🏷 Design and Technology (9252): Product Design Study Notes 🏷
Core Technical Principles: Materials and their Working Properties
Hello future Product Designers! Welcome to one of the most important chapters in your course. Understanding the working properties of materials is like knowing the superpowers of your ingredients. If you choose the wrong material, your amazing design will fail!
Don't worry if some of the terms sound scientific; we will break them down using simple analogies so you can remember exactly why you choose steel over plastic, or wood over ceramic. Let's get started!
1. What are Working Properties? (The Basics)
A material's working properties are the characteristics that determine how it behaves when subjected to forces (like pushing, pulling, or cutting) and how well it suits a specific environment (like heat, cold, or moisture).
✔ Quick Analogy: The Cake Recipe
Imagine you are baking a cake. If you want a light, fluffy sponge, you need ingredients with properties that allow them to expand (like raising agents). If you accidentally use a material that is too hard and dense (like cement!), your cake will fail. In design, choosing the right material properties determines whether your product succeeds or fails.
Working properties are generally split into two main groups:
- Mechanical Properties: How a material reacts to outside forces (e.g., strength, hardness, toughness).
- Physical Properties: Inherent characteristics of the material (e.g., density, conductivity, melting point).
2. Mechanical Properties: How Materials React to Force
These properties are critical for determining if a material can withstand the stresses and strains of everyday use without breaking or deforming permanently.
2.1. The Different Types of Strength
Strength is the ability of a material to resist a force without breaking or permanently bending (yielding). But there are different ways a material can be strong:
- Tensile Strength (Tension):
- Compressive Strength (Compression):
- Shear Strength (Shearing):
The ability to resist a pulling force that tries to stretch or tear it apart.
Example: A climbing rope needs high tensile strength to support weight without snapping.
The ability to resist a pushing or squashing force.
Example: Concrete pillars used in bridges or buildings need high compressive strength to hold up the structures above them.
The ability to resist forces that try to cause one part of the material to slide past another, usually resulting in a cutting action.
Example: Bolts or rivets holding two overlapping plates together need good shear strength to prevent the plates from sliding apart.
💭 Memory Aid: T-C-S
To remember the three types of strength, think: Tear, Crush, Slice.
2.2. Hardness vs. Toughness (Crucial Distinction!)
This is where many students get confused, but the difference is simple:
A) Hardness
Hardness is the material’s ability to resist scratching, abrasion, cutting, or indentation (denting). Hard materials often have a long surface life.
- Example: A kitchen worktop must be hard to resist scratches from knives or plates. Drill bits are made from very hard steel so they can cut through other materials.
B) Toughness
Toughness is the ability of a material to absorb energy from a sudden shock or impact without fracturing (breaking).
- Example: A safety helmet or a car bumper needs to be tough to absorb impact energy in an accident.
⚠ Common Mistake Alert!
A material can be very hard but not tough. Think about glass: it is hard (it resists scratches), but if you drop it, it shatters easily because it is brittle (it lacks toughness).
2.3. Deformation: Elasticity and Plasticity
When you apply a force to a material, it deforms (changes shape). What happens when you remove that force?
A) Elasticity (Elastic Deformation)
Elasticity is the ability of a material to return to its original shape and size once the force that caused the deformation is removed.
- Example: A spring or a rubber band stretches when pulled but snaps back perfectly when released.
B) Plasticity (Plastic Deformation)
Plasticity is the ability of a material to be permanently changed in shape without cracking or breaking. The deformation stays, even after the force is removed.
- Example: Clay or modelling dough is highly plastic—you can shape it and it keeps that new shape. This property is vital for manufacturing processes like moulding and forming.
💭 Memory Aid: P is for Permanent
Plasticity means the change is Permanent. Elasticity means it goes back (like an Elastic band).
2.4. Malleability and Ductility (Shaping Properties)
These properties describe how easily a material can be shaped or reformed. Both relate to plastic deformation.
