Task 1: plain carbon steel (0.15 C) can have both of these structures of either a body centredcubic or a face centred cubic, as shown in figure1. Fig.1 The structure of Plain Carbon steel depends on where about it places on thisgraph (Fig2) which illustrates temperature in which if it is below 910C it is abody centered cubic and if it is above 910C then it is a face centered cubicstructure. Fig.2 HDPE (High density polyethylene) HDPE has an atomic structure consisting of a simple longchain of hydrocarbon molecules with no side branches.
The carbon atoms form thespine of the molecule, whereas the hydrogen is the outer structure of themolecule. Because there is no side branches this means that each chain is ableto be closely packed together which ensures that it has a high density. Themore rigid and orderly the structure results in a improved tensile strength anda high resilience to high temperatures which usually means that once moulded toa shape it cannot be remoulded. Fig.3 Silicon Carbide:This is a man-made ceramic produced from silica sand andcarbon.
Silicon carbide exists in many different crystal forms but alphasilicon carbide is the most common form. It is formed at temperatures exceeding2000°C and has a hexagonal crystal structure. Carbon Fibre Reinforced Polymer:Fibre reinforced Plastics is a where strong stiff strands offibre are chemically bonded with a polymer or resin.The fibres have high tensile strength and thus this augmentsthe low stiffness and the strength of the resin or polymer. The resin/polymerspurpose is to transfer loads onto the fibres which has a high tensile strengthand it also serves to protect the fibre from damage.
Above is an image of a Carbon fibre lattice structure Piezoelectric:A piezoelectric is a type of Dielectric. Dielectrics are aninsulating material which is able to store an electrostatic charge. When thisis passed through an electric field it causes polarisation of its molecules.If a mechanical stress is applied to this, it causes strainwhich displaces molecules and therefore creating an electric field. Task 2: Austenitic SS: Austenitic Stainless Steel is mainly used forcutlery and cooking equipment. It is classified as a metal. its main propertiesare: · corrosion resistant, non-magnetic, highductility, high tensile strength, tough when working at very low temperatures,high melting point.
· For these reasons it is a metal, with corrosionresistance and high strength. PVC: Polyvinyl chloride in its unplasticised form is usedfor guttering and fascia boards on houses.Its main properties are:• easily UV stabilised, easy to mould, rigid, low density,non-conductor of electricity, does not degrade, does not need surfacefinishing/coating after being moulded (e.g. by extrusion).
• For these reasons it is a non-metal, with low density andnot requiring surface finishing after moulding. Melamine: Its main properties are:• good abrasion resistance, good resistance to attack by chemicals,can be moulded with a decorative surface finish, non-conductor of electricity,remains rigid at high temperatures, low thermal conductivity, low density.• For these reasons it is a non-metal with low density andnon-conductivity. Butyl:Its main properties are: • highly elastic, impervious to gases, not affected by UVradiation, non-conductor of electricity, highly resistant to outdoorweathering.• For these reasons it is a non-metal, with high elasticityand non-conductivity.
Copper:Its main properties are excellent thermal conductivity,excellent electrical conductivity, high melting point, hardness increases whencold worked, ductile, good tensile strength. For these reasons it is a metal,with electrical conductivity and ductility Diamond:Its main properties are: extreme hardness, high abrasionresistance, low coefficient of friction, low coefficient of thermal expansion,low toughness, high light dispersion. For these reasons it is a non-metal, withextreme hardness and low coefficient of thermal expansion CFRP:Its main properties are: very high strength to weight ratio,mouldable into complex shapes, low impact resistance, can work at high servicetemperatures, non-conductor of electricity. For these reasons it is anon-metal, with strength to weight ratio and non-conductivity TASK 3:Mechanical: These are properties which affect the way that amaterial reacts when subjected to the application of force. Tensile strength: this is the stress (measured in MPa) thata material can withstand before it breaks. It is of interest to an engineerbecause the values for all materials are well documented and can be used whenworking out the cross-sectional area of load-bearing components(area=load/tensile strength). Hardness: forexample, Vickers Pyramid Number (VPN).
The hardness value indicates how wellthe surface of a material will resist indentation and abrasion. It is importantto know this when designing components that slide against each other. Physical: These are properties determined by the atomicstructure of the material.Density: this is the mass per unit volume of a material. Itis of interest to an engineer when they are designing components to be used indynamic situations because low denisty objects need smaller amounts of energyto move them around. Glass transition temperature: this is the temperature atwhich a polymer changes from being rigid and brittle to being flexible andrubbery. It is of interest to an engineer because if a material such aspolythene is used below -120°C it will start to crack.
Magnetic properties Permeability: the amount a material will magnetise whenplaced in a magnetic field. Polarisation: the orientation of N and S poles.when a material is magnetised. Application: permeability – calculating thenumber of coils and armature dimensions for a solenoid that is being designedto operate a valve. Task4:Plain Carbon Steel.In the temperature range 3 to 25°C mild steel has mechanicalproperties such as It is tough, can withstand impact loads and shows ductilefracture when it fails due to overloading.
Sea water temperatures aroundfreezing occur when air temperatures are even colder, which means that theship’s hull could be well below freezing. The hull plates will have beenwelded. Mild steel has a BCC structureand at normal temperatures is a ductile material. As the temperature decreases,the metal’s ability to absorb the energy of impact decreases and there is aductile to brittle transition.Duralumin: Duraluminis an alloy of aluminium and copper and its tensile strength can be greatlyenhanced by cold working and age hardening. This gives a very high strength toweight ratio because of its low density compared to other metals.
The problemwith this material is that it suffers from fatigue cracking, initiated by Concentratedstress points and blemishes on the surface which is then extenuated by rhythmicor random variations in stress levels. Every time an aircraft takes off andlands, its airframe goes through a stress cycle because of the changing airpressure on the outside of the cabin, which effectively expands and thencontracts. Additionally, air turbulence causes small continuous vibrations onthe wings and control surfaces. Over a period of time tiny cracks will form inthe duralumin but this is not a problem provided they are monitored and repairpanels fitted at the correct time intervals. If a designer knows the operatingconditions of the plane, they can calculate what this time interval should be similarto the mileage recommendation for changing the brakes on a car. Hep20:Polybutylene can operate at temperatures up to 100°C withoutsoftening or distorting and it does not degrade over time – unlike copper andbrass which react with steel components, such as radiators, and will corrode.Its hoop stress is better than copper which means that pipes are stronger whenpressurised and it is chemically inert and therefore does not contaminatedrinking water. Polybutylene pipe has good dimensional stability, which meansthat it can be joined using mechanical fittings containing O-ring seals andstainless steel lock washers.