Modules for cotton storage and transport should be constructed with a shape that will resist collecting water to maintain the quality of seed cotton during storage. Meeting this specification requires knowledge of the relationship between the applied compressive force, deformation, and time for seed cotton. Several factors were tested to determine their effects on the height and density of seed cotton during compression, creep loading, and recovery. Models were used to describe these processes. These results were used to develop an algorithm capable of providing information on module shape to the module builder operator. The initial loading density did not affect the compressed density, but a slight effect was observed in the recovered density, due to the weight of the seed cotton. Picker harvested cotton was compressed to a greater density than stripper harvested cotton, but expanded more during recovery, resulting in similar final densities. Multiple compressions increased the density, but this increase was not physically significant after the third compression. Higher moisture content increased the density seed cotton could be compressed to slightly. Viscoelastic behavior was observed; however, the effect on density was small. Both the compression and creep curves were described using mathematical models. A compression model using an asymptotic true strain measure yielded high R2 values; however, some aspect of this process remained unexplained and the equation was limited in its predictive ability. Creep behavior was described using a modified Burgers model. This model was more accurate than the creep model, although a definite trend existed in the creep model residuals. A feedback algorithm was developed based on the observation that the compressed density was primarily dependent on the mass of seed cotton and not the initial density. By measuring the compressed depth of cotton in a module and the hydraulic pressure of the tramper foot cylinder, the resulting shape of the module can be predicted. Improved loading of the module builder is necessary to produce a desirably shaped module. More seed cotton needs to be placed in the center of the module, resulting in a surface that slopes down towards the outer edges.

Thesis (M.S.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains vii, 79 p. : ill. Includes abstract. Includes bibliographical references (p. 71-79).

Thesis (Ph. D.)--Institute of Paper Chemistry, 1955. / Includes bibliographical references (p. 195-198).

The mechanical behavior of asphalt binders is nonlinear. The binders exhibit shear thinning/thickening behavior in steady shear tests and non-proportational behavior in other standard viscoelastic tests such as creep-recovery or stress relaxation tests. Moreover, they develop normal stress differences even in simple shear flows - a characteristic feature of nonlinear viscoelastic behavior. Many researchers have asserted the importance of considering the nonlinearity of the mechanical behavior of asphalt binders for accurately estimating their performance under field conditions, and for comparing and ranking them accordingly. In order to do so, it is necessary to have a robust and reliable nonlinear viscoelastic model. However, most of the models available in the literature do not capture the various features of the nonlinear response of asphalt binders accurately. Those that could are too complicated and still possess other shortcomings. Considering these issues, a new nonlinear viscoelastic model is developed here using a new Gibbs-potential based thermodynamic framework. The model is then corraborated with data from experiments in which the shear-thinning behavior and the nonproportional creep-recovery behavior were observed together. Finally, the model is used to evaluate the various criteria available for predicting rutting susceptibility of asphalt binders. Results of the analysis of the rutting prediction criteria show that each criterion characterizes the resistance to permanent strain shown by asphalt binders over a different range of applied stress - the zero-shear viscosity at very low stress levels, the Superpave criterion at very high stress levels and the MSCR test in the intermediate range of stresses.

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The focus of this research is to advance the processing techniques of fabricating scaffolds for tissue engineering and to gain a better understanding of the scaffold properties and behaviours. To achieve these objectives, the fundamental properties of two widely used biomaterials, poly(lactide-co-glycolide acid) (PLGA), poly(ε-caprolactone) (PCL), and their composites with hydroxyapatite were examined. Though increasing the mechanical properties of the bulk polymers, the addition of hydroxyapatite did not affect the thermal and viscoelastic properties, suggesting little interactions may exist between the polymer and the particles. Interestingly, though the addition of the fillers increased the mechanical properties of the bulk materials, the particles worsened the mechanical properties of gas foamed/salt leached scaffolds possibly due to the struts of the porous structure having similar thicknesses as the particles. In such a case, the filler acted as stress raisers and decreased the properties of the struts. The viscoelasticity of the scaffolds was also not affected by the fillers but was affected by the testing environment. An aqueous environment caused the PLGA, but not PCL, to transition such that the porous structure was altered. These results suggest that PLGA may not be ideal for scaffolds for load bearing applications. For electrospinning, a parametric study was performed to control the scaffold morphology, but more importantly, a novel process to fabricate 3D electrospun scaffolds was developed. The novel technique exploited the plasticizing effect of pressurized carbon dioxide on the polymer such that multiple layers of the thin meshes can be sintered together without the use of heat. The process was optimized for adhering layers of PLGA and its composite with nano-hydroxyapatite, and these scaffolds have a high open-porosity and better mechanical properties compared to the gas foamed/salt leached scaffolds. Finally, a model was derived for the viscoelasticity of the bulk materials and their scaffolds by applying fractional calculus on the classical standard linear solid model based on a system of springs and dashpots. The model fitted the data, and correlations between the static mechanical properties and the fitting parameters were found such that by performing static mechanical tests, the viscoelastic behaviours can be approximated.