A) Malleability
Malleability is the ability of a material to be hammered, pressed, or rolled into thin sheets without cracking.
- Example: Aluminium is very malleable, allowing it to be rolled into thin foil (aluminium foil). Metals are often rolled or pressed into car body panels.
B) Ductility
Ductility is the ability of a material to be stretched, pulled, or drawn out along its length into a thin wire.
- Example: Copper is extremely ductile, which is why it is used extensively for electrical wiring.
💡 Quick Review: Mechanical Properties Key Takeaway
You must be able to choose a material based on its resistance to force. If a product needs to be hit (like a hammer head), it needs toughness. If it needs to keep its shape under heavy loads (like a bridge cable), it needs tensile strength.
3. Physical Properties: Inherent Material Characteristics
These properties are not about how the material reacts to force, but about its fundamental structure and interaction with heat, electricity, and the environment.
3.1. Density
Density is the mass (weight) of a material in relation to its volume (size). Put simply, it tells you how heavy a material is for its size.
\( \text{Density} = \frac{\text{Mass}}{\text{Volume}} \)
- High Density: Materials like steel or concrete are dense (heavy). This is good for stability or needing a high mass (e.g., foundations, weights).
- Low Density: Materials like balsa wood, foam, or certain plastics (e.g., expanded polystyrene) are low density (lightweight). This is vital for aerospace, transportation (saving fuel), and packaging.
🔊 Did You Know?
The difference between hardwood and softwood isn't just about how hard they are, but often about their density. Hardwoods generally have a much higher density than softwoods, making them heavier and stronger for their size.
3.2. Thermal Properties (Heat)
These properties relate to how a material reacts to and transfers heat energy.
A) Thermal Conductivity (Conductors)
Materials with high thermal conductivity allow heat to pass through them quickly and easily.
- Example: Metals (like copper and aluminium) are excellent thermal conductors. They are used for the base of cooking pans to quickly transfer heat to the food.
B) Thermal Insulators
Materials with low thermal conductivity (insulators) resist the flow of heat.
- Example: Wood, plastic, foam, and ceramics are good insulators. They are used for oven handles, thermos flasks, and wall insulation to keep heat in or out.
3.3. Electrical Properties
These describe how easily a material allows electricity to pass through it.
A) Electrical Conductivity (Conductors)
Materials that allow electricity to flow through them easily.
- Example: Metals (especially copper and gold) are used for electrical wiring and circuits.
B) Electrical Insulators
Materials that resist the flow of electricity.
- Example: Polymers (plastics) and rubber are used to coat electrical wires, ensuring the electricity stays in the conductor and doesn't cause a shock.
3.4. Resistance to Corrosion and Degradation
This property is essential for products that will be used outdoors or in wet/chemical environments.
Corrosion (Metals):
Corrosion (usually rusting for ferrous metals like steel) is the deterioration of a material due to reaction with its environment (usually oxygen and water). Materials that are corrosion resistant (like stainless steel or aluminium) are essential for outdoor furniture, car parts, or marine applications.
Degradation (Polymers and Timber):
Polymers (plastics) can degrade when exposed to UV light (sunlight), becoming brittle and discoloured. Timber degrades when exposed to moisture and insects (rot). Choosing materials with good degradation resistance, or applying protective finishes, is a vital technical principle.
💡 Quick Review: Physical Properties Key Takeaway
Physical properties often dictate the *function* and *lifespan* of the product. Low density is great for flying, high electrical resistance is great for safety, and high corrosion resistance is great for longevity.
📚 Study Checklist: Core Vocabulary
Make sure you can define these key terms clearly and provide a product example for each:
- Tensile Strength
- Compressive Strength
- Hardness
- Toughness
- Malleability
- Ductility
- Elasticity
- Plasticity
- Density
- Thermal Conductivity
- Corrosion Resistance
You’ve successfully navigated the core technical principles of materials! The better you understand these working properties, the smarter your design choices will be. Keep practising those definitions!