Topic 4.1 - Properties of Materials

Physical properties

Any property that is measurable that describes a state of materials, for example, mass, weight, volume, and density. These properties tend to be the characteristic of materials that can be identified through non-destructive testing (although some deformation is required to test hardness).

Mass

Relates to the amount of matter that is contained within a specific material. It is often confused with weight understandably as we use Kg to measure it. Mass is a constant whereas weight may vary depending upon where it is being measured.

Weight

Relies on mass and gravitational forces to provide measurable value. Weight is technically measured as a force, which is the Newton, i.e. a mass of 1 Kg is equivalent to 9.8 Newton [on earth].

Density

The mass per unit volume of a material. Its importance is in portability in terms of a product’s weight and size.

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. "How much space it takes up?"

Electrical resistivity

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

Thermal conductivity

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

Hardness

The resistance a material offers to penetration or scratching. The diamond is harder than the glass so it can scratch, the glass is not as hard as the diamond so it is scratched.

Mechanical properties

Properties of a material that involve the relationship between stress and strain or a reaction from an applied force. Basically how the material performs under applied force.

Compressive strength

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

Toughness

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

Tensile

The ability of a material to withstand pulling forces.

Stiffness

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

Ductility

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

Plasticity

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

Elasticity

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

Young’s modulus

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

Stress (Young’s modulus)

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

Strain (Young’s modulus)

The response of a material due to stress, defined as the change in length divided by the original length. From A to B- this straight line region is the elastic region. The material can regain its original shape after removal of load. The stress and strain are directly proportional up to point A. From B to E- Plasticity/plastic deformation/plastic region is the ability of a material to be changed in shape permanently. Deformation has taken beyond the elastic region.

Aesthetic characteristics

Aspects of a product that relate to taste, texture, smell, and appearance.

Taste

The ability to detect the flavour of substances in food and beverages.

Smell

Power of perceiving odours or scents by means of the organs in the nose.

Appearance

The visual impact that a designed object purveys to the user, viewer, or observer.

Texture

Relates to the tactile elements of designed products and environments.

Smart materials

Materials that have been designed to have one or more properties that can be modified when subject to an external stimulus in a way that the output can be controlled.

Piezoelectricity

A piezoelectric material gives off a small electrical discharge when deformed.

Shape memory alloy (SMA)

Shape memory alloys are metals that when deformed, can spring back into their original shape once released.

Photochromicity

A photochromic material changes colour in response to an increase in light. When the light source is removed, it returns to its original colour.

Thermoelectricity

This refers to a smart material that when heated can produce an electric current.

Magneto-rheostatic

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

Electro-rheostatic

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