Thesis (M.S.)--Mississippi State University. Department of Agricultural and Biological Engineering. / Title from title screen. Includes bibliographical references.

Transportation costs represent a significant role in the economics of packaged hay and biomass crops. The material’s low bulk density limits transportation efficiency. Density is currently limited by the ability of the baling twine to withstand the expansion forces generated by the baled material shortly after it is ejected from the bale chamber. It was hypothesized that compromising the structure of the plant, particularly the plant nodes could reduce the amount of energy stored in the material as it is compressed and thereby reduce the material’s elastic response to compression. Literature pertinent to the biomass material’s behavior in compression was reviewed. Bulk samples of switchgrass and miscanthus were subject to uniaxial compression, and the required pressure needed to obtain a target density of 256 kg/m3 was compared on a wet and dry density basis. Both switchgrass and miscanthus showed a statistically significant decrease in the required compression pressure, and the interaction between the moisture level and required pressure was also significant. Existing models for the pressure density relationship of compressed bulk material were evaluated for suitability. Individual nodes and internode sections were subject to radial compression and the apparent modulus of elasticity and maximum contact stress were determined.

abstract: This research focuses on the stress and structure evolution observed in-situ during the earliest stages of thin film growth in Cu on Au(111)-reconstruction. For the research, an ultra high vacuum-scanning tunneling microscopy (UHV-STM) system was modified to have the additional capabilities of in-situ deposition and in-situ stress evolution monitoring. The design and fabrication processes for the modifications are explained in detail. The deposition source enabled imaging during the deposition of Cu thin films, while also being columnar enough to avoid negatively impacting the function of the microscope. It was found that the stress-induced changes in piezo voltage occurred over a substantially longer time scale and larger piezo scale than used during imaging, allowing for the deconvolution of the two sources of piezo voltage change. The intrinsic stress evolution observed at the onset of Cu growth was tensile in character and reached a maximum of 0.19 N/m at approximately 0.8ML, with an average tensile slope of 1.0GPa. As the film thickness increased beyond 0.8 ML, the stress became less tensile as the observation of disordered stripe and trigon patterns of misfit dislocations began to appear. The transport of atoms from the surface of enlarged Cu islands into the strained layer played an important role in this stage, because they effectively reduce the activation barrier for the formation of the observed surface structures. A rich array of structures were observed in the work presented here including stripe, disordered stripe and trigon patterns co-existing in a single Cu layer. Heteroepitaxial systems in existing literature showed a uniform structure in the single layer. The non-uniform structures in the single layer of this work may be attributed to the room temperature Cu growth, which can kinetically limit uniform pattern formation. The development of the UHV-STM system with additional capabilities for this work is expected to contribute to research for the stress and structure relationships of many other heteroepitaxial systems. / Dissertation/Thesis / Ph.D. Materials Science and Engineering 2012

Metal sealing rings have been used widely in compressors, turbines and hydraulic devices. Such rings can extend out due to elasticity, and keep close contact with the valve wall, resulting in the formation of a functional seal under pressure. In this project, the failure of metal sealing rings is considered. Sealing component failure due to stress relaxation can threaten the safety of the whole steam turbine. The object of this study was to examine the stress relaxation response and corresponding changes in microstructure of metal sealing rings used in nuclear steam turbine under high temperature and applied stress. The two kinds of sealing ring samples were selected for GH4145 and GH2132. In this paper, all samples were tested by accelerated simulation experiment. The test temperature was controlled at 400℃, 600℃, and 800℃. The 400℃ experiments lasted for 10, 20, 30 and 40 hours, while the 600℃ and 800℃ experiments lasted for 5, 10, 15 and 20 hours. The surface morphology was observed by metallographic analysis. It was found that the two kinds of sealing ring samples presented with a continuous development of grain coarsening and a decrease of the twins when time and test temperature were increased. The prolongation of time and increase of test temperature will drive the grain coarsening and reduce the twins faster. Many precipitates and inclusions were observed on the surface. The composition of precipitation was examined by scanning electron microscopy (SEM). It was further studied by testing samples with applied stress. The differences between the two tests and their influence on mechanical properties are discussed. The grain coarsening and twinning in the alloy will reduce the stress relaxation resistance of the material. Additionally, the precipitates and inclusions in the alloy may adversely affect the stress relaxation performance. Sealing rings using the nickel-based superalloys have stronger anti-stress relaxation performance than sealing rings made of iron-based superalloys.

