Fiber Metal Laminates (FML) are hybrid composites with alternate layers of orthotropic fiber reinforced polymers (FRP) and isotropic metal alloys. FML can exhibit a nonlinear thermo-viscoelastic behavior under the influence of external mechanical and non-mechanical stimuli. Such a behavior can be due to the stress and temperature dependent viscoelastic response in one or all of its constituents, namely, the fiber and matrix (within the FRP layers) or the metal layers. To predict the overall thermoviscoelastic response of FML, it is necessary to incorporate different responses of the individual constituents through a suitable multi-scale framework. A multi-scale framework is developed to relate the constituent material responses to the structural response of FML. The multi-scale framework consists of a micromechanical model of unidirectional FRP for ply level homogenization. The upper (structural) level uses a layered composite finite element (FE) with multiple integration points through the thickness. The micromechanical model is implemented at these integration points. Another approach (alternative to use of layered composite element) uses a sublaminate model to homogenize responses of the FRP and metal layers and integrate it to continuum 3D or shell elements within the FE code. Thermo-viscoelastic constitutive models of homogenous orthotropic materials are used at the lowest constituent level, i.e., fiber, matrix, and metal in the framework. The nonlinear and time dependent response of the constituents requires the use of suitable correction algorithms (iterations) at various levels in the multi-scale framework. The multi-scale framework can be efficiently used to analyze nonlinear thermo-viscoelastic responses of FML structural components. The multi-scale framework is also beneficial for designing FML materials and structures since different FML performances can be first simulated by varying constituent properties and microstructural arrangements.

Low frequency mechanical vibrations (<100 Hz) are naturally generated by skeletal muscles during voluntary contractions. Recording of these vibrations at the muscle surface are called surface mechanomyograms (S-MMGs). In this study, S-MMGs were recorded over a 3 x 5 grid of skin mounted accelerometers on the biceps brachii muscle during submaximal voluntary isometric contractions with the arm in a pronated position for ten healthy and young male subjects with no overt sign of neuromuscular diseases. For a given pair of accelerometers, the spatial coherence of S-MMG is a measure of the similarity of the S-MMG signals propagating between those two sensors. Two common techniques to estimate the spatial coherence for narrowband S-MMG signals, namely the magnitude squared coherence function and the maximum of the time-domain cross-correlation function, were found to yield similar results. In particular, high spatial coherence values were measured for sensor pairs aligned along the proximal to distal ends of the biceps, i.e. the longitudinal direction. On the other hand, the spatial coherence values for sensor pairs oriented perpendicular to the muscle fiber, i.e. along the transverse direction, were found to be significantly lower. This finding indicates that coherent S-MMGs were mainly propagating along the muscle fibers direction (longitudinal) of the biceps brachii within a frequency band varying between 10Hz to 50Hz. Additionally, the spatial coherence of S-MMGs along the longitudinal direction was found to decrease with increasing frequency and increasing sensor separation distance and to increase with contraction level varying between 20% to 60% of the maximum contraction level.

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This thesis focuses on the generation of fine cell polymer foams using a heterogeneous nucleating agent (nanoclay), appropriate polymer blending strategies and accurate control of foam processing parameters. Foaming behaviour of HMSPP/ clay nanocomposites and HMS-PP/EVA/clay nanocomposite blends is studied using a batch and a continuous foam injection moulding system. Morphological studies using TEM and SEM led to a few interesting deductions. It is very difficult to attain complete exfoliation in case of HMS-PP/clay nanocomposites even at low clay loadings due to a non polar nature and low graft efficiencies of HMS-PP matrix. The addition of clay to an immiscible blend of HMS-PP/EVA results in compatibilization between the dispersed and the continuous phase. Nanocellular foams (290 nm) were subsequently generated in the batch process at a foaming temperature of 147oC and 25 seconds foaming time. The addition of immiscible EVA-28 to the HMS-PP matrix in presence of clay particles further results in reduction of foam cell sizes to 100 nm. The effect of gas concentration, foaming temperature, injection pressure, and foaming time on foam cell size was studied. It was found that the foam cell size was highly sensitive to the injection pressure at the mould gate (hence pressure drop rate) and foaming temperature. The cell size linearly decreased with increase in gas concentration and foaming time. The sensitivity of foam cell sizes to changes in processing parameters decreases with increase in clay concentration. The effect of addition of clay particle on gas solubility was modelled using the Guggenheims contact fraction approach and subsequently a new model to predict gas solubility was developed using statistical thermodynamic tools. Additionally the effect of shear and extensional rheology on foam cell morphology was modelled. It was found that the viscoelasticity of the polymer matrix greatly affects cell sizes as compared to extensional viscosity.

Thesis (M.S.)--University of Delaware, 2007. / Principal faculty advisor: Kausik Sarkar, Dept. of Mechanical Engineering. Includes bibliographical references.

Thesis (Ph. D.)--Lehigh University, 1999. / Includes vita. Includes bibliographical references (leaves R1-6).

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisor: Kenneth M. Liechti. Vita. Includes bibliographical references. Also available from UMI.

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 110-112). Available also in a digital version from Dissertation Abstracts.