Matching Items (29)
Description
The relationships between the properties of materials and their microstructures have been a central topic in materials science. The microstructure-property mapping and numerical failure prediction are critical for integrated computational material engineering (ICME). However, the bottleneck of ICME is the lack of a clear understanding of the failure mechanism as well as an efficient computational framework. To resolve these issues, research is performed on developing novel physics-based and data-driven numerical methods to reveal the failure mechanism of materials in microstructure-sensitive applications.
First, to explore the damage mechanism of microstructure-sensitive materials in general loading cases, a nonlocal lattice particle model (LPM) is adopted because of its intrinsic ability to handle the discontinuity. However, the original form of LPM is unsuitable for simulating nonlinear behavior involving tensor calculation. Therefore, a damage-augmented LPM (DLPM) is proposed by introducing the concept of interchangeability and bond/particle-based damage criteria. The proposed DLPM successfully handles the damage accumulation behavior in general material systems under static and fatigue loading cases.
Then, the study is focused on developing an efficient physics-based data-driven computational framework. A data-driven model is proposed to improve the efficiency of a finite element analysis neural network (FEA-Net). The proposed model, i.e., MFEA-Net, aims to learn a more powerful smoother in a multigrid context. The learned smoothers have good generalization properties, and the resulted MFEA-Net has linear computational complexity. The framework has been applied to efficiently predict the thermal and elastic behavior of composites with various microstructural fields. Finally, the fatigue behavior of additively manufactured (AM) Ti64 alloy is analyzed both experimentally and numerically. The fatigue experiments show the fatigue life is related with the contour process parameters, which can result in different pore defects, surface roughness, and grain structures. The fractography and grain structures are closely observed using scanning electron microscope. The sample geometry and defect/crack morphology are characterized through micro computed tomography (CT). After processing the pixel-level CT data, the fatigue crack initiation and growth behavior are numerically simulated using MFEA-Net and DLPM. The experiments and simulation results provided valuable insights in fatigue mechanism of AM Ti64 alloy.
ContributorsMeng, Changyu (Author) / Liu, Yongming (Thesis advisor) / Hoover, Christian (Committee member) / Li, Lin (Committee member) / Peralta, Pedro (Committee member) / Wang, Liping (Committee member) / Arizona State University (Publisher)
Created2023
Description
A unique geometry is presented that creates biaxial stresses and strains when subjected to uniaxial loading in order to facilitate further multiaxial fatigue research by reducing the need for the use of specialized multiaxial loading equipment. Cyclic plasticity is a critical process in fatigue and the geometry was successfully designed and fabricated to allow for the continuous monitoring of cyclic plastic strains of magnitude 10^(-4) mm/mm during cyclic loading. Simulation results show that plasticity occurs in a region central to the test specimen while also being subjected to biaxial stresses and strains characterized by average principal direction ratios of 1.18 and 1.39 respectively. Simulation shows fatigue life of the specimen to be 79 thousand cycles, which allows for a reasonable evolution of cyclic plasticity before reaching failure. Issues with the instrumentation process hindered experimental validation of the simulation results.
ContributorsHill, Alex (Author) / Peralta, Pedro (Thesis director) / Rajagopalan, Jagannathan (Committee member) / Barrett, The Honors College (Contributor) / Mechanical and Aerospace Engineering Program (Contributor)
Created2022-05
Design of a thermally stable nano-crystalline alloy with superior tensile creep and fatigue behavior
Description
Materials have been the backbone of every major invention in the history of mankind, e.g. satellites and space shuttles would not exist without advancement in materials development. Integral to this, is the development of nanocrystalline (NC) materials that promise multitude of properties for advanced applications. However, they do not tend to preserve structural integrity under intense cyclic loading or long-term temperature exposures. Therefore, it is imperative to understand factors that alter the sub-features controlling both structural and functional properties under extreme conditions, particularly fatigue and creep. Thus, this dissertation systematically studies the tensile creep and fatigue behaviour of a chemically optimized and microstructurally stable bulk NC copper (Cu)-3at.% tantalum (Ta) alloy.
