell reference

module.ii

A gain of 11 and 14% was recorded on cloudy and sunny days respectively for the

inverted U reflector. This implies a reduction in the additional cells of the 60-cell module

by 50% can produce the same amount of energy of the 60-cell module by a 48-cell module

with an inverted U reflector. The use of the back reflectors does not only affect the

additional energy gain but structural and land costs. Row to row spacing for bifacial

systems(arrays) is reduced nearly by half as the ground height clearance is largely

minimized, thus almost 50% of height constraints for mounting bifacial modules, using

back reflectors resulting in reduced structural costs for mounting of bifacial modules
ContributorsMARTIN, PEDRO JESSE (Author) / Tamizhmani, Govindasamy (Thesis advisor) / Phelan, Patrick (Committee member) / Wang, Liping (Committee member) / Arizona State University (Publisher)
Created2019
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Description
Mechanical fatigue has been a research topic since quite a long time. It is a complex phenomenon at molecular level. The fact that fatigue failure occurs much below material’s yield point, made it much interesting area for research. So, to understand the physics behind fatigue failure became an important research

Mechanical fatigue has been a research topic since quite a long time. It is a complex phenomenon at molecular level. The fact that fatigue failure occurs much below material’s yield point, made it much interesting area for research. So, to understand the physics behind fatigue failure became an important research topic. Fatigue failure is characterized by crack initiation and then crack propagation to finally fracture the material. If this could be modelled mathematically, then it would save lot of resources and would assure the structural integrity of given component. Many such mathematical models were published to calculate fatigue crack growth for Constant Amplitude Loading, but most of the time the applied loads are variable in nature. So, to address this problem a mathematical model which will predict fatigue life in terms of time history is needed. This research study focuses on improving previously developed subcycle fatigue crack growth model also known as small time scale model which works well in Paris regime. In the first part, focus has been given on estimating threshold point using subcycle model by applying load shedding techniques. Later subcycle model has been modified to include fatigue crack growth in threshold region. In the second part of this research study, the concept of Equivalent Initial Flaw Size (EIFS) and fracture mechanics approach has been used to compute fatigue life for Constant as well as Random Amplitude Loading. Further the model has been extended to compute the fatigue life under Mixed Mode Loading (Mode I & Mode II). Standard material properties are used to calibrate the model parameters. The fatigue life results were validated using available open literature data as well as experimental testing data. The subcycle model can be used to calculate fatigue life in case of HCF and LCF, which is suggested as a future work for this research study.
ContributorsShivankar, Sushant (Author) / Liu, Yongming YL (Thesis advisor) / Nian, Qiong QN (Committee member) / Jiao, Yang YJ (Committee member) / Arizona State University (Publisher)
Created2021
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Description
The tire blowout is potentially one of the most critical accidents that may occur on the road. Following a tire blowout, the mechanical behavior of the tire is extremely affected and the forces generating from the interaction of the tire and the ground are redistributed. This severe change in the

The tire blowout is potentially one of the most critical accidents that may occur on the road. Following a tire blowout, the mechanical behavior of the tire is extremely affected and the forces generating from the interaction of the tire and the ground are redistributed. This severe change in the mechanism of tire force generation influences the dynamic characteristics of the vehicle significantly. Thus, the vehicle loses its directional stability and has a risk of departing its lane and colliding with other vehicles or the guardrail. This work aims to further broaden our current knowledge of the vehicle dynamic response to a blowout scenario during both rectilinear and curvilinear motions. To that end, a fourteen degrees of freedom full vehicle model combined with the well-grounded Dugoff’s tire models is developed and validated using the high fidelity MSC Adams package. To examine the effect of the tire blowout on the dynamic behavior of the vehicle, a series of tests incorporating a tire blowout is conducted in both rectilinear and curvilinear maneuvers with different tire burst locations. It is observed that the reconstruction of the tire forces resulting from blowout leads to a substantial change in the dynamics of the vehicle as well as a severe directional instability and possibly a rollover accident. Consequently, a corrective safety control system utilizing a braking/traction torque actuation mechanism is designed. The basic idea of the stability controller is to produce a regulated amount of input torque on one or more wheels apart from the blown tire. The proposed novel control-oriented model eliminates the simplifying assumptions used in the design of such controllers. Furthermore, a double integrator was augmented to enhance the steady-state performance of the sliding mode closed-loop system. The chattering problem stemmed by the switching nature of the controller is diminished through tuning the slope of saturation function. Different apparatuses are used in terms of actuation, using an individual front actuator, utilizing multi-actuator, and using two-wheel braking torques successively. It is found that the proposed controllers are perfectly capable of stabilizing the vehicle and robustly track the desired trajectory in straight-line and cornering maneuvers.
ContributorsAl-Quran, Mahdi (Author) / Mayyas, Abdel Ra'Ouf (Thesis advisor) / Shuaib, Abdelrahman (Committee member) / Chen, Yan (Committee member) / Ren, Yi (Committee member) / Yong, Sze (Committee member) / Arizona State University (Publisher)
Created2021
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Description
Engineering materials and structures undergo a wide variety of multiaxial fatigue loading conditions during their service life. Some of the most complex multiaxial loading scenarios include proportional/non-proportional loading, mix-mode loading, overload/underload, etc. Such loadings are often experienced in many critical applications including aircraft, rotorcraft, and wind turbines. Any accidental failure

