No properties
are strengthened during hot working of materials. The intention behind hot
working of materials is to eliminate any imperfections: these can include
closing gas pores and reducing composition differences. In addition, through
hot rolling you can achieve anisotropic behaviour. This means that the
surface of the material will have a high surface finish. Ideally, brass would
require this kind of treatment in order to improve its overall appearance;
brass can be used for instruments and plating jewellery, so its appearances
is arguably an important property.

Cold working
can have an effect on various properties of materials. These include dislocations
moving through the metal structure. The metal becomes less malleable and
ductile, while the tensile strength and hardness is increased. In terms of
60/40 and 70/30 brass, these properties would be impacted similarly, as the
materials structural make up is relatively similar. A downside to cold
rolling of brass is that it may cause cracking, which has a detrimental
effect of the materials appearance. This is why brass is generally hot

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ii) The ability of a polymer to
sustain a mechanical load depends on the strength of covalent bonds and the
forces between the molecules. However, if a substantial fraction of the polymer
chains can be aligned in the load-bearing direction, a larger portion of the
load can be transmitted to the main-chain covalent bonds. This means that the
fibres must be as strong as possible in order to sustain their loads. Polymer
chains are oriented by subjecting them to extensional strain (flow) in the
melt, which occurs to some extent in most thermoplastic fabrication methods.
Significantly more orientation can be induced by mechanically drawing a fibre
as it leaves the die and just before it solidifies — thus freezing-in extended
chain conformations. This leads to uniaxial orientation in the draw direction.
An example is shown schematically underneath.


Uni- and biaxial Stretching of various polymer films has been studied under
well-defined conditions of temperature and elongational strain rate in order to
determine the relationship between stress and recoverable strain for both modes
of deformation. The extent of molecular orientation has been investigated with
the aid of stress optical methods: In amorphous polymers birefringence was found
to be directly proportional to the frozen-in internal entropic stress
irrespective of the latter’s relationship with recoverable strain. In a first
approximation, molecular orientation can be understood in terms of deformation
of a rubberlike network with temporary junction points. The total internal
stress in an oriented glassy polymer may be significantly larger than the
entropic stress. Experimental methods based on retractive force measurements,
able to distinguish between internal stresses of different nature, are
described. In uni- and biaxially drawn films of polyethylene terephtalate
preferred planar orientation of (100) planes has been studied by means of X-ray
diffraction and measurement of the three principal refractive indices. The
intrinsic birefringence of completely oriented PET films has been estimated
from these measurements with the aid of the Lorentz-Lorenz theory. The effect
of draw ratio and temperature on the rate of crystallization and its
consequences (increase of stretching stress and density, decrease of shrinkage)
has also been studied. Finally, the effect of molecular orientation on various
mechanical properties: modulus, tensile strength, impact resistance, creep
compliance, is discussed for both amorphous and semicrystalline polymers, with
special emphasis on the predominant influence of amorphous phase orientation.

iv) Generally, clay has a water content between 19.5 and 22.5%. The slightest
difference in water content (around 1%) can have a dramatic effect on the clays
properties: the clay can become either more malleable or stiffer as a result of
a loss/ increase in water content. Depending on what the clay is to be intended
to be used for, the water content should be decided prior to its use in any
form of manufacturing process. Some clay may be used in structures, such as
flood barriers. This would of course require it to be a sturdy, non-malleable
form of clay i.e. a lower percentage of water content present in the material.  

v) Concrete is used on a regular basis in various structures, such as
motorways, so they have to be able to support large volumes of weight and
tension across long periods of time. This means making the concrete stronger
during its processing. This can be achieved by the addition of more solid materials
into the mixture, making it more sturdy once constructed. These materials may
include large stones. Another way to make concrete stronger is using
reinforcement techniques. This can include positioning steel beams in the
material, making it ideal for structures such as motorway bridges or factory

vi) Smart materials are designed materials that have one or more properties that can be
significantly changed in a controlled fashion by external stimuli, such as
stress, temperature, moisture, pH, electric or magnetic fields. This means that these materials can be used
for a number of applications. One example of this could be water proof paint on
cars: a primer base coat and clear coat provide protection for a cars
professional finish from weather. If the correct properties that are required
were not present in the various layers of paint, the car would not be resistant
to weather. Another example could be when heat is applied to fire sprinklers; a
latch is released causing the sprinklers to activate. Moreover, piezoelectric
materials can be used in children’s shoes: the impact in the sole causes a
small electric current to be produced, resulting in a sudden flash of light.

Task 2 (M1)

Steel alloy has many uses
and contains other materials, such as iron. Low carbon steels generally contain less than
0.25% carbon and cannot be strengthened by heat-treating (strengthening can
only be accomplished through cold working). The low carbon material is
relatively soft and weak, but has extremely good ductility and toughness. In
addition, it is machineable, weld-able, and is relatively inexpensive to produce.
Moreover, Medium carbon steels
have carbon concentrations between 0.25% and 0.60%. These steels may be
heat-treated by quenching, and then tempering to improve their mechanical
properties. On a strength-to-cost basis, the heat-treated medium carbon steels
provide tremendous load carrying ability.

In addition, aluminum alloys contain magnesium, which has a light weight and dense structure. This
makes is a good material to use when constructing in the BIW stages of
manufacturing. This is one of the most effective and widely used alloying
elements for aluminum. Alloys in this series possess moderate to high
strength characteristics, as well as good weldablility and resistance to
corrosion in the marine environment. This differs from steel, as its alloy
contains iron; this means that under the wrong weather conditions, steel has a
tendency to rust. Overall I would say that aluminium alloy is the better
material to use for constructing a car’s body work and/ or chassis. 




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