A numerical study on the thermal expansion coefficients of fiber

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coefficients of thermal expansion of the orthotropic unidirectional lamina must be
known for design purposes. These composite properties can be experimentally
measured, which can be expensive and time consuming when evaluating many
different material systems, or predicted using the thermal and mechanical properties
of the constituents. Furthermore, as a result of the increasing computer technology,
<strong>numerical</strong> solutions such as finite element analysis are being used to determine the
thermal expansion coefficients of composite materials. Since polymer matrix
materials typically exhibit thermal expansion coefficients which are much higher
than those of fibers and the fiber may be thermally as well as mechanically
anisotropic, complex stress states are induced in the composite due to temperature
changes.
The problem of relating effective mechanical properties of fiber reinforced
composite materials to constituent properties has received considerable attention.
Many analytical models exist for the prediction of the coefficients of thermal
expansion for unidirectional composites. In the first half of the 20 th century the
mathematical complexity of the analysis in the various theories had been ranging
from the simple netting analysis to sophisticated statistical methods. The various
assumptions underlying these theories were not always explicitly stated. In general
they tended to be unrealistic simplifications of the physical state of the materials.
These simplifications resulted in theories which do not have satisfactory correlation
with experimental data. To obtain better theory-experiment correlation, some of the
investigators introduced correction factors. But application of these theories became
a matter of the user’s familiarity and talent, and resulted in a hopeless case of
confusion for the researchers. A critique on theories predicting thermoelastic
properties of fiber reinforced composite materials was presented by Chamis and
Sendeckyj (1968) where they had introduced basic principles of existing theories and
had reviewed individual papers.
A number of articles on thermal expansion of fiber reinforced composites had
appeared during 1960s in Russian literature (Shapery, 1968). In an important paper
by Levin (1967), effective thermal expansion coefficients for two-phase anisotropic