Describe the material out of equilibrium and

Describe the effects of hot
working and cold working
processes on the properties and behaviour of 60/40 and 70/30 brass respectively.

 

There are different reasons for why you would need to work
on metal. You can either hot/cold roll on metal to get them down to a specific
size. Depending on whether you either hot work or cold work, different
properties would be in the metal. For example, hot rolling brass would make it
more brittle as it can change the crystal structure in the brass. Below is some
characteristics of hot and cold rollingCB1 :

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Hot
Rolling Characteristics

Cold
Rolling Characteristics

Layout Orientation

The material characteristics are identical in all directions.

Care must be exercised in layout. The grains of the material
are deformed during the rolling process and stay deformed. The material will
be stronger with the grain than against the grain.

Price

Less Expensive

More Expensive

Strength

Weaker

Stronger

Weldability

Excellent for Welding.

Weldable, but the material will
take on the properties of hot roll
wherever it is welded

Dimensional Tolerance of stock

Fair.
Deviations from the stated size are present due to surface scale
and thermal shrinkage.

Good.
It is not as accurate as ground stock, but better than Hot
Roll.

Machinability
 

Experiences no warping when
machined

The removal of too many residual stresses, such as when a
large face is fly cut, will throw the material out of equilibrium and cause
deflection and warping.

Surface Finish

Fair to Poor.
The surface of the material will be covered with carbon scale.

Good.
Not as good as ground stock, but much better than Hot Roll.

 

 

 

 

 

Hot Working:

Hot rolling
uses large pieces of metal, often called slabs or steel billets, and it will
heat them above their recrystallization temperature. This is so they can then
be deformed between rollers which creates a thinner cross sections. When hot
working, you are able to get a thinner cross section than those formed by cold
rolling. This is done by the same number of processes. Only 60/40 brass can be
hot rolled as it gives better properties rather than if it was cold rolledCB2 .

Cold Working:

Cold rolling is
where metal will pass through rollers at room temperature. This means that it
is passed through below its recrystallization temperature. Cold rolling will
increase the yield strength and hardness of the metal. This is done by
introducing defects into the crystal structure of the metal creating a hardened
microstructure which prevents further slip. As cold rolling is done at room
temperature it is more labour intensive and is a more expensive process than
hot rolling. 70/30 brass has excellent cold rolling properties, and will give
better end properties rather than it being hot rolledCB3 .

 

 

 

(ii)

Describe the effect on
properties and behaviours of uni-axial orientation in thermoplastic polymers drawn into fibres.

Polymer chains can have different orientations which will
affect their properties that they possess. Polymer chains will be subjected to
extensional strain while they are being melted. This will occur in most
thermoplastic fabrication methods. When the polymer is in the melt, more
orientation can be induced by mechanically drawing an extrudate. This will then
be left in the die and it will solidifies in extended chain conformations. Once
it has solidifies, it will lead to uniaxial orientation. An example of the
uniaxial orientation method is shown belowCB4 .

(iii)

Describe the effects on the properties and behaviours
of biaxial orientation in film sheets.

Biaxial orientation is a procedure in which the film which
will be stretched in two different directions. This process will result in a
molecular redirection. This orientation tends to be much stronger in terms of
tear strength and it will usually be very well balanced in both directionsCB5 .

 

 

 

 

(iv)

Describe how, in an engineering
context, the water content of clay affects the properties and behaviour
of material during processing.

During the
process of manufacturing clay, there are different amounts of water content
which will affect the properties that the clay possess. Raw clay in its natural
state is dry and crumbly. This means that you are not able to work with clay in
its natural state as it will not be able to stick together. Slip is a mixture
of water and clay, at this stage the clay is still not workable as there is too
much water in the clay. The next stage is a plastic stage, this is the workable
stage and you can join the clay to other pieces and it will stick together. The
leather-hard stage is where the clay is stiff and it will hold its shape. As
the clay dries, water molecules escape from between the clay sheets, so these
move closer together (the clay shrinks by 5% or more). This is where it will be
in the next stages which is the greenware stage. The clay will become “bone
dry”, fragile, and you will be unable to join it to other pieces. If at this
point the clay object is put into water it will disintegrate and can be
returned into a workable state. After the clay has dried in the greenware stage
they can be glazed. This is where you cover it in a thin layer of glass. This
can be for aesthetic or for practical reasons, usually both. It is particularly
important for pots holding food. The three glazing stages are bisqueware,
earthenware, and stonewareCB6 .

(v)

Describe how the strength
of concrete is improved during
processing with the addition of reinforcement.

Concrete is a very popular building material, this is due to
it being cheap to produce and it uses readily available ingredients. Concrete
is made up of a mixture of coarse and fine aggregates (e.g. sand, gravel, and
stones), cement, and water. Concrete starts as a viscous liquid and therefore
can be used to make all kinds of shapes, which is very handy when using it in
construction. Concrete is fireproof and relatively waterproof. One of the main
reasons why it is used in construction is that it is extremely strong in
compression, this means that it can resists a great amount of weight that is on
top. However, concrete is around 10 times weaker in tension than compression
and therefore it can crack or snap very easily if bent or stretched. This can
be eliminated by reinforcing the concrete.

