COMPOSITES slides

Question 1

What is a composite material?

Answer 1

a mixture of two or more discrete materials, with one (reinforcement) dispersed through the volume of the other (matrix)

Question 2

Types of reinforcement materials

Answer 2

Particulate
Short fibre
Continuous (long) fibre

Question 3

Types of matrix materials

Answer 3

Ceramic
Metal
Polymer

Question 4

what is the role of fibres within a composite?

Answer 4

to provide stiffness and strength

Question 5

most common fibre types

Answer 5

Carbon
Glass
Aramid (kevlar)

Question 6

Types of fibre architectures

Answer 6

UD Carbon Fibre
Woven

Question 7

What is UD carbon fibre

Answer 7

a type of fibre architecture in which the fibres are straight, continuous and parallel. (often supplied as prepreg)

Question 8

What are woven fibres

Answer 8

A type of fibre architecture in which fibres are bundles into groups called tows or rovings

Question 9

5 roles of a matrix within a composite?

Answer 9

1. holds the fibres together
2. transfers the load between fibres and the composite and its supports/attachment points
3. protects the fibres from the environment and mech abrasion
4. carries a small amount of the load
5. has mech properties (creep/corrosion resistance/flammability)

Question 10

examples of matrix materials

Answer 10

thermoset Epoxy
polyester
vinyl ester
phenolic

Question 11

2 main aims in composite manufacture

Answer 11

1. maximise fibre volume fraction (as fibres contribute the most mech performance)
2. minimise void content (voids => points of failure initiation)

Question 12

2 general considerations to achieve aims when manufacturing composites

Answer 12

• usually require applying pressure
• may or may not require heat (depends on matrix)

Question 13

What two main things of the final composite does the manufacturing process affect?

Answer 13

the quality and the properties of final composite material

Question 14

9 composite manufacturing methods

Answer 14

1. wet layup
2. vacuum bag
3. pre-preg layup
4. autoclave processing
5. automated pre-preg layup
6. resin infusion
7. resin transfer moulding
8. filament winding
9. pultrusion

Question 15

differences between wet and spray layup

Answer 15

Wet layup is a manual process whereby dry fibres are placed into a mould and covered in resin using brushes and rollers

Spray layup uses a chopper gun to spray chopped fibres and resin into a mould

Question 16

What is prepreg layup

Answer 16

A manufacturing method whereby pre-pregs can be cut to shape and layered in the mould.

Question 17

what is prepreg

Answer 17

a fibre pre-impregnated with resin

Question 18

Why does prepreg layup require pressure and heat?

Answer 18

to consolidate the layers and cure the resin

Question 19

what are the critical parameters in resin infusion and what is their significance?

Answer 19

Distribution mesh flow and Laminate permeability

High flow and low permeability will lead to a dry laminate

Question 20

ROM limitations (reasons why E2 correlation is worse than E1)

Answer 20

• assumes fibres are perfectly parallel, but can’t be perfect (also depends on manufacture)
• assumes Vf is consistent throughout laminate, however the fibres will vary slightly from one part of the component to the other (eg more matrix in some places and more spread out in others)
• assumes perfect interfaces between fibres and matrix
• is often considered an upper limit for composite properties as is idealised (interactions at interface won’t be as good as assumption ∴ lower properties)
• limited use in the transverse direction, as loading is far more complex than the assumed series loading

Question 21

what is micro mechanics?

Answer 21

prediction of material properties within composite materials

Question 22

what is classical lamination theory?

Answer 22

the prediction of the behaviour of multiple layers at different orientations in a laminate

Question 23

classical beam theories

Answer 23

Euler-bernoulli beams
Kirchhoff plates

Question 24

assumptions of classical theories

Answer 24

• plane sections remain plane
• plane sections are inextensible
• plane sections remain perpendicular to the mid surface (zero transverse shear)

Question 25

what is a failure criterion?

Answer 25

a factor that determines whether the material will fail. Failure criteria must consider the stress state of a material and return a value that indicates if the material will fail

Question 26

What is first ply failure?

Answer 26

an approach to failure whereby the laminate has failed if a single ply fails

Question 27

what is progressive failure?

Answer 27

when a laminate continues to carry load after a single ply has failed. Can then assume failed ply isn't there and recalculate ABD matrix with the ply removed/reduced properties

Question 28

What is Autoclave processing?

Answer 28

is a molding process of thermoplastic composite manufacture in which the fibrous reinforcement and thermoplastic matrix are laid down on a tool in the desired sequence and spot welded to make sure that the stacked plies do not move relative to each other.