Strategic engineering of nanometer sized clusters of Ta into the alloy’s microstructure were found to suppress the microstructure instability and render remarkable improvement in the high temperature tensile creep resistance up to 0.64 times the melting temperature of Cu. Primary creep in this alloy was found to be governed by the relaxation of the microstructure under the applied stress. Further, during the secondary creep, short circuit diffusion of grain boundary atoms resulted in the negligible steady-state creep rate in the alloy. Under fatigue loading, the alloy showed higher resistance for crack nucleation owing to the inherent microstructural stability, and the interaction of the dislocations with the Ta nanoclusters. The underlying mechanism was found to be related to the diffused damage accumulation, i.e., during cyclic loading many grains participate in the plasticity process (nucleation of discrete grain boundary dislocations) resulting in homogenous accumulation rather than localized one as typically observed in coarse-grained materials. Overall, the engineered Ta nanoclusters were responsible for governing the underlying anomalous high temperature creep and fatigue deformation mechanisms in the alloy.
Finally, this study presents a design approach that involves alloying of pure metals in order to impart stability in NC materials and significantly enhance their structural properties, especially those at higher temperatures. Moreover, this design approach can be easily translated to other multicomponent systems for developing advanced high-performance structural materials.
Strategic engineering of nanometer sized clusters of Ta into the alloy’s microstructure were found to suppress the microstructure instability and render remarkable improvement in the high temperature tensile creep resistance up to 0.64 times the melting temperature of Cu. Primary creep in this alloy was found to be governed by the relaxation of the microstructure under the applied stress. Further, during the secondary creep, short circuit diffusion of grain boundary atoms resulted in the negligible steady-state creep rate in the alloy. Under fatigue loading, the alloy showed higher resistance for crack nucleation owing to the inherent microstructural stability, and the interaction of the dislocations with the Ta nanoclusters. The underlying mechanism was found to be related to the diffused damage accumulation, i.e., during cyclic loading many grains participate in the plasticity process (nucleation of discrete grain boundary dislocations) resulting in homogenous accumulation rather than localized one as typically observed in coarse-grained materials. Overall, the engineered Ta nanoclusters were responsible for governing the underlying anomalous high temperature creep and fatigue deformation mechanisms in the alloy.
Finally, this study presents a design approach that involves alloying of pure metals in order to impart stability in NC materials and significantly enhance their structural properties, especially those at higher temperatures. Moreover, this design approach can be easily translated to other multicomponent systems for developing advanced high-performance structural materials.
ContributorsKale, Chaitanya (Author) / Solanki, Kiran N (Thesis advisor) / Darling, Kristopher (Committee member) / Ankit, Kumar (Committee member) / Arizona State University (Publisher)
Created2019
Description
The study aimed to determine the relationship of subjective perception of wellness (Intrinsic Fatigue) and Global Positioning Satellite derived workload amongst elite high school soccer players. Twenty-nine (16.4 ± 1.54 years) male participants completed a mobile app-based wellness questionnaire comprising of 6 subjective markers prior to 10 workload variables being measured by STATSports 10Hz GPS units later that same day. Only instances where both wellness and GPS reports qualified for analyses (N=231 exposures). No significant differences were reported in reported wellness within- or between-weeks (p > 0.05) with average Effect Sizes (ES) ranging from 0.001 to 0.15. Total Distance (TD) was significantly different (p < 0.05) within week. All GPS variables except TD and Distance per Minute (DpM) were significantly different (p < 0.05) between-weeks. Average GPS ES sizes ranged from 0.02 to 0.58. Wellness and GPS or it’s ESs were not correlated, with correlations ranging from -1.000 to 0.207. The results suggest monitoring of GPS reports to be a practical method of monitoring variation in player workload but does not support subjective questionnaires as a means of monitoring player wellness reflecting these workload variations in youth populations.
