Non metals

Question 1

What is a composite?

Answer 1

Mixture of two or more materials

Question 2

What are the benefits of polymer fibre composite?

Answer 2

stiffer, better support non axial load

Question 3

What are the different types of composites?

Answer 3

particulate
short fibre (aligned, random)
long fibre (unidirectional, woven)
nanocomposite (can be like fibre or particulate composite, short reinforcements but can act like long fibres)

Question 4

What are the different fibre types?

Answer 4

glass, carbon, Kevlar, silicon carbide fibres

Question 5

What are the different matrix types?

Answer 5

polymer matrix (thermosetting, thermoplastic)
ceramic matrix (silicon carbide, carbon)

Question 6

What materials are used for the fuselage?

Answer 6

glass and carbon fibres
unsaturated polyester resin and epoxy resin

Question 7

What materials are used for the wing?

Answer 7

same as fuselage materials
exotic resins like bismaleimides near engine
glass fibre and thermoplastic resins on leading edge for impact resistance

Question 8

What materials are used for radomes?

Answer 8

glass-fibres, epoxy resins
recently, fibre reinforced ceramics for high speed

Question 9

What materials are used for engine parts and brakes?

Answer 9

silicon carbide, carbon fibres and ceramic matrices for hot end applications
Kevlar based composites for containment rings

Question 10

Why are fibres important?

Answer 10

fibres have smaller flaws and higher strength than bulk materials

Question 11

How are glass fibres made?

Answer 11

storage of materials
weighing and mixing
melting at 1400ºC
refining at 1350ºC
forehearth at 1250ºC
bushings
cooling spray and sizing
fibres spools rotating at 2 miles per minute

Question 12

What are the types of glass fibres?

Answer 12

E-glass dominates
S-glass and R-glass have better properties
Fused silica/quartz have the maximum service temperature

Question 13

How are carbon fibres made?

Answer 13

PAN or pitch fibres in
stabilisation at 200-400ºC
carbonisation at 500-1500ºC
graphitisation at 2000-3500ºC
electrolytic bath
wash
sizing
drier
spool

Question 14

How are polymer fibres (Aramid) made?

Answer 14

The solvated polymer is pumped to spinnerets,
with the liquid-crystalline polymer squirting through and forming fibres.
Some of the solvent is removed at this point, and further solvent comes out in the spinning bath, giving solid fibres.
Further solvent is removed in the coagulating
bath.
A sizing can be applied but isn’t always necessary with
aramids

Question 15

What are the properties of polymer fibres?

Answer 15

generally highly aligned chains
often high temperature use
often badly affected by ultraviolet light
backbone chain gives difference in properties

Question 16

How are ceramic fibres made?

Answer 16

Polymer synthesis and thermal decomposition
to polycarbosilane
Melt spinning of fibres through a Spinneret at 500°C
Curing in air~ 200°C / Curing by electron beam
irradiation in an oxygen free environment
Pyrolysis~1000°C N2 atmosphere
SiCfibre bundle

Question 17

What is a polymer?

Answer 17

a material consisting of long chains usually of carbon atoms

Question 18

How do polymers deform?

Answer 18

chain motion

Question 19

What are the properties of thermoplastic polymers?

Answer 19

fairly linear chains - some branching
high performance = difficult processing
can be recycled
technically viscous behaviour above Tg

Question 20

What are the properties of thermosetting polymers?

Answer 20

typically highly cross linked
either very rigid or rubber
processing involves a chemical reaction
typically high thermal stability
generally processed from liquids so high performance ≠ difficult processing
can chemically bond to surfaces during processing

Question 21

How are composites made?

Answer 21

take an uncured resin and fibres and make a fully formed component in 1 step.

Question 22

What do we want when making composites?

Answer 22

surround fibres with uniform coating of resin
maximise volume fraction of fibres
uniform distribution of fibres
minimise number of voids

Question 23

Where do voids come from when making composites?

Answer 23

Resins absorb water which evaporates on cure
air mixing in during impregnation
improper impregnation

Question 24

What is a cure?

Answer 24

the process of turning a liquid resin into a solid polymer

Question 25

What is injection moulding?

Answer 25

plasticising the polymer
forcing the polymer in to a mould cavity
letting it solidify
ejecting the part
good for forming small components

Question 26

What is used for wet lay-up

Answer 26

lower performance resins such as epoxy resins

Question 27

What is wet lay-up?

Answer 27

apply the final surface finish as gel coat into mould prior to the first reinforcement layer
lay fibres into mould (often chopped strand mat)
mix resins and curing agent
apply resins to fibres and work in
may use vacuum/pressure to consolidate
prior to first layer, laminate fixing points into/onto part

Question 28

What materials are used for wet lay-up?

Answer 28

usually glass fibres and polyester resin

Question 29

What is wet lay up used for?

Answer 29

small low performance aircraft bodies such as sailplanes
radomes
simple fairings

Question 30

What is resin transfer moulding?

Answer 30

lay fibres into mould
close the mould and seal under pressure
inject resin into the cavity
until some leaks at the vent hole
allow the component to cure
eject and repeat

Question 31

What materials are used for RTM?

Answer 31

any fibre type
low viscosity resin such as unsaturated polyester resin or epoxy resin

Question 32

What are the benefits and disadvantages of RTM?

Answer 32

two good surfaces
high pressure so low low void content
expensive
care needed to make preforms

Question 33

What is VARTM?

Answer 33

lay fibres into the mould
the mould and fibres are covered by several layers of consumables
resin drawn through the assembly using the vacuum

Question 34

What are the benefits and disadvantages of VARTM?

Answer 34

only need a single sided mould and cheap moulds
only one good face

Question 35

What is the filament winding process?

Answer 35

fibre tow impregnated with liquid resin
excess resin squeezed out
from tows that are under
tension
Wetted tow/filaments
wound onto mandrel
Vary winding direction and
angle by altering the speed of rotation of the mandrel and of the fibre delivery head
Cure the part, by vacuum
bagging or using shrink wrap

Question 36

What materials are used for filament winding?

Answer 36

any continuous fibre tow and low viscosity resin (can be heated to reduce viscosity)
Hollow structures require a removable mandrel of a
hollow liner

Question 37

What is the cure process of filament winding?

Answer 37

• The resin bath and winding tension force the resin in to the bundles
• Air is forced out as well
• Low porosity if tension is
  correct
• Once wound, the resin is
  cured

Question 38

What is the pultrusion process?

Answer 38

continuous process
* Assemble bundles of
fibres
* Draw into die & inject
resin
* Die draws down
controlling volume fraction
* End of die heated to cure
* Draw out and cut to length

Question 39

What materials are used for pultrusion?

Answer 39

• Any reinforcement can be used
  – Continuous filament
  – Woven fabric
  – Chopped strand mat
  low viscosity resin

Question 40

What is the cure process of pultrusion?

Answer 40

• The fibres and mats are drawn through resin
• The fibres travel in to the mould section and are shaped and heated.
• The shape of the mould squeezes resin through the fibres, and excess resin and entrapped air is removed in the process
• The resin cures as the part is pulled through the mould
• At the end of the mould a continuous, cured, composite section is obtained
• This can be further shaped in to curve sections if required.

Question 41

What are the applications of pultrusion?

Answer 41

• Floor beams
• Fuselage frames
• Overhead locker components
• Any other repeated section

Question 42

What is a preform?

Answer 42

a package of fibres that make us a significant part of reinforcements of the composite