Browsing by Author "McQuigg, Thomas Dale"

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    Acoustic Analysis of Spacecraft Cavities using the Boundary Element Method
    Marshall, Peter Johannes (Virginia Tech, 2018-06-05)
    Spacecraft structures are subject to a series of load environments during their service life, with the most severe of these occurring during the spacecraft's launch and ascension through the atmosphere. In particular, acoustic loads imposed on stowed satellites within the launch vehicle fairing can result in high mechanical loads on sensitive spacecraft hardware. These acoustic loads have the potential to damage important components and as such it is necessary to accurately characterize and predict the acoustic launch environment for a given mission. This research investigates the Sound Pressure Level (SPL) that can be measured in and around spacecraft cavities resulting from a known excitation and the resultant structural responses. Linear finite element analysis (FEA) is coupled with the Boundary Element method (BEM) to analyze spacecraft acoustic environments and corresponding structural responses at low frequencies on the order of the structural modes. Analytical capability for predicting acoustic environments inside the launch vehicle has improved significantly in recent years; however, while it is easy to perform an analysis and obtain results, the modeling effort can become unnecessarily complicated and analytical data can be hard to interpret. This work seeks to alleviate unnecessary complexity in the low-frequency regime of acoustic modeling by examining the fundamentals of coupled BEM-FEM analysis and applying simplification to a spacecraft model where possible to achieve results verified against direct field acoustic testing (DFAT) methods.
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    Compression After Impact Experiments and Analysis on Honeycomb Core Sandwich Panels with Thin Facesheets
    McQuigg, Thomas Dale (Virginia Tech, 2011-05-27)
    A better understanding of the effect of impact damage on composite structures is necessary to give the engineer an ability to design safe, efficient structures. Current composite structures suffer severe strength reduction under compressive loading conditions, due to even light damage, such as from low velocity impact. A review is undertaken to access the current state-of-development in the areas of experimental testing, and analysis methods. A set of experiments on Nomex honeycomb core sandwich panels, with thin woven fiberglass cloth facesheets, is described, which includes detailed instrumentation and unique observation techniques. These techniques include high speed video photography of compression after impact (CAI) failure, as well as, digital image correlation (DIC) for full-field deformation measurements. The effect of nominal core density on the observed failure mode is described. A finite element model (FEM) is developed to simulate the experiments performed in the current study. The purpose of this simulation is to predict the experimental test results, and to conrm the experimental test conclusions. A newly-developed, commercial implementation of the Multicontinuum Failure Theory (MCT) for progressive failure analysis (PFA) in composite laminates, Helius:MCT, is included in this model. The inclusion of PFA in the present model gives it the new, unique ability to account for multiple failure modes. In addition, significant impact damage detail is included in the model as a result of a large amount of easily available experimental test data. A sensitivity study is used to assess the effect of each damage detail on overall analysis results. Mesh convergence of the new FEM is also discussed. Analysis results are compared to the experimental results for each of the 32 CAI sandwich panel specimens tested to failure. The failure of each specimen is accurately predicted in a high-fidelity, physics-based simulation and the results highlight key improvements in the understanding of honeycomb core sandwich panel CAI failure. Finally, a parametric study highlights the strength benefits compared to mass penalty for various core densities.
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    Local and Global Sensitivity Analysis of Thin Ply Laminated Carbon Composites
    Neigh, Thomas Alexander (Virginia Tech, 2024-05-14)
    Recent work in the area of composite laminates has focused on the characterization of the strength of laminates constructed from very thin plies. Interlaminar shear and normal stress components have been shown to be concentrated on the edges, the so-called edge effect, of unidirectional laminates at the interface between plies of different fiber orientation. Research has shown that decreasing ply thickness can reduce these interlaminar stress edge effects, and delay delamination in quasi-isotropic laminate specimen for laminates of equal total thickness. First ply failure stress has also been shown to increase with decreasing ply thickness. For these reasons, there has been a great deal of interest in laminated composites constructed from very thin plies. This work studies the impact of manufacturing tolerances on ply orientation on the mechanical properties of the constructed laminate. Direct Monte Carlo simulation is used to model the variance introduced in the manufacturing process. First-order variance-based sensitivity analysis using a local analysis of variance technique is used to study the contribution of each individual ply to the variation in as built mechanical properties. Variation in mechanical properties of thick-ply and thin-ply laminate designs are compared to study if thin-ply laminate designs show more or less variation than their thick-ply counterparts. This work has found potential impacts of ply angle variation on variance of as-built stiffness in laminates of different ply thicknesses. These differences are attributable to the total ply count in a laminate. For a fixed height laminate, the ply count is inversely proportional to thickness, yielding the apparent benefit of thin plies. Using thinner plies in a sub-laminar stacking arrangement, repeating a sublaminate instead of repeating plies, reduces sensitivity to manufacturing errors and would suppress tranverse failure modes.