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 member Binding 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: Honeycomb Balsa wood Foam 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.