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Stitched Composites 169
(f)
Figure 8.4 (Continued) Photographs and illustrations of stitching damage. (e) A region
of low fibre content due to stitching is shown within the circle, and this develops into a
resin-rich region when the composite is consolidated. (f) Schematic of the distortion to
stitches caused by heavy compaction of the preform (From Mouritz and Cox, 2000).
8.3 MECHANICAL PROPERTIES OF STITCHED COMPOSITES
8.3.1 Introduction
The application of stitched composites to load-bearing structures on aircraft, such as
wing skin panels and fuselage sections, requires an in-depth understanding of their
mechanical properties and failure mechanisms. The mechanical property data is needed
to validate design codes for stitched composites to be used in high performance
structures. In this section the effect of stitching on the tensile, compressive, flexure,
interlaminar shear, creep and fatigue properties of composite materials will be
described. It will be shown that there is not a complete understanding of the effect of
stitching on the mechanical properties of composites. In addition, models for predicting
changes to the properties of composites due to stitching are not fully developed.
Until a strong modeling capability combined with a comprehensive database of
mechanical properties for stitched composites is achieved, then the certification and
application of these materials to primary aircraft structures will be difficult. Despite
some shortcomings in our knowledge, there is much about the mechanical properties of
stitched composites that is understood.