Plain fibres have a high tensile strength

Plain carbon steel (0.15 C)

This is a ferrous metal, a metal that has iron in it, which contains
between 0.1 and 1.7% of carbon together with small amounts of manganese,
phosphorus, silicon and sulphur. As it contains more than a single element in
it, it is known as an alloy but it is not referred to as one due to this
classification being reserved for steels that will contain alloying elements that
will significantly change the properties of the material. The crystal like
structure is that of iron and below 910 C is the centred cubic (BCC). Above
910C the structure will change to face centred cubic (FCC) resulting in the
material being more malleable. The unit cube is the basic build for iron and
they will produce crystals, these could also be referred to as grains.

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High
density polyethylene (HDPE)

HDPE has the atomic structure which consists of simple long chain
hydrocarbons with no side branches.

The carbon atoms form the spine of the molecule.

Each
pair of carbon atoms and their associated hydrogens are called a ”mer” and
”poly” means many. Due to there being no side branches the molecules will fit
together in a close and neatly packed way which is why LDPE has a lower density
than HDPE.

Silicon
carbide

This is a man-made ceramic which is produced from silica sand and
carbon. Silicon carbide exists in a variety of different crystalline forms but
alpha silicon carbide is the most common one of all. This is formed when a temperature
of 2000C occurs and has a hexagonal crystalstrucutre.

Carbon
fibre reinforced polymer (CFRP)

Materials which consist of fibre which is reinforced with plastic
(FRP) is stiff and has strong fibres bonded together with a polymer or it can
be bonded together with a resin matrix. The fibres have a high tensile strength
and enhances the low stiffness and strength of the resin involved. The resin’s
main purpose is to distribute loads into the stiff brittle fibres and to
protect them from damage. The carbon can be in a form of a woven mat or as a
strand when wound around onto a circular former for making a tube.

Piezoelectric

Insulating materials are commonly known as dielectrics and have the
capacity to store an electrical charge. When a dielectric is placed in an
electric field, polarisation of its molecules occur. If a mechanical stress is
applied to this, it will introduce a strain which will displace molecules in
the polarised material which creates an electrical field.

 

 

Task 2

The following table contains the names of engineering materials.
Classify each one as either a metal or a non-metal by according to their
properties.

Material

Metal or Non-metal

Properties

Austenitic Stainless Steel

Metal

Used for cutlery and cooking equipment, corrosion resistant and high
strength.
 

Melamine Formaldehyde (M-F)

Non-Metal

low density and non-conductivity.
 

PVC

Non-Metal

Easy to mould, low density not surface finishing after moulding.
 

Butyl

Non-Metal

High elasticity and non-conductivity.

CFRP

Non-Metal

Strength to weight ratio and non-conductivity.

Piezo Crystal

Non-Metal

Deforms/change effect and non-conductivity.

Duralumin

Metal

Heat treatable and good electric conductivity.

Porcelain

Non-Metal

High temperature and voltage properties.

Copper

Metal

Ductile and good electric conductivity.

Diamond

Non-Metal

extreme hardness and low coefficient of thermal expansion.

 

 

 

 

 

 

 

 

 

 

 

 

Task 3

The properties of materials can be classified as:

            • electrical

            •  physical

            • thermal

• mechanical

            • magnetic.

 

Physical

Density: Density is the mass to volume ratio of a material. This is of
interest when designing an object that is to be used in dynamic situations,
this is due to lighter materials require less amount of energy to be moved
around.

Glass transition temperature: This is the temperature where at the
polymer changes from being delicate and rigid to being flexible and ductile.
Engineers are interested in this as if polythene was used below -120 C it would
crack and fail.

Electrical

Electrical resistivity: This property indicates how resistant a
material is and if it will conduct electricity. It is of interest to engineers
when designing components that carry an electrical source/charge because too
much resistance will cause unwanted heating effects.

Permittivity: This property indicates how well a material can hold an
electrical charge and is of interest to an engineer. This is because engineers
need to use this for when designing electrical circuits that use capacitors as
they need to hold a charge.

