Material Properties

Physical Properties

Properties that can be identified through non-destructive testing.

Property	Definition
Mass	Amount of matter contained with a specific material. Mass is a constant and it's measured in Kilograms(Kg)
Weight	Technically measured as a force in Newtons. It relies on mass and gravitational forces
Volume	Quantity of three-dimensional space enclosed within the closed boundaries of an object
Density	The mass per unit volume of a material
Electrical Resistivity	How much electricity a material conducts. The lower the resistivity the more electricity it conducts
Thermal Conductivity	How fast a material conducts heat. The higher the conductivity the faster the heat is conducted
Thermal Expansion	How much a material expands once heated
Hardness	How resistant a material is to scratching and penetration

Mechanical Properties

Properties that can be identified through destructive testing.

Property	Definition
Tensile Strength	The ability of a material to withstand pulling forces
Compressive Strength	The ability of a material to or structure to withstand forces that reduce in size
Stiffness	The resistance of elastic materials to deflect applied forces
Toughness	The ability of a material to prevent cracking and breaking
Ductility	The ability of a material to be drawn or extruded into extended shapes
Malleability	The ability of a material to be shaped

Young's Modulus

The measure of the stiffness of an elastic material. Defined as the ratio of the stress along an axis to the strain along that axis in the range of stress.

Also known as the tensile modulus or elastic modulus, is a measure of the stiffness of an elastic material and is a quantity used to characterize materials. It is defined as the ratio of the stress (force per unit area) along an axis to the strain (ratio of deformation over initial length) along that axis in the range of stress.

$S t r e s s = \frac{F o r c e}{C r o s s S e c t i o n a l A r e a}$

$S t r a i n = \frac{C h a n g e i n L e n g t h}{O r i g i n a l L e n g t h}$ .

The straight line region is known as the elastic region, it's when the material can regain its original shape after the load is removed.

Once the material has passed the "Yield Point" it can't go back to its original shape.

The "Plastic Stage" is the stage in which the material has passed the "Yield Point" but hasn't reached the "Ultimate Tensile Strength" which therefore means that it's the stage in which the material will not be able to return to its original shape.

The "Break Point" or "Ultimate Stress Point" is the point at which a material is considered to have completely failed.

Aesthetic Characteristics

Aesthetic characteristics of a material or product are what makes it interesting, appealing, likeable, unattractive, etc. They are all based on personal preferences. They are very difficult to quantify scientifically. There are some characteristics that are only for food.

Characteristic	Definition
Taste	The ability to detect the flavour of a substance
Smell	The ability to perceive odours
Appearance	How something looks aesthetically
Texture	The properties and sensations caused by the external surface of the product. Received through the sense of touch
Colour	Visual perceptual property corresponding to the categories of the colours. Optical: Opaque, Translucent, Transparent Colour: Hot, Cold, Warm, Cool, Vivid Effects on Emotion: Warmth, Coldness

Smart Materials

Smart materials are those materials that have at least one property that can be dramatically altered.

Material	How it Works
Piezoelectricity	A term that is derived from the Greek meaning for piezo, squeeze or pressure where electricity is generated when a piezoelectric material is deformed, The pressure acting upon the material it gives off a small electrical discharge.
Shape Memory Alloy (SMA)	Metals that exhibit pseudo-elasticity and shape memory effect due to rearrangement of the molecules in the material. Pseudo-elasticity occurs without a change in temperature or electrical voltage. The load on the SMA causes molecular rearrangement, which reverses when the load is decreased and the material springs back to its original shape.
Photochromicity	Material that can be described as having a reversible change of colour when exposed to light. One of the most popular applications is for colour-changing sunglass lenses, which can darken as the sunlight intensifies. A chemical either on the surface of the lens or embedded within the glass reacts to ultraviolet light, which causes it to change form and therefore its light absorption spectra.
Magneto-rheostatic (MR) Electro-rheostatic (ER)	Magneto-rheostatic (MR) and electro-rheostatic (ER) materials are fluids that can undergo dramatic changes in their viscosity. They can change from a thick fluid to a solid in a fraction of a second when exposed to a magnetic (for MR materials) or electric (for ER materials) field, and the effect is reversed when the field is removed.
Thermoelectricity	Thermoelectricity is, at its simplest, electricity produced directly from heat. It involves the joining of two dissimilar conductors that, when heated, produce a direct current. Thermoelectric circuits have been used in remote areas and space probes to power radio transmitters and receivers.

Metals and metallic alloys

Usually hard and shiny. Metals have good electrical and thermal conductivity.

Extracting Metal from Ore

A metal ore is a rock that contains a metal or metal compound with a high enough concentration that it's economically safe to extract it. The method used to extract the metal from the ore will depend on how reactive the metal is.

Material	Extraction Method
Aluminium	Aluminium ore is called bauxite. The bauxite is purified to produce aluminium oxide, a white powder from which aluminium can be extracted. The extraction is done by electrolysis
Steel	Iron ore is smelted in a blast furnace or an electric furnace. The impurities are removed and carbon is added.

Grain Size

Metals are crystalline structures that contain many individual grains. The size of said grains will vary from metal to metal and can be modified by heat treatment, particularly the speed at which the metal is cooled. The quicker the cooling process is the smaller the grains are. The grain size affects density, tensile strength and flexibility of the metal.

The smaller the grains are the higher the density of the metal which results in lower flexibility and often tensile strength too. Tensile strength and flexibility will also be affected by how the metal is tempered.

The rate of cooling and the number of impurities will affect the grain size:

Gradual cooling - a few crystals are formed - large grain size
Rapid cooling - many crystals are formed - small grain size
Reheating a solid metal/alloy allows the grain structure to re-align itself
Directional cooling in a structure is achieved by selectively cooling one area of a solid

The addition of impurities in a molten metal can induce a large number of small grains that will make the metal harder and stronger.

Modifying Physical Properties

Method	How it works/what it does
Alloying	An alloy is a mix between two elements of which at least one is a metal
Work Hardening	The strengthening of a metal by plastic deformation. The metal becomes hard after the process. The metal doesn't receive any heat at all. The structure gets deformed as do the grains. Shape changes but the volume stays the same. The defects of these structures reduce the ability for crystals to move within the metal structure, becoming more resistant to more deformation as they recrystallize. The processes for work hardening are: Rolling Bending Shearing Drawing
Annealing	A heat treatment that alters the physical and sometimes chemical properties of a metal to increase its ductility and make it more workable. The process involves heating the metal up, keeping at a suitable temperature and then gradually reducing the temperature until cool. Annealing softens the metal up after it has been work hardened.
Case Hardening	When the steel is heated through the direct application of heat and then rapidly cooled. This creates a layer of martensite on the surface which improves the hardness of the surface while keeping the inner core untouched so that it still has its properties such as flexibility and relative softness.
Tempering	Process of heat treating used to increase the toughness of metals containing iron. It's usually done after hardening to remove some excess hardness in the metal. The process involves the metal being heated and then left to cool down in still air usually at room temperature. Tempering reduces the brittleness of the metal after it has been quenched.

Editors

Iñigo21 - 1367 words.

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Raw Material to Final Product