Selecting Engineering Materials Part 1 = Properties of Materials. Part 2 = Metallic Materials (Ferrous). Part 3 = Metallic Materials (Non-Ferrous). Part 4 = Non – Metallic Materials. Part 5 = Material Forms of Supply.

Properties of Materials HARDNESS Hardness is a measure of a materials ability to resist indentation, scratching or wear. A good test for hardness is to file the material. The more difficult it is to file, the harder the material. The principle of Hardness Testing can be seen on the following slide.

TESTING FOR HARDNESS

Properties of Materials DUCTILITY Ductility is the ability of a material, which allows it to be drawn into rod or wire. This is an extremely important property of a material. A material that is ductile can undergo a considerable amount of deformation in tension before fracture will occur. The operations that require a good degree of ductility fall into wire drawing and cold forming areas of production. Metals that are widely recognised as high in ductility are prioritised as follows: - Gold, Silver, Copper, Aluminium, Brass, Low carbon steel. Metals of low ductility are - medium carbon steel, high carbon steel and cast iron. The following slide shows examples of Ductility.

Examples of Ductility.

Properties of Materials. MALLEABILITY A malleable material is one, which can be formed either hot or cold, by hammering, pressing or bending, without cracking or rupturing occurring. Malleability may seem to be an identical property to ductility, but if we examine a metal such as lead, which is very malleable, we find a metal that is far too weak to be drawn into thin wire. Gold is an extremely malleable material, examples of this property are displayed when this metal is pressed into leaf form (can be as fine 0.04mm) . The order of malleability when cold is as follows: - Gold, Silver, Aluminium, Copper, Tin, Lead, Zinc, Iron. The following slide shows examples of Malleability.

Examples of Malleability.

Properties of Materials BRITTLENESS. A material is classed as brittle when it fractures (Breaks) under a suddenly applied load rather than bending. Brittleness is almost the opposite of ductility, and the material usually associated with brittleness is grey cast iron. Glass is also good example of a BRITTLE material. An example of this can be seen on the following slide.

Brittle Materials

Properties of Materials. STRENGTH. The strength of a material is usually measured by its tensile strength, in other words a tensile (stretching} load is applied until the material fractures or yields. The point at which the material fractures (breaks) is referred to as the Ultimate Tensile Strength (U.T.S.). To measure the tensile strength of a material a test piece of known dimensions is placed between two jaws and a load applied. The load is gradually increased until the material fractures and the fracture (break) load is noted. The fracture load is then divided by the original cross sectional area of the test piece and the resulting figure is a measure of tensile strength in N/mm2 (see example on following slide).

Example of Tensile Strength Testing.

Example of Tensile Strength.

Properties of Materials. TOUGHNESS. Toughness is a property that is hard to describe. It is also difficult to measure accurately and to relate it to other properties. The term maybe loosely used as the general strength of the material. The standard test for toughness is to break or bend a test specimen of the material by allowing a load to swing freely against it. This test is known as the Izod Test. The energy absorbed in breaking the specimen is measured, and the more energy absorbed, the tougher the material. The results from this type of test would show lack of toughness both lead (which would bend easily) and cast iron (which would break on impact). Therefore a tough material is one that displays reasonable ductility, good strength in tension and compression, together with good hardness and resistance to wear. In addition, a material regarded as tough will stand up to repeated blows without cracking. Medium carbon steel has a good degree of toughness and the hot forging process tends to promote this property. Crankshafts for internal combustion engines are an excellent example of this.

Examples of Toughness.

Properties of Materials. CONDUCTIVITY The conductivity of a material refers to its ability to allow the passage of heat or electricity through its structure. Usually, thermal and electrical conductivity are allied in the same material. Comparing the table on the following slide it will show that silver is an extremely good conductor of both heat and electricity. On the other hand rubber obstructs both the passage of heat and electricity and is termed an INSULATOR.

COMPARITIVE LEVELS OF ELECTRICAL AND THERMAL CONDUCTIVITY. Thermal conductivity. Electrical conductivity. Silver Silver Copper Copper Aluminium Aluminium Brass CONDUCTORS Brass Low Carbon Steel Low Carbon Steel Cast Iron Cast Iron Lead Lead Nylon INSULATORS Nylon Wood Wood Rubber Rubber Polystyrene Polystyrene

Properties of Materials. MAGNETISIUM. The most common magnetic materials are based on iron; these materials are said to be “ferromagnetic”. The only other metals which are strongly magnetic are Cobalt, Nickel, and Gadolinium. “Soft” magnetic materials, such as low carbon steel, become magnetised when they lie in a magnetic field but lose most of their magnetism when removed from that field. The magnetic field can come from a “permanent” magnet or from a coil of wire carrying an electric current see following slide “Hard” magnetic materials, such as quench hardened high carbon steel, will retain their magnetism when the magnetising influence is removed. They are called “permanent” magnets. Strong permanent magnets can be made from alloys containing cobalt, chromium, tungsten, aluminium, copper, nickel, niobium, and titanium as well as iron.

Electro-Magnets.

Summary

Materials that are Brittle GLASS GREY CAST IRON

Materials that are HARD Cast Iron. High Carbon Steel. Medium Carbon Steel. Stainless Steel.

Materials that are Ductile (In order of Ductility) Gold. Silver. Copper. Aluminium, Low Carbon Steel.

Gold. Silver. Lead. Aluminium. Copper. Tin. Low Carbon Steel. Zinc. Malleable Materials. Gold. Silver. Lead. Aluminium. Copper. Tin. Low Carbon Steel. Zinc.

Materials in Order of Strength. High Tensile Steel. Stainless Steel. Aluminium Alloy. Brass. Low Carbon Steel. Copper. Grey Cast Iron. Pure Aluminium. Nylon P.V.C. Lead. Polythene.

Materials in order of Thermal & Electrical Conductivity. Thermal conductivity. Electrical conductivity. Gold Gold Silver Silver Copper Copper Aluminium Aluminium Brass CONDUCTORS Brass Low Carbon Steel Low Carbon Steel Cast Iron Cast Iron Lead Lead

Thermal Insulator. Electrical Insulator. Polystyrene Polystyrene INSULATORS Thermal Insulator. Electrical Insulator. Nylon Nylon Wood Wood Rubber Rubber Polystyrene Polystyrene

Materials that are Magnetic. Iron. Nickel.