Chapter 1: Materials and their properties

Question 1

Definition of strength

Answer 1

the amount a material can withstand a force applied to it

Question 2

Definition of ductility

Answer 2

the amount a material can be deformed

Question 3

Definition of toughness

Answer 3

the amount a material can withstand an impact without breaking

Question 4

Definition of hardness

Answer 4

the amount a material can resist wear and abrasion

Question 5

Definition of stiffness

Answer 5

the amount a material can resist bending

Question 6

Definition of brittleness

Answer 6

the potential for a material to shatter when in contact with a force

Question 7

Definition of malleability

Answer 7

the amount a material can be deformed without rupturing

Question 8

What is Young’s Modulus

Answer 8

The ratio of stress to strain of a material. it shows how stiff a material is

FORMULA: STRESS/STRAIN

Question 9

Formula for stress

Answer 9

Stress = force/cross-sectional area

units for stress is in* N/mm^2*

Question 10

Formula for strain

Answer 10

Strain = change in length/original length

no units!

Question 11

Type of strengths

Answer 11

Tensile: ability to resist a pulling force
Compressive: the ability to resist a squeezing force
Torsional: the ability to resist a twisting force

Question 12

Give examples of ferrous metals, and non-ferrous

Answer 12

Ferrous metals and alloys:
* cast iron
* low and high carbon steels
* steel alloys (stainless steel).

Non-ferrous metals and alloys:
* aluminium
* copper
* lead
* zinc
* alloys (brass and bronze).

Question 13

What is annealing?

-modifying the structure of metals-

Answer 13

A heat treatment that makes a metal softer and easier to work with (more malleable/ductile)
* metal is heated to specific temp/colour, allowed to cool down after

Question 14

What is hardening?

Answer 14

a heat treatment that increases the hardness & strength material (due to changed in arangement of atoms)
* Heat to a temp a bit above the lower critical point, soaks (often oil/brine) at that temp so grains have time to rearrange
* tempered: to remove some of the brittleness

* quenching: rapid cooling of a hot metal by immersing in a liquid (oil)

Question 15

What is normalising?

Answer 15

A heat treatment that results in metal that is tough, with some ductility.
* Metal is heated to temp under melting point, cools in the air

Question 16

What is cold working?

Answer 16

A process of strengthening metals through plastic deformation.
Metals become harder to resist any further change.

-non heat process-
eg: hammering

Question 17

What is corrosion?

Answer 17

a reaction between the surface of the material and the environment that consumes some of its material.
* often possible to alter effects of environment by managing corrosion or adding/subtracting carbon (to change structure of surface. )

Question 18

How to add or subtract carbon in steels?

Answer 18

Adding:
* heat the steel part until it becomes cherry red, then dip it into the carbon powder. Do this a few times and some of the carbon powder will be absorbed into the steel surface.
* Using a wire brush, clean off the excess carbon
* (complete hardening process): heat to cherry red, and quench in oil. (tempering is not needed)

Question 19

Difference between thermoplastic and thermosetting polymers

Answer 19

Thermoplastic: recyclable, can be reshaped and reheated
thermosetting: not recyclable, cannot be reshaped and reheated

Question 20

ABS

thermoplastic

Answer 20

recycling number 9:
* strong
* rigid
* harder and tougher than polystrene

1.plastic pipes
2.children’s toy

Question 21

Polystyrene

thermoplastic

Answer 21

recycling symbol 6:

• good toughness
• good impact strength
  1. packaging
  2. foam cups

Question 22

Acrylic

thermoplastic

Answer 22

Recycling symbol 7:
* transparent
* hard wearing
* not shatter
1. plastic windows
2. bath tubs

Question 23

Polyester resin

thermosetting

Answer 23

• stiff
• brittle
• good strength
  1. suitcases

Question 24

Nylon

thermoplastic

Answer 24

Recycling number 7:
* ductile
* durable
1. gear wheels
2. bearings

Question 25

melamine resin

thermosetting

Answer 25

• stiff
• hard
• strong
  1. kitchen worktops

Question 26

Epoxy

thermosetting

Answer 26

• stiff
• brittle
  1. printed circuit boards

Question 27

CRP

composite

Answer 27

• carbon fibres in resin matrix
• low density
• high strength
  1. aircraft structure

Question 28

GFP

composite

Answer 28

• glass fibres in resin matrix
• high strength
• low density
  1. water tanks

Question 29

Plywood

composite

Answer 29

• layers of wood bonded at right angles
• uses adhesives
• smooth surface
  1. furniture making

Question 30

MDF

composite

Answer 30

• wood fibres and adhesive matrix
• smooth
• able in veneered form
  1. furniture, internal panelling

Question 31

OBS

composite

Answer 31

• strands of wood compressed with adhesive matrix
• more uniform
• lower cost
  1. walls, roof decking

Question 32

structural concrete

composite

Answer 32

• most common
• concrete reinforced with steel bars to increase tensile strength
  1. bridges