Este trabalho apresenta um estudo sobre deformações de geotêxteis ao longo do tempo, considerando interações entre reforço e solo confinante em muros de solo reforçado. O programa experimental desenvolvido para esse fim envolveu duas etapas básicas. Na primeira etapa, um novo equipamento foi desenvolvido na Escola de Engenharia de São Carlos/USP, para a realização de ensaios de fluência com um elemento de solo reforçado. O equipamento desenvolvido permite simular o mecanismo típico de transferência de carga em estruturas de solo reforçado, isto é, o solo solicita o geotêxtil. Esse equipamento também possibilita que solo e geotêxtil apresentem deformações ao longo do tempo de forma interativa. Nessa etapa, o programa de ensaios foi conduzido utilizando-se uma areia pura e um geotêxtil de polipropileno. Na segunda etapa deste trabalho, modelos de muros de solo reforçado foram ensaiados em centrífuga na Universidade do Colorado em Boulder, EUA. Os referidos modelos foram construídos utilizando-se uma areia e mantas de poliéster e de polipropileno. Alguns modelos foram carregados até a ruptura com acréscimo de aceleração, enquanto outros foram observados, no decorrer do tempo, sob aceleração constante. Nos ensaios para investigação de fluência, deformações significativas foram observadas, ocorrendo, inclusive, a manifestação de ruptura em determinados modelos, após algumas horas de ensaio. Os ensaios realizados nas duas etapas do trabalho revelaram aspectos importantes relativos à interação solo-reforço. Com base na interpretação dos resultados experimentais, apresenta-se uma discussão sobre mecanismos de deformação, em função do tempo, em muros de solo reforçado. / This thesis presents a study on the time- ependent deformations of geotextiles in reinforced soil walls considering the long-term interactive behavior between the reinforcement and the confining soil. The experimental program comprised two distinct phases. In the first phase, a new equipment was designed and constructed at the School of Engineering at Sao Carlos/USP, Brazil, in an attempt to perform creep tests with an element of reinforced soil. This equipment simulates the typical load transfer mechanism in reinforced soil structures, that is, the load is transferred from the soil to the reinforcement. This equipment also allows long-term interactive deformations between the soil and the geotextile. The testing program of this phase was conducted using a pure dry sand and a polypropylene geotextile. In the second phase of this research, models of reinforced soil walls were tested in a centrifuge facility at the University of Colorado at Boulder, USA. The models were built using a pure dry sand and a polyester or polypropylene geotextile. The models were either loaded until failure increasing the centrifugal acceleration or tested under constant acceleration. Considerable strains were observed in the creep tests, and some of the models failed after a few hours. The testing programs carried out in this study revealed important aspects of the soil-reinforcement interaction. Based on the analyses of the experimental results a broad discussion on long-term deformation mechanisms in reinforced soil walls is made herein.

The assumption that EMG biofeedback cultivates an antistress response was tested under stress conditions while investigating the comparative efficacy of low versus high arousal treatment strategies. Biofeedback-assisted, cue-controlled relaxation training was used as the low arousal treatment strategy for half of the 20 normal subjects used in the study. The other half received a high arousal treatment strategy which used the same training in combination with an avoidance conditioning procedure. In this procedure mild electric shock was used as contingent aversive stimulation designed to reinforce relaxation responses. Both groups received four in-lab training sessions with a 4-day interim of home practice of cuecontrolled relaxation prior to the last in-lab training session. Pretraining assessment consisted of four 10-minute periods of alternating no-stress and stress conditions. Mild electric shock and loud tones were used as stressors. Posttraining assessment was identical to pre training except subjects employed self-directed, cue-controlled relaxation rather than self-directed relaxation based on instructions without training. Frontal EMG, subjective mental and muscle tension ratings, and behavioral observations of relaxation behavior served as dependent measures during pre- and posttraining assessment. EMG readings were used during in-lab training and the two subjective rating scales were used during home practice.

