Browsing by Author "Pandurangan, Pradeep"

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    Defect Identification in GRID-LOCK(R) Joints
    (2006-12-21) Pandurangan, Pradeep; Dr. Kara J. Peters, Committee Member; Dr. Fuh-Gwo Yuan, Committee Member; Dr. Mohammed N. Noori, Committee Member; Dr. Gregory D. Buckner, Committee Chair
    Bonded metallic GRID-LOCK® structures are being adopted for a variety of aerospace applications due to their structural efficiency and damage tolerance. The development of non-destructive evaluation (NDE) methods is necessary to identify bond defects that can lead to failures in these structures. However, this task is complicated by the lack of interior access and complex geometry of GRID-LOCK® components. In this dissertation, the feasibility of various NDE techniques for detecting the existence, location, and extent of bond defects in GRID-LOCK® joints is investigated. Experiments are conducted on customized test structures to compare the effectiveness of optical NDE, ultrasonic C-scans and vibration-based damage detection. Finite element analysis (FEA) is used to interpret experimental results and highlight the advantages of candidate methods. The qualitative effectiveness of optical NDE is further investigated using full-field surface slope measurements (shearography). Because accurate characterization of structural defects is critical to flight safety, a quantitative non-destructive evaluation (QNDE) method using artificial neural networks (ANNs) is developed. This method involves the use of radial basis function networks (RBFNs) trained and validated using FEA simulation data. The effectiveness of this QNDE approach is demonstrated using experimental data from a custom-built optical scanning system.
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    Mechanics of fabric drape
    (2004-07-08) Pandurangan, Pradeep; Dr. Eric Klang, Committee Member; Dr. Traci May-Plumlee, Committee Member; Dr. Jeffrey Eischen, Committee Chair
    Three dimensional virtual representations of fabrics done based on particle modeling lack accuracy in their representation of various fabrics due to very little understanding of how fabric mechanical properties affect drape. Particle models represent cloth as a mesh of particles connected by springs. The springs exert forces on the particles causing them to move thus representing the deformation of fabric. The spring constant values input to the simulation correspond to the mechanical properties of the modeled fabric. Fabric mechanical property values obtained from standard testing like the Kawabata evaluation cannot be input directly to the particle modeling software to produce simulations resembling reality. A systematic way of selecting various input parameters to the particle model is developed by comparison of 3D scans of the drape of simple forms of various fabrics to matching simulations produced by the particle model. Since drape is a complex function of many unpredictable variables a simple way of varying only a few parameters in simulations without compromising on their resemblance to reality has been developed. Subtle and not-so-subtle differences in drape shapes occur each time a fabric is draped. This nearly random behavior presents a challenge for deterministic modeling approach. Criterions are developed based on drape variability studies for the classification of a simulation as a good match to reality or not and a relationship is developed between measured fabric material properties and simulation input parameters. The relationship was then tested on more complex apparel and found to produce excellent results. A theoretical approach was developed to determine how various spring constants that are input to the particle model simulation affect drape shapes. A simplified 2D (a strip of particles) version of the particle model was programmed in order to compare its deformation with that of a cantilever beam undergoing large deflections. By comparing the deflection of the particle model beam to the theoretical results a relationship was developed between material constants input to the simulated particle model beam and the standard material constants for a beam such as modulus of elasticity.