Engineering materials and structures undergo a wide variety of multiaxial fatigue loading conditions during their service life. Some of the most complex multiaxial loading scenarios include proportional/non-proportional loading, mix-mode loading, overload/underload, etc. Such loadings are often experienced in many critical applications including aircraft, rotorcraft, and wind turbines. Any accidental failure of these structures during their service life can lead to catastrophic damage to life, property, and environment. All fatigue failure begins with the nucleation of a small crack, followed by crack growth, and ultimately the occurrence of final failure; however, the mechanisms governing the crack nucleation and the crack propagation behavior depend on the nature of fatigue loading and microstructure of the material. In general, ductile materials witness multiple nucleation sites leading to its failure; however, high strength material fails from the nucleation of a single dominant crack. Crack propagation, on the other hand, is governed by various competing mechanisms, which can act either ahead of the crack tip or in the wake region of the crack. Depending upon the magnitude of load, overload/underload, mode-mixity, and microstructure, dominant governing mechanisms may include: crack tip blunting; crack deflection, branching and secondary cracking; strain hardening; residual compressive stresses; plasticity-induced closure, etc. Therefore, it is essential to investigate the mechanisms governing fatigue failure of structural components under such complex multiaxial loading conditions in order to provide a reliable estimation of useful life. The research presented in this dissertation provides the foundation for a comprehensive understanding of fatigue damage in AA 7075 subjected to a range of loading conditions. A series of fatigue tests were conducted on specially designed specimens under different forms of multiaxial loading, which was followed by fracture-surface analysis in order to identify the governing micromechanisms and correlate them with macroscopic fatigue damage behavior. An empirical model was also developed to predict the crack growth rate trend under mode II overloads in an otherwise constant amplitude biaxial loading. The model parameters were calculated using the shape and the size of the plastic zone ahead of the crack tip, and the degree of material hardening within the overload plastic zone. The data obtained from the model showed a good correlation with the experimental values for crack growth rate in the transient region.
ContributorsSingh, Abhay Kumar (Author) / Chattopadhyay, Aditi (Thesis advisor) / Dai, Lenore (Committee member) / Liu, Yongming (Committee member) / Jiao, Yang (Committee member) / Fard, Masoud Y (Committee member) / Arizona State University (Publisher)
Created2021
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Description
This research seeks to present the design and testing of exoskeletons capable of assisting with walking gait, squatting, and fall prevention activities. The dissertation introduces wearable robotics and exoskeletons and then progresses into specific applications and developments in the targeted field. Following the introduction, chapters present and discuss different wearable

This research seeks to present the design and testing of exoskeletons capable of assisting with walking gait, squatting, and fall prevention activities. The dissertation introduces wearable robotics and exoskeletons and then progresses into specific applications and developments in the targeted field. Following the introduction, chapters present and discuss different wearable exoskeletons built to address known issues with workers and individuals with increased risk of fall. The presentation is concluded by an overall analysis of the resulting developments and identifying future work in the field.
ContributorsOlson, Jason Stewart (Author) / Redkar, Sangram (Thesis advisor) / Sugar, Thomas (Committee member) / Honeycutt, Claire (Committee member) / Arizona State University (Publisher)
Created2021
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Description
How to effectively and accurately describe, character and quantify the microstructure of the heterogeneous material and its 4D evolution process with time suffered from external stimuli or provocations is very difficult and challenging, but it’s significant and crucial for its performance prediction, processing, optimization and design. The goal of this

