- Slides: 26
Materials Science • Introduction to Materials • Properties of Materials • Metals • Plastics • Woods • Composites • Heat Treatment
Introduction to Materials • Materials are used to make or build objects. • During the past 200 years there has been an enormous increase in the range of materials available to us. It is therefore important that the correct materials be used for a particular use. • In Selecting the best material you need to look at 4 things: Physical properties, Cost and Time, Shaping and Forming and Availability.
Selecting the best material – A checklist 1 PHYSICAL PROPERTIES Hardness Tensile Strength Compressive Strength Shear Strength Stiffness Toughness Malleable Corrosive Appearance Weight Conductivity S E L E C T I O N 2 WHAT COST? The materials The extras (fittings etc) 3 SHAPING & FORMING Cutting out Moulding Casting Joining 4 AVAILABILITY Are they easy to obtain including fittings.
Properties of Materials • Each material has many properties. It is incorrect, for example to describe a material as just ‘strong’ or ‘weak’ as for example concrete is strong in compression but weak in tension. Hardness Toughness Strength Brittleness Malleability Ductility Elasticity Plasticity Conductivity Density Fatigue Stiffness
Hardness • The ability of a material to resist wear indentation and scratching. An example of a hardness test that can be carried out in the lab. Different materials are used and the depth of indentation measured
Toughness • The ability of a material to withstand blows or sudden impact. Different materials are used, the hammer is swung from the same height each time about a fixed fulcrum. The distance travelled after impact or fracture is used to find toughness
Strength • The ability of a material to withstand forces of tension, compression and torsion Tensile Strength – the ability to withstand pulling forces or Tension forces Compressive Strength – the ability to withstand ‘squeezing’ forces or Compression forces Torsional Strength – the ability to withstand ‘twisting’ forces or Torsion forces
Brittleness • A material that is easily fractured by impact is said to be brittle e. g. Glass The same as the toughness test however those materials that fracture easily are said to be brittle.
Malleability • A material that can be rolled or hammered into shape without rupture. As ring rises the side of Coke can is thinned out
Ductility • A material that can be pulled or stretched into a thin wire or thread. Get picture of wire drawing
Elasticity • The ability of a material to return to its original shape after deformation. Get picture of someone stretching elastic band
Plasticity • The ability of a material to be permanently deformed without fracture. .
Conductivity • The ability of a material to allow Heat or electricity to flow through it. Ball Bearing drops from most conductive 1 st.
Density • Is the mass of 1 cubic centimetre (cm 3) of a substance. (Mass per unit Volume) Q. Which is heavier a tonne of feathers or a tonne of lead? Q. Which has the greatest density? Density = Mass Volume
Fatigue • Occurs when materials have become overworked and fracture or fail. Find picture
Stiffness • The ability of a material to resist bending deformation.
Metals • There are two types of metals • Ferrous • Non- Ferrous
Ferrous Metals All the metals in this group contain Iron. They include wrought iron, mild steel and cast steel. Ferrous metals rust easily when exposed to the atmosphere and are magnetic. Plain Carbon Steels Alloy Steels
Plain Carbon Steels These steels are a series of iron and carbon alloys with carbon content varying between 0. 05% and 1. 4% Dead mild Steel • Low carbon content 0. 05 -0. 15%. • Ductile and easily formed • Uses: chains, rivets, nails, thin wire
Mild Steel • carbon content 0. 15 -0. 30%. • Bright mild and Black mild, Bright mild used in benchwork Black mild used forging • Ductile, easily cut, machined and welded, cannot be hardened or tempered • Uses: General engineering work, girders, plates for ship building, gates.
Medium Carbon Steel • carbon content 0. 30 -0. 60%. • Greater strength than mid steel but not as ductile or malleable. • Uses: Axles, rail tracks, spades wire ropes. .
High Carbon Steel (Cast Steel) • carbon content 0. 6 -1. 4%. • Hard and wear resistant can be hardened and tempered. • Uses: Cutting tools (chisels, saws, files) dies punches springs hammers. .
Silver Steel • carbon content @ 1. 0%, contains chromium • Does not contain silver gets its name from appearance • Uses: Scribers and screwdriver heads. Tool Steel • Used for making engineering tools.
Tinplate • Tinplate is produced by coating thin sheets of steel containing 0. 1% carbon with Tin. • The process of coating the steel is called Electro-plating. • Uses: for food containers. It is also used as containers for many other products such as paint, lubricants etc.
Galvanised Iron • This is mild steel coated with Zinc. • The coating is usually achieved by dipping the steel article in a bath of molten zinc. • Uses: for roof sheeting, gates, water tanks, dust bins and other outdoor articles.
Alloy Steels These steels are produced from adding elements such as chromium, tungsten, nickel and manganese to steel.