Generally,when we design an engineering material we should bare in mind that the lowtemperature can affect the tensile toughness of the materials. Using thetress-strain graph the ductility of the material can be studied by calculatingthe he area under the stress-strain curve. The ductility of the material meansit can absorb a bit of energy before it fractures on the other hand, thebrittleness 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 totemperature change and they experience a shift from ductile to brittlebehaviour when the surrounding material reaches certain point and the mildsteel I one of those material, this behaviour I known as ductile-to-brittle-transition”temperature (DBTT). Most material with BCC (body-centred cubic) structure faceDBTT. The energy/temperature graph shows this transition. The above explanationtells us that the ships hulls will not survive under freezing temperature forlong and become brittle and be very dangerous. When building an aircraft structures very strong and light inweight is the priority. Aluminium alloy is an excellent material to be used foraircraft structure due to its high strength and light weight. However, to evenincrease 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 formedgiving high strength to weight ratio, it is also resistance to fatigue. It hasa density of 2.78 g/cm³ (0.1 lb/in³) in addition to high tensile and yieldstrength making it just perfect to be used to build the aircraft structure.
However, when the aluminium is alloyed it loses its corrosion resistancetherefor, 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 crackor fatigue due to pressure change while taking off and landing. Before anything when we compare Copper& Brass with Polybutylene, the first thing wenotice is the price.
Building pipes wising Copper & Brass can be extremelycostly 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 hasa crystal structure making them very strong with high molecular weight and verygood elastic recovery. The Polybutylene also has a good resistance to chemicalssuch as oils, fats, acids, hydrocarbons etc. Unlike Copper & Brass the Polybutylenecan also act as a good insulator with high creep resistance.
Unfortunately, thedown side, the Polybutylene is not trust worthy as long-lasting material, thechemical reactions due to oxidants in water will cause it to change in itchemical structure and once the chemical structure is change the Polybutylenechanges its property and become brittle; in this case Copper & Brass isbatter than Polybutylene. Yet, the Polybutylene is highly used as a reliablematerial for pluming and excellent placement for any damage in pipes. There are three grades of stainless steel that are being usedfor cutlery’s; 18/8, 18/10 and 18/0. The number refers to the percentage ofChromium and Nickle. Each grade has its quality and slight different in itproperties. 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 handand it also do not attract magnets neither do they can be harden by heattreatments.
This type of steel is used because it can resist corrosion, easy toclean and do not have any electrolytic activity that may affect the food norare they toxic. Theshear pin is normally designed to break to protect other part of the machinefor example, it will break if an outside object touches the moving part beforethe whole machine gets jammed. The shear pins are designed of high carbon steeland whenever we say high carbon steel we know that the material is very strongbut also very brittle as a result if high load were to add on it will snap. Inour case, if anything gets jammed the pin will snap straight stopping themachine; the pin than can be removed easily and replaced. An important thing tobear in mind, no matter how strong the shear pin is the material it is used toprotect must be stronger for it to deliver high protection as a result heattreatment for the shear pin is not ideal. In the stress/strain graph we can seethe blue line representing the high carbon steel and how is snaps on highstress which in our case when the machine gets jammed.
Titanium alloy (codeTi-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 highresistant 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 whenexposed to oxygen and 6% content of Molybdenum. This material is not only agood resistor to corrosion but also has a high strength to weight ratio plusvery high melting point making the excellent material to be used in aerospaceindustry.
The Titanium alloy normally has HCP structure which are closelypacked to each other and when the temperature exceeds certain limit this bodystructure changes from HCP to BCC and this concept apply to all titanium alloy dependingon the content of alloy. The Titanium 6246 can even get stronger with heattreatment giving them even batter special properties such as high fatigue andcreep strength on high temperature, toughness etc.