Materials Science and Engineering Materials

Polycarbonate is a thermoplastic. Thermoplastics have a linear or branched molecular structure which determines their strength, solid at room temperature. The polymer chain is held together by relatively weak van der Waals forces; because the molecules are long the forces are considerable. The molecules become tangled. When heated the van der Waals forces are weakened, the molecules are able to slide over one another, the material becomes weaker and less rigid, so it can easily be moulded. Repeating chemical structure unit of Polycarbonate made from Bisphenol A c)Glass

To meet the criteria you will need to describe how the structure develops as it solidifies from the molten state. The amorphous structure of glass makes it brittle because glass doesn’t contain planes of atoms that can slip past each other, there is no way to relieve stress; the amorphous structure is formed by cooling. When cooled quickly from its molten state the resulting solid is amorphous and transparent. Amorphous structure of glass is more loosely packed and random. d)Glass-fibre reinforced plastic. To meet the criteria you will need to describe: – •The matrix material The reinforcement material •How they are blended to make the final composite material Glass-fibre reinforced plastic (GRP) is a composite material made by combining two materials where one of the materials is a reinforcement (glass fibre) and the other material is a matrix (resin). Epoxy and polyester resins are the usual matrix materials. The combination of the glass fibre and matrix provide characteristics superior to either of the materials alone. The most widely used reinforcement material is fibreglass in polyester resin, which is commonly referred to as just fibreglass.

Fibreglass is lightweight, corrosion resistant, easily processed, and has good mechanical properties. The glass fibres woven in different directions are impregnated with the resin while in its liquid state, the result, after curing, is a cohesive completely integrated matrix of resin and fibres. The matrix can have a surprising range of properties. In general, the GRP laminate will have excellent tensile and compressive strength, acceptable thermal conductivity, a low coefficient of linear expansion, reasonable chemical resistance and good dielectric properties. Also it will be light durable, moisture-resistant, non-rusting and economic. )Piezoelectric materials. To meet the criteria you must describe how the structure and properties change with the application of an external force. Piezoelectricity is a coupling between a material’s mechanical and electrical behaviours. In the simplest of terms, when a piezoelectric material is squeezed, an electric charge collects on its surface. Conversely, when a piezoelectric material is subjected to a voltage drop, it mechanically deforms. The piezoelectric effect occurs only in non conductive materials. Piezoelectric materials can be divided in 2 main groups: crystals and ceramics.

The most well-known piezoelectric material is quartz. Piezoelectric materials have two crystalline configurations. One structure is organized, while the other is not. Organization of the structure has to do with polarization of the molecules that make up the material. Hence, a non-polarized material has a non-organized structure, while the polarized material is organized. To polarize the material, voltage or electricity must be conducted through it. As a result of this electrical force, the molecules of the material reorient themselves, thus changing the shape of the material; this is called electrostriction.

The picture below shows this process at a microscopic level. Change in shape can produce mechanical force, as well as changes in physical characteristics (like density, shown below). Non-polarized material: Polarized material: On the right, shape change is produced with input of electricity. On the left, electricity is produced with input of shape change. Similarly, if mechanical force is exerted on the material to change its shape, an electrical field is produced; this is called piezoelectric effect. Electrostriction and piezoelectric effect are opposite phenomena.

Answering the above questions correctly will allow the P1 criteria to be met. Question 2: (P2, P3) (i) Define the following properties, giving one practical engineering example in each case: – a)Ductility Ductility is the ability of a material to be permanently deformed by stretching. Some metals are very ductile such as the steel used for manufacture of car body sections by pressing. The metal copper, used for wire, has to be ductile. This is because the wire is produced by drawing it though dies in order to make it longer and thinner. b)Toughness Toughness is the ability of a material to resist impact or shock loads.

Hammer heads, cold-chisels, springs and high tensile bolts are examples of products possessing the property of toughness. c)Density The density of a material is the mass per unit volume. Expressed mathematically Density = Mass Volume Manufactured products for aircraft may be made from materials with low density such a aluminium alloys. Other products such as polyethylene may also be made from low-density materials. At the other end of the scale, car batteries contain components that are made from lead which has a high density. d)Melting point The melting point is the temperature at which a solid begins to liquefy.