How to effectively and accurately describe, character and quantify the microstructure of the heterogeneous material and its 4D evolution process with time suffered from external stimuli or provocations is very difficult and challenging, but it’s significant and crucial for its performance prediction, processing, optimization and design. The goal of this research is to overcome these challenges by developing a series of novel hierarchical statistical microstructure descriptors called “n-point polytope functions” which is as known as Pn functions to quantify heterogeneous material’s microstructure and creating Pn functions related quantification methods which are Omega Metric and Differential Omega Metric to analyze its 4D processing.In this dissertation, a series of powerful programming tools are used to demonstrate that Pn functions can be used up to n=8 for chaotically scattered images which can hardly be distinguished by our naked eyes in chapter 3 to find or compare the potential configuration feature of structure such as symmetry or polygon geometry relation between the different targets when target’s multi-modal imaging is provided. These n-point statistic results calculated from Pn functions for features of interest in the microstructure can efficiently decompose the structural hidden features into a set of “polytope basis” to provide a concise, explainable, expressive, universal and efficient quantifying manner. In Chapter 4, the Pn functions can also be incorporated into material reconstruction algorithms readily for fast virtualizing 3D microstructure regeneration and also allowing instant material property prediction via analytical structure-property mappings for material design. In Chapter 5, Omega Metric and Differential Omega Metric are further created and used to provide a time-dependent reduced-dimension metric to analyze the 4D evaluation processing instead of using Pn functions directly because these 2 simplified methods can provide undistorted results to be easily compared. The real case of vapor-deposition alloy films analysis are implemented in this dissertation to demonstrate that One can use these methods to predict or optimize the design for 4D evolution of heterogeneous material. The advantages of the all quantification methods in this dissertation can let us economically and efficiently quantify, design, predict the microstructure and 4D evolution of the heterogeneous material in various fields.
ContributorsCHEN, PEI-EN (Author) / Jiao, Yang (Thesis advisor) / Ren, Yi (Thesis advisor) / Liu, Yongming (Committee member) / Zhuang, Houlong (Committee member) / Nian, Qiong (Committee member) / Arizona State University (Publisher)
Created2021
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Description
The Vortex-lattice method has been utilized throughout history to both design and analyze the aerodynamic performance characteristics of flight vehicles. There are numerous different programs utilizing this method, each of which has its own set of assumptions and performance limitations. This thesis highlights VORLAX, one such solver, and details its

The Vortex-lattice method has been utilized throughout history to both design and analyze the aerodynamic performance characteristics of flight vehicles. There are numerous different programs utilizing this method, each of which has its own set of assumptions and performance limitations. This thesis highlights VORLAX, one such solver, and details its historic and modernized performance characteristics through a series of code improvements and optimizations. With VORLAX, rapid synthesis and verification of aircraft performance data related to wing pressure distributions, stability and control, and Federal Regulation compliance can be quickly and accurately obtained. As such, VORLAX represents a class of efficient yet largely forgotten computational techniques that allow users to explore numerous design solutions in a fraction of the time that would be needed to use more complex, full-fledged engineering tools. In the age of modern computers, one hypothesis is that VORLAX and similar “lean” computational fluid dynamics (CFD) solvers have preferential performance characteristics relative to expensive, volume grid CFD suites, such as ANSYS Fluent. By utilizing these types of programs, tasks such as pre- and post-processing become trivially simple with basic scripting languages such as Visual Basic for Applications or Python. Thus, lean engineering programs and methodologies deserve their place in modern engineering, despite their wrongfully decreasing prevalence.
ContributorsSouders, Tyler Jeffery (Author) / Takahashi, Timothy T. (Thesis advisor) / Herrmann, Marcus (Thesis advisor) / Dahm, Werner J.A. (Committee member) / Arizona State University (Publisher)
Created2021
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Description
Nanoholes on the basal plane of graphene can provide abundant mass transport channels and chemically active sites for enhancing the electrochemical performance, making this material highly promising in applications such as supercapacitors, batteries, desalination, molecule or ion detection, and biosensing. However, the current solution-based chemical etching processes to manufacture these

Nanoholes on the basal plane of graphene can provide abundant mass transport channels and chemically active sites for enhancing the electrochemical performance, making this material highly promising in applications such as supercapacitors, batteries, desalination, molecule or ion detection, and biosensing. However, the current solution-based chemical etching processes to manufacture these nanoholes commonly suffer from low process efficiency, scalability, and controllability, because conventional bulk heating cannot promote the etching reactions. Herein, a novel manufacturing method is developed to address this issue using microwave irradiation to facilitate and control the chemical etching of graphene. In this process, microwave irradiation induces selective heating of graphene in the aqueous solution due to an energy dissipation mechanism coupled with the dielectric and conduction losses. This strategy brings a remarkable reduction of processing time from hour-scale to minute-scale compared to the conventional approaches. By further incorporating microwave pretreatment, it is possible to control the population and area percentage of the in-plane nanoholes on graphene. Theoretical calculations reveal that the nanoholes emerge and grow by a repeating reduction–oxidation process occurring at the edge-sites atoms around vacancy defects on the graphene basal plane. The reduced holey graphene oxide sheets obtained via the microwave-assisted chemical etching method exhibit great potentials in supercapacitors and electrocatalysis. Excellent capacitive performance and electrocatalytic activity are observed in electrochemical measurements. The improvements against the non-holey counterpart are attributed to the enhanced kinetics involving ion diffusion and heterogeneous charge transfer.
ContributorsWang, Dini (Author) / Nian, Qiong (Thesis advisor) / Alford, Terry (Committee member) / Wang, Qing Hua (Committee member) / Zhuang, Houlong (Committee member) / Arizona State University (Publisher)
Created2021