Introduction to Composites
An Aerospace
Manufacturing
Perspective
Course Overview
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Composite Material Structure
Composite Material Components
Aluminum versus Composites
Advantages and Disadvantages in Aerospace
Composite Applications
Composite Manufacturing Techniques
Subsequent Composite Modules
copyright J. Anderson, 2008
Composites in Aviation
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What are composites?
 Combinations of different materials which yield
a product with superior properties
 Composite armor used by the Greeks in
antiquitiy
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(http://www.youtube.com/watch?v=Aznz9mj5grA)
 Modern
composites, or advanced composites
are typically fiber reinforced plastics.
copyright J. Anderson, 2008
Fiber Reinforced Plastic (FRP)
Composites
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Consists of at least two materials
– Plastic which binds the fibers together, also called
the matrix
– Fibers, typically small in diameter and long in
length
 Fibers may also be short in length to facilitate
processing – e.g., injection molded nylon with
glass fibers
– In general the matrix imparts toughness, or crack
resistance, and the fiber imparts ultimate strength
copyright J. Anderson, 2008
Fiber Reinforced Plastic Composites,
contd.
Fibers
Plastic Matrix
copyright J. Anderson, 2008
Function of the Fiber
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Carry the load
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Provide structural properties to the
composite
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70 to 90% of load carried by fibers
Stiffness
Strength
Thermal stability
Provide electrical conductivity or insulation
copyright J. Anderson, 2008
Function of the Matrix
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Binds the fibers together
Provides rigidity and shape to the structure
Isolates fibers to slow crack propagation
Surface quality
Corrosion and wear protection for fibers
copyright J. Anderson, 2008
Relative Strength of Fiber and Matrix
Note that for the same level of
stress, the fiber deforms much less
than the resin.
Stress
Carbon
Fiber
Polyester Resin
Strain
This leads to the composite material
being much stronger in the direction
of the fiber. If the fibers are
unidirectional (all in the same
direction) the composite material is
strong in the direction of the fibers,
but weak in the directions
perpendicular to the fibers.
We can alleviate this by adding
multiple plies laid with the fiber
direction different.
copyright J. Anderson, 2008
Varying Fiber Direction in Plies
Varying fiber direction
in plies builds a
laminate structure with
strength in more than
one direction
copyright J. Anderson, 2008
Commercial Fiber
Fibers are available as
 Yarn – a bundle of fibers twisted together
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Tow - Large bundles (Carbon Fiber), several
thousand fibers
Roving - Large bundles (Fiber Glass)
Uni-directional tape
Woven fabric or mat
copyright J. Anderson, 2008
Material Configurations
courtesy Ten Cate Avdanced Composites
copyright J. Anderson, 2008
Composite Fiber Materials
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Common Fibers Used in Composites
– Glass, or fiberglass
 Starts as a silica sand
– Carbon
 Starts as a polyacrylonitrile fiber
copyright J. Anderson, 2008
Types of Plastics used in
Composites
Plastics are polymer materials, that is to say that they
are made up of long chain molecules. There are two
types of plastics based on how these molecules are
bonded together.
•Thermoplastics
•Thermoplastics can be melted and re-solidified
when cooled.
• Thermosets
• Start out as liquids or paste-like solids and
become rigid when cured. Thermosets can’t be
re-melted once cured.
copyright J. Anderson, 2008
Common Thermoset Plastics used in
High Performance Composites
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Thermosets
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Epoxy
Polyester
Phenolics
Cyanate Esters
Bismaleimide (BMI)
Polyimide
Thermoplastics
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Nylon
Polyetheretherketone (PEEK)
copyright J. Anderson, 2008
Aluminum vs. Composites
Aluminum is an “isotropic material”, which means it
has the same properties in all directions.
Composites are “anisotropic” which means they
have different properties depending on the direction of the
fibers vs. the direction of the applied loading.
•Composites are built in layers called ply’s that are
stacked “laid-up” to form a laminate.
•Each layer has fibers that run in defined
directions.