Pure crystalline materials, eutectics, and some intermediate constituents melt at a constant temperature; alloys generally melt over a range. Glasses, whether inorganic, metallic or polymeric, have no well-defined transition from solid to liquid. An engineering example of melting point is soldering, when the hot soldering iron tip melts the solder. e)Expansivity Expansivity is a measure of the effect of temperature change on the dimensions of a material when heated. It is defined as the increase in length, per unit of original length, per degree of temperature rise. When metals are heated they generally expand.

The same occurs with many polymers and ceramic materials, although the effect is not so pronounced. Some thermoplastics contract when heated, like shrink insulation sleeving, gentle heating causes it to shrink. f)Thermal conductivity Thermal conductivity is the ability of a material to conduct heat. Generally the materials most able to conduct heat are the same as those that are most able to conduct electricity. Therefore metals such as copper and aluminium are the most thermally conductive. Such metals are used for the manufacture of cook-ware and soldering iron bits. )Electrical conductivity Electrical conductivity is the ability of a material to conduct electricity. Metals are usually good conductors, and non metals are poor conductors. The most common metal used for electrical conductors is copper. It is a very good conductor of electricity and can be easily soldered to make a permanent connection. h)Magnetic permeability • Can be thought of as the ability Magnetic permeability is a measure of a materials ability to intensify the magnetic field produced by a current carrying coil when it is used as a core material.

Electromagnets, transformers, motors and generators all contain current carrying coils around which a magnetic field is produced. The wounded core material can greatly affect the intensity and strength of the magnetic field. Ferromagnetic materials like iron nickel and cobalt have the greatest effect. (ii) Research and describe the properties of the following materials and from this establish whether they are metals or non-metals. •Plain carbon steel Plain carbon steel is made from iron, with a maximum carbon content of 1. 5% with small percentages of silica, sulphur, phosphorus and manganese.

With a low amount of carbon the steel is soft and ductile, the greater the carbon content the metal becomes harder and stronger but less ductile. •Copper Copper is a malleable and ductile metal, which is also a good conductor of heat and electricity and like most non-ferrous metals copper is resistant to corrosion. •Brass Brass is an alloy of copper and zinc, as a general rule, brasses with a higher copper content are more ductile and suitable for cold forming. Brasses with higher zinc content are less ductile and more suitable for hot forming, again malleable and resistant to corrosion. Brass is a metal. Polycarbonate Polycarbonate is a linear chain polymer. The form of the chain makes for a very stiff structure. Polycarbonate is strong, stiff, hard and transparent and retains its properties well with increases in temperature. It has a good electrical resistance. Polycarbonate is a (thermoplastic) non-metal. •Polyester resin Polyester resins are thermosetting. They are malleable until they are heated and at which time they permanently harden. Polyester resins are resistant to both water and UV rays. They have a good adhesion, chemical and heat resistance and are brittle with good electrical insulation properties.

Polyester resin is a non metal. •Rubber Rubber is a polymeric material with long flexible molecular chains, with the ability to deform elastically when vulcanised. Rubber is a good electrical insulator, resistant to alkaline and weak acids, has a long fatigue life and high strength. Rubber is a non-metal. •Quartz Quartz is a mineral, with great physical strength and chemical resistance. It has low coefficient of expansion up to 320°C. Quartz has good thermal shock resistance, is an excellent electrical insulator with great hardness but brittle. Quartz crystals have piezoelectric and optical properties.

Quartz is a non-metal. •Laminated glass Laminated glass consists of two or more panes of glass with one or more layers of polyvinyl butyral (PVB) sandwiched between them. Properties of glass are high impact strength, shatter proof, flexible, high melting point, and good insulation properties. Laminated glass is anon-metal. Answering the above questions correctly will allow the P2 and P3 criteria to be met. Question 3: (M1) With the aid of clear and annotated diagrams explain why: – a)The structure of copper allows it to be drawn out into wire. Copper is a malleable and ductile material with a face centred cubic structure.

