This thesis is for the investigation of the design and analysis processes of filament wound composite tubes under combined loading. The problem is studied by using a computational tool based on the Finite Element Method (FEM). Filament wound tubes are modeled as multi layered orthotropic tubes. Several analyses are performed on layered orthotropic tubes by using FEM. Results of the FEM are examined in order to investigate characteristics of filament wound tubes under different combined loading conditions. Winding angle, level of orthotropy and various ratios of the loading conditions were the main concerns of the study. The results of the FEM analysis are discussed for each loading condition. Both pure loading and combined loading analysis results were consistent with the ones mentioned in literature, such as optimum winding angles, optimum loading ratios and optimum level of orthotropy. Modeling parameters, assumptions and source of errors are also discussed. Finally, the required data is obtained for the design of filament wound composite tubes under combined loading.

<div> <p>Fiber reinforced polymer composites are widely used in manufacturing advanced light weight structures for the aerospace, automotive, and energy sectors owing to their superior stiffness and strength. With the increasing use of composites, there is an increasing need to monitor the health of these structures during their lifetime. Currently, health monitoring in filament wound composites is facilitated by embedding piezoelectrics and optical fibers in the composite during the manufacturing process. However, the incorporation of these sensing elements introduces sites of stress concentration which could lead to progressive damage accumulation. In addition to introducing weak spots in the structure, they also make the manufacturing procedure difficult. </p> <p> </p> <p>Alternatively, nanofiller modification of the matrix imparts conductivity which can be leveraged for real time health monitoring with fewer changes to the manufacturing method. Well dispersed nanofillers act as an integrated sensing network. Damage or strain severs the well-connected nanofiller network thereby causing a local change in conductivity. The self-sensing capabilities of these modified composites can be combined with low cost, minimally invasive imaging modalities such as electrical impedance tomography (EIT) for damage detection. To date, however, EIT has exclusively been used for damage detection in planar coupons. These simple plate-like structures are not representative of real-world complex geometries. This thesis advances the state of the art in conductivity-based structural health monitoring (SHM) and nondestructive evaluation (NDE) by addressing this limitation of EIT. The current study will look into damage detection of a non-planar multiply connected domain – a filament-wound glass fiber/epoxy tube modified by carbon black (CB) filler. The results show that EIT is able to detect through holes as small as 7.94 mm in a tube with length-to-diameter ratio of 132.4 mm-to-66.2 mm (aspect ratio of 2:1). Further, the sensitivity of EIT to damage improved with decreasing tube aspect ratio. EIT was also successful in detecting sub-surface damage induced by low velocity impacts. These results indicate that EIT has much greater potential for composite SHM and NDE than prevailing work limited to planar geometries suggest.</p> </div> <br>