Theses and Dissertations
This collection includes both ASU Theses and Dissertations, submitted by graduate students, and the Barrett, Honors College theses submitted by undergraduate students.
Displaying 1 - 10 of 95
Description
This research examines the current challenges of using Lamb wave interrogation methods to localize fatigue crack damage in a complex metallic structural component subjected to unknown temperatures. The goal of this work is to improve damage localization results for a structural component interrogated at an unknown temperature, by developing a probabilistic and reference-free framework for estimating Lamb wave velocities and the damage location. The methodology for damage localization at unknown temperatures includes the following key elements: i) a model that can describe the change in Lamb wave velocities with temperature; ii) the extension of an advanced time-frequency based signal processing technique for enhanced time-of-flight feature extraction from a dispersive signal; iii) the development of a Bayesian damage localization framework incorporating data association and sensor fusion. The technique requires no additional transducers to be installed on a structure, and allows for the estimation of both the temperature and the wave velocity in the component. Additionally, the framework of the algorithm allows it to function completely in an unsupervised manner by probabilistically accounting for all measurement origin uncertainty. The novel algorithm was experimentally validated using an aluminum lug joint with a growing fatigue crack. The lug joint was interrogated using piezoelectric transducers at multiple fatigue crack lengths, and at temperatures between 20°C and 80°C. The results showed that the algorithm could accurately predict the temperature and wave speed of the lug joint. The localization results for the fatigue damage were found to correlate well with the true locations at long crack lengths, but loss of accuracy was observed in localizing small cracks due to time-of-flight measurement errors. To validate the algorithm across a wider range of temperatures the electromechanically coupled LISA/SIM model was used to simulate the effects of temperatures. The numerical results showed that this approach would be capable of experimentally estimating the temperature and velocity in the lug joint for temperatures from -60°C to 150°C. The velocity estimation algorithm was found to significantly increase the accuracy of localization at temperatures above 120°C when error due to incorrect velocity selection begins to outweigh the error due to time-of-flight measurements.
ContributorsHensberry, Kevin (Author) / Chattopadhyay, Aditi (Thesis advisor) / Liu, Yongming (Committee member) / Papandreou-Suppappola, Antonia (Committee member) / Arizona State University (Publisher)
Created2013
Description
Aluminum alloys and their composites are attractive materials for applications requiring high strength-to-weight ratios and reasonable cost. Many of these applications, such as those in the aerospace industry, undergo fatigue loading. An understanding of the microstructural damage that occurs in these materials is critical in assessing their fatigue resistance. Two distinct experimental studies were performed to further the understanding of fatigue damage mechanisms in aluminum alloys and their composites, specifically fracture and plasticity. Fatigue resistance of metal matrix composites (MMCs) depends on many aspects of composite microstructure. Fatigue crack growth behavior is particularly dependent on the reinforcement characteristics and matrix microstructure. The goal of this work was to obtain a fundamental understanding of fatigue crack growth behavior in SiC particle-reinforced 2080 Al alloy composites. In situ X-ray synchrotron tomography was performed on two samples at low (R=0.1) and at high (R=0.6) R-ratios. The resulting reconstructed images were used to obtain three-dimensional (3D) rendering of the particles and fatigue crack. Behaviors of the particles and crack, as well as their interaction, were analyzed and quantified. Four-dimensional (4D) visual representations were constructed to aid in the overall understanding of damage evolution. During fatigue crack growth in ductile materials, a plastic zone is created in the region surrounding the crack tip. Knowledge of the plastic zone is important for the understanding of fatigue crack formation as well as subsequent growth behavior. The goal of this work was to quantify the 3D size and shape of the plastic zone in 7075 Al alloys. X-ray synchrotron tomography and Laue microdiffraction were used to non-destructively characterize the volume surrounding a fatigue crack tip. The precise 3D crack profile was segmented from the reconstructed tomography data. Depth-resolved Laue patterns were obtained using differential-aperture X-ray structural microscopy (DAXM), from which peak-broadening characteristics were quantified. Plasticity, as determined by the broadening of diffracted peaks, was mapped in 3D. Two-dimensional (2D) maps of plasticity were directly compared to the corresponding tomography slices. A 3D representation of the plastic zone surrounding the fatigue crack was generated by superimposing the mapped plasticity on the 3D crack profile.
