Materials Properties
Properties
Mechanical properties
| Strength | The general ability of a material to withstand an applied force. See tensile and compressive strength below. |
| Hardness | Hardness is a measure of how easily a material can be scratched or indented. Hard materials are often also very brittle - this means they have a low resistance to impact . Well known hard materials include diamond and hardened high carbon steels. Same units as for tensile strength. The methods used for testing hardness are the Brinell test which uses a hardened steel ball and produces a hardness number HB which can be used to compare the hardness of materials. The Vickers hardness test uses a diamond square based pyramid - a microscope is needed to observe the indent -the VHN is also used for comparisons. The Rockwell test uses a ball for softer materials and a pyramid cone for hard materials - the reading is taken directly using a dial. This method is less accurate. |
| Brittleness | A material that has a tendency to break easily or suddenly without any extension first. Good examples are Cast iron, concrete, high carbon steels, ceramics, and some polymers such as urea formaldehyde (UF). Opposite to toughness. |
| Toughness | A material that absorbs impact (sudden forces or shocks such as hammer blows) well is tough - this is the opposite to brittleness. [units for toughness are energy per unit area - Joules/m²] |
| Plasticity | The materials which deform permanently when small forces are applied show plasticity. Plasticine and clay are good examples |
| Elasticity | The ability of a material to return to its original form after a load has been applied and removed. Good examples include rubber, mild steel and some plastics such as nylon. |
| Stiffness | The ability to resist bending. |
| Malleability | The ability to plastically deform and shape a material by forging, rolling or by any other method of applying pressure. Being easy to beat into a thin sheet is the literal meaning. Good examples are lead, gold and copper. |
| Ductility | The ability to be drawn out into a thin wire or threads. It is a measure of how easily a material can be worked. Good examples are gold, copper, titanium, wrought iron, low carbon steels and brass. |
| Compressive strength | The ability to withstand pushing or squeezing forces (compression). |
| Tensile strength | The ability to withstand pulling or stretching forces (tension). The unit for tensile strength is the MN per square metre |
| Durability | A general property. The ability to withstand wear and tear through weathering and corrosive attack etc. |
| Stability | A general property of resistance to changes in shape or size. |
Physical properties
| Thermal conductivity | How well a material conducts heat. most metals are good conductors of heat, especially copper and aluminium.Unit for thermal conductivity are Watts per metre Kelvin - W/mK So copper which is a good conductor has a value of 283 whereas lead has a value of 35 and rubber which is an insulator has a value of 0.15. Poor conductors are called insulators - clearly this will often be the property which is needed. |
| Electrical conductivity | How well the material conducts electricity - metals and graphite are good conductors. Insulators are materials that do not conduct electricity - plastics (polymers), rubber (elastomers) and ceramics are all insulators. Tables of data usually show the resistivity of materials. The unit of resistivity is the ohm metre. Very low values are conductors and high values are insulators. So copper which is a good conductor has a value of 17 x 10 to the power of minus 9 while polythene has a value of 100 x 10 to the power of 9. |
| Magnetic | Some metals can be magnetised (most steels). Ferrous metals are generally able to be attracted by a magnet. There are also some ceramic materials which have magnetic properties. |
| Corrosion resistance | The ability to withstand environmental attack and decay. Plastics have been developed or mofified to withstand hostile environments e.g. uPVC is resistant to the effects of UV light which would quickly cause normal PVC to become brittle. A range of coatings and surface finishes are used to enhance materials appearance and corrosion resistance. |
| Fusibility | The abilty to change easily into a molten state when heated (without chemical breakdown/burning). Especially important for metals and polymers which are to be cast, moulded or welded. |
| Appearance and Optica Propertiesl | A measure of light transmission. Opacity light cannot pass through easily, translucency - light passes through but is diffuse, translucency - light passes through but may be refracted. Shiny surfaces reflect light. Self finishing materials need no further treatment other than cleaning or polishing. |
| Density | Density is mass per unit volume. The unit of density is the Kg per metre cubed. |
Material description - what do your senses tell you. These properties determine how you you interact with the products i.e. the look and feel. Some are directly related to their mechanical and physical properties - density/heavy, cold/thermal conductivity, hard/impact resistance etc.
| Metals | Metals are :- Shiny, hard, heavy, cold to the touch. They can also have sharp edges, ring when struck and have a metallic shine or sheen - usually silver in colour (some are gold or reddish). Examples of metals include:- copper, aluminium, steels (mild steel, stainless steel, high and medium carbon steel, mild steel), silver, gold, zinc. Also includes alloys which are a mixture of a metal and another element (usually another metal) to give new properties. e.g. aluminium alloy, solder, magnesium alloy, brass, bronze, zinc alloy. |
| Polymers (Plastics) | Polymers are:- Dull sheen (usually), slightly flexible, light weight, can be any colour,warm to the touch. Examples of polymers - thermosets which once formed cannot be reformed by the use of heat - epoxy resins, polyester resins, bakelite, melamine, ural. Thermoplastics which can be reformed - polyethylene, acrylic, ABS, nylon, PET(polyester teraphthalate), polypropylene, PVC. |
| Ceramics | Ceramics are:- Not shiny unless glazed, hard, often brittle, heavy, can be any colour (often white, pale brown to dark brown), cold to the touch. Examples include porcelain, china, stoneware.
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| Composites | Composites are :- Very strong, usually tough and durable. Dull sheen, can be any colour, usually warm to the touch. Examples include Glass reinforced epoxy resin and polysester resin. Carbon fibre reinforced epoxy resin. |
