Materials Materials are all around us, we use them is
our everyday life, but what are the most common materials? What do they make? And what properties
do they hold? These are the key insights that we will try to uncover in this module.
For engineering purposes, materials can be divided into 4 key areas:
The first is Metals Metals are the widest used of the four materials.
Even if a material is not made of metal, metal will have been used at some point during it's
manufacture. Metals are used for everyday objects like cars, buildings and bridges,
but also go in to extreme applications like; jet engines, mining equipment and space exploration.
Even the tallest buildings in the world are only possible due to metals.
The second material is polymers, which includes plastics.
Polymers are widely used in many different industries. Natural polymers consist of amber,
wool, silk, natural rubber and cellulose which is the main constituent of wood and paper.
These natural polymers have been used for centuries. More recently Synthetic polymers
have been produced and these have revolutionised modern society. These include synthetic rubber,
nylon, PVC, polystyrene, silicone and many more.
The third is Ceramics
Ceramics have been used for thousands of years and the most common two are glass and clay.
Clay was the first material that we learnt to transform into another state using fire.
This was done about 29000 years ago when clay was formed into decorative figures. Much later
clay was used to form items like jugs and bowls.
Glass which is mainly made from sand, was mastered by the Romans who unlocked the secret
of blown glass by mixing it with minerals. The romans were the first people to use glass
for windows. The fourth material is Composites.
A composite is a combination of two or more materials. Composites have been used for centuries
in the form of concrete. Again it was the Romans who really mastered the process, in
text from 25BC different aggregates are discussed for use in lime mortars. In 1853 steel bars
were first added to concrete making one of our widest used composites: reinforced concrete.
Metals can be divided into two sub groups; ferrous and non-ferrous.
In Ferrous metals the main constituent is iron, and this group consist of steels and
cast irons. For the amount of strength that is achievable
in steel and cast irons, it is a cheap material. This is because iron is one of the most plentiful
elements in the earth's crust. Non-ferrous metals include any other metals,
some examples are aluminium, copper, zinc, titanium, and nickel.
Metals have good electrical and thermal properties. They are ductile, strong, tough and have strength
at temperature. Polymers are organic carbon containing molecular
chains. They have a wonderful array of properties
and are primarily made up from Hydrocarbons these are the building blocks of plastic,
Hydrocarbons are a by-product from petroleum industry and due to this they are an abundant,
and therefore a cheap material. The carbon and hydrogen which make up the
plastics are the key to how they work, because these can form together to produce long chains,
this enables plastics to be versatile and easily processed.
How the material is processed can produce the desired combination of properties; the
strength can be varied, the toughness can be varied, they can be a good conductor of
electricity and are often very good insulators. Again ceramics can have a wide array of properties
and in recent years we have really begun to understand them. Semi-conductors have been
produced which, when cooled, have virtually 100% efficiency in electrical conductivity.
To put this into perspective, current electricity cables lose about 5% of electricity through
resistance. With the loss in the world's electrical energy for one year you would be
able to power over 3 million washing machines constantly for 100 years, meaning that each
person on the earth could run a washing machine constantly for 15days for free.
Ceramics are an inorganic non-metallic material, they are chemically bonded and can have a
structure that is crystalline, non-crystaline or a mixture of both.
Ceramics are known for their light weight, high strength, high hardness, good heat and
wear resistance making them excellent for furnace lining. Although ceramics can be brittle.
Composites consist of a matrix or binder and a reinforcement. Composites affect our everyday
life, probably without our awareness. Concrete is likely to be the most common composites
and has shaped the modern world we live in. Concrete consist of a cement matrix and a
stone or aggregate Reinforcement. Another is fibre glass, with a matrix of plastic and
a reinforcement of fine strands of glass. In the 1960's Scientists set out to make
plastics as strong as metals. Through their research they produced carbon fibre, this
is also known as carbon fibre composite and it is made from fibres of carbon and plastic
(similar to glass fibre). This gives unique properties of strength, stiffness while being
light weight. But carbon fibre is very expensive. Script:
Only over the past 60 years have we really understood metals on an atomic scale.
In metals, atoms are arranged in an orderly manner giving them a crystalline structure.
Metals consist of two common arrangement of atoms. One with an atom at each of the corner
of a cube and one atom at the centre, this is called Body Centred Cubic.
The other has an atom at each corner of a cube and one atom on each face of the cube
this is called Face Centred Cubic. Mild steel arranged in a crystalline manner
should have a strength of approximately 20,000MPa which is equivalent to supporting the weight
of an elephant on a 1mm thick piece of wire, but mild steel has a strength much lower than
this. It has a strength of approximately 1000MPa (or a strength 20x lower) which is equivalent
to supporting the weight of a sheep from a 1mm thick piece of wire.
The reason that steel is reduced in strength is due to the imperfections in the atomic
structure, these are called DISLOCATIONS. Normally when we think of crystals we imagine
that we can smash them under a load like a hammer but the interesting thing about metals
is that when pressure is applied the atoms can move and this is how a they can be formed
and worked into different shapes. The dislocations help this deformation process.
In metal the atoms are arranged in groups, these groups are galled grains, these are
evident when you look at a zinc coated surface or what is known in the industry as a galvanised
surface. These grains can work both in favour and against the steel, they can increase the
ductility of the steel, but where the grains join (the grain boundaries) are areas where
impurities collect. Metals can be strengthened by adding more
than one metal together such as copper and tin to make bronze. In this example the two
combined has far greater strength than each of the individual metals (the sum is greater
than the parts). We can also change the properties of metals by adding non metallic elements
like carbon. If we take steel, there are hundreds of steels
all with slightly different properties, some tough, some strong, other resistant to rust.
These steels are produced by the same principle as bronze, we take one element IRON, which
is the bulk of all steels and add another chemical elements. Often called alloying elements
to it, to name a few we could add Carbon, Manganese, Nickel, Copper, Molybdenum, Boron,
Chromium, Niobium, Titanium, Vanadium. In this way we can tailor a steel to a specific
application. So we take our grains of iron atoms
And our alloying additions, which often have a different atomic size, for example Carbon
is small, Nickel is slightly smaller that iron and Molybdenum is slightly larger than
iron. And add them together
And we get a distorted structure When we add atoms that distort the atomic
structure this makes it more difficult for the atoms to move around and makes the material
stronger. Depending on the type and amount we can make a metal much stronger.
The smallest elements like carbon lay in between the iron atoms, these are call interstitial.
We have the largest atoms which replace an iron atom, like Molybdenum, this is called
substitutional, this type expands the structure. Or we can have smaller substitutional atoms,
like Nickel, that collapse the structure. Script:
So in Summary Engineer materials can be divided in to 4
key areas, Metals, Polymers, Ceramics and Composites.
Composites are as high tech as carbon fibre and as abundant as concrete.
Composites are a combination of two or more materials
Composites consist of a binder and a reinforcement Ceramics were the first material that we learned
to transform from one state to another. Ceramics are inorganic non-metallic materials.
We have really begun understand ceramics in recent years with semi-conductors.
Polymers have revolutionised modern society. Plastics are made from hydrocarbons which
are a by-product of the petroleum industry, this make them abundant and cheap.
How the polymer is processed has a large influence over its properties.
Metals are the widest used of the 4 materials. Metals are divided in to two sub-groups; ferrous
(containing iron) and non-ferrous (not containing iron).
Iron is one of the most plentiful elements in the earth's crust. This is used to make
steel and cast iron, which makes them efficient in terms of cost per the amount of strength
achievable. The atoms in metals are arranged in an orderly
manner, they have a crystalline structure. The theoretical strength of metals is much
higher than reality due to dislocations. The crystals of metals are arranged in grains.
The properties of metals can be manipulated by adding other chemical elements to them.
These elements distort the atomic structure making it more difficult for atoms to move
around.