Classification of Materials• Engineering materials can be classified into three basic categories: 1.Metals 2.Ceramics 3.Polymers 4.CompositesTheir chemistries are different, their mechanical and physical properties are dissimilar
Metals• Metal used in manufacturing are usually alloys ,which are composed of two or more elements ,with atleast one being metallic element.Metals can be divided into two basic categories: a) Ferrous b) Non ferrous
• Ferrous Metals : Ferrous metals are based on iron: the group includes steel and cast iron.Pure iron has limited commercial use, but when alloyed with carbon .iron has more uses and greater commercial value than any other metal• Non ferrous: They include the other metallic elements and their alloys.They iclude metals and alloys of aluminum ,copper ,gold silver and other metals.
Ceramics• A ceramic is defined as a compound conatining metallic or semimetallic and nonmetallic elements.typical non metallic elemets are oxygen,carn and nitrogen.Ceramics include variety of traditinal and modern materials .Traditinal ceramics include clay ,silica , alumin and silicon carbide.Newer ceramics include carbides and nitrides.
Polymers• A polyer usually consists of carbon plus one or more other elements such as hydrogen ,nitogen ,oxyggen and chlorine.Polymers are divided into three categories: 1.Thermoplastic polymers 2.Elastomers 3.Thermosetting plastics
• Thermoplastic Polymers : They become soft on heating and melt on he ating and can be mouldrd again and againare known as thermoplastic.Repeative heating does not cause permanent change in properties or composition.• Elastomers : Polymers that strech and then return to their original form.• Thermosetting plastic : These are palstics that can be softened on heating but become permanently hard on cooling.
Composites• Composites materials are multiphase materials obtained by artificial combination of different materials to attain properties that individual component cannot attain• Example is lightweight brake disc obtained by embedding SIC particles in Al-alloy matrix• Composites are non homogenous mixture of other three basic tyes.
Properties of Materials By Ahsan Mahmood 11-MC-27
Physical Properties• Density - The mass per unit volume of a material.• Electrical Resistivity - This is a measure of a material’s ability to conduct electricity. A material with a low resistivity will conduct electricity well.• Thermal Conductivity - A measure of how fast heat is conducted through a slab of material with a given temperature difference across the slab. 3.2
Physical Properties• Thermal Expansion - A measure of the degree of increase in dimensions when an object is heated. This can be measured by an increase in length, area or volume. The expansivity can be measured as the fractional increase in dimension per Kelvin increase in temperature.• Hardness - The resistance a material offers to penetration or scratching. 3.2
DensityDensity is an important consideration inrelation to product weight and size (e.g. forportability). Pre-packaged food is sold byweight/volume and a particular consistencyis required. 3.2
Electrical ResistivityElectrical resistivity is an importantconsideration in selecting particularmaterials as conductors or insulators forparticular design contexts. 3.2
Thermal ConductivityThermal conductivity is an importantconsideration for objects which will beheated, which must conduct heat or whichmust insulate against heat. 3.2
Thermal ExpansionThermal expansion (expansivity) is animportant consideration where two dissimilarmaterials are joined, such as glazed metals.These may then experience largetemperature changes while staying joined. 3.2
HardnessHardness is an important considerationwhere resistance to penetration orscratching is required. Ceramic floor tiles areextremely hard and resistant to scratching. 3.2
Mechanical Properties• Tensile Strength - The ability of a material to withstand pulling forces.• Stiffness - The ability of a product to withstand bending. 3.2
Mechanical Properties• Ductility - The ability of a material to be drawn or extruded into a wire or other extended shape.• Toughness - The ability of a material to resist the propagation of cracks.• (Tough guys don’t crack) 3.2
Tensile Strength• The tensile strength of ropes and cables is an important safety consideration in climbing and in elevators. 3.2
Stiffness• Stiffness is an important consideration when maintaining shape is crucial to the performance of an object for example an aeroplane wing. 3.2
Toughness• Toughness is an important consideration where abrasion and cutting may take place 3.2
Ductility• Ductility is an important consideration when metals are extruded (do not confuse this with malleability—the ability to be shaped plastically). 3.2
NON-FERROUS METALSNon-ferrous metals do not have iron in them. Therefore they do not rust and are not attracted to magnets.
NON-FERROUS METALS Most non-ferrous metals are soft. By ‘alloying’ with other materials,they form new materials and become stronger for further applications. These are known also as ‘non-ferrous alloys’.