The goal of this work was to quantify the mechanical properties of cellulose nanocrystal (CNC)-based thin films using a polystyrene (PS) structuring approach. This structuring approach was used to biaxially wrinkle CNC-polymer and all-CNC films, in order to assess how changes in the film fabrication process affected the elastic modulus of these films. All films were prepared on pre-stressed PS substrates and structured by heating them above the glass transition temperature of PS, which caused the substrates to shrink and the films to wrinkle biaxially. CNC-polymer films were prepared using the layer-by-layer approach, where three parameters were modified to obtain films of varying compositions: 1) type of polymer (xyloglucan, XG, or polyethyleneimine, PEI), 2) polymer concentration (0.1 wt% or 1 wt%), and 3) film thickness (i.e., number of deposited bilayers). After these films were structured, their elastic moduli were calculated to be 70 ± 2 GPa for CNC-XG0.1, 72 ± 2 GPa for CNC-PEI0.1, and 32.2 ± 0.8 GPa for CNC-PEI1.0 films, indicating that the mechanical properties of CNC-polymer films changed with film composition. This structuring method was also found to provide a humidity-independent measurement of the modulus due to the irreversible nature of the wrinkling. Next, to prepare all-CNC films, CNC suspensions were evaporated under conditions designed to control the film thickness (using 0.005 wt% – 8 wt% CNC suspensions) and CNC nanoparticle orientation (chiral nematic, isotropic, or uniaxial). Suspensions were dried slowly under vacuum, quickly by heating, or by spin-coating to form films with chiral nematic, isotropic, or uniaxial (radial) CNC orientations, respectively. Following structuring, these wrinkled films showed unique morphologies that changed with nanoparticle orientation, suggesting that their mechanical properties are dependent on the CNC orientation within the films. The work presented in this thesis implies that the mechanical properties of films fabricated from hygroscopic bio-based nanomaterials can be assessed in a humidity-independent way by using the structuring method presented. Quantifying the mechanical properties of these films is critical to assess the potential applications of CNCs, where CNC-based materials may be used in developing paper-based electronics, extracellular matrix mimics, and plant cell wall mimics. / Thesis / Master of Science (MSc)

The response of wide flange steel columns subjected to constant axial loads and lateral blast loads was examined. The finite element program ABAQUS was used to model W8x40 sections with different slendernesses and boundary conditions. For the response calculations, a constant axial force was first applied to the column and the equilibrium state was determined. Next, a short duration, lateral blast load was applied and the response time history was calculated. Changes in displacement time histories and plastic hinge formations resulting from varying the axial load were examined. The cases studied include single-span and two-span columns. In addition to ideal boundary conditions, columns with linear elastic, rotational supports were also studied. Non-uniform blast loads were considered. Major axis, minor axis, and biaxial bending were investigated. The effects of strain rate and residual stresses were examined. The results for each column configuration are presented as a set of curves showing the critical blast impulse versus axial load. The critical blast impulse is defined as the impulse that either causes the column to collapse or to exceed the limiting deflection criterion. A major goal of this effort was to develop simplified design and analysis methods. To accomplish this, two single-degree-of-freedom approaches that include the effects of the axial load were derived. The first uses a bilinear resistance function that is similar to the one used for beam analysis. This approach provides a rough estimate of the critical impulse and is suitable only for preliminary design or quick vulnerability calculations. The second approach uses a nonlinear resistance function that accounts for the gradual yielding that occurs during the dynamic response. This approach can be easily implemented in a simple computer program or spreadsheet and provides close agreement with the results from the finite element method. / Ph. D.

Around 80% of women experience vaginal tears during labor when the diameter of the vagina must increase from ~2.5 cm to ~9.5 cm to allow the passage of a full-term baby. Vaginal tears vary from superficial cuts of the mucosal lining to tears propagating through the entire vaginal wall and into the surrounding tissues and organs. Complications associated with vaginal tears include postpartum hemorrhaging, fecal incontinence, urinary incontinence, and dyspareunia. Beyond the agonizing pain, these complications are emotionally and psychologically traumatic for women. Prevention, evaluation, and treatment of vaginal tears and subsequent conditions are limited due to the lack of studies examining the mechanical behavior of the pelvic floor tissues. Therefore, the mechanical response of healthy and torn vaginal tissue is investigated here to establish quantitative metrics for maternal healthcare. Toward this end, swine and rat vaginal tissue is subjected to biaxial loads until tearing to reveal its mechanical properties. The resulting large inhomogeneous deformations are measured by the digital image correlation optical method to calculate material strain. The influence of these strains near to and far from the immediate vicinity of the tears on the tearing behavior is studied. Coupling mechanisms of the mechanical properties in the circumferential and axial directions as well as their effect on the nature of tear resistance is studied. Collagen fibers, the component within tissue responsible for its strength under tension, are imaged using a multiphoton microscopy technique known as second-harmonic generation imaging to investigate the change in organization with mechanical loading. Furthermore, imaging is performed in the near-regions of tears to reveal the relationship between collagen fibers and tearing resistance. The data collected through these studies provide new knowledge on the nonlinear elastic behavior of vaginal tissue, the geometrical and micro-structural characteristics of tears, and the mechanisms that contribute to the formation and propagation of tears. The mechanical properties and tearing mechanisms of vaginal tissue will be crucial in developing new prevention and treatment methods for maternal trauma following childbirth. Episiotomy, late-term stretching, surgical treatment with graft materials and other protocols will all benefit from a mechanically-informed perspective. It is our hope that this work will raise awareness to the serious complexities of pelvic floor trauma and encourage a more refined and systematic approach to the inspection, imaging, and treatment of all vaginal tears following delivery. This work was supported in part by the National Science Foundation fund #1511603 and the Institute for Critical Technology and Sciences at Virginia Tech. / Doctor of Philosophy / Every year nearly three million women give birth vaginally with 80% experiencing vaginal tears. These injuries sustained during delivery vary with severity and are associated with several conditions, including pelvic floor disorders. These disorders are a set of long-term conditions of the pelvic region presently affecting one-fourth of adult women in the United States. Pelvic floor disorders are: pelvic organ prolapse - a pelvic organ such as the uterus "falls" from its natural position, urinary incontinence - difficulty controlling urination, and fecal incontinence - difficulty controlling bowel movements. Pelvic floor disorders lower the quality of life for women not only physically due to pain and daily discomfort, but also mentally as the disorders are generally perceived as an embarassing and private matter. The pelvic floor represents a complex system of muscles, organs, and support structures that work together to ensure everything stays in place and is functioning properly. Injury to any of these structures poses the risk of developing a disorder. As a central supporting organ, injuries to the vagina may be particularly worrisome. Surprisingly, little is known about the magnitude of forces and/or stretching that is placed on the pelvic floor during delivery, how much force and/or stretching is required for an injury, or how various injuries relate to future complications. The goal of this research is to describe how much the normal, healthy vagina stretches to various forces including forces that will result in injuries. The research further examines the stretching of injured vaginas to quantify any observable differences due to this injury. Finally, the relationships between the biological components of the vagina, such as collagen, and the forces placed on the vagina are examined. The result of this work will provide doctors and engineers with guidelines for understanding the conditions that produce vaginal injuries. The relationships examined between the tissue makeup and forces exerted onto the tissue may also aid in identifying any irregularities that would place a woman at risk for injury. Many of the medical procedures surrounding childbirth as well as surgical treatment for pelvic floor disorders will benefit from knowing how far the vagina can stretch before being injured. It is our hope that this work will raise awareness to the serious complexities of pelvic floor injuries and encourage a more refined and systematic approach to the inspection, imaging, and treatment of all vaginal tears following delivery. This work was supported in part by the National Science Foundation fund #1511603 and the Institute for Critical Technology and Sciences at Virginia Tech.

The uterosacral ligament (USL) and cardinal ligament (CL) are the two major suspensory tissues of the uterus, cervix, and vagina. These supportive structures can be weakened or damaged, leading to the development of pelvic floor disorders (PFDs) such as urinary incontinence, fecal incontinence, and pelvic organ prolapse. In the surgical treatment for PFDs, the USL and CL are extensively used as anchor structures to restore the normal position of the prolapsed organs. Therefore, the mechanical properties of the USL and CL may be critical for the development of new surgical reconstruction strategies for PFDs. In chapter 1, we present the first histo-mechanical characterization of the swine USL and CL using histological analysis, scanning electron microscopy and quasi-static uniaxial tensile tests. Our results suggest that the histological and uniaxial tensile properties of the swine CL and USL are very similar to those in humans. The swine is found to be a suitable animal model for studying the mechanical properties of these ligaments. To capture both the active and passive mechanical responses of biological tissues containing SMCs such as the USL and CL, a new structural constitutive model is proposed in chapter 2. The deformation of the active component in such tissues during isometric and isotonic contractions is described using an evolution law. This model is tested with published active and passive, uniaxial and biaxial, experimental data on pig arteries due to lack of data on the active properties of the USL and CL. Subjected to constant forces in-vivo, the structure and length of the USL and CL are sig- nificantly altered over time. In chapter 3, we present the first rigorous characterization of the fiber microstructure and creep properties of the USL/CL complex by using scanning electron microscopy and planar biaxial testing. Fibers are found to be oriented primarily along the main in-vivo loading direction. In such direction, the creep proceeds significantly faster under lower load. Overall, our experimental findings advance our knowledge about the passive elastic and viscoelastic properties of the USL/CL complex. The novel structural constitutive model proposed enhances our understanding of the active mechanical behavior of biological tissues containing SMCs. Knowledge about the mechanical behavior of the USL and CL from experimental and theoretical studies such as those presented here will help to improve, in the long term, the medical treatment for PFDs. / Ph. D.

The strength and durability of proton exchange membranes for use in fuel cells has received much attention recently due to the increased push for sustainable alternatives to the internal combustion engine. To be viable, these alternatives must have comparable lifetimes and power outputs to the internal combustion engines they replace. Chemical degradation was once viewed as the most common culprit of early fuel cell failure, but as membranes and catalysts improved, mechanical failure became an important factor. As a result, fundamental research on the mechanically-induced failure mechanisms of fuel cell membranes, coupled with development and processing of less expensive membranes, has become an important topic. The use of the blister test geometry, along with digital image correlation of the deformed shape, creates a self-contained analysis tool useful for measuring the biaxial strength of membranes. In this work, blister tests are used to measure biaxial stress and strain for fuel cell membranes subjected to ramped pressure loading to form stress-strain curves that indicate the onset of yielding under biaxial stress conditions. Stress-life curves are developed experimentally for Gore-Selec? series 57 members using data collected under constant pressure conditions. These results are used to predict blister failure under ramped and fatigue loadings. A newly implemented hydrocarbon membrane system is evaluated with constant-pressure-to-leak blister testing. Improved strength following an isothermal hold at 100°C (pretreatment) is shown to occur. Ramped pressure testing indicates that the material after the pretreatment is stiffer and has a higher yield stress than the material before treatment. Morphological and constitutive characterization indicated differences in the materials that are consistent with the improved performance. / Master of Science

This research is the first systematic investigation of solid-state orientation as a novel method for controlling drug release from biodegradable polymers. The effect of various degrees of polymer orientation was studied in oriented Poly (L-lactic acid) (PLA) films containing curcumin and theophylline as model drugs. Additionally, direction specific drug release was studied from oriented PLA rods containing paracetamol. The films oriented to 2X uniaxial constant width (UCW) or 2X2Y biaxial draw ratio showed retardation of drug release, when their nematic structure was stabilised by the presence of crystalline theophylline. Contrarily, the same films when contained solid solution of curcumin, shrunk in the release medium and exhibited a release profile similar to the un-oriented films. All films oriented to the UCW draw ratio ≥ 3X contained α crystalline form of PLA and showed acceleration of drug release proportionate to the draw ratio. According to the proposed mechanism augmented formation of water filled channels in these films was responsible for faster drug release. Similarly, the paracetamol loaded PLA rods die-drawn to uniaxial draw ratios ≥ 3X exhibited enhancement of drug release. Importantly, the amount of drug released along the oriented chain axis was significantly larger than that in the perpendicular direction. Drug release from the die-drawn rods was accelerated by a greater degree than that observed from the oriented films. This can be correlated to the differences in their size, geometry and the crystalline form of PLA. In conclusion, the current study provided substantial evidence that solid-state orientation can offer a control over drug release from PLA.

Los soportes de hormigón armado, en general, están sometidos a una ley de momentos flectores no uniforme debido a la existencia de excentricidades desiguales en sus extremos. Además, el empleo de hormigón de alta resistencia en la construcción de estructuras ordinarias está cada vez más extendida, lo que supone la fabricación de soportes más esbeltos. Sin embargo, los ensayos experimentales existentes en la literatura técnica para soportes fabricados con hormigón de alta resistencia y sometidos a excentricidades distintas en los extremos son escasos y centran su estudio en el comportamiento de soportes cortos, fabricados con hormigón convencional y bajo esfuerzos de flexo-compresión recta. Por otra parte, los códigos de diseño, en general, proponen métodos simplificados con la finalidad de predecir la carga de agotamiento de soportes esbeltos sometidos a esfuerzos de flexo-compresión con excentricidades desiguales en sus extremos. Sin embargo, los métodos simplificados han sido contrastados, en su gran mayoría, con soportes fabricados con hormigón convencional. La extrapolación de estos métodos a hormigones de alta resistencia sin un soporte científico y verificación experimental adecuados puede conducir a resultados poco fiables. En la presente tesis doctoral se ha estudiado el comportamiento de 68 soportes esbeltos sometidos a compresión con excentricidades y ángulos de esviaje desiguales en sus extremos, fabricados con hormigón convencional y de alta resistencia. Estos ensayos tienen como objetivo conocer el comportamiento de este tipo de elementos estructurales y además han de servir para poder calibrar modelos numéricos y validar métodos simplificados. La importancia de la investigación se centra en la contribución de aumentar el banco de datos experimentales disponibles con el fin de corroborar los métodos de diseño propuesto por las distintas normativas para soportes de hormigón armado sometidos a este tipo de solicitación. / Da Costa Lino Leite, LC. (2011). Estudio teórico-experimental de soportes esbeltos de hormigón armado sometidos a compresión con excentricidades y ángulos de esviaje desiguales en sus extremos [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/14178

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Strain hardening cement‐based composites (SHCC) are fibre‐reinforced composites designed to form multiple fine cracks under tensile and flexural load. The cracks are controlled to small widths, whereby significant toughness, or energy dissipation, is realised on the one hand, and high resistance to gas and liquid ingress is maintained on the other hand. These two physical phenomena define application fields of SHCC, i.e. for instance elements of buildings and infrastructure for enhanced earthquake resistance, and protection of steel bars under service loads which lead to crack formation. Also exploiting the potential protection offered by SHCC to existing structures, thin overlays have been applied to existing dam faces, reinforced concrete retaining walls, water channels and RC road pavements. The layers vary between 20 and 40 mm in thickness. Considering the fibre length, usually 8 or 12 mm, as well as the application method, such thin layers may have dominantly two dimensional fibre orientation, with little or no component in the layer thickness direction. While several research groups have performed uniaxial tensile tests and flexural tests on SHCC specimens, little or no information is available on SHCC response to biaxial loading, as is to be expected in road pavement repair layers, or other repair layers. This paper reports the results of biaxial testing of 20 mm thick SHCC specimens produced in such a way to have dominantly two‐dimensional fibre orientation, and another group of specimens produced by cutting from larger specimens, whereby three‐dimensional fibre orientation was preserved in the resulting 20 mm thick specimens. Biaxial tests were performed in three quadrants, i.e. compressioncompression, compression‐tension, and tension‐tension. A clear fibre orientation‐related difference in the failure patterns involves out‐of‐plane splitting under biaxial compression of specimens with twodimensional fibre orientation, at significantly lower load, as opposed to in‐plane tensile splitting of specimens containing three‐dimensional fibre orientation. / AFRIKAANSE OPSOMMING: Vervormingsverhardende sement‐gebaseerde saamgestelde materiale (SHCC) is veselversterke saamgestelde materiale wat ontwerp is om verskeie fyn krakies te vorm onder trekspanning en buig spanning. Die kraakbreedtes word beheer, waardeur betekenisvolle taaiheid verkry, of energie verlies beheer word aan die een kant, en die hoë weerstand teen die gas en die vloeistof penetrasie aan die ander kant gehandhaaf word. Hierdie twee fisiese verskynsels definieer die toepassingsvelde van SHCC, d.w.s vir byvoorbeeld elemente van geboue en infrastruktuur vir verbeterde aardbewing weerstand, en die beskerming van staal stawe onder die dienslaste wat lei vorming te kraak. By eksploitasie van die potensiële beskerming aangebied deur SHCC aan bestaande strukture, is dun oorlae op bestaande dam walle, versterkte beton keermure, water kanale en staal‐versterkte beton paaie gebruik. Die SHCC lae wissel tussen 20 en 40 mm in dikte. Met inagneming van die vesel lengte, gewoonlik 8 of 12 mm, sowel as die toepassingsmetode, kan so 'n dun lag ‘n oorheersend tweedimensionele vesel oriëntasie hê, met min of geen komponent in die rigting van die laag dikte nie. Terwyl verskeie navorsingsgroepe eenassige trektoetse en buigtoetse op SHCC monsters gedoen het; is daar min of geen inligting beskikbaar op SHCC se reaksie op biaksiale belasting, soos verwag kan word in die pad herstel lae, of ander herstel lae. Hierdie verslag rapporteer die resultate van die biaksiale toetsing van 20 mm dik SHCC monsters wat op so 'n manier gemaak word om dominante twee‐dimensionele vesel oriëntasie te hê, en 'n ander groep monsters wat deur die sny van groter monsters, waarvolgens die drie‐dimensionele vesel oriëntasie verseker is. Biaksiale toetse is uitgevoer in drie kwadrante, d.w.s druk‐druk, druk‐trek en trek‐trek. 'n Duidelike verskil in die falingspatrone, aan die hand van vesel oriëntasie, behels uit‐vlak splyting onder biaksiale toetsing van monsters met twee‐dimensionele vesel oriëntasie, op 'n aansienlik laer lading, in teenstelling met die in‐vlak trek splyting van monsters wat ‘n drie‐dimensionele vesel oriëntasie het.

Approved for public release, distribution is unlimited / This study evaluated dome test samples of a superplastic AA5083 aluminum alloy deformed at nominally constant strain rates under biaxial strain conditions. Dome test samples resulted from gas-pressure forming of sheet material; for this study, samples were deformed at strain rates corresponding either to grain boundary sliding or dislocation creep control of deformation. Orientation Imaging Microscopy was utilized to determine texture development, grain size and grain-to-grain misorientation angle distributions for locations located along a line of latitude of the dome samples. The goal was to identify the location of the transition from grain boundary sliding to dislocation creep. Grain boundary sliding, which dominates at lower strain rates, can be recognized by a randomized texture and a higher concentration of high disorientation angles. Dislocation creep, which dominates at higher strain rates, is characterized by fiber texture formation and development of a peak at lower angles in the grain-to-grain misorientation angle distribution. / Ensign, United States Navy

De nombreuses études ont permis de développer des modèles de plasticité cristalline rendant compte de l’anisotropie d’un monocristal. Les matériaux à solidification dirigée (DS) peuvent être simulés avec des modèles semblables, sous réserve de connaître la morphologie et l'orientation cristallographique des grains contenus dans la pièce. Pour éviter ces analyses microstructurales coûteuses, il est possible de développer des approches, déterministes ou analysant les dispersions de la réponse sur un lot de << pièces synthétiques >> résolues par la méthode des éléments finis. Dans cette étude, nous avons tenté d'apporter les outils nécessaires aux deux types de modélisation. Avant tout, un modèle du monograin de DS200+Hf a été identifié pour une gamme de température allant de l’ambiante à 1200°C. Ensuite, plusieurs montées d'échelle ont été envisagées, d'abord sur un volume élémentaire représentatif (VER) puis sur une structure tridimensionnelle (éprouvette cruciforme). Sur le VER, la réponse de plusieurs modèles micromécaniques a été confrontée à des calculs de référence utilisant la méthode des éléments finis. Puis, le comportement mécanique d'une éprouvette cruciforme en DS200+Hf a été étudié, en réalisant des essais expérimentaux biaxiaux qui, ensuite, ont permis d'évaluer les prévisions du modèle. Ces résultats amènent à s'interroger sur la modélisation adaptée aux structures oligogranulaires (i.e. constituées d’un faible nombre de grains) : faut-il mailler explicitement l'échelle locale (les grains) dans la structure ou malgré la non-séparabilité des échelles, le modèle homogénéisé continue-t-il de fournir des résultats satisfaisants ? / Various studies were aimed at developing crystal plasticity models to account for the anisotropic mechanical behaviour of single crystals. Directionally solidified (DS) materials can be modeled using such approaches, taking into account the underlying crystallographic structure. It requires the knowledge of the position, shape and crystallographic orientations of grains. To prevent heavy microstructure analyses, other models have to be developed for industrial calculations, using homogenization theory or considering a batch of synthetic pieces calculated using Crystal Plasticity Finite Elements Method (CPFEM). The aim of this thesis is to bring computational tools to carry out the two types of modeling for industrial applications. First of all, a crystal plasticity model for one grain of DS200+Hf is defined ranging from room temperature to 1200°C. Some scale transition rules, using full-field or mean-field approaches, are studied first in the theoretical case of a representative volume element (RVE) and then on tri-dimensional structures in order to access overall and local responses. For the RVE responses, micromechanical models are compared with a reference produced by CPFEM for various loadings. Moreover, the mechanical behaviour of a DS200+Hf cruciform specimen is studied. Biaxial tests with digital image correlation allow us to check the model predictions. These results raise questions about the modeling of oligogranular structures (i.e. with a small number of grains): should it be accepted that the local scale must be explicitly meshed, or, despite the fact that scale separability is not ensured, can we consider that the homogenized model still produces reliable results?