The focus of this research is to advance the processing techniques of fabricating scaffolds for tissue engineering and to gain a better understanding of the scaffold properties and behaviours. To achieve these objectives, the fundamental properties of two widely used biomaterials, poly(lactide-co-glycolide acid) (PLGA), poly(ε-caprolactone) (PCL), and their composites with hydroxyapatite were examined. Though increasing the mechanical properties of the bulk polymers, the addition of hydroxyapatite did not affect the thermal and viscoelastic properties, suggesting little interactions may exist between the polymer and the particles. Interestingly, though the addition of the fillers increased the mechanical properties of the bulk materials, the particles worsened the mechanical properties of gas foamed/salt leached scaffolds possibly due to the struts of the porous structure having similar thicknesses as the particles. In such a case, the filler acted as stress raisers and decreased the properties of the struts. The viscoelasticity of the scaffolds was also not affected by the fillers but was affected by the testing environment. An aqueous environment caused the PLGA, but not PCL, to transition such that the porous structure was altered. These results suggest that PLGA may not be ideal for scaffolds for load bearing applications. For electrospinning, a parametric study was performed to control the scaffold morphology, but more importantly, a novel process to fabricate 3D electrospun scaffolds was developed. The novel technique exploited the plasticizing effect of pressurized carbon dioxide on the polymer such that multiple layers of the thin meshes can be sintered together without the use of heat. The process was optimized for adhering layers of PLGA and its composite with nano-hydroxyapatite, and these scaffolds have a high open-porosity and better mechanical properties compared to the gas foamed/salt leached scaffolds. Finally, a model was derived for the viscoelasticity of the bulk materials and their scaffolds by applying fractional calculus on the classical standard linear solid model based on a system of springs and dashpots. The model fitted the data, and correlations between the static mechanical properties and the fitting parameters were found such that by performing static mechanical tests, the viscoelastic behaviours can be approximated.

The purpose of this thesis is to provide an overview of ETFE foil, as it applies to pneumatic cushion cladding, with a focus on creep behavior of the material. Characteristics of ETFE, including weight, optics, insulation, flexibility, environmental properties, fire performance, cushion span and other features are discussed, and, where possible, are compared to the characteristics of glass panels used in similar applications. Relevant chemical and mechanical properties of ETFE are given. Load carrying concepts of tension structures and inflated cushions are discussed, as well as structural design methods for ETFE cushions. Several prominent structures constructed using ETFE foil are introduced and benefits and design issues associated with these structures are reviewed. When used in cushion applications, ETFE films are placed in constant tension, and are therefore subject to creep. Quantifying this creep is desirable so that it can be predicted during the design phase. Therefore, this thesis summarizes the findings of other researchers in the area of creep of ETFE as well as the general mechanical behavior of the material, and presents the results of uniaxial creep tests done for the purpose of this study. These tests included 24 hour uniaxial creep tests done at four stress levels on both the transverse and longitudinal directions of three different brands of film. Two thicknesses of the third film were acquired and both were tested. The stress levels were chosen to coincide with typical design tensile stresses for ETFE film, and to be similar to the levels tested by other researchers. The effects of the different stresses, brands, directions and thicknesses are evaluated and discussed. Three seven day creep tests were also done on one of the films, each at a different stress level. Constitutive viscoelastic and viscoplastic models were developed to represent the 24-hour creep data. The viscoelastic models were based on a four-element Kelvin model and the viscoplastic models were based on a power-law model. The model parameters were determined from the data using linear least squares fitting. Models were also developed for the seven day creep data. Several of these models were based only upon the first 24 hours of data, and were used to determine the applicability of the 24-hour creep models to long-term behavior. It was found that while a viscoelastic model appears to fit long-term creep most closely, the 24-hour models are inadequate for modeling longer time frames. Another method is required for predicting long-term creep. Nonlinear fitting of the parameters is recommended as a possible alternative for creating more accurate models. Longer-term creep tests are also recommended. Tensile tests were also done on the films to confirm mechanical properties supplied by the film manufacturers. Good agreement to the given values was found in the test data.