Materials and Their Properties

Material Categorisation

• Materials can be categorized in three ways:

  • Traditional: Used for many centuries (e.g., stone, wood, textiles, iron, bronze).

  • Modern: Developed in the last century (e.g., titanium, polymers, concrete, composites).

  • Smart: Change physical properties (e.g., thermochromic pigment, shape memory alloys, ferrofluid).

Material Classification

• Materials for product design and engineering are generally split into these groups:

  • Metals

  • Timber/Woods

  • Polymers

  • Paper and board

  • Composites

  • Smart and modern materials

• Materials can be divided into categories and sub-categories with suitable applications for each material.

Materials and Their Applications

• The purpose of this unit is to provide the knowledge to choose the best material for a particular product or manufacturing process.

• Key points:

  • Material properties are largely determined by its structure.

  • Metals: Made up of crystals containing atoms and molecules.

  • Woods: Fibrous materials made up of plant cells and resins.

  • Paper and card: Derived from wood, sharing the same molecular structure.

  • Polymers: Made up of long chain molecules containing carbon, hydrogen, and oxygen atoms, along with other chemicals like chlorine and fluorine.

Material Properties

• To select the correct materials and manufacturing processes, a working knowledge of physical and mechanical properties is needed.

• Two main characteristics:

  1. Physical properties: Refer to the actual makeup or structure of the material.

  2. Mechanical properties: Refer to how a material reacts to external forces.

Physical Properties

• Refer to the actual matter that forms the material. These include:

  • Fusibility: Ability to change into a molten or liquid state when heated to a certain temperature.

  • Density: Defined as mass per unit volume. Relative density is the ratio of the density of the substance to that of pure water at 4 degrees C.

  • Electrical conductivity: Materials resist the flow of electricity, but conductors offer very low resistance.

  • Electrical Insulation: Offer a high resistance to the flow of electricity.

  • Semi-conductors: Range between conductors and insulators, allowing current flow under certain conditions.

  • Thermal properties: How a material reacts to heat (expansion, conductivity, and insulation).

More Physical Properties

• Opacity: How much light is allowed to pass through. Opaque materials do not allow light to pass through, while semi-opaque materials allow some light through (translucency).

• Transparency: Ability for light to fully pass through, allowing visibility through the material (e.g., glass).

• Translucency: Ability to transmit light even if you cannot clearly see through the material (e.g., thin paper).

• Colour: Perceived by light reflecting off the surface, considered an optical property.

• Surface: How light bounces off indicates smoothness or roughness.

Mechanical Properties

• Plasticity: Ability to be permanently changed in shape by an external force without damage. This is why plastic materials are referred to as Polymers.

• Malleability: Ability to withstand deformation by compression.

• Ductility: Ability to be drawn out (stretched).

• Elasticity: Ability to flex and return to its original shape when the force is removed.

• Toughness: Ability to withstand a sudden impact; can also refer to bending resistance.

• Hardness: Ability to withstand abrasive wear (indentation or scratching).

• Durability: Ability to withstand wear and tear, weathering, and corrosion.

• Stability: Ability to resist changes in shape and size due to its environment.

• Strength: Ability to withstand forces without breaking or being permanently deformed.

Strength (Mechanical Property)

• Strength is the ability to withstand a particular force.

  • Tensile strength: Ability to withstand stretching or pulling forces.

  • Compressive strength: Ability to withstand pushing or crushing forces.

  • Bending strength: Ability to withstand forces that attempt to bend a material.

  • Shear strength: Ability to withstand sliding forces acting against each other.

  • Torsional strength: Ability to withstand twisting forces.