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Utilization of modernized global navigation satellite systems for aircraft-based navigation integrity.

机译：利用现代化的全球导航卫星系统实现基于飞机的导航完整性。

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The objective of this dissertation is to assess whether or not two particular biocomposite materials, made from hemp fabric and cellulose acetate or polyhydroxybutyrate matrices, are capable of being used for structural and/or construction purposes within in the construction and building industry. The objective of this dissertation was addressed by conducting research to meet the following three goals: (1) to measure the basic mechanical properties of hemp/cellulose acetate and hemp/PHB biocomposites and evaluate if they suitable for use in construction applications, (2) to determine how quickly moisture diffuses into the biocomposite materials and how the moisture affects the mechanical behavior, and (3) to determine how well simple models can predict behavior of structural scale laminates in tension and flexure using biocomposite ply behavior.;Compression molding was used to manufacturing the biocomposites from hemp fabric and the themoplastic matrices: cellulose acetate and polyhydroxybutyrate. Four methods for determining the fiber volume fraction were evaluated, and the dissolution method, using different solvents for each matrix type, was used to determine the fiber volume fraction for each composite plate manufactured. Both types of biocomposite were tested in tension, compression, shear, and flexure and the measured properties were compared to wood and engineered wood products to assess whether the biocomposite properties are suitable for use in the construction industry. The biocomposites were conditioned in a humid environment to determine the rate of moisture diffusion into the materials. Then saturated specimens and specimens that were saturated and then dried were tested in tension to evaluate how moisture absorption affects the mechanical behavior of the biocomposites. Finally, simple models of laminate behavior based on laminate plate theory were evaluated to determine if ply level behavior could be used to predict structural scale laminate behavior.;While the biocomposite strengths in flexure, compression, and shear were comparable to the strengths of wood and wood-based products parallel to grain, the biocomposite strengths exceeded the strengths perpendicular to the wood grain, as would be expected with fabric reinforcement. The biocomposite moduli of elasticity were between 35% and 75% of the wood moduli parallel to grain. While structural shape of the biocomposites could be manipulated to achieve a comparable structural stiffness to replace wood and short fiber FRPs, the biocomposites have comparable stiffness to the engineered wood-products. Thus, in terms of mechanical properties, the biocomposites can be used in place of engineered-wood products. Yet, the higher densities of the biocomposites as compared to wood and engineered-wood products may limit their implementation in construction.;The diffusion coefficients for both biocomposites were comparable to wood and higher than the coefficients for synthetic composites as expected due to the hydrophilicity of the natural fibers. Significantly greater moisture absorption of the hemp/cellulose acetate composite as compared to the hemp/PHB composite was attributed to the cellulose acetate itself being hydrophilic whereas PHB is hydrophobic. The rate of diffusion for both materials was found to increase with increasing