Composites

Question 1

What are the phase types of a composite?

Answer 1

Matrix

Dispersed

Question 2

What are the branches of the composite ‘tree’?

Answer 2

Particle-Reinforced
    - Large-particle
    - Dispersion Strengthened
Fiber Reinforced
    -Continuous (aligned)
    -Discontinuous (short)
        >Aligned
        >Randomly Oriented
Structural
    -Laminates
    -Sandwich panels

Question 3

Describe an MMC composite

Answer 3

Increase yield strength, tensile strength, and creep resistance.
Usually disperses ceramics or other metals.

Question 4

Describe a CMC composite

Answer 4

Increase Toughness

Usually imbedded with fibers.

Question 5

Describe a PMC composite

Answer 5

Increase Modulus, yield strength, tensile strength, and creep resistance.
Usually resins imbedded with filler.

Question 6

Compare traditional and synthetic composites.

Answer 6

Traditional - occur in nature or have been made for millenia. (wood, concrete, asphalt.)
Synthetic - components created seperately and then combined to create structure, properties, and geometry.

Question 7

What are the roles of the matrix and dispersed phase when the composite is holding stress.

Answer 7

The matrix shares the load and sometimes deforms to put the majority of the stress on the reinforcing agent.

Question 8

What are the common shapes of reinforcing agents?

Answer 8

Fibers (1D)
Flakes (2D)
Particles (3D)

Question 9

Why are fibers used?

Answer 9

The filament form of a material is much stronger than the bulk form.
Fewer defects.

Question 10

What are continuous fibers? Discontinuous Fibers? Whiskers?

Answer 10

Continous - very long, in theory, as long as the material
Discontinous - short, L/D roughly 100
Whiskers - Very short, very strong

Question 11

How are fibers oriented?

Answer 11

1D, planar, or random 3D

Question 12

What are common fiber materials?

Answer 12

Glass, carbon, boron,

Carbon and boron have high elastic modulus’s

Question 13

How are flakes and particles distributed?

Answer 13

Randomly

Question 14

What is the interface? Why is it important?

Answer 14

It is the contact point between the matrix and the reinforcing agent. There must be bonding at the interface in order for the composite to function.

Question 15

What is an interphase? What does it cause?

Answer 15

A bonding agent added to the interface. It causes an area of mixed solution of matrix and reinforcing agent at each interface.

Question 16

What determines the properties of a composite?

Answer 16

The materials used
The shapes of the components and the resulting structure
How the phases interact with each other.

Question 17

What is the relationship between the elastic modulus of a composite and the modulus of it’s matrix and fibers.

Answer 17

Longitudinally : Ec = EmVm + EfVf
Transversely : 1/Ec = Vm/Em + Vf/Ef
For random fibers : Ec = kEfVf + EmVm

Question 18

What is a laminar composite structure?

Answer 18

layers bonded together, but layers have different orientations
(wood boards with different grains)

Question 19

What is a sandwich structure?

Answer 19

A thick core of low density foam between two thin sheets of a different material

Question 20

What is a honeycomb structure?

Answer 20

A sandwich, but with a honeycomb core.

Question 21

What are cermets?

Answer 21

MMCs with particles of ceramics. Mostly ceramic, up to 96% volume.
Cemented cermets - carbide compounds
Oxide Based Cermets

Question 22

What are the most common type of composites?

Answer 22

PMCs

Question 23

Describe FRPs

Answer 23

Fiber Reinforced Polymers
The matrix is usually a thermoset, but sometimes a thermoplast
Glass is most common fiber
Often used in a laminar structure
High strength/weight ratio
Good fatigue strength
Good corrosion resistance
Often low thermal expansion

Question 24

What are reinforcing fillers and extenders

Answer 24

Reinforcing fillers: used to strengthen and improve mechanical properties of PMCs
Extenders: used to increase bulk and reduce cost per unit weight, don’t change properies