Thermal

Expansion coefficient: This means that the material will change its
shape when cooled or heated. This is of interest to an engineer because when
components are fitted together if a component changes their shape it will end
up distorted due to thermal stress.

Thermal Conductivity: This property is about how well the material can
conduct heat through itself. Engineers will be interested in this because when
designing components that need to be used in places where heat is generated and
needs to be dispersed to prevent other components from overheating and
malfunctioning.

Mechanical

Tensile strength: Tensile strength it the maximum amount of internal
stress that the material can withhold before it breaks. Engineers value this
property as all materials are documented and can be used when working out the
cross sectional area of load-bearing components.

Hardness: This means how well the surface of the material can resist
and withstand indentations and abrasion. It is important to know about a
materials hardness for when developing something where two or more parts need
to slide against each other.

Magnetic

Permeability: This property indicates the amount a material will
magnetise when placed in a magnetic field.

Polarisation: This is the direction of North and South poles when a material
is magnetised.

Engineers will need to know about both of these as they might
interfere with other components that are needed to be used for direction,
orientation and other uses.

 

 

 

Task 4

Plain
carbon steel

·        
Plain
carbon steel is tough and it can withstand high impact loads and exhibits
ductile fracture when it fails due to overloading.

·        
Sea
water temperatures around freezing occur when air temperatures are even colder
which means that the hull of the ship could be far past freezing temperatures.

·        
The
plates will have been welded onto the hull of the ship.

·        
Mild
steel has a BCC structure and at average temperatures it is a ductile material.

·        
As
the temperatures begin to drop, the metal’s capability to absorb the energy of
impact is decreased as it becomes more brittle

 

Duralumin

·        
Duralumin
is an alloy which is made up of both aluminium and copper and its tensile
strength can be enhanced by vast amounts by cold working and age hardening.

·        
This
gives an extremely high strength to weight ratio because of its low density.

·        
The
most common problem with this material is that it suffers from fatigue
cracking, this happens when stress is introduced and the surface will begin to
blemish and then propagated by cyclic or random variations in stress levels.

·        
Every
time an aeroplane lands and takes off, the frame will go through a stress cycle
due to the changing air pressure.

·        
Over
a set amount of time tiny cracks will multiply in the duralumin but this isn’t
a problem as they are repaired and monitored.

Hep2O

·        
Polybutylene
will operate at temperatures up to 100 C without beginning to soften or distort
and it does not degrade over time.

·        
Its
hoop stress is better than those of copper which means that pipes will be
stronger when pressurised and it is chemically inert and therefore does not contaminate
drinking water.

·        
The
piping has good dimensional stability, this means that it could be joined using
mechanical fitting which would also include O-ring seals and stainless steel
lock washers.

 

 

High carbon steel

·        
High
carbon steel has a well-controlled shear strength and can be thoroughly
hardened so that when it fractures or brakes it will do so in a brittle manner.

·        
This
is why it would be used for making shear pins, which protect equipment from
being overloaded.

·        
If
its diameter is correctly calculated, the pin will fail at a specific loading
point and the broken halves of the pin could easily be pushed out because they
aren’t distorted.

·        
The
fracture surface will be flat with no tearing as would be the case with
ductile, low carbon steel.

 

Titanium alloy

·        
The
lattice structures of a metal are never perfect because of missing atoms, this
will produce dislocations and distortions that will move throughout the
material when stress is applied to it.

·        
This
causes a small change of shape.

·        
Metals
are made up from grains which have boundaries of where they will touch together,
like a jigsaw.

·        
High
stress and temperatures will make the dislocations more moveable and will
increase distortion at the grain boundaries of where they touch.

·        
The
alloying elements have the effect of stabilising the structure of the material
so that it is less prone to creep.

·        
Titanium
alloy also performs well at high temperatures because it is not corroded by
high amounts of heat (also known as combustion), gases or chemicals.   

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