Page 316 - Mechanics Analysis Composite Materials

Chapter 7

ENVIRONMENTAL, SPECIAL LOADING, AND
MANUFACTURING EFFECTS

Properties of composite materials, as well as properties of all structural materials
are affected by environmental and operational conditions. Moreover, for polymeric
composites this influence is more pronounced than for conventional metal alloys
because polymers are more sensitive to temperature, moisture, and time than
metals. There exists also a specific feature of composites associated with the fact
that they do not exist apart from composite structures and are formed while these
structures are fabricated. As a result, material characteristics depend on the type
and parameters of the manufacturing process, e.g., unidirectional composites
made by pultrusion, hand lay-up, and filament winding can demonstrate different
properties.
This section of the book is concerned with the effect of environmental,
loading, and manufacturing factors on mechanical properties and behavior of
composites.

7.I. Temperature effects

Temperature is the most important of environmental factors affecting the
behavior of composite materials. First, because polymeric composites are rather
sensitive to temperature and have relatively low thermal conductivity. This
combination of properties allows us, on one hand, to use these materials in
structures subjected to short-term heating, and on the other hand, requires us to
perform analysis of these structures with due regard to temperature effects.
Second, there exist composite materials, e.g., carbon-carbon and ceramic
composites, that are specifically developed for the operation under intense heating
and materials like mineral-fiber composites that are used to form heatproof layers
and coatings. And third, fabrication of composite structures is usually accompa-
nied with more or less intensive heating (e.g., for curing or carbonization), and
the further cooling induces thermal stresses and strains to calculate which we need
to attract equations of thermal conductivity and thermoelasticity that are
discussed below.

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