1 composite materials what are composite materials? two or more materials bound together example...

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COMPOSITE MATERIALS

• What are composite materials? Two or more materials bound together

• Example from civil engineering: Concrete reinforced with steel bars

Reinforced concrete wall

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COMPOSITE MATERIALS

• Fiber reinforced composite materials

Reinforcement: Main load carrying memberBinding material:transfers load to fibers, keeps the fiber together

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FIBER MATERIALS

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• A Fiber (reinforcement) may be defined as an elongated stringy man-made material.

• A polymer (matrix) is a large molecule consisting of repeating units connected by covalent chemical bonds.

• Once the polymer is combined with the fibers, the polymerization process must take place in order to obtain a solid structural composite material.

• Another critical issue is the fiber-matrix bonding. When the composite material is loaded, both fibers and matrix must be strongly bonded so that they work as a solid rigid.

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FABRIC ARCHITECTURES

Unidirectional

Woven

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COMPOSITE LAMINATES

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SANDWICH CONSTRUCTION• When loads are applied to any beam, such as wing spar most stress occurs at the outer surfaces.

• Therefore, SANDWICH structure is commonly used in composite construction to increase the thickness without significant weight penalty

Core material:HoneycombBalsa woodFoam etc.

Valid for honeycomb cores

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Typical SANDWICH structure

Core material: Honeycomb, wood, foam etc.

Upper and lower layers:Composite material composed of suitable fiber + matrix combination

Typical fiber materials:E-Glass: Standard fiber glass; workhorse of composites, moderate strength, good bonding with epoxy, cheap

Kevlar: Organic fibers, high impact resistance, high strength, difficult to work, poor bonding with epoxy, moderate prize

Carbon: 93-95% carbon content, very high strength and fatigue resistance, excellent bonding with epoxy, expensive

Bonding material between layers: Epoxy resin

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Typical resin(matrix) materials:

Epoxy: Excellent adhesion to fibers, highest strength, low shrinkage, will bond to dissimilar or already cured materials

Vinly ester: Moderate strength, more resistant to degradation from water/moisture

Polyester: Low strength , fast curing times, exhibit shrinkage, low weathering resistance, cheapest (non adequate for advanced composites: poor adhesion to carbon and Kevlar)

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COMPOSITE MANUFACTURING

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COMPOSITE MANUFACTURING

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COMPOSITE MANUFACTURING

INFUSION

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COMPOSITE MANUFACTURING

INFUSION APPLICATIONS

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COMPOSITE MANUFACTURING

VACUUM BAGGING

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COMPOSITE MANUFACTURING

VACUUM BAGGING

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COMPOSITE MANUFACTURING

VACUUM BAGGING

•Release agent: facilitates the extraction of the part.

•Peel ply: leaves the part surface apt to be bonded or painted.

•Prepreg.

•Release film: prevents the resin to reach the bleeder fabric but not the volatiles.

•Bleeder fabric: takes out the excess of resin in order to get the desired fiber fraction.

•Breather fabric: makes the vacuum uniform along the part.

•Vacuum bag/seal: seals the cavity to be vacuumed.