Metals can have a wide range of properties to suit different applications. Their specific properties are defined by keywords;
Malleability is defined as a meterials ability to be deformed under pressure without breaking and is unique to metals. This includes being hammered, pressed, or rolled into thin sheets. This is measured by the compressive stress that can be applied before fracture and is determiend by a materials crystal structure. As pressure is applied the atoms within the crystaline structure slide over each other and try to maintain their metallic bond
Malleable metals include; gold, iron, aluminum, copper, silver, and lead. Gold and Silver are highly malleable and used in jewelry to for complex, intricate designs
------------------------------------------------------------------------------------------------------Ductility is the opposite of malleability and defines a materials ability to be stretched under tensile stress. As with malleability the property considers the plasticity of a material, or the ability to be deformed without fracture. The loose valence electrons in the outer shell of metal atoms allows them to slide over or away from each other without being subjected to repulsive forces that cause shattering. Many metals are therefore considered ductile and can increase in ductility when heated
Copper is both highly conductive & ductile making it ideal for electrical wires as well as Gold which can be stretched to incredibly fine wire. Aluminum, copper, tin, mild steel & platinum are also very ductile
------------------------------------------------------------------------------------------------------
Shear strength is a material property that determines how resistant a it is to opposing parallel forces. It helps to consider it as a sliding force replicated by the action of scissors cutting paper. When sheared a material is separated permanently down the fracture line into two pieces. Metals with high ductility tend to have a low shear strength as they have a lower hardness. A Shear Press, or guillotine, is mechanical device to shear metals using levers & linkages to gain a mechanical advantage.
A material is rated by it's shear modulus, a ratio between shear stress and strain that is linked to Hookes Law. As with ductility and malleability, temperature can alter this property in metals ------------------------------------------------------------------------------------------------------
Hardness is a property that defines a materials ability to resist permanent deformation under compressive force. There are three measures of hardness due to the complex nature of a material behavior; scratch hardness, indentation hardness, & rebound hardness.
- Indention hardness determine the ability for a material to resist deformation from a focussed compressive force. Vickers and Rockwell hardness tests are commonly used for the shape of the point used. The surface area deformed is measured after pressure is applied to determine the material hardness
- Scratch hardness is a materials resistance to fracture or permanent deformation from a sharp point. The principle is that a harder material will always scratch a softer one. This was measured using the Mohs Scale from 1-10 with 10 being the hardest as Diamond and Tungston Carbide the highest metal at 8.5 - 9. Recently the Vickers Scale is used
- Rebound Hardness or dynamic hardness is a measure of a metals elasticity. A diamond or tungston carbide tipped hammer is dropped from a set height onto the surface of the material and the height bounced/rebounded is measured. The amount of energy absorbed by the test piece affects the height of bounce. A small magnet follows the movement of the hammer through a coil of wire recording a measurable voltage which is proportional to the speed