  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 that
vary throughout a single panel, such as elastic modulus, heat
resistance, dielectric properties, specific strength, corrosion
resistance, environmental resistance, damping, and many other
properties without the weakness inherent in fastening or adhering
multiple types of composites together.
Benefits:
• Continuous load paths
• Tailored structures
• Flexibility in design
• Reduced machining costs
• No fastened or adhered joints
• Labor savings
• Unitized manufacturing
• Weight savings
• Reduced maintenance costs
• Reduced material costs
Applications
Graded composites offer greater design possibilities
and functionality in aircraft. Large, dynamic seamless parts
can be fabricated with entirely smooth surfaces. 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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