1. Composites

2. Take a piece of Styrofoam and have a student bend it. What happens?
The board will break!

3. Repeat the activity but place a piece of tape on both sides of the Styrofoam
Once again bend the board after the tape is applied. What observations can be made?

4. What are composite materials?
Engineered or naturally occurring materials made from two or more constituent materials with significantly different physical or chemical properties
Two components remain separate and distinct at the macroscopic or microscopic scale
Two materials are not soluble in each other
Composite material usage is continually growing

5. Composites: Composition
Contain two distinct materials
Multiphase material
“Binder material” – matrix material that surrounds other material
“Reinforcement” – material that is providing the extra support (fibers, or fragments) that are bound together

6. Material properties that can be improved by forming a composite
Naturally not all of these improvements occur at the same time!

7. Composites in Nature Nature is a great composite manufacturer: Wood
Lignin matrix reinforced with cellulose fibers
Bone
Bone plates reinforced with collagen
Sea shells
Abalone shell: calcium carbonate held together by proteins

8. Early Examples of Composites
Israel
mud bricks + straw
Straw strengthened the mud bricks in building materials
Ancient Egyptians (1500 BC)
Use of glue laminated wood (plywood)
Use of straw to reinforce clay walls
Medieval swords and armor (1800 AD)
constructed with layers of metals

9. Modern Composites 1950’s -1960’s
Demand for materials with low weight and high strength, rigidity for applications such as aerospace, electronics, etc.
Post-war economy: companies invested in large-scale laboratories
Cold War: drive for aerospace technology
Example: Fiberglass – glass fibers are surrounded by a plastic matrix

10. Composite Example: Fiberglass
Glass fibers are surrounded by a plastic matrix
Glass fibers are brittle on their own
Plastic matrix holds the fibers together and protects from damage and outside forces

11. Modern Composites
1970’s+
Development of new types of fibers (carbon, boron, and more)
Carbon Fibers – stronger than fiberglass, but more expensive
Used in aerospace and military applications
Fibers consist mostly of the atom carbon
Fibers have similar structure to graphite

12. Types of Composites Commonly types of composites:
Combinations of some or all of the above are also used

13. Fiber-reinforced Composites
Long fibers placed into materials
material is stronger and stiffer
Example…..Ordinary glass plate fractures with little stress of a few thousand pounds per square inch.
With a fibrous composite added to the plate, fractures need 400,000 pounds per square inch to as much as 1 million pounds per square inch.

14. Properties of Matrix Materials
Fibers and whiskers are of little use unless they are bonded together to take the form of a structural element that can carry loads
The binder material is known as the Matrix
The purpose of the matrix is to
–Support of the fibers or whiskers
–Protection of the fibers and whiskers
–Matrix is of considerably lower density, stiffness or strength than a fiber or whisker
–The combination of fiber or whiskers with a matrix can have very high stiffness and strength and a very low density

15. Matrix Materials Matrix materials can be: Polymers – polymer resins
Metals – Metal matrix composites
Ceramics
Carbons

16. Common Fiber Materials
carbon or graphite (C)
glass (Si02)
organic fibers
silicon carbide fibers (SiC)
boron fibers (B)
metallic fibers (Mg, Ti)

17. Common Fiber – reinforced composites
Fiberglass
Carbon Fiber Reinforced Polymer (CFRP)
Fiber reinforced concrete
Bicycles – carbon fiber reinforced plastic
Automobile materials – metal matrix composites

18. Characteristics of Fiber Composites
Fiber Length
Amount/Concentration of Fiber
Volume fraction of fiber can increase strength and stiffness
Max volume fraction with better properties: 80%
Orientation of Fiber
Shape of Fiber

19. Fiber Length Critical Length needed for strength improvement
This length is dependent on diameter and tensile strength of fiber
Longer fibers with small diameters are preferred
Large aspect ratio (length/diameter of fibers) leads to a high strength

20. Fiber Orientation
How does the orientation of the fibers affect the composite properties?
What other factors might influence the properties?

21. Fiber Orientation Orientation can affect the properties
Can make the properties anisotropic

22. Fiber Shapes Fiber can be different shapes
Cylindrical fibers are most common

23. Carbon fiber reinforced polymers (CFRP)
Carbon Fibers – 5-10 um in diameter
Polymer is often an epoxy (thermosetting polymer)
Applications:
Aerospace, transportation
Boeing 787 is composed of CFRP
Sports equipment – hockey sticks, racing bicycles

24. Carbon Fibers Composed of >90% carbon high flexibility
high tensile strength
low weight
low thermal expansion
High strength-to-volume ratio

25. Particle-Reinforced Composites
Often Isotropic
Examples:
Reinforced rubber
Carbon black particles help strengthen auto tires
Concrete
Gravel and sand help to reinforce cement

26. Structural Composites
Properties depend on the geometric design
Laminar Composites:
Structural Sandwich

27. Laminar Composites
Panels of materials are combined to make a stronger material
Panels are arranged in different orientations to maximize strength overall
Examples: plywood, skis

28. Structural Sandwich
Sandwich Panels – consists of two outer sheets, separated by an inner core of less dense material
Outer sheets are stronger material
Bear most of in-plane loading
Core material separates outer sheets and provides shear rigidity
Applications: building materials, aerospace

29. Limitations of Composites
High cost of fabrication
Mechanical characterization of structure is complicated
Repair of composites is not simple due to complicated structures
Flaws/cracks can go undetected

30. Applications Aerospace Airbus 380 superjet is made of 20% composites
Boeing 787 has 50% composite materials

31. Why composites? Offer unique properties unlike individual materials
Often lightweight, but strong materials
Offer flexibility in design of materials

32. Supplementary Slides

33. Websites http://www.tms.org/pubs/journals/JOM/9602/Scala-9602.html
History of composites
Composites videos
Article on materials in aerospace