Welcome to the Building Blocks of Design!

Ever wondered why a soda can is made of aluminum but a hammer is made of steel? Or why some plastics melt when heated while others don't? In this chapter, we explore Materials and Standard Components. Understanding these is like knowing the ingredients in a kitchen—once you know what they do, you can create amazing products!

This chapter is part of Strand 2: Technological Principles. We will focus on how materials are structured, their properties, and the ready-made parts (standard components) that help us build things quickly and reliably.

1. The Science Behind Materials

To choose the right material, we need to understand what’s happening inside it. Don't worry if science isn't your favorite subject; we’ll keep it simple!

Structure and Bonding

Everything is made of atoms. How these atoms "hold hands" (bonding) determines how the material behaves:

  • Metals: Have "metallic bonds" where electrons float around. This is why they conduct electricity so well!
  • Polymers (Plastics): Made of long chain-like molecules. Imagine a bowl of spaghetti; how the strands tangle determines if the plastic is flexible or stiff.
  • Ceramics: Have very strong bonds that don't like to move. This makes them hard but brittle (they snap instead of bending).

Stress and Strain

In DAT, we often look at how materials react when we pull or push them. Here are two terms you must know:

1. Stress (\(\sigma\)): This is the internal "pressure" felt by a material when a force is applied.
Formula: \( \text{Stress} = \frac{\text{Force}}{\text{Cross-sectional Area}} \)

2. Strain (\(\epsilon\)): This is how much the material stretches or deforms compared to its original length.
Formula: \( \text{Strain} = \frac{\text{Change in Length}}{\text{Original Length}} \)

Quick Tip: Think of Stress as the "load" and Strain as the "result." If you pull a rubber band, the force you use creates stress, and the stretching you see is the strain!

2. Woods (Timber)

Wood is a natural material categorized by how the tree grows and how we process it.

Softwoods

These usually come from needle-leaved trees (conifers) that grow quickly. They are generally cheaper and easier to work with.

  • Pine & Spruce: Common for construction and cheap furniture.
  • Cedar: Naturally resists rot, great for outdoor use.

Hardwoods

These come from broad-leaved trees. They grow slowly and are usually denser and more durable.

  • Balsa: Very light and soft (used for model airplanes).
  • Oak & Beech: Very strong, used for high-quality furniture.
  • Teak: Contains natural oils, excellent for boats and outdoor decks.
  • Others in syllabus: Birch, San Cheong, Poplar, Cherry, Mahogany, Walnut.

Manufactured Boards

These are "man-made" by Gluing wood layers or fibers together. They are stable and come in large sheets.

  • Plywood: Layers of wood glued at 90-degree angles. Very strong in all directions.
  • MDF (Medium-Density Fibreboard): Made of wood dust and glue. Smooth surface, great for painting.
  • Blockboard & Particle Board: Often used for kitchen worktops or cheap "flat-pack" furniture.

Key Takeaway: Use Softwoods for budget projects, Hardwoods for durability/beauty, and Manufactured Boards for large, flat surfaces.

3. Metals

Metals are divided into two main families: those with iron and those without.

Ferrous Metals (Contain Iron)

Note: Most ferrous metals will rust if not protected!

  • Mild Steel: Tough and ductile. Used for car bodies and nuts/bolts.
  • Stainless Steel: Contains chromium, so it doesn't rust. Used for cutlery and medical tools.
  • Cast Iron: Very hard but brittle. Used for heavy engine blocks or manhole covers.
  • Galvanised Steel: Steel coated with zinc to prevent rust.

Non-Ferrous Metals (No Iron)

These do not rust (though they may tarnish) and are often not magnetic.

  • Aluminium: Light and resists corrosion. Think of soda cans or airplane parts!
  • Copper: Excellent conductor of heat and electricity. Used in wires and pipes.
  • Brass (Alloy of Copper + Zinc): Looks like gold, used for musical instruments and plumbing.

Did you know? An Alloy is a mixture of two or more metals (or a metal and another element) to make it stronger or better! For example, Duralumin is a strong aluminum alloy used in aircraft.

4. Polymers (Plastics)

Plastics are incredibly versatile. In DAT, we group them by how they react to heat.

Thermoplastics (The "Recyclable" Ones)

These can be heated, shaped, cooled, and then reheated and reshaped again. Think of them like chocolate!

  • Acrylic (PMMA): Stiff and clear. Used for signs and "glass" replacements.
  • ABS: Very tough. This is what LEGO bricks are made of!
  • PET: Clear and strong. Used for plastic water bottles.
  • PVC: Used for pipes and "vinyl" records.
  • HIPS/PS: Used for vacuum forming (like yogurt pots).

Thermosetting Plastics (The "One-Shot" Ones)

Once these are heated and set, they cannot be remelted. If you heat them again, they just char or burn. Think of them like a baked cake!

  • Epoxy Resin: Used as a very strong glue.
  • Urea-formaldehyde: Excellent electrical insulator. Used for light switches and plug sockets.
  • Polyester Resin: Often used with glass fibers to make boat hulls.

Elastomers

These are polymers that are very stretchy (elastic), like Synthetic Rubber or Silicon Rubber.

5. Other Modern Materials

Technology is always evolving! Here are a few special categories:

  • Ceramics: Hard, heat-resistant materials like porcelain or glass.
  • Composites: Combining two materials to get the best of both (e.g., Carbon Fibre or Glass Fibre).
  • Smart Materials: Materials that react to their environment.
    • Shape Memory Alloys (SMA): "Remember" their shape when heated.
    • Nano-materials: Extremely tiny structures used to make things stronger or water-repellent.

6. Standard Components

Why reinvent the wheel? Designers use Standard Components because they are cheap, reliable, and easy to replace. If you lose a screw, you can buy the exact same size at any hardware store!

Common Fasteners (Joining things)

  • Bolts and Nuts: Used for temporary joints that might need to be taken apart.
  • Screws: Grip into the material (wood or metal).
  • Washers: Spread the pressure of a nut or bolt to protect the surface.
  • Rivets & Pop Rivets: Permanent ways to join metal sheets.
  • Knock-down (KD) Fittings: The plastic/metal bits used to put together IKEA furniture!

Movement Components

  • Ball Bearings & Roller Bearings: These help shafts rotate smoothly with very little friction.
  • Hinges: Allow doors or lids to swing open.
  • Pins and Keys: Used to lock gears or pulleys onto a rotating shaft.

Quick Review: Why use standard components?
1. Cost: Mass-produced, so they are cheap.
2. Consistency: You know exactly how strong they are (ISO standards).
3. Maintenance: Easy to find a replacement anywhere in the world.

Summary Checklist

Before moving to the next chapter, make sure you can:

  • Distinguish between Softwood, Hardwood, and Manufactured Boards.
  • Identify a metal as Ferrous or Non-ferrous.
  • Explain the difference between Thermoplastics (can remelt) and Thermosetting plastics (cannot remelt).
  • Define Stress and Strain using simple formulas.
  • Give three reasons why designers use Standard Components.

Note: For more details on how to calculate the strength of these materials (Young's Modulus), see the "Design Implementation and Material Processing" elective module notes.