Metals

Question 1

What two groups can metals be split into?

Answer 1

ferrous

non-ferrous

Question 2

What do ferrous metals contain?

Answer 2

iron

Question 3

What is a metal alloy?

Answer 3

a material formed by adding various elements to a basic metal in order to improve the mechanical and chemical properties

Question 4

what is steel an alloy of? How are steels classified?

Answer 4

iron and carbon (mainly iron)

steels are classified by carbon content

Question 5

Why is chromium used in stainless steel? what % of chromium is contained in these alloys?

Answer 5

it provides a corrosion resistant property.

12-18%

Question 6

What are some examples of stainless steel in medical applications?

Answer 6

cardiac pacemaker housing
limb prostheses
orthoses
accupuncture needles

Question 7

Name a type of non-ferrous alloys

Answer 7

titanium based alloys

Question 8

what are the advantages of titanium based alloys?

Answer 8

lower density compared to steel
higher strength to weight ratio compared to aluminium
excellent corrosion resistance

Question 9

What are the disadvantages of titanium based alloys?

Answer 9

high material cost
high fabrication cost
low youngs modulus compared to stainless steels (thicker sections can be used to combat this)

Question 10

What are polymers?

Answer 10

lightweight, corrosion resistant, electrical insulators with relatively low tensile strengths and melting points formed from single units called monomers

Question 11

What are the two main types of polymer?

Answer 11

plastics

elastomers

Question 12

What are the two types of plastic?

Answer 12

thermoplastic

thermosets

Question 13

What are thermoplastics?

Answer 13

display plastic behaviour at high temperatures - their structure is stable at temperature and can be heated, cooled and reheated without much change.

examples are - Polyethylene (acetabular cups) - PVC - ankle foot orthoses - PMMA - bone cement

Question 14

What are thermosets?

Answer 14

plastics that can not be reformed as during their formation at high temperature, a by product is released from the material - restricts their recyclability

Question 15

What are elastomers better known as? What are their mechanical properties?

Answer 15

rubbers - they can be deformed enormous amounts (700%) before permanently changing shape

Question 16

Describe ceramic materials

Answer 16

they are crystalline in structure with an extreme hardness. they are hard, brittle materials with a high melting point , low conductivity of heat and electricity. ceramics do not creep

Question 17

Give some examples of ceramic materials

Answer 17

glass
brick
diamond

Question 18

Why is it desirable to reduce grain size during manufacture of ceramics?

Answer 18

reduces pore size between grains therefore reduce the amount of defects and prevent reductions in tensile strength and toughness.

Question 19

Name the 3 types of composite materials

Answer 19

particulate-reinforced
fibre-reinforced
laminar reinforced

Question 20

Describe particulate reinforced composites - give an example

Answer 20

hard brittle material dispersed in a softer more ductile material e.g. concrete (gravel + cement)

Question 21

Describe fibre reinforced composites - give an example and examples of the benefits

Answer 21

incorporate a strong, stiff, brittle material dispersed in a softer more ductule material to improve strength, fatigue resistance and strength to weight ratio.

e.g. fibreglass / concrete blocks reinforced with steel rods

Question 22

Describe laminar reinforced composites and give examples.

Answer 22

Can take different forms - LAYERED

a very thin corrosion resistant coating may cover a material to improve corrosion resistance

thicker layers may be laminated together to improve strength e.g. plywood alternating layers of wood veneer at right angles each layer.