ContributorsHruby, Peter (Author) / Chawla, Nikhilesh (Thesis advisor) / Solanki, Kiran (Committee member) / Liu, Yongming (Committee member) / Arizona State University (Publisher)
Created2014
Description
Using data from an eight-year longitudinal study of 214 children's social and emotional development, I conducted three studies to (1) examine patterns of agreement for internalizing (INT) and externalizing (EXT) symptomatology among different informants (mothers, fathers, teachers, and adolescents) using a recently developed structural equation modeling approach for multi-trait, multi-method data; (2) examine the developmental trajectories for INT and EXT and predict individual differences in symptom development using temperament and parenting variables; and (3) describe patterns of INT and EXT co-occurrence and predict these patterns from temperament and parenting. In Study 1, longitudinal invariance was established for mothers', fathers' and teachers' reports over a six-year period. Sex, age, and SES did not substantially moderate agreement among informants, although both sex and age were differentially related to symptomatology depending on the informant. Agreement among teachers and mothers, but not among mothers and fathers, differed by domain of symptomatology, and was greater for EXT than for INT. In Study 2, latent profile analysis, a person-centered analytic approach, did not provide easily interpretable patterns of symptom development, a failure that is likely the result of the relatively modest sample size. Latent growth curve models, an alternative analytic approach, did provide good fit to the data. Temperament and parenting variables were examined as predictors of the latent growth parameters in these models. Although there was little prediction of the slope, effortful control was negatively related to overall levels of EXT, whereas impulsivity and anger were positively related. Mutually responsive orientation, a measure of the parent-child relationship, was a more consistent predictor of EXT than was parental warmth. Furthermore, the relation between mutually responsive orientation and EXT was partially mediated by inhibitory control. Across informants, there were few consistent predictors of INT. In Study 3, latent profile analysis was used to classify individuals into different patterns of INT and EXT co-occurrence. In these models, a similar class structure was identified for mothers and for teachers. When temperament and parenting were examined as predictors of co-occurring symptomatology, few significant interactions were found and results largely replicated prior findings from this data set using arbitrary symptom groups.
ContributorsSulik, Michael John (Author) / Eisenberg, Nancy (Thesis advisor) / Spinrad, Tracy L (Thesis advisor) / Lemery-Chalfant, Kathryn (Committee member) / Wolchik, Sharlene A (Committee member) / Arizona State University (Publisher)
Created2013
Description
This research focuses on the benefits of using nanocomposites in aerospace structural components to prevent or delay the onset of unique composite failure modes, such as delamination. Analytical, numerical, and experimental analyses were conducted to provide a comprehensive understanding of how carbon nanotubes (CNTs) can provide additional structural integrity when they are used in specific hot spots within a structure. A multiscale approach was implemented to determine the mechanical and thermal properties of the nanocomposites, which were used in detailed finite element models (FEMs) to analyze interlaminar failures in T and Hat section stringers. The delamination that first occurs between the tow filler and the bondline between the stringer and skin was of particular interest. Both locations are considered to be hot spots in such structural components, and failures tend to initiate from these areas. In this research, nanocomposite use was investigated as an alternative to traditional methods of suppressing delamination. The stringer was analyzed under different loading conditions and assuming different structural defects. Initial damage, defined as the first drop in the load displacement curve was considered to be a useful variable to compare the different behaviors in this study and was detected via the virtual crack closure technique (VCCT) implemented in the FE analysis.
Experiments were conducted to test T section skin/stringer specimens under pull-off loading, replicating those used in composite panels as stiffeners. Two types of designs were considered: one using pure epoxy to fill the tow region and another that used nanocomposite with 5 wt. % CNTs. The response variable in the tests was the initial damage. Detailed analyses were conducted using FEMs to correlate with the experimental data. The correlation between both the experiment and model was satisfactory. Finally, the effects of thermal cure and temperature variation on nanocomposite structure behavior were studied, and both variables were determined to influence the nanocomposite structure performance.
Experiments were conducted to test T section skin/stringer specimens under pull-off loading, replicating those used in composite panels as stiffeners. Two types of designs were considered: one using pure epoxy to fill the tow region and another that used nanocomposite with 5 wt. % CNTs. The response variable in the tests was the initial damage. Detailed analyses were conducted using FEMs to correlate with the experimental data. The correlation between both the experiment and model was satisfactory. Finally, the effects of thermal cure and temperature variation on nanocomposite structure behavior were studied, and both variables were determined to influence the nanocomposite structure performance.
ContributorsHasan, Zeaid (Author) / Chattopadhyay, Aditi (Thesis advisor) / Dai, Lenore (Committee member) / Jiang, Hanqing (Committee member) / Rajadas, John (Committee member) / Liu, Yongming (Committee member) / Arizona State University (Publisher)
Created2014
Description
Low-income Mexican American women face significant risk for poor health during the postpartum period. Chronic stressors are theorized to negatively impact mental and physical health outcomes. However, physiological factors associated with increased self-regulatory capacity, such as resting heart rate variability, may buffer the impact of stress. In a sample of 322 low-income Mexican American women (mother age 18-42; 84% Spanish-speaking; modal family income $10,000-$15,000), the interactive influence of resting heart rate variability and three chronic prenatal stressors (daily hassles, negative life events, economic stress) on maternal cortisol output, depressive symptoms, and self-rated health at 12 weeks postpartum was assessed. The hypothesized interactive effects between resting heart rate variability and the chronic prenatal stressors on the health outcomes were not supported by the data. However, results showed that a higher number of prenatal daily hassles was associated with increased postpartum depressive symptoms, and a higher number of prenatal negative life events was associated with lower postpartum cortisol output. These results suggest that elevated chronic stress during the prenatal period may increase risk for poor health during the postpartum period.
