Design and Technology: Technical Principles - Materials and Applications

Materials and Applications

Learning Outcomes

By the end of this unit, you should understand:

• The basic classification of material groups.

• The mechanical properties and working characteristics of a range of materials.

• The different physical properties of materials.

• How and where to identify forces and their relative strength.

• The different mechanical properties that specific materials possess.

• How to take notes and revise the material effectively.

Material Categorization

To aid learning and revision, materials are categorized into three types:

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

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

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

Material Classification

Materials for product design and engineering are generally split into groups or classifications:

• Metals

• Timber/Woods

• Polymers

• Paper and board

• Composites

• Smart and modern materials

We can divide materials into categories and sub-categories with suitable applications for each material.

Material and Applications

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

Key points:

• A material's properties are largely determined by its structure.

• Metals: Made of crystals containing atoms and molecules.

• Woods: Fibrous materials of plant cells and resins. Paper and card are derived from wood and share the same molecular structure.

• Polymers: Long-chain molecules containing carbon, hydrogen, and oxygen atoms, with other chemicals like chlorine and fluorine.

Material Properties

To select correct materials and manufacturing processes, a working knowledge of the physical and mechanical properties of materials is needed including how they can be worked with, shaped, formed, joined, and finished.

Two main characteristics of a material:

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

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

Physical Properties

These refer to the actual matter that forms the material. Examples include:

• Fusibility: The 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.
  Density = \frac{Mass}{Volume}

• Electrical conductivity: Materials resist the flow of electricity to varying extents; conductors offer very low resistance.

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

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

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

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

• Transparency: The ability for light to fully pass through, allowing you to see through the material (e.g., glass).

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

• Colour: Perceived by light bouncing off the surface of a material, and is thus an optical property.

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

Mechanical Properties

• Plasticity: The ability of a material to be permanently changed in shape by an external force without damage. Materials displaying this property are referred to as polymers.

• Malleability: The ability to withstand deformation by compression.

• Ductility: The ability to be drawn out (stretched).

• Elasticity: The ability to flex and return to its normal shape when the force is removed.

• Toughness: The ability to withstand a sudden impact, or bending.

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

• Durability: The ability of a material to withstand wear and tear, weathering, and corrosion.

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

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

Strength

Strength is the ability to withstand a particular force. Types of strengths and forces include:

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

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

• Bending strength: Ability to withstand forces attempting to bend the material.

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

• Torsional strength: Ability to withstand twisting forces.

Forces in Structures

Examples of forces in a house:

• Tension: Across the roof.

• Shear: Where the support meets the deck.

• Bending: In the stairs.

• Torsion: In handle and hinges.

• Compression: In the supports.

Material Properties Table

Example of filling in a material properties table:

Summary

• Materials have both physical and mechanical properties.

• Strength is resistance to force; each force has an associated strength (or weakness).

• Physical properties relate to the material's makeup but also contribute to aesthetic qualities like color and texture.

• Materials are categorized as traditional, modern, or smart. Smart materials are also modern materials.

• Each material has specific properties that make it suitable for a particular application, depending on the intended manufacturing process.

• Workshop and industrial tests exist for materials, addressing their mechanical properties.

Revision Notes

• The syllabus covers seven categories of materials (metals, woods, polymers, paper and board, composites, smart materials, modern materials), but familiarity with textiles, glass, and ceramics is also important.

• Break down each category into three to aid memory.

• Name one common application for each specific material; avoid generic terms like ‘wood’ or ‘metal’.

For each material group you study, understand:

• Classification

• Properties

• Stock forms

Refer to the physical and mechanical properties of each material and why those properties make them suitable for the particular application.

Please attempt the past paper for next lesson, focusing on question 1 from the first sample 2018 paper.

Give two physical and two mechanical properties of the metal used for the kitchen sink. In each case, state why the property is suitable for this product.