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This work originated from a need for understanding heat transfer in carbon-fiber/epoxy natural-gas tanks undergoing rapid heating during refilling. The dissertation is focused on the determination of the anisotropic thermal properties of carbon-fiber/epoxy composite materials for in-plane and through-thickness directions. An effective anisotropic parameter estimation system consisting of the 3ω experimental technique and an anisotropic two-dimensional heat transfer model is developed.
In the present work, the 3ω method, an experimental technique that has been well established to evaluate the thermal properties of isotropic materials, especially thin film materials, is extended to treat the thermal properties of bulk anisotropic materials. A platinum film deposited on the sample surface is periodically heated by a sinusoidally oscillating current at frequency ω, and thereby causes a time-harmonic electrical resistance variation at frequency 2ω. The heat-induced resistance variation at frequency 2ω coupled with the current at frequency ω produces a voltage variation component at frequency 3ω. The phase and amplitude data of the voltage signal at frequency 3ω are collected from the experiment. An impedance analysis model is employed to convert the voltage data to temperature data.
The anisotropic thermal properties are deduced from an inverse parameter estimation model, which is a least-square systematic comparison between experimental data and the theoretical model. The anisotropic theoretical model is based on the Green’s function approach. A careful sensitivity analysis is used to demonstrate the feasibility of simultaneous estimation of the in-plane and through-thickness thermal conductivities. Poly methyl methacrylate (PMMA) samples were applied as reference samples to verify the measurement system. The parameter estimation result for experimental data from PMMA samples agree very well with handbook values. Experimental results from carbon-fiber/epoxy samples are presented.
Advisor: Kevin D. Cole