Fibre-reinforced composites usually exhibit anisotropy of
thermal as well as mechanical properties. For example, in
a unidirectional carbon fibre-reinforced plastic of 60%
volume fraction, the longitudinal thermal conductivity may
be greater than that in the transverse direction by a factor
of 50, and greater than that of the unreinforced polymer by
more than two orders of magnitude.
In order to evaluate the engineering applications of thermal
anisotropy, this thesis concentrates on the development and
validation of a generalised finite element model of heat
conduction in an anisotropic medium. This uses a variational
formulation of the anisotropic time-dependent heat
conduction equation, and is implemented for two and threedimensional
quadratic finite elements. The model may be
used for the solution of problems having any combination of
steady or time-dependent boundary conditions (fixed
temperature, convection, radiation, heat flux and internal
heat generation), as well as nonlinear properties. Anisotropy
is specified by the components of the two or threedimensional
thermal conductivity tensor; efficient representation
of nonhomogeneous materials is achieved by the
specification of properties at element integration points.
Theoretical validation of the model is carried out by means
of a number of mathematical solutions to orthotropic and
anisotropic problems. Experimental validation is performed
by comparison of calculations with measured steady-state
surface temperatures on a cylindrical specimen of unidirectional
carbon fibre-reinforced epoxy resin. The thermal
property data for this exercise are obtained from measurements
of principal thermal conductivities on absolute and
comparative steady-state apparatus.
The use of the finite element model in two industrial
applications is briefly described. These concern thermal
cycling during composite fabrication with reinforced
thermoplastic tape, and an analysis of heat transfer in a
composite propeller blade.
Date of Award | Oct 1985 |
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Original language | English |
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Awarding Institution | |
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Anisotropy of Heat Conduction in Fibre-Reinforced Composites
Grove, S. (Author). Oct 1985
Student thesis: PhD