ANALYTICAL METHODS FOR TEXTILE COMPOSITES
co-curing if joints of moderate strength suffice; or by stitching if joints must be very
strong. The handling advantages of textiles are so considerable that even when the finished
product is intended to be a 2D laminated structure, for example a laminate of uniweave
plies, with no special demand for the excellent delamination resistance of textiles, there is
still a case for preferring textile fabrics over tape laminates.
But textiles allow designers to step beyond conventional laminate concepts. For
example, with conventional tape layup, a laminar skin is stiffened against buckling by
nonintegral ribs, which must be attached in a separate process. The use of textile preforms
and processes such as RTM allows the manufacture of integral parts to net shape. Thus the
skin and stiffeners can be manufactured as one piece. Some other examples of integral
structures were recalled in Sect. 2. Net shape manufacture of integral structures provides
considerable potential cost savings over tape layup, because forming complex shapes via
layup is difficult and integral structures eliminate joining steps. Integral structures are
superior in performance too, because failure by debonding of attached parts should be
eliminated as a mechanism of failure, given correct design.
3.2 Consistency of Fiber Content
Since the stiffness and strength of polymeric composites are dominated by the
reinforcing fibers, maintaining accurate positioning of fibers tows during all steps of
manufacture is paramount. Poorly made textile preforms can have considerable variance in
tow spacing, which translates directly into total fiber volume fraction and thence mechanical
properties (e.g. [3.1]). In contrast, well made preforms, especially those manufactured by
well established textile processes, such as 2D braiding and weaving, regularly achieve a
high degree of consistency. However, even in the best cases, poor handling and processing
after textile manufacture can destroy this uniformity. Uncontrolled material handling, laying
material over curved tools, debulking, and tool closure can spread or distort tows.
Manufactured prove-out parts should be examined to establish that minimum fiber volume
fractions have been met throughout, with particular attention paid to geometric details such
as joints.
The problem of maintaining the designed fiber content is most challenging when
fabrics are draped. Fabrics are therefore often chosen for complex geometries because of
their handling characteristics. The draping characteristics of a fabric over a singly curved
(e.g., cylindrical) surface are directly related to its shear flexibility. Satin weaves have
fewer cross-over points than a plain weave; and therefore have lower shear rigidity and are