ContributorsJewell, Shannon Linda (Author) / Luecken, Linda J. (Thesis advisor) / Lemery-Chalfant, Kathryn (Committee member) / Perez, Marisol (Committee member) / Arizona State University (Publisher)
Created2015
Description
The current study delineated the developmental trajectories of early childhood externalizing and internalizing symptoms reported by mothers and fathers, and examined the role of the 18-month observed parenting quality × Respiratory Sinus Arrhythmia
(RSA) interaction in predicting these trajectories. Child sex was tested as a covariate and moderator. It was found that children's low baseline RSA or high RSA reactivity , in comparison to high baseline RSA or low RSA reactivity , was more reactive as a function
of early parenting quality when predicting the development of early childhood problem symptoms. Differential patterns of the interaction between parenting quality and RSA were detected for mothers' and fathers' reports. Mother-reported models showed a diathesis-stress pattern, whereas the father-reported model showed a vantage-sensitivity pattern, especially for internalizing symptoms. This may imply the potential benefit of fathers' active engagement in children's early development. In addition, the effect of the parenting quality × RSA interaction in predicting the mother-reported models was found
to be further moderated by child sex. Specifically, the parenting quality × baseline RSA interaction was significantly predictive of girls' 54-month internalizing, and the parenting quality × RSA reactivity interaction significantly predicted boys' internalizing slope. Girls with low baseline RSA or boys with high RSA reactivity were vulnerable to the less positive parenting, exhibiting high levels of 54-month internalizing symptoms or slow decline in internalizing over time, respectively. Future research directions were discussed in terms of integrating the measures of SNS and PNS in psychopathology study,
exploring the mechanisms underlying the sex difference in parenting quality × RSA interaction, and comparing the findings of children's typical and atypical development.
(RSA) interaction in predicting these trajectories. Child sex was tested as a covariate and moderator. It was found that children's low baseline RSA or high RSA reactivity , in comparison to high baseline RSA or low RSA reactivity , was more reactive as a function
of early parenting quality when predicting the development of early childhood problem symptoms. Differential patterns of the interaction between parenting quality and RSA were detected for mothers' and fathers' reports. Mother-reported models showed a diathesis-stress pattern, whereas the father-reported model showed a vantage-sensitivity pattern, especially for internalizing symptoms. This may imply the potential benefit of fathers' active engagement in children's early development. In addition, the effect of the parenting quality × RSA interaction in predicting the mother-reported models was found
to be further moderated by child sex. Specifically, the parenting quality × baseline RSA interaction was significantly predictive of girls' 54-month internalizing, and the parenting quality × RSA reactivity interaction significantly predicted boys' internalizing slope. Girls with low baseline RSA or boys with high RSA reactivity were vulnerable to the less positive parenting, exhibiting high levels of 54-month internalizing symptoms or slow decline in internalizing over time, respectively. Future research directions were discussed in terms of integrating the measures of SNS and PNS in psychopathology study,
exploring the mechanisms underlying the sex difference in parenting quality × RSA interaction, and comparing the findings of children's typical and atypical development.
ContributorsLi, Yi (Author) / Eisenberg, Nancy (Thesis advisor) / Spinrad, Tracy (Thesis advisor) / Lemery-Chalfant, Kathryn (Committee member) / Wilkens, Natalie (Committee member) / Arizona State University (Publisher)
Created2014
Description
In this dissertation, the results of our comprehensive computational studies of disordered jammed (i.e., mechanically stable) packings of hard particles are presented, including the family of superdisks in 2D and ellipsoids in 3D Euclidean space. Following a very brief introduction to the hard-particle systems, the event driven molecular dynamics (EDMD) employed to generate the packing ensembles will be discussed. A large number of 2D packing configurations of superdisks are subsequently analyzed, through which a relatively accurate theoretical scheme for packing-fraction prediction based on local particle contact configurations is proposed and validated via additional numerical simulations. Moreover, the studies on binary ellipsoid packing in 3D are briefly discussed and the effects of different geometrical parameters on the final packing fraction are analyzed.
ContributorsXu, Yaopengxiao (Author) / Jiao, Yang (Thesis advisor) / Oswald, Jay (Committee member) / Liu, Yongming (Committee member) / Arizona State University (Publisher)
Created2014
Description
The focus of this investigation is on the formulation and a validation of reduced order models (ROMs) for the prediction of the response of structures with embedded piezoelectric actuators. The ROMs considered here are those constructed in a nonintrusive manner from a commercial finite element software, NASTRAN is adopted here. Notwithstanding the popularity of piezoelectric materials in structural dynamics related applications such as structural health monitoring and energy harvesting, not all commercial finite element software allow directly their modeling. In such cases, e.g., with NASTRAN, one can proceed with an analogy and replace the electric actuation in the piezoelectric material by a fictitious thermal effect producing the same strain. This process recasts the determination of a ROM for a structure with embedded piezoelectric actuator into a similar ROM but for a heated structure, the framework of which has recently been developed. Yet, the temperature field resulting from the analogy would be quite different from the one considered in past effort and would excite a broad array of structural modes. Accordingly, as a preamble to considering a beam with a piezoelectric layer, a simpler plate model is considered that is subjected to a uniform temperature but a complex pressure loading that excites the entire set of modes of the plate in the broad frequency band considered. The very good match of the predictions obtained by this ROM in comparison to their full finite element counterparts provides the necessary confidence to next address a beam with embedded piezoelectic actuator. The test model considered for this validation is a built-up nano beam analyzed recently in nonlinear geometric conditions by full finite elements and by a non-intrusive ROM procedure under harmonic variations of the piezoelectic voltage. This structural model and its loading conditions are very different from those considered in past applications of nonintrusive ROMs, thus the excellent results obtained here provide further support of the broad generality of the nonintrusive ROM methodology, including of the appropriateness of the "dual modes" basis functions.
ContributorsVyas, Varun (Author) / Mignolet, Marc (Thesis advisor) / Hollkamp, Joseph (Committee member) / Liu, Yongming (Committee member) / Arizona State University (Publisher)
Created2014
Description
Fibromyalgia (FM) is a chronic musculoskeletal disorder characterized by widespread pain, fatigue, and a variety of other comorbid physiological and psychological characteristics, including a deficit of positive affect. Recently, the focus of research on the pathophysiology of FM has considered the role of a number of genomic variants. In the current manuscript, case-control analyses did not support the hypothesis that FM patients would differ from other chronic pain groups in catechol-O-methyltransferase (COMT) and mu-opioid receptor (OPRM1) genotype. However, evidence is provided in support of the hypothesis that functional single nucleotide polymorphisms on the COMT and OPRM1 genes would be associated with risk and resilience, respectively, in a dual processing model of pain-related positive affective regulation in FM. Forty-six female patients with a physician-confirmed diagnosis of FM completed an electronic diary that included once-daily assessments of positive affect and soft tissue pain. Multilevel modeling yielded a significant gene X environment interaction, such that individuals with met/met genotype on COMT experienced a greater decline in positive affect as daily pain increased than did either val/met or val/val individuals. A gene X environment interaction for OPRM1 also emerged, indicating that individuals with at least one asp allele were more resilient to elevations in daily pain than those homozygous for the asn allele. In sum, the findings offer researchers ample reason to further investigate the contribution of the catecholamine and opioid systems, and their associated genomic variants, to the still poorly understood experience of FM.
ContributorsFinan, Patrick Hamilton (Author) / Zautra, Alex (Thesis advisor) / Davis, Mary (Committee member) / Lemery-Chalfant, Kathryn (Committee member) / Presson, Clark (Committee member) / Arizona State University (Publisher)
Created2011
Description
The present study tested the factor structure of the externalizing disorders (e.g. attention-deficit hyperactivity disorder (ADHD), conduct disorder (SE), and substance experimentation (SE) ) in adolescence. In addition, this study tested the influence of the GABRA2 gene on the factors of the externalizing spectrum. Confirmatory factor analyses were used to test the factor structure of the externalizing spectrum. Specifically, three competing alternate confirmatory factor analytic models were tested: a one-factor model where all disorders loaded onto a single externalizing factor, a two-factor model where CD and SE loaded onto one factor and ADHD loaded onto another, and a three-factor model, where all three disorders loaded onto separate factors. Structural equation modeling was used to test the effect of a GABRA2 SNP, rs279858, on the factors of the externalizing spectrum. Analyses revealed that a three-factor model of externalizing disorders with correlated factors fit the data best. Additionally, GABRA2 had a significant effect on the SE factor in adolescence, but not on the CD or ADHD factors. These findings demonstrate that the externalizing disorders in adolescence share commonalities but also have separate sources of systematic variance. Furthermore, biological mechanisms may act as a unique etiological factor in the development of adolescent substance experimentation.
ContributorsWang, Frances L (Author) / Chassin, Laurie (Thesis advisor) / Lemery-Chalfant, Kathryn (Committee member) / Geiser, Christian (Committee member) / Arizona State University (Publisher)
Created2012