A numerical study on the thermal expansion coefficients of fiber

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The area covered by a strain gauge is usually quite small, 1-5 mm, and this means
that it samples the local behavior rather than the longer range average. In composites
which have homogeneous reinforcement, such as flat laminates, unidirectional
reinforcements and particulate composites, the technique can be used reliably, but
caution needs to be exercised with woven structures. The active part of the strain
gauge needs to cover several representative reinforcement units for the results to be
representative of bulk material behavior.
3.4 Theoretical Consideration
Micromechanics is a <strong>study</strong> of mechanical properties of composites in terms of
those of constituent materials (Tsai, & Hahn 1980). In discussing composite
properties it is important to define a volume element which is small enough to show
the microscopic structural details, yet large enough to represent the overall behavior
of the composite. Such a volume element is called the representative volume
element. A simple representative volume element can consist of a fiber embedded in
matrix block.
Once a representative volume element is chosen, proper boundary conditions are
prescribed. Ideally, these boundary conditions must represent the in situ states of
stress and strain within the composite. That is, the prescribed boundary conditions
must be the same as those if the representative volume element were actually in the
composite.
Finally, a prediction of composite properties follows from the solution of the
forgoing boundary value problem. Although the procedure involved is conceptually
simple, the actual solution is rather difficult. Consequently, many assumptions and
approximations have been introduced, and therefore, various solutions are available.
General assumptions in micromechanics of composites are: