The focus of the research is to develop a consistent and repeatable method to evaluate the coefficient of thermal expansion (CTE) of carbon fibers at high temperatures. Accurate measurement of the CTE of carbon fibers is essential to understand and develop optimal processing procedures as well as computational simulations to predict properties and allowables for fiber-reinforced composites. The mismatch between the coefficient of thermal expansion of the fiber and the matrix has a profound impact on the development of residual stresses and the subsequent damage initiation and progression, potentially diminishing the performance of composite structures. In situ transmission electron microscopy (TEM) is selected to perform the experimental work on account of the high resolution and the capability of evaluating both the longitudinal and transverse CTE. The orthotropy in the CTE is tested by rotating the fibers through 45° about their axis. The method is validated by testing standard tungsten filaments of known CTE. Additionally, the microstructure of the fibers is studied in a field emission scanning electron microscope as well as through selected area diffraction patterns in a TEM to observe presence of any potential orthotropy. The pitch based P55 fiber revealed a cylindrically orthotropic microstructure, but the PAN based IM7 and T1000 fibers did not reveal any orthotropy. Finite element models of hexagonally arranged IM7 fibers in a 977 epoxy matrix are developed using PATRAN and analyzed using the commercial FEA code ABAQUS 6.4. The fiber properties were considered temperature independent where as the matrix properties were varied linearly with temperature. The lamina properties evaluated from the finite element modeling are in agreement with the experimental results in literature within 10% in the temperature range of room temperature to the stress free temperature of the epoxy, however at cryogenic temperatures the difference is greater. The residual stresses developed during processing of the composite indicated a potential location for fiber matrix debonding to be in the matrix dominant regions.

¡@¡@The purpose of thesis is to study the responses of nanoindentation in fused silica. By experiments the mechanical properties of intrinsic fused silica were obtained. From the finite element simulation the response of material was estimated. Our main work is on simulation. This part includes the effects of different coefficient of friction, different indentation depth, tip rounding, and substrates of thin films. ¡@¡@First, the experimental load¡Vdisplacement curves were obtained through the nanoindentation sensing system. Then, a three-dimensional finite element was successfully modeled through the comparison of the load¡Vdisplacement curves of the experiment and the simulation. The yield stress and the strain-hardness trend of intrinsic fused silica were obtained. ¡@¡@For different coefficient of friction and different tip radii, no significant differences were found through the load¡Vdisplacement curves and von Mises stress distributions. For different indentation depths, varied trends were found through the load¡Vdisplacement curves and von Mises stress distributions. For substrate effect, no significant differences could be found through the normalized hardness. The intrinsic film hardness could be obtained for indentation depth less 20% of the total indentation depth.

This paper is to study the scattering problem and radiation problem between incident wave and a moored dual pontoon platform by using both a fully nonlinear numerical wave tank (NWT) and a physical tank. The nonlinear numerical wave tank is developed based on the velocity potential function and the boundary element method (BEM). In addition, a moored dual floating pontoon physical model is tested in an experimental wave tank to validate the numerical model for simulation of wave and structure interaction including mooring tension, structure translation and rotation. The phenomena of wave reflection and transmission due to a floating platform are also considered in the study. The experimential results indicate that the platform surge-RAO decays as the wave frequency increases. Similarly, the platform heave-RAO decays first until at the vicinity of the resonance frequency happening where the vertical amplitude rises up and then decays again. The tension-RAO has two resonance frequencies, the lower resonance is resulted by the surge montion, while the higer resonance is caused by the heave motion. Both wave reflection and transmission coefficients decrease near the heave resonance frequency. This indicates that the platform has the best performance in wave shelter effect at heave resonance to protect costal zone. In general, the comparisons of the numerical simulations and experimental results indicate the numerical horizontal motion have a good agreement, but for the vertical motion, the numerical predictions are larger than experiments especially near the heave resonance frequency. This may be due to the structure vertical velocity increases dramatically causing flow separation occurred below the structure sharp corner, thus the fluid viscous damping effect may play an important role in heave motion.

The present study developes a mixed finite element formulation for the analysis of piezoelectric circular and annular plates. This formulation combines the conventional displacement-electric potential type variational principle and the piezoelectric Reissner`s principle with a weighting factor which represents ratio of weights imposed on the above two variational principles, and which can be adjusted by comparing with experiment results. With this formulation, stresses and electric displacements, like displacements and electric potential, are primary variables and are continuous across elements and element interfaces. Also, all displacement, stress, electric displacement, and electric potential boundary conditions can be easily and exactly imposed. Static deformations and vibration frequencies of some typical piezoelectric circular and annular plates are then obtained with the present approach and are compared with those by other methods. Based on experiment results in the literature, it is found that better results could be obtained in general by the present mixed finite element formulation than the others when 1 is chosen as the weighting factor.

The user programmable features (UPF) of the finite element code ANSYS® are used to generate a customized ANSYS-executable including a more general creep behaviour of materials and a damage module. The numerical approach for the creep behaviour is not restricted to a single creep law (e.g. strain hardening model) with parameters evaluated from a limited stress and temperature range. Instead of this strain rate - strain relations can be read from external creep data files for different temperature and stress levels. The damage module accumulates a damage measure based on the creep strain increment and plastic strain increment of the load step and the current fracture strains for creep and plasticity (depending on temperature and stress level). If the damage measure of an element exceeds a critical value this element is deactivated. Examples are given for illustration and verification of the new program modules.

Ziel der Arbeit ist es, auf der Basis von Messungen ein rheologisches Materialmodell für technische Gummiwerkstoffe zu erstellen, welches deren Eigenschaften nachbildet, insbesondere vorhandene komplexe Zusammenhänge zwischen Relaxation, Erholung, Versuchsgeschwindigkeit und Belastungsamplitude. Dabei wird sich auf die Simulation von großen einfachen, aber beliebigen Scherverformungen beschränkt, woraus ein skalarwertiges Modell resultiert. Anwendung finden generalisierte Maxwell-Elemente und generalisierte kontinuierliche Prandtl-Elemente. Verschiedene Modellvarianten werden diskutiert. Es wird ein Berechnungsprogramm unter MATLAB erstellt.

Thesis (Ph. D.)--Lehigh University, 2000. / Includes bibliographical references and vita.

Thesis (M.S.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains vii, 93 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 71-75).

Thesis (Ph.D.)--Memorial University of Newfoundland, 2001. / Bibliography: leaves 146-152.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: correlation; modal analysis; valve train. Includes bibliographical references (p. 157-158).