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- All Subjects: Mechanical Engineering
- Genre: Masters Thesis
- Creators: Arizona State University
- Status: Published
Description
Multi-material fabrication allows for the creation of individual parts composed of several materials with distinct properties, providing opportunities for integrating mechanisms into monolithic components. Components produced in this manner will have material boundaries which may be points of failure. However, the unique capabilities of multi-material fabrication allow for the use of graded material transitions at these boundaries to mitigate the impact of abrupt material property changes.
The goal of this work is to identify methods of creating graded material transitions that can improve the ultimate tensile strength of a multi-material component while maintaining other model properties. Particular focus is given towards transitions that can be produced using low cost manufacturing equipment. This work presents a series of methods for creating graded material transitions which include previously established transition types as well as several novel techniques. Test samples of each transition type were produced using additive manufacturing and their performance was measured. It is shown that some types of transitions can increase the ultimate strength of a part, while others may introduce new stress concentrations that reduce performance. This work then presents a method for adjusting the elastic modulus of a component to which graded material transitions have been added to allow the original design properties to be met.
The goal of this work is to identify methods of creating graded material transitions that can improve the ultimate tensile strength of a multi-material component while maintaining other model properties. Particular focus is given towards transitions that can be produced using low cost manufacturing equipment. This work presents a series of methods for creating graded material transitions which include previously established transition types as well as several novel techniques. Test samples of each transition type were produced using additive manufacturing and their performance was measured. It is shown that some types of transitions can increase the ultimate strength of a part, while others may introduce new stress concentrations that reduce performance. This work then presents a method for adjusting the elastic modulus of a component to which graded material transitions have been added to allow the original design properties to be met.
ContributorsBrauer, Cole (Author) / Aukes, Daniel (Thesis advisor) / Chen, Xiangfan (Committee member) / Sugar, Thomas (Committee member) / Arizona State University (Publisher)
Created2020
Description
Unmanned subsurface investigation technologies for the Moon are of special significance for future exploration when considering the renewed interest of the international community for this interplanetary destination. In precision agriculture, farmers demand quasi-real-time sensors and instruments with remote crop and soil detection properties to meet sustainability goals and achieve healthier and higher crop yields. Hence, there is the need for a robot that will be able to travel through the soil and conduct sampling or in-situ analysis of the subsurface materials on earth and in space. This thesis presents the design, fabrication, and characterization of a robot that can travel through the soil. The robot consists of a helical screw design coupled with a fin that acts as an anchor. The fin design is an integral part of the robot, allowing it to travel up and down the medium unaided. Experiments were performed to characterize different designs. It was concluded that the most energy-efficient speed from traveling down the medium is 20 rpm, while 60 rpm was the efficient speed for traveling up the medium. This research provides vital insight into developing subsurface robots enabling us to unearth the valuable knowledge that subsurface environment holds to help the agricultural, construction, and exploration communities.
ContributorsOkwae, Nana Kwame Kwame (Author) / Marvi, Hamidreza (Thesis advisor) / Tao, Jungliang (Committee member) / Lee, Hyunglae (Committee member) / Arizona State University (Publisher)
Created2020
Description
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.
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
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 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.
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
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 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
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
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 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
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 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
Description
Laser Powder Bed Fusion (LPBF) is an additive manufacturing (AM) technology that has emerged as the predominant technology for metal 3D printing. An alloy of particular interest to the aerospace industry is the nickel-based superalloy, Inconel 718 (IN718), which is widely used for its superior performance in elevated temperature conditions, particularly for gas-turbine engine blades and heat exchangers. With LPBF providing new ways of exploiting complex part geometry, the high-temperature properties of the AM version of the alloy must be understood. Of additional interest is how these properties change as a function of geometry and post-processing. This research focuses on the behavior of LPBF IN718 as a function of hot isostatic pressing (HIP) and specimen thickness at elevated temperatures. These results and behavior were compared to the behavior of IN718 sheet metal for properties such as True Ultimate Tensile Strength (UTS), Yield Strength, Young’s Modulus, percent elongation, and necking. The results showed dependence of strength on both thickness and HIP condition, and also exhibited a steep drop in UTS and yield strength at 1600 °F, linearly declining modulus, and excess dynamic strain ageing (DSA) behavior at certain temperatures.
