9.1 & 9.2 & 9.3 - Basic Properties

Question 1

What is corrosion?

Answer 1

When metals and alloys are attacked / eaten away by chemical substances

Question 2

What is degradation?

Answer 2

When non-metals are attacked by chemicals, they are weakened / destroyed

Question 3

Corrosion example?

Answer 3

Rusting of ferrous metals caused by the action of atmospheric oxygen in the presence of water

Question 4

Degradation example?

Answer 4

Rubber (if not compounded) is attacked by prolonged oil exposure, and is also damaged by UV rays

Question 5

What is electrical resistance?

Answer 5

Low resistance results in good conduction whilst high resistance means good insulation (metals are good conductors, whilst non-metals insulators, except for carbon)

Question 6

What does electrical resistance depend on?

Answer 6

Length (longer means more resistant)
Cross-sectional area (thicker means less resistant)
Temperature (higher temp leads to greater resistance)
Resistivity (resistance measured between opposite faces of a metre cube of a material)

Question 7

Ferromagnetic material examples?

Answer 7

Iron
Nickel
Cobalt

Question 8

What are soft magnetic materials?

Answer 8

Materials that can be magnetised via a magnetic field, but cease to be magnetised once the field is removed

Question 9

How to make soft magnetic materials more efficient?

Answer 9

Adding silicon or nickel to pure iron

Question 10

Soft magnetic material examples?

Answer 10

Soft iron
Silicon-iron alloys are used for the rotor and stator cores of electric motors and generators, as well as power transformers

Question 11

What are hard magnetic materials?

Answer 11

Materials that can be magnetised, and retain this property once the field has been removed, becoming permanent magnets

Question 12

How to make soft magnetic materials more powerful?

Answer 12

Adding cobalt to the steel to make an alloy

Question 13

Hard magnetic material examples?

Answer 13

High carbon steel that has been hardened by cooling it rapidly (quenching) from red heat

Question 14

What is strength?

Answer 14

The ability of a material to resist an applied force without fracturing maximum stress it can handle), and to not yield (elongate under pressure, changing shape permanently)

Question 15

Examples of applied loads?

Answer 15

Tensile load - material is pulled, made longer
Compression load - material is pushed inwards, made shorter
Shear load - material pushed inwards at different points, changed shape (parallelogram)

Question 16

Tensile elongation?

Answer 16

ε strain = extension/original length (ductility)

Question 17

Compressive reduction?

Answer 17

ε strain = -extension/original length (malleability)

Question 18

Shear deflection?

Answer 18

ε strain = extension/original length (length as height)

Question 19

Equation for stress?

Answer 19

Stress = force/area (cylinder, force active at both ends, area being that of the circle)

Question 20

What is toughness?

Answer 20

The ability to resist impact loads, amount of energy absorbed before failure

Question 21

How to test toughness?

Answer 21

Izod test, uses a notched specimen that is hit by a heavy pendulum (test conditions are controlled)

Question 22

Example of toughness?

Answer 22

Tough steel - a 1.2% carbon steel rod in the annealed (soft) condition will bend under a hammer impact with a tensile strength of 925MN/m2
Hard steel - the same rod, after quench hardening, will fracture when hit, despite having a tensile strength of 1285MN/m2

Question 23

What is elasticity?

Answer 23

The ability to change shape when subjected to an applied force but spring back to the original size and shape once the force is removed
Opposite of plasticity

Question 24

What is plasticity?

Answer 24

The ability to flow into a new shape when subjected to an applied force and keep that shape once the force has been removed
Opposite of elasticity

Question 25

What is ductility?

Answer 25

The ability to change shape via plastic flow when subjected to a tensile force

Question 26

What is malleability?

Answer 26

The ability to change shape via plastic flow when subjected to a compressive force

Question 27

What is hardness?

Answer 27

The ability to withstand scratching or indentation by and even harder object

Question 28

What are the 3 tests for hardness?

Answer 28

Brinell hardness test
Vickers hardness test
Rockwell hardness test

Question 29

What is the Brinell hardness test?

Answer 29

Hardened steel ball pressed into specimen by controlled load, diameter of indentation measure using a microscope, hardness value obtained via conversion table

Question 30

What is the Vickers hardness test?

Answer 30

Diamond pyramid pressed into material via controlled force, square indentation is made, diagonal length of square measured to used for conversion value

Question 31

What is the Rockwell hardness test?

Answer 31

Diamond cone makes small indentation (minor load applied), major load then applied which increases indentation depth, the increase is directly converted into a hardness number to be read from the machine

Question 32

What is rigidity?

Answer 32

The ability to resist changing shape under a load

Opposite of flexibility

Question 33

What is flexibility?

Answer 33

The ability to change shape under a load

Opposite of rigidity

Question 34

Example of rigidity vs flexibility?

Answer 34

Cast iron is more rigid than steel, which is stronger and tougher, but the ability to be rigid makes cast iron a better material for machine frames and beds

Question 35

What is melting temperature?

Answer 35

The temperature at which a material loses its solid properties, some plastics only become charred and destroyed

Question 36

What is thermal conductivity?

Answer 36

The ability to conduct heat, metals are typically heat conductors whilst non-metals insulators

Question 37

What is thermal expansion?

Answer 37

When materials expand then contract due to the application and removal of heat, metals have high coefficients of linear expansion (expand more than non-metals which have a low coefficient)

Question 38

Ohm’s law?

Answer 38

V = I x R (voltage = current x resistance)