Reinforcing concrete is where steel bars are tied together
to make a cage and then wet concrete will be poured in surrounding the steel
cage. Once the concrete sets around the steel bars a new composite material
will be made, reinforced concrete. The steel bars will help to prevent cracking
or snapping by stopping the concrete from bending/stretching. Steel is the most
popular material to use because concrete and steel have similar properties when
it expands and contracts in the hot and cold weathers. This will help it to
stop cracking the concrete is different weather conditions. Below is an image
of reinforced concreteCB7 .

(vi)

Write a brief outline of so called ‘Smart’ materials and the special
properties they possess for particular
applications, quoting examples
of applications you may find.

Smart materials are materials which properties can change by
reacting to the environment it is in. This means that an external condition can
change its properties. The conditions can be for example, temperature, light,
pressure or electricity. There are many different smart materials and they all
offer different properties which are changed due to their environment. Some
different examples of smart materials are piezoelectric materials,
quantum-tunnelling composite, electroluminescent materials, and colour changing
materials.

A piezoelectric material can produce a small electrical
voltage when it is squeezed rapidly. If
a voltage is put across the material it makes a tiny change in shape. This
material can be used for contact sensors for alarm systems and in
microphones/headphones.  A
quantum-tunnelling composite is a flexible polymer which contains tiny metal
particles. It would normally be used for an insulator but if it is squeezed it
can be used as a conductor. This composite will be used to make membrane
switches on mobile phones, pressure sensors and speed controllers.  An electroluminescent material is a material
which will give out light when an electrical current is applied to it. These
are often used for safety signs and clothing for use at night. There are two colour-changing materials which are smart materials.
Thermochomic materials will change colour when temperature changes. These are
often used on contact thermometers made from plastic strips and
test strips on the side of batteries. Photochromic
materials change colour according to different lighting
conditions. They are used for security markers that can only be seen in
ultraviolet lightCB8 .

Task 2 (M1)

Compare and
contrast the properties of low and medium carbon steel to aluminium alloy in relation to their behaviour in the manufacture of a motor
vehicle frame, chassis and panels.

Low Carbon Steel

In order for low carbon steel to be considered
steel there are certain characteristics which it must meet. The steel must only
contain a maximum of 0.28% carbon in its total makeup, otherwise it wouldn’t be
considered as a low carbon steel. LowCB9  carbon steel also contains pearlite and
ferrite as major components. Low carbon steel is generally used straight from
the forming process, whether that process is hot forming or cool forming,
because that’s when it’s most workable and easiest to form. Low carbon steel is
often used in the manufacturing of vehicle frames, chassis and panels, this is
due to the properties that low carbon steel possess. Low carbon steel has some
of the best weldability over any metal. This is due to there being a low carbon
content in the metal. When there is a high amount of carbon present in the
metal, it will be more prone to cracking while it is being welded, therefore
low carbon steel doesn’t have that problem. Another property that low carbon
steel possess’ which makes it very suitable in the motor manufacturing industry
is good formability. This means that low carbon steel is easier to form into
certain shapes, through such methods as pouring, molding and pressing. The
ability of the steel to be turned into a number of different forms makes it
quite versatile. Low carbon steel can also be used for to produce hardened
machined parts which will also be used when producing vehicles. These parts are
chain, rivets, stampings, nails, wire and pipeCB10 .

Medium Carbon
Steel

The carbon content in
medium carbon steel must be over 0.29% and below 0.55%. Usually the average
amount of carbon that is found in its composition is around 0.4%. Medium carbon steel won’t be
used vehicle manufacturing due to its properties. Medium carbon steel will
often be used for the manufacturing of tools such as drill bits, knives, nails,
and saws. Medium carbon steel is a hard material. However, due to the extra carbon
content this will make the metal more brittle and is likely to fracture if it
is misused. Medium carbon steel also is highly rated for wear resistance, which
makes it good for tooling. Medium carbon steel doesn’t have high weldability,
it is very likely to fracture or break if it exposed to weld. Due to this it
would be unsuitable for it to be used in the manufacturing of vehicle chassis
and partsCB11 .

Aluminum Alloy

Aluminum alloy is
another material that is often used in the automotive industry to produce
chassis, frames, and panels. This is due to the properties that aluminum alloy
possess. Aluminum is a light metal, which is about the third of the density of
steel. This metal has a high corrosion resistance which is good for building
chassis on cars, as you know that they will last for a long time. Another
property that some aluminum alloys has is that they can exceed the strength of
common steel. This makes them very strong and vehicle parts will be very strong
and unlikely to break. Aluminum alloy also retains its toughness at low
temperatures, this means that the car parts are not likely to deform or have
its properties change in various temperatures. This is suitable for a car manufactures
as they know that cars will be sold all over the world in different climates, therefore
this metal is a good metal for them to be made out of. Unlike high carbon
steel, aluminum alloy doesn’t become brittle in different temperatures.
Similarly to low carbon steel, aluminum alloy also has good formability. This
means that the aluminum can be formed into many different shapes easily. Aluminum
uses a variety of different forming processes for this. Due to these
properties, aluminum alloy is also another good metal for motor manufacturers
to use when building vehicles and partsCB12 .

 

 

 

 

 

 

 

 

 

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