ContributorsArmistead, Scott (Author) / Wardenaar, Floris (Thesis advisor) / Foskett, Andrew (Committee member) / Kavouras, Stavros (Committee member) / Arizona State University (Publisher)
Created2020
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
Special thermal interface materials are required for connecting devices that operate at high temperatures up to 300°C. Because devices used in power electronics, such as GaN, SiC, and other wide bandgap semiconductors, can reach very high temperatures (beyond 250°C), a high melting point, and high thermal & electrical conductivity are required for the thermal interface material. Traditional solder materials for packaging cannot be used for these applications as they do not meet these requirements. Sintered nano-silver is a good candidate on account of its high thermal and electrical conductivity and very high melting point. The high temperature operating conditions of these devices lead to very high thermomechanical stresses that can adversely affect performance and also lead to failure. A number of these devices are mission critical and, therefore, there is a need for very high reliability. Thus, computational and nondestructive techniques and design methodology are needed to determine, characterize, and design the packages. Actual thermal cycling tests can be very expensive and time consuming. It is difficult to build test vehicles in the lab that are very close to the production level quality and therefore making comparisons or making predictions becomes a very difficult exercise. Virtual testing using a Finite Element Analysis (FEA) technique can serve as a good alternative. In this project, finite element analysis is carried out to help achieve this objective. A baseline linear FEA is performed to determine the nature and magnitude of stresses and strains that occur during the sintering step. A nonlinear coupled thermal and mechanical analysis is conducted for the sintering step to study the behavior more accurately and in greater detail. Damage and fatigue analysis are carried out for multiple thermal cycling conditions. The results are compared with the actual results from a prior study. A process flow chart outlining the FEA modeling process is developed as a template for the future work. A Coffin-Manson type relationship is developed to help determine the accelerated aging conditions and predict life for different service conditions.
ContributorsAmla, Tarun (Author) / Chawla, Nikhilesh (Thesis advisor) / Jiao, Yang (Committee member) / Liu, Yongming (Committee member) / Zhuang, Houlong (Committee member) / Jiang, Hanqing (Committee member) / Arizona State University (Publisher)
Created2020
Description
Estimates indicate that in the United States 1 in 8 women will develop breast cancer in their lifetime. Improved cancer screenings, early detection, and targeted treatments have increased breast cancer survival rates. However, breast cancer patients treated with chemotherapy are at an increased risk for cardiovascular disease, functional impairments, and loss of cardiorespiratory fitness. These negative outcomes have implications for early morbidity and mortality. The purpose of this thesis was to test the hypothesis that high-intensity exercise preconditioning (exercise commenced prior to initiating chemotherapy and continued throughout treatment cycles) preserves health-related outcomes in breast cancer patients treated with anthracycline-containing chemotherapy. Here, we present a subset of preliminary data from an ongoing trial (NCT02842658) that is focused on VO2peak and skeletal muscle outcomes from the first 10 participants that have enrolled in the trial. Breast cancer patients (N=10; 50 ± 11 y; 168 ± 4 cm; 92 ± 37 kg; 32.3 ± 12.3 kg/m2) scheduled to receive anthracycline-containing chemotherapy were randomly assigned to one of two interventions: 1) exercise preconditioning, (3 days per week of supervised exercise throughout treatment) or 2) standard of care (attention-control). Pre-testing occurred 1-2 week prior to chemotherapy. The interventions were initiated 1 week prior to chemotherapy and continued throughout anthracycline treatment. Post-testing occurred 3-7 days following the last anthracycline treatment. VO2peak (L/min) was reduced by 16% in the control group (P < 0.05), whereas VO2peak was preserved in the exercise preconditioning group. Trends for greater preservation and/or improvement in the exercise preconditioning group were also observed for lean body mass and peak heart rate. Hand grip strength was not changed in either group (P > 0.05). Both groups demonstrated an increase in ultrasound-derived echogenicity measures of the vastus lateralis (P < 0.05), indicating changes in the composition of the skeletal muscle during treatment. These preliminary data highlight that exercise preconditioning may serve as a strategy to preserve cardiorespiratory fitness and perhaps lean mass during anthracycline treatment of breast cancer. There remains a need for larger, definitive clinical trials to identify strategies to prevent the array of chemotherapy-induced toxicities that are observed in breast cancer patients treated with anthracyclines.
