1. Characteristics of Composite Materials
Chapter 13

2. Unique Characteristics of Composites
A substance consisting of a minimum of 2 materials
At least one material serves as a solid reinforcement
The second is a binding material (matrix)
Binding material begins as a liquid or slurry
Will saturate the binding material as it solidifies
Hold the reinforcement in a desired orientation

3. Mechanical properties of the composite determined by:
Position of the reinforcement material
Shape of product
Manufacturing process used
Reinforcement materials carry the load
Matrix material distributes the load and protects the reinforcement material

4. Composites can be used in a wide variety of service and performance conditions
Depends on:
Selection of reinforcement materials
Proper placement of reinforcement materials
Selection of suitable matrix material

5. Structure of Composite Materials
Fiber reinforced plastic (FRP)
Most widely recognized
Consists of glass fibers and polymer resin
Glass fiber very susceptible to damage
Polymer resin has low tensile strength
Resin is tough, and protects glass fibers
FRP composites made up of layers
Called “lay-up” or “buildup”

6. FRP used in open molding (layup procedure)
A common low cost manufacturing process
Layer of polymer resin is sprayed in a mold
Layer of glass fiber is added
Fiber is “wetted” with more resin
Another layer of glass is added
Process is repeated until desired buildup is achieved

7. FRP is competitive with woods, metals and plastics
Material costs more
Lower cost comes from less expensive manufacturing processes for composites

8. Reinforcements Variety of reinforcement materials Three categories:
Fillers
Fibers
Solids

9. Fillers
Added to resins to change their flow characteristics and increase the volume
Dust like particles and short fibers
Easy to handle – paste like
Modest mechanical properties
Typically used to fill in gaps and voids and improve surface finish
Reduce cost
Referred to as an extender

10. Classes of Fillers Mineral fillers Organic fillers Specialty fillers
Calcium carbonate
Wood flour
Microspheres
Calcium sulfate
Solid glass spheres
Talc
Walnut shells (ground)
Hollow glass spheres
Mica
Corncobs (ground)
Ceramic spheres
Thermoplastic spheres
Phenolic spheres

11. Fibers Mainstay of reinforcement Economical Good mechanical properties
Dependent on type of glass fiber and orientation
Ingredients:
Silica sand (primary)
Metal oxides (added)
Size of fibers – 3.5 to 24 microns

12. Most economical glass fiber
E-glass
Most economical glass fiber
Sufficient strength
Low cost
At least 50% silica oxide
Also can have aluminum, boron, calcium, limestone, and others
Accounts for nearly 90% of the glass reinforcements
“E” refers to it’s outstanding electrical insulating characteristics

13. Chemical Resistant Glass
Glass fiber has good chemical resistance
Over exposure to hot water will cause erosion to exposed glass fibers
Corrosion resistant resin is added to slow the erosion
Result it a composite with good chemical resistance
Selection of appropriate fibers based on chemical exposure is also important

14. Specialty Fibers
Higher tensile strength and stiffness than glass fibers
Made from:
Carbon
Boron
Aramid
Much higher cost
Exceptional performance for customer willing to pay
Hybrid – specialty fibers mixed with glass fibers
Helps control cost

15. Reinforcement Enhancements
Single strands of reinforcement are hard to handle and keep in place when adding a binding matrix
Can result in a product with variable mechanical properties
Time consuming to manufacture
To solve this problem glass fiber must go through further processing
Glass fiber gathered into bundles or strands
Strand – collection of more than one continuous filament
Roving – bundle of untwisted glass strands packaged like thread on a large spool

16. Fabrics are popular reinforcement
Mat – nonwoven fabric made from fibers held together by a chemical binder
Chopped mat – randomly distributed fibers cut to length
Lower cost
Continuous-strand mat – swirls of unbroken fiber strands
Stronger
Plain weave – simple fabric, over under weave

17. Protecting the glass fiber during processing
Glass fibers can be damaged by abrasion while being handled
Can cause breakage
Sizing – chemical mixture to coat and protect glass fibers

18. Solid Reinforcement Creates stiff and lightweight composites
Also called laminate
Core material - the solid reinforcement material
Sandwich construction
Face skin laminate (fiber reinforcement)
Core material
Reinforced back skin laminate
Results in thicker, stiffer laminates

19. Weight is always a concern Core materials must be light and economical
Must be able to be bonded by the resin being used
Polystyrene foam – dissolved by resin

20. Laminate bonds to the end grain of the wood
Balsa wood
Marine hulls and decks
Lightweight and rigid
6 to 16 lbs per cubic foot
Laminate bonds to the end grain of the wood
Improved crush strength
Polyvinyl chloride (PVC) foam
Combination of strength and low weight
4 to 30 lbs per cubic foot
Linear PVC foam
Mainly for marine industry
Allows deflection before failure

21. In sheet stock or liquid that is foamed into place
Polyurethane foam
In sheet stock or liquid that is foamed into place
Used in cavity of boat hulls
Add stiffness
Buoyancy
Low shear strength
Not structural applications
Also good thermal insulator (wall panels of refrigeration units)
2 to 20 lbs per cubic foot

22. Honeycomb cores
Aerospace and transportation
Made from: paper, aluminum, glass reinforced phenolic
1 to 6 lbs per cubic foot
Very stiff
Lightweight
High crush strength

23. Creating the matrix in the composite
Matrix generally a resin
Function to transfer the load to and protect the reinforcement fiber
Most popular matrix materials are plastics
Thermoplastic (re-formable)
Thermosets (not re-formable) (primarily used)

24. Gel Coat
Resin formulated to provide a quality finish to the outer surface of a composite
Improves durability
Provides color, gloss and environmental protection
Not paint

25. Resin Additives
Improve the chemical and physical properties of the matrix resin
Many available additives:
Fire retardants/suppressants
UV inhibitors
Conductive additives

26. Composite Stock Prepregs – sheets of fiber saturated with resin
Manufacturer molds prepregs into shapes
Composite stocks usually made on site
Purchase resins, reinforcement and additives separately
Mix themselves