1

COMPOSITE MATERIALS

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

• Example from civil engineering: Concrete reinforced with steel bars

Reinforced concrete wall

2

COMPOSITE MATERIALS

• Fiber reinforced composite materials

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

3

FIBER MATERIALS

4

• 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.

5

FABRIC ARCHITECTURES

Unidirectional

Woven

6

COMPOSITE LAMINATES

7

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

8

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

9

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)

10

COMPOSITE MANUFACTURING

11

COMPOSITE MANUFACTURING

12

COMPOSITE MANUFACTURING

INFUSION

13

COMPOSITE MANUFACTURING

INFUSION APPLICATIONS

14

COMPOSITE MANUFACTURING

VACUUM BAGGING

15

COMPOSITE MANUFACTURING

VACUUM BAGGING

16

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.