ContributorsTemes, Samuel (Author) / Bhate, Dhruv (Thesis advisor) / Azeredo, Bruno (Committee member) / Das, Partha (Committee member) / Arizona State University (Publisher)
Created2021
Description
Gas Diffusion Layers (GDL) based on PUREBLACK® carbon and VULCAN® (XC72R) carbon along with catalyst coated membranes were used to fabricate the membrane electrode assemblies for use in proton exchange membrane fuel cells (PEMFCs). Polyethylene glycol was used as the pore-forming agent on the microporous layer to improve the lower and higher relative humidity performance of the fuel cells. Accelerated stress tests based on the dissolution effect of GDLs were conducted and the long-term performance of the GDLs was evaluated. A single-cell fuel cell was used to evaluate the effect of porosity of the micro-porous layer and the effect of different types of carbon powder on the performance of the fuel cell at different operating relative humidity conditions and compared with commercial GDLs.Both PUREBLACK® and VULCAN® (XC72R) based GDLs show crack-free surface morphology in the Scanning electron microscopy and hydrophobic characteristics in the contact angle measurements. The fuel cell performance is evaluated under relative humidity conditions of 60 and 100 % using H2/O2 and H2/Air at 70 ℃ and the durability is also evaluated for the sample with and without 30% PEG for both carbons. The pristine PUREBLACK® based GDL sample with 30% pore-forming agent (total pore volume of 1.72 cc.g-1) demonstrated the highest performance (peak power densities of 432 and 444 mW.cm-2 at 100 and 60 % RH respectively, using H2/Air). There was a significant increase in the macropores when GDLs are aged in H2O2 and the contact angle dropped to about 14 and 95° for PUREBLACK® and VULCAN® carbon, respectively. Overall PUREBLACK® based GDLs performed the best after ageing both in H2O2 and H2O (average performance degradation of 8% in H2O2 and 8.25% in H2O).
ContributorsChauhan, Nitin (Author) / Kannan, Arunachala Mada (Thesis advisor) / Phelan, Patrick (Committee member) / Nian, Qiong (Committee member) / Arizona State University (Publisher)
Created2021
Description
This paper introduces a variable impedance controller which dynamically modulates both its damping and stiffness to improve the trade-off between stability and agility in coupled human-robot systems and reduce the human user’s effort. The controller applies a range of robotic damping from negative to positive values to either inject or dissipate energy based on the user’s intent of motion. The controller also estimates the user’s intent of direction and applies a variable stiffness torque to stabilize the user towards an estimated ideal trajectory. To evaluate the controller’s ability to improve the stability/agility trade-off and reduce human effort, a study was designed for human subjects to perform a 2D target reaching task while coupled with a wearable ankle robot. A constant impedance condition was selected as a control with which to compare the variable impedance condition. The position, speed, and muscle activation responses were used to quantify the user’s stability, agility, and effort, respectively. Stability was quantified spatially and temporally, with both overshoot and stabilization time showing no statistically significant difference between the two experimental conditions. Agility was quantified using mean and maximum speed, with both increasing from the constant impedance to variable impedance condition by 29.8% and 59.9%, respectively. Effort was quantified by the overall and maximum muscle activation data, both of which showed a ~10% reduction in effort. Overall, the study demonstrated the effectiveness of the variable impedance controller.
ContributorsArnold, James (Author) / Lee, Hyunglae (Thesis advisor) / Berman, Spring (Committee member) / Yong, Sze Zheng (Committee member) / Arizona State University (Publisher)
Created2021