京都大学 / 0048 / 新制・論文博士 / 博士(工学) / 乙第13337号 / 論工博第4186号 / 新制||工||1740(附属図書館) / 京都大学大学院工学研究科材料化学専攻 / (主査)教授 瀧川 敏算, 教授 中村 洋, 教授 古賀 毅 / 学位規則第4条第2項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Pour améliorer la caractérisation et le dimensionnement des disques de turbines pour les moteurs d’avion, le motoriste Safran Aircraft Engines (SAE) développe des modèles de comportement, des lois d’endommagement et des critères de fatigue plus adaptés aux chargements réels. Pour aider à cette démarche, le but de cette étude est de développer un modèle de plasticité adapté à l'Inco718DA (un alliage à base nickel utilisé dans la fabrication des turbines haute pression), capable de représenter différents chargements (monotone, cyclique symétrique et non-symétrique). La proposition puis l'identification du modèle a été possible grâce à une campagne expérimentale favorisant des tests complexes et innovants aux essais de fatigue nombreux et coûteux. Les essais faits incluent un essai monotone avec décharges élastiques, un essai multi-niveau à Rε=-1 et deux essais multi-niveau à Rε=0 pour mieux caractériser la relaxation de la contrainte moyenne et un essai pour quantifer le rochet. Le comportement cyclique du matériau a été identifié en utilisant un écrouissage cinématique non saturant avec des éléments s'inspirant de la surface mémoire de Chaboche. Un des défis a été d'obtenir des boucles stabilisées "pointues" dans un régime de plasticité cyclique saturante, en utilisant une évolution du paramètre Γ en fonction de la déformation plastique équivalente maximale (prefacteur du terme de rappel de la loi d'écrouissage cinématique).Une deuxième difficulté apparaît dans la description de la relaxation de la contrainte moyenne, phénomène complexe avec un impact considérable sur la durée de vie en fatigue. Dans le chapitre 3, un modèle est proposé pour la caractérisation de la relaxation partielle de la contrainte moyenne. Une originalité du modèle est l'idée que la relaxation incomplète est une conséquence directe de la différence entre la charge et la décharge de la boucle de hystérésis. Le paramètre choisi pour décrire cette différence a été le préfacteur du terme de rappel Γ, pour lequel la thermodynamique donne de la liberté. Par rapport à d'autres lois d'écrouissage confirmées, notre modèle présente l'avantage d'utiliser un seul terme de rappel, mais avec une formulation plus complexe. En plus, le modèle est incrémental (écrit en taux/en vitesse), il peut donc prendre en compte des chargements complexes tels que aléatoires ou plus simplement tels que dans les essais multi-niveaux pilotés en déformation. Dans le dernier chapitre de la thèse, une campagne biaxiale vaste est présentée, avec les développements pour réaliser des essais biaxiaux pilotés en déformation. La campagne biaxiale a été réalisée sur des éprouvettes cruciformes en utilisant des capteurs LASER et des mesures de champs mono et stéréo analysées en utilisant la Corrélation d'Images Numeriques (CIN). Pour analyser la relaxation de la contrainte moyenne en biaxial un moyen de mesure et de contrôle fiable a dû être développé, adapté aux déformations plastiques élevées qui apparaissent dans la région d'intérêt de l'éprouvette. En utilisant la corrélation d'images intégrée (I-CIN) avec des fonctions de forme adaptées sur un seul élément et des calculs sur GPU, on a obtenu des fréquences de mesure de 100~Hz. En plus, avec sa précision et vitesse, I-CIN a été une technique adaptée pour contrôler une machine d'essais multiaxiale hydraulique. Un résultat important obtenu quand on a réalisé des essais equi-biaxiaux pilotés en déformation a été l'observation d'une relaxation de la contrainte moyenne très faible par rapport au cas uniaxial. Ce résultat doit être pris en compte dans les études futures avec des calculs éléments finis sur l'éprouvette complète. / To improve the characterization and design of aircraft engine turbine disks, the propulsion systems manufacturer Safran Aircraft Engines (SAE) develops constitutive equations, damage laws and fatigue criteria that are more adapted to real loadings. As part of this effort, the purpose of the current study is to develop a plasticity model for Inco718DA (a nickel-based alloy used in the manufacturing of high-pressure turbine disks), capable of representing several loading conditions (monotonic, symmetrical and non-symmetrical cyclic loading). The identification of the model was possible thanks to a uniaxial campaign, favoring a few but complex, innovative, tests to numerous costly fatigue tests. The tests we performed include a monotonic test with elastic discharges, a multi-level Rε = -1 test and two multi-level Rε = 0 tests that better quantify the mean stress relaxation and a test to identify ratcheting. The cyclic behavior was identified using a non-saturating kinematic hardening law with elements of Chaboche's memory surface. One of the challenges was to obtain sharp stabilized loops in a saturated cyclic plasticity regime, which was possible using parameter Γ evolving with respect to the maximum equivalent plastic strain, in the back-stress of kinematic hardening rule.A second difficulty appears in the description of mean stress relaxation, which has a considerable impact on fatigue lifetime. In chapter 3, a model is proposed for the description of the incomplete mean stress relaxation. One of the originalities is the idea that incomplete mean stress relaxation is a direct consequence of the difference between the loading and the unloading part of the hysteresis loop. The parameter we used to describe this difference, was the prefactor of the back-stress term Γ, for which the thermodynamics allows liberty. When compared to confirmed kinematic hardening laws that model non-zero mean stress relaxation, our model presents the advantage of using only one backstress, even if its description is more complex. Moreover, the model is incremental (written in a rate form in chapter 3 section 5) so it can take into account complex loadings such as multi-level strain-controlled tests.In the last chapter of the thesis, a vast biaxial campaign is presented, along with developments to make biaxial strain-controlled tests. The biaxial campaign was performed on cross-shaped samples using LASER sensors, mono and stereo full-field measurements using Digital Image Correlation (DIC). In order to analyze biaxial mean stress relaxation, a reliable measurement and control method had to be developed for the high plastic strains occurring in the region of interest of the sample. By using an Integrated-DIC (I-DIC) algorithm with adequate shape functions on one element and GPU computations we were able to obtain measurement frequencies of 100 Hz. Moreover, with its precision and speed, I-DIC proved to be a suitable technique for controlling a biaxial hydraulic machine. An important result obtained when performing equi-biaxial I-DIC strain-controlled tests was that there was very little biaxial mean stress relaxation, with respect to the uniaxial case. This result will have to be taken into account in future studies when performing finite element computations of the whole sample.

Test anxiety can be debilitating to test performance, thus the abilities of test anxious individuals may not be measured accurately. This study examined the efficacy of relaxation training, guided imagery, positive self-talk, and study skills training on anxiety reduction and academic self - esteem in test-anxious , learning disabled high school and college students. A randomized treatment control group design with pretest and post-test measures was used to assess the efficacy of treatment. Participants in the treatment group showed a greater reduction in test anxiety, and improvements in academic self-esteem from pretest to post-test relative to participants in the control group. Implications of the results are discussed.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第17828号 / 工博第3771号 / 新制||工||1576(附属図書館) / 30643 / 京都大学大学院工学研究科分子工学専攻 / (主査)教授 渡辺 宏, 教授 金谷 利治, 教授 山本 量一 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM