<p>In order to better understand work hardening behavior of pure magnesium, latent hardening experiments with magnesium single crystals were carried out. Large magnesium single crystal samples were first deformed in tension, and subsequently sectioned for secondary tension tests. Three different initial crystallographic orientations of magnesium single crystals were prepared: crystals A and B were oriented for basal <a> slip, while crystal C was oriented for {1 012} twinning. The latent hardening test from type A and B crystals revealed that the LHR in coplanar system arising from basal - basal dislocations interactions was close to unity, whereas the LHR in non-coplanar system arising from basal - 2nd order pyramidal dislocation interactions was around 15. The interactions between {1012} twins and various slip dislocations were investigated using type C crystals. It was found that the {10 12} twins contributed to large strain hardening from at least a dynamic Hall - Petch mechanism. However, the role of {10 12} twins is complicated and further studies to understand the hardening mechanism due to {10 12} twinning are necessary.</p> / Master of Science (MS)

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Indentation is a useful technique for studying the mechanical properties of a material. Measurable mechanical properties from indentation include time-dependent as well as time independent properties. Among these mechanical properties, time-dependent permanent deformation (creep) is of interest in this study. The purpose of this study is to explore the behavior of creep deformation of a solid under indentation. The main scientific research tool will be the finite element method. Existing works by others provide limited solutions that allow us to correlate uniaxial creep to indentation creep. In this study, the task is taken a step further to enhance and modify previous solutions to more realistic indentation situations. Indentations with spherical and conical indenter geometries are considered. Practical data obtained from indentation creep are usually in the form of displacement (h) – time (t) or load (P) – displacement (h). Results in this study are derived to describe this behavior and obtain fundamental creep parameters from it. Elasticity may not be ignored in the majority of indentation situations. Therefore, the effect of finite elastic deformation is considered in this study with the intention of characterizing elastic transient phenomena. From the results, certain criteria in terms of an experimentally measurable parameter will be suggested in order to avoid misinterpreting indentation data influenced by the initial elasticity. The effect of finite strain – finite deformation in indentation is investigated. Creep solutions provided by others usually assume infinitesimal strain – infinitesimal deformation. As a result, only blunt cones approaching the geometry of a flat punch indenter have been considered for the most part in previous works. In this study, the problem of finite strain – finite deformation is addressed for conical indentation. Various half-included cone angles of the indenter are considered to account for finite strain – finite deformation problems. The power law relation is the most common general description of creep deformation when strain rate and steady-state stress are involved. However, power law breakdown, due to large strain rates and stresses may occur during the initial parts of indentation, especially for conical indenters. Modeling of power law breakdown in indentation creep is presented and corresponding relations between uniaxial to indentation creep behavior are proposed in this study.

Focus of this research is on developing cotton-based nonwoven mattress pads with flame retardant (FR) properties by blending cotton with other commercially available fibers, binders, and followed by chemical treatments; offering a cost-effective recipe to meet the upcoming flammability standards. Furthermore this research explores the opportunities taking advantage of possible synergistic effects to achieve maximum performance. Recent changes in the flammability regulations require improvements in the flame resistance of cotton-containing consumer goods such as upholstered furniture, mattresses, and pillows. Cotton, synthetic fibers, fabrics, and foam are the basic constituents of these goods that are often the first to be engulfed by fire. Hence there is a need to impart certain degree of flame resistance based on their end use. In case of real fires, these improvements in flame retardancy would provide more time for people to escape from a fire with fewer injuries, and result in savings of life as well as property. Cotton being a highly flammable fiber, to achieve higher degree of flame resistance, it is necessary to incorporate additional fibers and chemicals into cotton products. Choice of appropriate materials can help to achieve a synergistic role in the combustion process to slow down burning, reduce flame spread, or even extinguish the fire. Many of these chemicals are expensive and lead to a spike in the product cost. Moreover there are certain FR chemicals that are likely to pose environmental and health hazards. The FR chemicals used in this research are halogen free and have been considered safe. Finally, a cost effective recipe for constructing mattress pads that passes the latest flammability tests was developed. As planned, these nonwoven pads were produced by blending cotton with other commercially available fibers, binders, and followed by chemical treatments that take advantages of various synergistic effects to achieve maximum performance at low cost. The product of this research is a good candidate for mattress pads as well as other products such as upholstered furniture, mattress ticking, and pillows, which are required to comply with the open flame standards.