1. Introduction to Composites
An Aerospace Manufacturing Perspective

2. Course Overview 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 2

3. Composites in Aviation
What are composites?
Combinations of different materials which yield a product with superior properties
Composite armor used by the Greeks in antiquitiy (
Modern composites, or advanced composites are typically fiber reinforced plastics.
copyright J. Anderson, 2008

4. Fiber Reinforced Plastic (FRP) Composites
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

5. Fiber Reinforced Plastic Composites, contd.
Fibers
Plastic Matrix
copyright J. Anderson, 2008

6. Function of the Fiber Carry the load
70 to 90% of load carried by fibers
Provide structural properties to the composite
Stiffness
Strength
Thermal stability
Provide electrical conductivity or insulation
copyright J. Anderson, 2008 6

7. Function of the Matrix 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 7

8. Relative Strength of Fiber and Matrix
Note that for the same level of stress, the fiber deforms much less than the resin.
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

9. 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

10. Commercial Fiber Fibers are available as
Yarn – a bundle of fibers twisted together
Tow - Large bundles (Carbon Fiber), several thousand fibers
Roving - Large bundles (Fiber Glass)
Uni-directional tape
Woven fabric or mat
copyright J. Anderson, 2008

11. Material Configurations
copyright J. Anderson, 2008
courtesy Ten Cate Avdanced Composites 11

12. Composite Fiber Materials
Common Fibers Used in Composites
Glass, or fiberglass
Starts as a silica sand
Carbon
Starts as a polyacrylonitrile fiber
copyright J. Anderson, 2008

13. 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

14. Common Thermoset Plastics used in High Performance Composites
Thermosets
Epoxy
Polyester
Phenolics
Cyanate Esters
Bismaleimide (BMI)
Polyimide
Thermoplastics
Nylon
Polyetheretherketone (PEEK)
copyright J. Anderson, 2008

15. 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

16. 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

17. 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

18. Design Comparison Studies for Lockheed L-1011 Aircraft
Inboard Aileron
Aluminum
Composite
Weight (lbs)
141
104
# of Ribs 18 10
# of Parts
398
205
# of Fasteners
5253
2574
Vertical Fin Box
Aluminum
Composite
Weight (lbs)
858
623
# of Assemblies 21 15
# of Parts
714
229
# of Fasteners
40800
10150
copyright J. Anderson, 2008
From “Composite Airframe Structures”, Niu

19. Composite Usage in Boeing 777
copyright J. Anderson, 2008

20. Composite Component Content
copyright J. Anderson, 2008
Chart courtesy of Composites Market Reports

21. 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

22. 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 22

23. 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.
copyright J. Anderson, 2008
Photo courtesy Accudyne Systems, Inc

24. 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 24

25. Wet Lay Up, contd.
copyright J. Anderson, 2008 25

26. 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 26

27. Debulking the Part
copyright J. Anderson, 2008 27

28. 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 28

29. Autoclave Cure copyright J. Anderson, 2008 29
Photo courtesy WSF Ind & ASC Process Sys.
copyright J. Anderson, 2008 29

30. Typical Autoclave Cycle
copyright J. Anderson, 2008 30

31. 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 31

32. Automated Lay Up
copyright J. Anderson, 2008 32

33. Tow Placement copyright J. Anderson, 2008
Photo courtesy Accudyne Systems, Inc & Cincinnati Machine

34. High Dexterity Tape Placement
copyright J. Anderson, 2008
Photo courtesy Accudyne Systems, Inc

35. Variable Angle Ply Lamination
copyright J. Anderson, 2008
Photo courtesy Accudyne Systems, Inc

36. Large Parts
copyright J. Anderson, 2008
courtesy ATK

37. Future Directions Embedded sensors and actuators
More Automation
Embedded sensors and actuators
“Out of Autoclave” high performance materials
copyright J. Anderson, 2008

38. Subsequent Composites Modules
Composite Specifications in Drawings
Manufacturing Techniques
Process Control and Tooling
You Have Just Completed
The Introduction To Composites
copyright J. Anderson, 2008