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Systems Engineering Portfolio
  Graded
Composites
Graded composites are integrated, continuous
panels featuring areas or zones of differing material properties.
Unlike conventional composites, graded composites offer continuous
load paths through areas of differing properties. Multiple resins
and fabric reinforcements are used during fabrication, reducing
the part count and eliminating the need for joints and, therefore,
the possibility of joint failure. This breakthrough composite
technology eliminates bulky assembly, offers stronger and stiffer
parts, and reduces cost. Since the zones are tailored and integrated
during fabrication, there are no seams or connection points to
weaken the panel.
CRG’s graded composites are a
new approach to composite design. Differing properties can be
engineered into various zones of a fabricated composite panel.
This process offers the capability for parts with a broader range
of performance. For example, expensive, high-performance resins
need only be used in areas that will be exposed to extreme conditions
while inexpensive, off-the-shelf resins can comprise the remaining
sections of the composite part.
Zoned Composite Parts
As an example of using different resins in varying
zones, CRG has demonstrated a continuous load path in a panel
where 90% of the area is made with an epoxy matrix and 10% of
the area is made with cyanate ester. The resulting graded composite
is much less expensive than a 100% cyanate ester-based part, with
a zone of high-service temperature tailored to a specific application.
These zoned composite parts are integrated panels with customized
properties, such as elastic modulus, heat resistance, dielectric
properties, specific strength, corrosion resistance, environmental
resistance, damping, and many other properties that vary throughout
a single panel without the weakness inherent in fastening or adhering
multiple types of composites together.
Benefits:
• Continuous load paths
• Tailored structures
• Design flexibility
• Elimination of fastened or adhered joints
• Unitized manufacturing
• Reduced weight
• Decreased labor costs
• Reduced machining costs
• Reduced maintenance and materials costs
Applications
Graded composites offer greater design possibilities
and functionality in aircraft. Large, dynamic seamless parts can
be fabricated with entirely smooth surfaces, and flexure points
can be built into the skin where needed, an important factor in
the design of morphing aircraft. An additional benefit is the
reduced number of seams and panels for low-observability applications.
The manufacturing process of graded composites is compatible with
existing composite manufacturing techniques, with the added benefit
of affordability. High-performance materials need only be used
where necessary, such as near the engine or in the wings. Using
high-performance materials only in the zones where they are essential
offers the potential to lower the cost and increase the versatility
of composites.
A variety of materials transitions are available
through graded composites. The following are examples of options
available with CRG’s expertise in graded composite technology.
• Carbon fiber can be
transitioned to high-performance glass for seamless,
transparent windows built directly
into a composite panel.
• High modulus can grade to low modulus
by transitioning resin and ply drops.
• Carbon fiber for peak load can be
transitioned to Kevlar fiber for added
abrasion resistance.
• High service temperature resin can
be transitioned to less expensive resin
to accommodate varying temperature
requirements while maintaining a
continuous load path.
• High-strength, low-strain material
can be transitioned to an intermediate-
strength, high-strain composite
with a non-linear transition for morphing
aircraft skins, increasing
life cycle.
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