Topic 4.1

4.1 Specifically

Mass

Relates to the amount of matter that is contained with a specific material. It is often confused with weight, understandably, as we use Kg to measure it.

Weight

Relies on mass and gravitational forces to provide measurable value. Mass is a constant, whereas weight may vary depending on where it is being measured. Weight is technically measured as a force, which is Newton, i.e. a mass of 1 Kg is equivalent to 9.8 Newton \[on earth\].

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.

Density

The mass per unit volume of a material. Its importance is in portability in terms of a product’s weight and size. Design contexts include, pre-packaged food (instant noodles) is sold by weight and volume, packaging foams.

* Any other context where weight and volume are important.
* Pre-packaged food (instant noodles) is sold by weight and volume is important.
* Packaging foams/material volume is important.

Electrical Resistivity

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

Electrical Insulator

Reduces transmission of electric charge.

Thermal Conductivity

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

* It is important for objects that will be heated or must conduct or be insulated against heat gain or loss.
* Design contexts include: pots & pans.

Thermal Expansion (Expansivity)

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.

* It is important when two dissimilar materials are joined. These may then experience large temperature changes while staying joined.
* Different materials (even within the same material group, e.g. metals) expand at different rates.
* Design contexts include oven doors, glass pot lids with metal rims.

Electrical Resistivity

* It is important when selecting materials as conductors or insulators
* Design contexts include: electrical plugs.

Hardness

The resistance a material offers to penetration or scratching.

Tensile Strength

The ability of a material to withstand pulling (apart) forces.

* It is important in selecting materials to resist stretching.
* Design contexts include: ropes (climbing or towing), cables (in elevators) and fishing lines.

Compressive Strength

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

* Design contexts include: ceramic floor tiles, concrete and bricks for buildings or anything that requires to bear weight.

Stiffness

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

* It is important for maintaining shape is an important performance.
* Design contexts include;  aircraft wing, diving boards or panels on cars.

Toughness

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

* It is important where abrasion and cutting may take place.
* Design contexts include:
* Any design context where impact is likely.
* Automobile bumpers

Ductility

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

* It is important when metals are extruded (extrusion).
* Typically, has high toughness.
* Design contexts include the production of extended extrusions.
* (not to be confused with malleability: the ability to be shaped plastically – see in the below section).

Brittle (Brittleness)

Breaks into numerous sharp shards.

* Typically, has low toughness.
* Design contexts include: glasses

**Ductility**

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

* It is important when metals are extruded (extrusion).
* Typically has high toughness.
* Design contexts include production of extended extrusions.

Stress

The load on a structural member divided by its cross-sectional area is called the “stress in the member”.

Strain

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

**Young’s Modulus**

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

**Elasticity** (Elastic region)

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

* A material behaves elastically, when the stress on the material is released before it breaks, the extension (strain) relaxes and the material returns to its original length or shape.
* If you squash a drinking

**Plasticity** (Plastic region)

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

* When bent/deformed beyond yield point and the stress is removed, it cannot change back to original shape.
* It maintains the new shape or stretches/tears/breaks.

**Material Selection Charts**

 *A chart used to identify appropriate materials based on the desired properties.*

**Aesthetic Characteristics**

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

 Aesthetic Appeal 

Favorable in terms of appearance.

Piezoelectricity

Materials give off a small electrical discharge when deformed.

Photochromicity

A material that can described as having a reversible change of colour when exposed to light.

Magneto-rheostatic & Electro-rheostatic

*  *Materials, which 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

Electricity produced directly from heat. It involves the joining of two dissimilar conductors that, when heated, produce a direct current.