ContributorsCasey, Kathleen (Author) / Angadi, Siddhartha (Thesis director) / Gaesser, Glenn (Committee member) / Dickinson, Jared (Committee member) / College of Health Solutions (Contributor) / Barrett, The Honors College (Contributor)
Created2020-05
Description
A key aspect of understanding the behavior of materials and structures is the analysis of how they fail. A key aspect of failure analysis is the discipline of fractography, which identifies features of interest on fracture surfaces with the goal of revealing insights on the nature of defects and microstructure, and their interactions with the environment such as loading conditions. While fractography itself is a decades-old science, two aspects drive the need for this research: (i) Fractography remains a specialized domain of materials science where human subjectivity and experience play a large role in accurate determination of fracture modes and their relationship to the loading environment. (ii) Secondly, Additive Manufacturing (AM) is increasingly being used to create critical functional parts, where our understanding of failure mechanisms and how they relate to process and post-process conditions is nascent. Given these two challenges, this thesis conducted work to train convolutional neural network (CNN) models to analyze fracture surfaces in place of human experts and applies this to Inconel 718 specimens fabricated with the Laser Powder Bed Fusion (LPBF) process, as well as to traditional sheet metal specimens of the same alloy. This work intends to expand on previous work utilizing clustering methods through comparison of models developed using both manufacturing processes to demonstrate the effectiveness of the CNN approach, as well as elucidate insights into the nature of fracture modes in additively and traditionally manufactured thin-wall Inconel 718 specimens.
ContributorsVan Handel, Nicole (Author) / Bhate, Dhruv (Thesis director, Committee member) / Guo, Shenghan (Thesis director, Committee member) / Barrett, The Honors College (Contributor) / Engineering Programs (Contributor) / Dean, W.P. Carey School of Business (Contributor) / School of Mathematical and Statistical Sciences (Contributor)
Created2022-05
Description
This thesis analyzes how Arizona State University’s disability resource center, Student Accessibility and Inclusive Learning Services (SAILS), impacts access fatigue among students with disabilities. Access fatigue is rhetorical fatigue borne from the continuous need for people with disabilities to perform accommodation negotiations, or requests for practices that will grant them access to certain spaces. This study theorizes access fatigue as an intersection between scholarship about embodied rhetorical fatigue and interactional rhetorical phenomena that occur during accommodation negotiations. This research is guided by user experience (UX) methodologies, including a textual heuristic analysis of two SAILS documents; stakeholder interviews with students, teachers, and a SAILS representative; and a comparative analysis situating SAILS in relation to other disability resource centers. This thesis frames accommodation negotiations and access fatigue through the lens of institutional relationality and identifies four key dimensions of institutional relationality that affected participants’ experiences with access fatigue, including: burden sharing between students and SAILS, misfitting between students and SAILS, institutional culture shaping facilitated by relationships between non-registered stakeholders and SAILS, and institutional access fatigue resulting from design inconsistencies between SAILS and other disability resource centers. To relate this theorization to design practices, this thesis includes UX-informed guidelines for designing disability resource centers that promote fatigue relief through the integration of theories of institutional relationality.
ContributorsCaputo, Courtney (Author) / Hannah, Mark (Thesis advisor) / Lauer, Claire (Committee member) / Long, Elenore (Committee member) / Arizona State University (Publisher)
Created2024