Composite Materials FAQ: Composites:

What are composite materials? Composites materials are a combination of two or more chemically different materials that when combined, produce a material with properties superior, or different, to the individual materials alone. When combinded, the materials must maintain their oringal state. For example, a metal wire suspended in a ceramic matrix such as concrete is a composite while two metals being combined is considered an alloy because they will not maintain a chemically seperate state.

Reinforcements :
Carbon Fiber is an synthetic fiber comprised of up to 95% pure carbon. Because of the interlocking crystalline structure of the carbon, these fibers have an extremely high tensile strength. It is made by heating Polyacrylonitrile (PAN) to exceedingly high temperatures 1000°C - 3000°C . Carbon fiber will exhibit different properties depending on the temperature used to create it. For example the higher the temperature, the higher the Modulus of Elasticity. In laymen's terms this means that carbon fiber manufactuered at higher temperature will be stiffer than carbon fiber at a relatively lower temperature. Carbon fiber fabric is comprised of thousands of strands of carbon fiber that are bundled together in various weaves and weights.
Properties:
- Very high Strenght to Weight ratio
- Very high tensile strength
- Very high Modulus of Elasticity (Stiffness)
- Expensive


Fiberglass is a a fabric where strands of glass fibers are bundled together in different weaves. Unlike carbon fiber, fiberglass can be purchased in the form of cloth where long continuous stands of glass are woven into a fabric using a predetermined weave, or chopped strand mat where short strands of glass are formed randomly into a fabric and held together by a weak styrene styrene bonding agent. Fiberglass cloth has good direction strength while fibergas mat has a lower strenght but is equal in all directions. The two most common glass types are E-glass and S-glass. S-glass is a higher strength glass reinforcement, sometimes referred to as structural-glass, and as you can imagine it is a bit more expensive.


Properties:
- Medium Strenght to Weight ratio
- Low tensile strength
- Low cost


KevlarŪ is an one of many types of aramid organic fibers. Kevlar is most commonly known for use in bulletproof vests. Kevlar has very good abrasion resistance, penitration resistances and is similar in strenght to fiberglass but is less dense so it has a higher strenght to weight ratio.
Properties:
-High Modulus of Elasticity (Stiffness)
-High Strength to Weight ratio
-Low Electrical Conductivity
-High Chemical Resistance
-Low Thermal Shrinkage
-High Toughness (Work-To-Break)
-Excellent Dimensional Stability
-High Cut Resistance
-Flame Resistant, Self-Extinguishing


Spectra is a fabric/fiber made of Ultra High Molecular Weight Polyethylene or UHMWPE. It has excellent resistance to chemicals, water, and UV light. It is very durable, has a very low coefficient of friction and according to Honeywell, the producer of Spectra, has a 40% higher Strength to Weight Ratio than Kevlar.

Tow Count/Size is a measure of fibers in a strand. For example fabric with a rating of 3k means that the fabric is made from strands containing 3,000 individual fibers. 3K to 12K is the standard tow size but higher counts are available. A smaller tow size generally means more uniform properties and a higher quality product.

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