temperature. Moisture absorption negatively affected the biocomposites as shown through lower initial stiffnesses and higher strains at failure of saturated specimens. The hemp/cellulose acetate composites were much more affected by moisture absorption than the hemp/PHB composites likely because the moisture plasticized the cellulose acetate and also weakened the interfacial fiber-matrix bond. Moisture was assumed to cause permanent damage because the stress-strain behavior did not return to the unconditioned behavior upon drying of the saturated specimens. The degradation of mechanical properties upon introduction to humid environments limits the potential applications of these biocomposites. For these biocomposites to be used widely within the construction industry, they must therefore be protected from moisture for example through sealants and/or fiber treatments.;Classical laminate plate theory was shown to be effective in predicting the initial linear behavior of all of the laminates in tension and flexure, but did not capture stiffness degradation or the full nonlinear stress-strain response of the biocomposites because the model was for linear elastic materials. Use of this model would be appropriate for design of deflection-limited applications within certain stress ranges. The modified nonlinear laminate plate theory predicted the initial stress-strain response well, but at higher strains overestimated the strength and stiffness. The overestimation was attributed to the constitutive model assuming uncoupled stress-strain behavior for each strain component and, additionally in flexure, to the use of tensile behavior as the constitutive behavior in compression. While the simple models provided an adequate prediction of laminate behavior at low strains, to predict behavior at higher strains, it is recommended instead to evaluate the use of finite element analysis to predict response using experimental stress-strain as models for orthotropic materials and non-linear behavior are well-established. (Abstract shortened by UMI.)
机译：本文的目的是评估由麻织物和醋酸纤维素或聚羟基丁酸酯基体制成的两种特定的生物复合材料是否能够在建筑和建筑行业中用于结构和/或建筑目的。通过满足以下三个目标的研究，实现了本文的目的：（1）测量大麻/醋酸纤维素和大麻/ PHB生物复合材料的基本力学性能，并评估它们是否适合用于建筑应用，（2）确定水分扩散到生物复合材料中的速度有多快，以及水分如何影响机械性能，以及（3）确定利用生物复合层的行为，简单的模型如何很好地预测结构尺度层压板在拉伸和挠曲中的行为。由大麻织物和热塑性基质生产生物复合材料：醋酸纤维素和聚羟基丁酸酯。评估了四种确定纤维体积分数的方法，并使用了每种基质类型使用不同溶剂的溶解方法来确定制造的每个复合板的纤维体积分数。对两种类型的生物复合材料均进行了拉伸，压缩，剪切和挠曲测试，并将测得的性能与木材和人造木产品进行了比较，以评估该生物复合材料的性能是否适用于建筑行业。在潮湿的环境中调节生物复合材料，以确定水分扩散到材料中的速率。然后，对饱和样品和先饱和后干燥的样品进行张力测试，以评估水分吸收如何影响生物复合材料的机械性能。最后，评估了基于层压板理论的简单的层压板行为模型，以确定是否可以使用层级行为来预测结构规模的层压板行为。;同时，弯曲，压缩和剪切的生物复合强度可与木材和木材的强度相媲美。与谷物平行的木质产品，其生物复合材料的强度超过了垂直于木质谷物的强度，这是织物增强所期望的。生物复合材料的弹性模量介于平行于木纹的木材弹性模量的35％至75％之间。尽管可以操纵生物复合材料的结构形状以达到可替代木材和短纤维FRP的相当的结构刚度，但生物复合材料的刚度与工程木制品相当。因此，就机械性能而言，可以使用生物复合材料代替工程木产品。然而，与木材和人造木制品相比，生物复合材料的密度较高可能会限制其在建筑中的应用。由于两种材料的亲水性，两种生物复合材料的扩散系数均与木材相当，并且高于合成复合材料的扩散系数。天然纤维。与大麻/ PHB复合材料相比，大麻/醋酸纤维素复合材料的吸湿性明显更高，这归因于醋酸纤维素本身是亲水的，而PHB是疏水的。发现两种材料的扩散速率均随温度升高而增加。吸湿对生物复合材料产生负面影响，如饱和样品破坏时的较低初始刚度和较高应变所显示。大麻/醋酸纤维素复合材料比大麻/ PHB复合材料受水分吸收的影响更大，这可能是因为水分使醋酸纤维素增塑并且还削弱了界面纤维与基质的键合。假定水分会造成永久性损坏，因为在干燥饱和样品后应力应变行为不会恢复为无条件行为。引入潮湿环境后机械性能的下降限制了这些生物复合材料的潜在应用。为了使这些生物复合材料在建筑行业中得到广泛使用，因此必须通过例如密封胶和/或纤维处理等措施保护其免受潮气的影响；经典的层压板理论被证明可有效预测所有层压板的初始线性行为拉伸和挠曲性，但没有捕获生物复合材料的刚度退化或完整的非线性应力-应变响应，因为该模型适用于线性弹性材料。使用此模型将适合在某些应力范围内设计挠度受限的应用。改进的非线性层压板理论可以很好地预测初始应力-应变响应，但是在较高的应变下会高估强度和刚度。高估归因于本构模型，假设本构模型假定每个应变分量的应力-应变行为不耦合，而且在挠曲中，使用拉伸行为作为压缩中的本构行为。虽然简单的模型可以对低应变下的层压板行为进行充分的预测，而可以预测较高应变下的行为，但建议改为使用有限元分析来评估使用实验应力应变作为正交各向异性材料和非正交各向异性模型的响应线性行为是公认的。 （摘要由UMI缩短。）

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