Design - Materials

Aesthetic Properties

Properties / aspects of a product that relate to appearance, smell, texture, taste

Alloy

A mixture that contains at least one metal: mixture of metals or mixture of metals and non-metals

Composite

A material comprised of two or more constituent materials that have different properties.

Compressive strength

The ability of a material to withstand being pushed or squashed.

Creep

The slow, permanent deformation of a solid material under the influence of a mechanical stress

Density

The mass per unit volume of a material.

Ductility

The ability of a material to be drawn or extruded into a wire or other extended shape.

Elasticity

The extent to which a material will return to its original shape after being deformed.

Electrical insulator

Reduces transmission of electric charge

Electrical resistivity

The measure of a material's ability to conduct electricity. A material with low resistivity will conduct electricity well.

Electro-rheostatic

This smart property relates to a fluid that can undergo a dramatic change in its viscosity when exposed to an electric field.

Glass

A hard, brittle and typically transparent amorphous solid made by rapidly cooling a fusion of sand, soda and lime.

Grain size (metals)

Metals are crystalline structures comprised of individual grains. The grain size can vary and be determined by heat treatment, particularly how quickly a metal is cooled. Quick cooling results in small grains, slow cooling results in large grains. Grain size in metals can affect the density, tensile strength and flexibility.

Hardness

The resistance a material offers to penetration or scratching.

Magneto-rheostatic

This smart property relates to a fluid that can undergo a dramatic change in its viscosity when exposed to a magnetic field.

Mass

Relates to the amount of matter that is contained with a specific material. Mass is a constant whereas weight may vary depending upon where it is being measured.

Mechanical properties

The properties exhibited by a material when subjected to different forces:

• hardness

• tensile strength

• compressive strength

• stiffness

• toughness

• ductility/malleability

• elasticity

• plasticity

• Young’s modulus

• stress and strain

Oxidization resistance

A property of a metal that means that it does not readily react with oxygen and degrade.

Photochromicity

Photochromic materials undergo a reversible chemical reaction in response to the level of UV light. The more UV light present, the more light is absorbed.

Physical properties

Physical Properties are properties that can be tested without the damage or destruction of the material.

• Mass

• Weight

• Volume

• Density

• Electrical resistivity

• Thermal conductivity

• Thermal expansion

Piezoelectricity

A property of certain smart materials that allows them to generate a small electrical charge when mechanically deformed, and to change shape (expand or contract) when an electric current is applied.

Plasticity

The ability of a material to be changed in shape permanently.

Shape memory alloys

A smart material that can be deformed and then return to its original, pre-set shape when exposed to a change in temperature or stress

Smart material

Materials that respond to external stimuli (eg. heat, light, pressure, or electricity) by changing one or more of their properties in a controlled, reversible, and repeatable way.

• human-made

Stiffness

The resistance of an elastic body to deflection by an applied force

Strain

The response of a material due to stress, defined as the change in length divided by the original length.

Stress

A force on a material divided by the cross-sectional area of that material.

Super alloys

An alloy that exhibits excellent mechanical strength, resistance to thermal creep deformation, good surface stability and resistance to corrosion.

Tensile strength

The ability of a material to withstand pulling forces.

Thermal conductivity

The measure of how fast heat is conducted through a slab of material with a given temperature difference across the slab.

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

Thermo-electricity

Thermoelectric materials generate electricity when heat flows through two different conductors joined together. The temperature difference causes an electric current to form

Thermoplastic

A type of plastic that can be heated and formed into a new shape repeatedly.

Toughness

The ability of a material to resist the propagation of cracks.

Transparency

Ability to allow light to be transmitted with minimal scattering allowing a clear view through material.

Volume

The quantity of three-dimensional space enclosed by a boundary, for example, the space that a substance solid, liquid, gas, or shape occupies or contains.

Young's Modulus

A measure of the stiffness of an elastic material and defined by stress/strain.

Chemical Properties

Characteristics that describe how a material reacts with other substances, resulting in a change in its chemical composition

• Corrosion Resistance

• Reactivity (Food Safe)

• Hygroscopy (Ability to retain moisture)

• Flammability

Mass

• the measure of the amount of matter

• not affected by gravity - does not change until some matter is added or removed

• measured in kg

Weight

• The force on an object acted upon by gravity, which depends on the gravitational force, and the mass of the object

• Measured in Newtons (N)

• F = ma

Volume

• the amount of space an object occupies

• measured in m³

Density

• mass of an object divided by the volume it takes up

• measured in kg/m³

Electrical resistivity and conductivity

• a measure of how easily free electrons flow through a material. 

• They are inversely related; meaning that when a material has high resistive properties, it is a poor conductor of electricity, and vice versa

Factors affecting conductivity: Resistivity is described in terms of the free flow of electrons, which can be caused by...

• Collision with lattice imperfections in the material (could be caused by cold working)

• Collisions with other atoms (e.g. impurities)

• Collisions with thermally induced vibrations (temperature)

RWE: Gold plating is often chosen for sensitive electronic components due to its high conductivity/low resistance, and its low reactivity

Resistivity of Different Materials

• Metals = good conductors

• silicone and water = somewhere in between

• plastics, ceramics and glass = good insulators.

Thermal Conductivity

• A material’s ability to transfer heat through conduction.

• The better a conductor a material is, the faster heat will travel from one side to the other.

• Metals track their electrical conductivity to match their thermal conductivity, but this does not hold true of other material families

Copper Pans are considered the best in cooking.

• Copper is chosen for its thermal conductivity for the pan.

• Cast iron is chosen for the handle due to lower thermal conductivity.

• Tin is chosen as a lining for the inside as a sacrificial layer that is more resistant to corrosion

Thermal Expansion

• Materials expand or contract when heat is either applied or removed.

• This expansion can be devastating on a product, depending on the context

Flammability

• How quickly a material can be ignited, and how quickly it burns

• Grenfell tower disaster - use of flammable materials that accelerated the spread of the fire

Corrosion Resistance

• The ability of a material to withstand damage caused by oxidization or other chemical reactions

• Both steel and aluminum are used for vehicles, but steel needs a protective layer of paint to avoid corrosion.

• Aluminium does from an oxide layer, but it protects it and doesn’t corrode further.

Reactivity (food safe)

• The extent to which a material will react with another (including air) to become unsafe for use to come in contact with food.

• Some plastics are food safe, others are not. You should not store water for long periods in a single-use bottle, as over time it will leach chemicals into the water

• Copper is quite reactive, and will react with oxygen/acids/alkalis found in foods and cleaning fluids —> why copper pans are always lined with tin

Hygroscopy

• The ability to absorb moisture from the surrounding environment.

• Wood = absorbent material + needs protecting from wet rot, dry rot, and fungal/lice attack.

• Not all timber products absorb moisture at the same rate.

• MDF for example, is very absorbent and needs sealing and coating or it expands and becomes ineffective

• Natural textiles eg. cotton readily absorb moisture

• Synthetic fibres like nylon = much less absorbent.

This important distinction helps designers choose appropriate fabrics based on their intended use.

Thermochromism

Thermochromic materials undergo a reversible chemical reaction in response to a temperature increase.