The closely packed atoms move more readily over each other when external forces are applied, allowing the copper to be drawn into wire. FACED CENTERED CUBIC STUCTURE OF COPPER b)The structure of plain carbon steel allows it to be used for structural work. Plain carbon mild steel has a body centred cubic lattice structure. The open-packed planes of atoms make the structure rigid, and hard. When external forces are applied the atoms don’t easily move over each other. The greater the carbon content the metal becomes harder and stronger but less ductile.

Plain carbon steel is a great material for structural work, as it is strong and rigid, easy to weld. BODY CENTERED CUBIC STUCTURE OF PLAIN CARBON STEEL c)The structure of a thermoplastic polymer allows for it to be recyclable. Thermoplastic polymers have a linear or branched molecular structure, solid at room temperature. The polymer chain is held together by van der Waals forces; because the molecules are long, the forces are considerable. The molecules become tangled. When heated the van der Waals forces are weakened, the molecules are able to slide over one another, the material becomes weaker and less rigid.

Once the thermoplastic becomes a viscous liquid it can be reshaped or reformed, then cooled to become a solid again, without significant degradation. Which make’s a thermoplastic polymer idea for it to be recycling. d)The structure of laminated glass makes it suitable for a car windshield. Laminated glass, regarded as Safety glass, consists of two panes of glass with one layer of polyvinyl butyral (PVB) sandwiched between them. If the glass is broken fragments tend to adhere to the PVB interlayer thereby reducing the risk of injury from falling glass and helping to resist further impact or weather damage.

The PVB will absorb large amount of impact energy and disperse it rapidly. Furthermore this will protect the safety of the passengers in the car. These properties make laminate glass idea for a windscreen. e)The structure of rubber makes it suitable for a car tyre. Synthetic rubber is widely used in the manufacture of car tyres. It consists of polybutadiene, an elastomer built up by chemically linking multiple molecules of butadiene to form giant molecules, or polymers. The polymer is noted for its high resistance to abrasion, low heat build up, and resistance to cracking, which are good properties for a tyre.

When sulphur or certain metal oxides are added to the rubber during manufacture, cross links are formed between the polymers this is known as vulcanising. The cross links enables the rubber to retain its elasticity and return to its original shape all most to the point of failure. All tyres are reinforced with steel wire and textile fabric to help maintain stability by widening the tread in contact with the road. Tyre Structure f)The structure of GRP makes it suitable for a crash hat Glass-fibre reinforced plastic (GRP) is a composite material.

Crash helmets are made with layers of glass fibres, woven in many directions mixed with a resin. This increases the strength and stiffness of the helmet. GRP is a good material for a crash helmet as it is light in weight, has a high impact resistance and is resistant to corrosion, meaning it can be worn in all weathers without damage. Glass-fibre roving strands g)The structure of a thermosetting polymer makes it suitable for an electrical socket Thermosetting plastics undergo a chemical change during the moulding process.

Strong covalent bonds are formed between the polymers known as cross links which cannot be broken. The structure makes the material strong, with a high tensile strength, usually hard and brittle with a resistance to high temperatures. If heat is added to the thermoplastic it will degrade and char. Thermoplastics is a good material to use in electrical sockets as it is a good insulator, if there was a short circuit or fault you would possibly have two warning signs, one would be the smell of the Charing, and the second, visual signs of chars, indicating were the fault occurred. )The structure of tungsten carbide makes it suitable for a lathe cutting tool. Tungsten carbide is a composite material consisting of tungsten carbide particles bonded together in cobalt matrix. Tungsten carbide is a hard and tough material due to its hexagonal structure. The greater content of cobalt the strength, hardness and wear resistance decreases, while toughness and tool life increases. Has a high melting point, which helps keep the cutting tip in good condition, when cutting.

Designed for high speeds and high feeds to increase the speed of production with a good finish. Hexagonal structure of Tungsten Carbide Answering the above question correctly will allow the M1 criteria to be met. Bibliography and Sources Callister W D Materials science and engineering an introduction 6th edition 2003 John Wiley & Sons KalpakjianManufacturing engineering and technology 3rd Edition 1995 Addison – Wesley Publishing Phillip M Bolton W Technology of Engineering Materials 2002Butterworth – Heinemann