Composites and Smart Materials

Question 1

What are the three types of composites?

Answer 1

Particle, Laminate, Textile

Question 2

Give an example of a particle composite

Answer 2

Concrete (sand, water, cement, aggregate)
MDF
Chipboard

Question 3

Give an example of a laminate composite

Answer 3

Plywood
CFRP (carbon fibre reinforced plastic)
GRP (fibre glass and polyester resin)
Kevlar (aramid)

Question 4

Give an example of a textile composite

Answer 4

Gore tex
- polyester/nylon
- PTFE/Teflon

Question 5

Advantages of GRP

Answer 5

• Cheaper than the other composites
• Lightweight, corrosion resistant, easily processed and good mechanical properties.
• Generally easy to manufacture and build items from.
• Often used in combination with another material to provide additional support

Question 6

What is GRP made of

Answer 6

chopped up glass strands from mat form combined with polyester resin

Question 7

Disadvantages of GRP

Answer 7

Brittle - impact will cause cracking and it is difficult to repair - it usually means the part will have to be replaced

Question 8

What is Kevlar?

Answer 8

Strong artificial fibre (aramid carbon fibre composite) which can be woven into materials that is used for light and flexible body armour, but also used in sport equipment

Question 9

What is carbon fibre (CFRP)?

Answer 9

Can be in a strand form, a fibre form or woven into a sheet form. Often combined with phenolic, polyurethane or epoxy resins as the matrix

Question 10

Advantages of Kevlar

Answer 10

• Strong tensile strength but very flexible as the molecules can pack closely together.
• Tough - very resistant to impact and abrasion damage, hence its use in bullet and stab proof vests - but also used in sports gear as it is good at resisting high velocity objects like balls.
• Can be made waterproof when combined with other matrix materials like epoxy.
• Can also be combined with rubber to increase the flexibility of sports equipment.

Question 11

Disadvantages of Kevlar

Answer 11

Poor compressive strength
Frays easily

Question 12

Advantages of CFRP

Answer 12

• High temperature resistance
• Corrosion resistance
• Lightweight
• High mechanical strength
• High strength to weight ratio
• Due to strength can be made in very thin sections so it is lightweight. Can be made in thinner sections than other composites.

Question 13

Disadvantages of CFRP

Answer 13

• More expensive than most other composites
• Often used to create stiffness in equipment. Greater stiffness resists bending forces and transfers more power to an object (useful in sports equipment).
• Not especially tough does not resist impact forces well and tends to break. Often combined with Kevlar to resist this. This composite is very strong but flexible and expensive)-

Question 14

What is gore tex?

Answer 14

A synthetic waterproof fabric permeable to air and water vapour

Question 15

How does gore tex work?

Answer 15

There is a microporous membrane which allows water vapour to pass through but not water droplets so it it breathable and waterproof

Question 16

Advantages of gore tex

Answer 16

waterproof
breathable
lightweight
durable

Question 17

Disadvantages of gore tex

Answer 17

Can be expensive
Hard to care for (should be cleaned)
Not absorbent

Question 18

What is nomex?

Answer 18

A flame-resistant aramid material, e.g. used for firefighter’s suits

Question 19

Advantages of Nomex

Answer 19

Heat Proof
Durable
Extremely strong in tension and tough

Question 20

Disadvantages of nomex

Answer 20

Not absorbent
Weak in compression
Can be expensive

Question 21

Give 3 examples of smart/modern materials

Answer 21

• thermochromic and photochromic inks
• shape memory polymers
• phosphorescent materials

Question 22

Describe a use for a thermochromic ink

Answer 22

Used on kettles - shows when water is hot so you don’t need to reboil your kettle
Used on baby thermometers - place strip of paper with these inks on forehead and it will change colour according to temperature, means you don’t need to stick a thermometer in young babies mouth

Question 23

Describe a use for photochromic inks

Answer 23

Glasses for indoor and outdoor use (Reactolite Lenses) - change with light intensity to go darker when there is high UV to protect retinas from direct sunlight, acts as sunglasses with prescriptions

Question 24

Describe an example of a shape memory alloy

Answer 24

Medical equipment - tube is cooled and squashed into a smaller tube. it is inserted into an artery and will expand due to body heat keeping the channel open for blood flow

Car bumpers - if in a crash, metal can be heated and it returns the shape. It is still strong to act as a bumper when at normal temperature. Means you don’t need to replace bumpers as much.

Question 25

What is a shape memory alloy

Answer 25

a metal that can be bent out of its original shape and then returned to its original shape when heated.