Properties of Materials

Properties of Materials

Mechanical

Hardness - the ability to withstand abrasion (scratches) and indentation.

Toughness - the ability to withstand sudden impact without breaking or fracturing.

Elasticity - the ability of a material to return to its original shape after being stretched or compressed (to withstand elastic deformation).

Plasticity - the ability of a material to be shaped and formed without returning to its original shape (permanent deformation).

Ductility - the ability of a material to be drawn out into long thin wire.

Malleability - the ability of a material to be deformed and easily worked into shape.

Compressive Strength - the ability of a material to resist breaking under compression.

Tensile Strength - the ability of a material to resist breaking under tension.


Physical

Density - the degree of compactness in a material, measured in kg/m


Thermal

Melting Point - the temperature at which a given solid will melt.

Thermal Conductivity - the ability of a material to conduct heat.


Electrical

Conductivity - the degree to which a given material conducts electricity.

Resistivity/electrical resistance - how strongly a given material opposes the flow of electric current.

Insulator - a material that does not readily conduct electricity, or allow the passage of heat or sound.


Magnetic

You will need to know the difference between hard magnetic and soft magnetic materials:

○ Hard Magnetic - Materials which are permanently magnetic. They retain their magnetism and are difficult to demagnetise.

○ Soft Magnetic - Materials that are easy to magnetise and demagnetise. The material may not be magnetic in the first place.

- For the exam, you need to be able to distinguish between magnetic and non-magnetic materials:

Magnetic Non-magnetic
Cast iron Aluminium
Nickel Titanium
Low/medium/high carbon steel Duralumin
Stainless steel Copper
High speed steel Zinc
Brass
Tungsten
Tin
All plastics, composites, ceramics, and new materials (on the specification)

For the exam, you should try to remember that iron, nickel and all steels are magnetic as they are ferrous (iron is magnetic). Everything else is not magnetic.

Note: Some of the 'non-magnetic' materials are magnetic ever so slightly. If a powerful enough magnet was applied to them, they may react to it. However, the level of magnetism that these materials contain is not high enough to be acknowledged, and they are considered to be non-magnetic for the exam and all other practical uses. In addition, there are more materials than this, but they are not relevant to this exam.


Property Tests

Izod - The Izod test is used to find out how tough a material is. The test measures the impact resistance of a material by hitting a small specimen of the material with a pivoting arm. The point at which the material breaks is measured and determines how tough the material is.

- This is measured in Joule per cubic metre (J. m−3)

izod test image

Brinell - The Brinell test is used to find out how hard a material is. The test measures the width of indentation made by a spherical indenter applied to a test specimen at a given load, for a given length of time.

- This is measured by using the Brinell test scale


Deterioration of Materials

Corrosion/oxidation - Ferrous metals, such as iron and steel, rust when they come into contact with water and oxygen. It is an oxidation reaction, where the ferrous metal reacts with water and oxygen to form rust, which usually appears on the surface of the material. Both water and oxygen are needed for the reaction, hence why unprotected ferrous metals rust when outside, as they are exposed to moisture and oxygen.

- One type of Corrosion is Galvanic Corrosion, which occurs when two dissimilar metals are immersed in a conductive solution and are electrically connected (like electroplating). One metal (the cathode) is protected, whilst the other (the anode) is corroded.

Fatigue - Fatigue is the weakening of a material caused by repeatedly applied loads. This occurs over time, when a load is constantly placed on and off a material. This weakens the material, making it more likely to break when the same load is applied each time.

UV degradation (the effects of UV lights on some polymers) - When polymers are exposed to intense UV light for long periods of time, they can start to degrade and erode. An example of this is leaving untreated plastics in direct sunlight on a sunny day. The polymers absorb the energy from the sun which causes the polymer to degrade.

- Possible examples of degradation include: erosion (surface of the plastic turning white and forming a powdery residue), lower tensile and compressive strength, loss of elastic behaviour and cracking.

For more information: http://www.drb-mattech.co.uk/uv%20degradation.html


Price of Materials

For the exam, you will need to know the rough price of materials. You will not need to know the exact price of them, but more which materials are cheap, mid priced and expensive. Below is a table which contains the rough location of each material on a price spectrum.

Note: I have left all plastics, elastomers and new materials out of the table as their cost is not significant enough to be on the table. They are cheaper than all materials on the table.

Cheap Mid-priced Expensive
Cast iron Zinc GRP
Low/medium/high carbon steel Copper Carbon Fibre
Pyrex (borosilicate glass) Tin Titanium
Aluminium Stainless steel High speed steel
Duralumin Brass Nickel
Porcelain Tungsten