•Because of the layers the properties are different
“in-plane” vs. “through the thickness”
copyright J. Anderson, 2008
Advantages of Composite Materials
over Metals for Aerospace
• Light weight
• Resistance to corrosion
• High resistance to fatigue damage
• Reduced machining
• Tapered sections and compound contours easily accomplished
• Can orientate fibers in direction of strength/stiffness needed
• Possible reduced number of assemblies and reduced fastener count
when co-cure or co- consolidation is used
• Absorb radar microwaves (stealth capability)
• Thermal expansion close to zero reduces thermal problems in outer
space applications
copyright J. Anderson, 2008
Disadvantages of Composite
Materials over Metals for Aerospace
• Corrosion problems can result from improper coupling
with metals, especially when carbon or graphite is used
(sealing is essential)
• Degradation of structural properties under temperature
extremes and wet conditions
• Poor energy absorption and impact damage
• May require lightning strike protection
• Expensive and complicated inspection methods
• Reliable detection of substandard bonds is difficult
copyright J. Anderson, 2008
Design Comparison Studies for
Lockheed L-1011 Aircraft
Vertical Fin Box
Inboard Aileron
Aluminum
Weight (lbs)
Composite
141
104
# of Ribs
18
10
# of Parts
398
205
5253
2574
Aluminum
Weight (lbs)
# of Assemblies
# of Parts
# of Fasteners
# of Fasteners
From “Composite Airframe Structures”, Niu
Composite
858
623
21
15
714
229
40800
10150
copyright J. Anderson, 2008
Composite Usage in Boeing 777
copyright J. Anderson, 2008
Composite Component Content
Chart courtesy of Composites Market Reports
copyright J. Anderson, 2008
Building Composite Parts
Composite parts are built by
laying up multiple plies
(layers) using molds (or
tools) then cured under heat
and pressure.
copyright J. Anderson, 2008
Combining the Fibers with Matrix
There are several methods for arranging the fibers
and plastic in the desired shape. We can arrange the
fibers, usually as a fabric, in the mold and then pour
on the liquid matrix material. For one part we might
hand cut the fabric and fit it into the mold .
copyright J. Anderson, 2008
Ply Cutting and Kitting
For a production system we
wish to make the same part
many times, in the most
efficient manner, and have the
same process every time.
In this case we use a CNC
cutting machine to cut the
patterns out, then assemble a
“kit” of raw materials to make a
part.
Photo courtesy Accudyne Systems, Inc
copyright J. Anderson, 2008
Wet Lay Up
We can arrange the fibers, usually as a fabric, in the mold and
then pour on the resin. Typically the resin is a two part
formulation that, once mixed reacts in a fixed time.
In order to make the lightest part with the necessary strength, we
must control the amount of resin we use on the part.
The process includes;
•Laying the fabric in the mold
•Saturating the fabric with mixed liquid resin
•Working the resin into the fabric so that it conforms to the mold
•Adding another ply of fabric
•Repeat the application of resin and working as above
•Continue until all the plys are in place, excess resin has been
worked to the edges, and the composite conforms to the mold
copyright J. Anderson, 2008
Wet Lay Up, contd.
copyright J. Anderson, 2008
PrePreg Lay Up
In wet layup it is very hard to control the amount of
resin.This problem may be addressed by
impregnating fabric with a pre-mixed resin. This
“prepreg” material is held at low temperatures to
retard the curing process.
The prepreg sheets or tape are laid into the mold, and
heated to cure.
copyright J. Anderson, 2008
Debulking the Part
copyright J. Anderson, 2008
Oven Cure
Once the layup is accomplished and
the part is debulked, we can put it into
a furnace to cure the resin. Typically
the parts are instrumented with a
thermocouple to track the temperature
of the part in the oven. The
temperature of the oven is increased
until the thermocouple registers the
correct curing temperature and then
the part is “soaked” at temperature
until it is cured.
copyright J. Anderson, 2008
Autoclave Cure
Photo courtesy WSF Ind & ASC Process Sys.
copyright J. Anderson, 2008
Typical Autoclave Cycle
copyright J. Anderson, 2008
Vacuum Resin Infusion
Vacuum resin infusion is similar to wet
lay up except that the fabric is laid out
in the mold, the part is vacuum
bagged, and resin is pulled into the
bag and through the fabric by a
vacuum pump.
Photos courtesy Airtech Adv. Materials
copyright J. Anderson, 2008
Automated Lay Up
copyright J. Anderson, 2008
Tow Placement
Photo courtesy Accudyne Systems, Inc & Cincinnati Machine
copyright J. Anderson, 2008
High Dexterity Tape Placement
Photo courtesy Accudyne Systems, Inc
copyright J. Anderson, 2008
Variable Angle Ply Lamination
Photo courtesy Accudyne Systems, Inc
copyright J. Anderson, 2008
Large Parts
courtesy ATK
copyright J. Anderson, 2008
Future Directions
• More Automation
• Embedded sensors and actuators
• “Out of Autoclave” high performance
materials
copyright J. Anderson, 2008
Subsequent Composites Modules
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Composite Specifications in Drawings
Manufacturing Techniques
Process Control and Tooling
You Have Just Completed
The Introduction To Composites
copyright J. Anderson, 2008