OVERVIEW OF TEXTILES
Textile composites for engineering structures draw on many traditional textile forms
and processes. In this section, the processes and architectures that can yield composites
with the high performance required for aerospace structures will be summarized. These
textiles are generally those that most effectively translate stiff, strong yarns into stiff, strong
composites.
A textile composite has internal structure on several scales. At the molecular scale,
both the polymer matrix and the fibers exhibit structural details that profoundly affect
strength and stiffness. Matrix properties are determined by chain morphology and cross-
linking, among other things. Carbon fibers, which are often the preferred choice in
aerospace materials, owe their axial stiffness and strength to the arrangement of carbon
atoms in oriented graphitic sheets. On a coarser scale, typically ~1 mm., lots of 10
3
- 10
4
fibers are bundled into yarns or tows. Within the finished composite, each tow behaves as
a highly anisotropic solid entity, with far greater stiffness and strength along its axis than in
transverse directions. Because tows are rarely packed in straight, parallel arrays, stresses
and strains often possess strong variations from tow to tow. Thus composite mechanical
properties such as elasticity can only be considered approximately uniform on scales that
are even larger still, say ~ 10 mm or higher, where the effects of the heterogeneous
structure at the tow level are averaged out. Finally, the textile forms part of an engineering
structure, perhaps the stiffened skin of a wing or fuselage. Since the engineering structure
itself usually has some dimensions as small as ~ 10 mm, the fabrication of the composite
material and the fabrication of the engineering structure may no longer be considered
distinct operations. To fabricate the textile composite
to fabricate the structure.
Figure 2-1 illustrates scales in one textile process. The part shown is an integrally
formed skin/stiffener assembly. The first processing step is the formation of yarns from
fibers. In the second step, the yarns are woven into plain woven cloth. The cloths are then
laid up in the shape of the skin and stiffener and stitched together to create an integral
preform. Finally, the composite part is consolidated by the infiltration of resin and curing in
a mold.
