TOOLED THICK COMPOSITES by ARVEN H. SAUNDERS III ...

Figure 1.3. Fiber/Layer Waviness in a Section of a Thick S2/8552 Composite
Laminate.
within the plane (sideways) of each layed up ply; out-of-plane waviness involves a wave in the
thickness direction. This defect has caused great concern in the manufacture of thick tapered
section composites for the rotorcraft producers. Extensive testing and analysis has shown that
fiber waviness has significant impact on the overall structural integrity of thick laminates.
Degradation in compressive strength, fatigue properties, and tensile strength has been reported
by various researchers (Adams, 1996). As a result, the tolerance for this nonconformance has
been reduced.
To meet these challenges, research and development effort continues in a number of
directions. Greater demands have been made of suppliers to reduce material property variation.
Designed experimental work has sought to find those aspects of the layup and cure preparation
work that are most critical and how better to control them. Because much of composites
fabrication involves manual labor, automation has been applied to selected operations such as
tape laying, laminate debulk, and fiber placement. More advanced NDI technology has
produced greater defect detection capabilities. The composites producers community has also
continued its focus on cure cycle improvement and optimization.
1.3 Problem Statement
Thick (at least ½”) composite laminates are increasingly employed to applications such
as rotorcraft components. Of the many process steps involved in their fabrication, the cure
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