Generally,
when we design an engineering material we should bare in mind that the low
temperature can affect the tensile toughness of the materials. Using the
tress-strain graph the ductility of the material can be studied by calculating
the he area under the stress-strain curve. The ductility of the material means
it can absorb a bit of energy before it fractures on the other hand, the
brittleness is the complete opposite on impact they can shatter in to pieces.
In many case, depending on the material the material can be very sensitive to
temperature change and they experience a shift from ductile to brittle
behaviour when the surrounding material reaches certain point and the mild
steel I one of those material, this behaviour I known as ductile-to-brittle-transition”
temperature (DBTT). Most material with BCC (body-centred cubic) structure face
DBTT. The energy/temperature graph shows this transition. The above explanation
tells us that the ships hulls will not survive under freezing temperature for
long and become brittle and be very dangerous. 
 

  

 

When building an aircraft structures very strong and light in
weight is the priority. Aluminium alloy is an excellent material to be used for
aircraft structure due to its high strength and light weight. However, to even
increase its property the aluminium alloy is mixed with 90% aluminum,4% copper,
1% magnesium and 0.5% to 1% manganese. by that the Duralumin 2024 is formed
giving high strength to weight ratio, it is also resistance to fatigue. It has
a density of 2.78 g/cm³ (0.1 lb/in³) in addition to high tensile and yield
strength making it just perfect to be used to build the aircraft structure.
However, when the aluminium is alloyed it loses its corrosion resistance
therefor, pure layers of aluminium sheet is used to protect the duralumin core.
The Finite life are used at certain part of the aircraft to monitor any crack
or fatigue due to pressure change while taking off and landing.

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Before anything when we compare Copper
& Brass with Polybutylene, the first thing we
notice is the price. Building pipes wising Copper & Brass can be extremely
costly if we were to cover billions of houses around the UK. On the other hand,
the Polybutylene is quite cheaper and very flexible. The Polybutylene also has
a crystal structure making them very strong with high molecular weight and very
good elastic recovery. The Polybutylene also has a good resistance to chemicals
such as oils, fats, acids, hydrocarbons etc. Unlike Copper & Brass the Polybutylene
can also act as a good insulator with high creep resistance. Unfortunately, the
down side, the Polybutylene is not trust worthy as long-lasting material, the
chemical reactions due to oxidants in water will cause it to change in it
chemical structure and once the chemical structure is change the Polybutylene
changes its property and become brittle; in this case Copper & Brass is
batter than Polybutylene. Yet, the Polybutylene is highly used as a reliable
material for pluming and excellent placement for any damage in pipes.

 

 

There are three grades of stainless steel that are being used
for cutlery’s; 18/8, 18/10 and 18/0. The number refers to the percentage of
Chromium and Nickle. Each grade has its quality and slight different in it
properties. However, the most common grade is 18/8, it has 18% chromium and 8%
nickel. It s autunitic and very weak in a way you can deform it with your hand
and it also do not attract magnets neither do they can be harden by heat
treatments. This type of steel is used because it can resist corrosion, easy to
clean and do not have any electrolytic activity that may affect the food nor
are they toxic.    

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The
shear pin is normally designed to break to protect other part of the machine
for example, it will break if an outside object touches the moving part before
the whole machine gets jammed. The shear pins are designed of high carbon steel
and whenever we say high carbon steel we know that the material is very strong
but also very brittle as a result if high load were to add on it will snap. In
our case, if anything gets jammed the pin will snap straight stopping the
machine; the pin than can be removed easily and replaced. An important thing to
bear in mind, no matter how strong the shear pin is the material it is used to
protect must be stronger for it to deliver high protection as a result heat
treatment for the shear pin is not ideal. In the stress/strain graph we can see
the blue line representing the high carbon steel and how is snaps on high
stress which in our case when the machine gets jammed.

 

Titanium alloy (code
Ti-6Al-2Sn-4Zr-6Mo) also known as Titanium 6246 is strong Titanium alloy with 6%
Aluminium 2% Tin 4% Zirconium and 6% Molybdenum. This material has very high
resistant to corrosion when exposed to sea water or in a reducing environment such as Hydrogen Sulphide
(H2S) and the secret relay behind the oxide layer that forms spontaneously when
exposed to oxygen and 6% content of Molybdenum. This material is not only a
good resistor to corrosion but also has a high strength to weight ratio plus
very high melting point making the excellent material to be used in aerospace
industry. The Titanium alloy normally has HCP structure which are closely
packed to each other and when the temperature exceeds certain limit this body
structure changes from HCP to BCC and this concept apply to all titanium alloy depending
on the content of alloy. The Titanium 6246 can even get stronger with heat
treatment giving them even batter special properties such as high fatigue and
creep strength on high temperature, toughness etc. 

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