Performance characteristics of materials

Welcome to Performance Characteristics of Materials!

Ever wondered why a coffee cup is made of card and not cast iron? Or why a car bumper is made of plastic instead of solid oak? It all comes down to performance characteristics. This chapter is about understanding how materials behave and why designers choose them for specific jobs. Don't worry if it seems like a lot of names at first; we’ll break it down into simple groups with easy-to-remember examples!

1. Papers and Boards

Papers and boards are more than just things to write on. In Design and Technology, we look at how they can be manipulated to create packaging and models.

Key Performance Characteristics:

• The ability to be scored: This means cutting a shallow line into the surface to make it easier to fold accurately.
• Folding: How well the material holds a crease without snapping.
• Surface qualities for printing: Some papers are "thirsty" and soak up ink (like cartridge paper), while others are smooth for high-quality photos (like treated paper).
• Impact resistance: Think of corrugated card; those "wavy" layers inside act like cushions to protect products during shipping.

Common Types and Their Uses:

• Layout paper: Thin and slightly transparent. Perfect for sketch pads and quick ideas.
• Bleed proof paper: Has a special coating so marker pens don't "bleed" (spread out).
• Duplex card: This has different colors or textures on each side. You’ll see this a lot in food packaging (white on the outside for printing, brown on the inside).
• Foil backed card: Card with a foil lining. It’s a "barrier" material used for drinks packaging to keep liquid in and light out.

Quick Review: Think of "scoring" like pre-bending a joint. It ensures the card folds exactly where you want it to, giving you a professional, sharp edge.

2. Polymer-Based Sheet and Film

These are plastic versions of paper. They are often used for signs, packaging, and models because they are waterproof and durable.

Key Characteristics:

• Transparency vs. Translucency: Transparency means you can see through it clearly (like a window). Translucency means light gets through, but you can’t see clear images (like a frosted bathroom window).
• Flexibility: How much it can bend without breaking.
• Recyclability: Most polymers can be melted down and used again, which is great for the environment.

Examples:

• Foam board: Two layers of card with foam in the middle. It’s very stiff but light—ideal for architectural models.
• Styrofoam: That blue or pink dense foam. It’s easy to sand and shape, making it great for 3D formers.
• Polyactide (PLA) sheet: A special plastic made from corn starch. Unlike most plastics, it is biodegradable!

3. Performance Characteristics of Woods

Wood is a "natural" material, which means it can be a bit unpredictable. Designers need to understand its "personality" to use it well.

Working with the Grain:

Think of wood like a bundle of drinking straws glued together. These straws are the grain.
• Grain direction: Wood is much stronger when you pull it along the grain than across it.
• Splitting: If you drive a nail too close to the end of a board, it follows the grain and "splits" the wood open.

Common Problems (Defects):

• Warpage: Wood can twist or "cup" if it gets damp or dries too fast.
• Shrinkage: As wood loses moisture, it gets smaller. This is why old wooden doors sometimes rattle in the winter!

Types of Wood:

• Softwoods (e.g., Pine, Cedar): Usually come from evergreen trees. They grow fast and are generally cheaper.
• Hardwoods (e.g., Oak, Mahogany, Beech): Come from deciduous trees (those that drop leaves). They are usually denser and more expensive.
• Manufactured Boards: These are "man-made" from wood scraps and glue.
- MDF: Smooth and easy to paint, but don't get it wet!
- Plywood: Made of layers glued at 90-degree angles. This makes it incredibly strong in all directions.

Key Takeaway: If you need a material that won't warp or twist, choose a manufactured board like Plywood over natural timber.

4. Performance Characteristics of Metals

Metals are the "heavy hitters" of materials. We use them when we need strength, heat resistance, or electricity.

The Big Five Properties:

1. Hardness: Resistance to scratching or denting (think of a file).
2. Toughness: Resistance to breaking when hit suddenly (think of a hammer).
3. Malleability: The ability to be hammered or pressed into shape without cracking.
4. Ductility: The ability to be stretched into a long wire.
5. Tensile Strength: How much "pulling" force the metal can handle before it snaps.

Metal Categories:

• Ferrous Metals: These contain Iron and are usually magnetic (e.g., Low Carbon Steel). They usually rust if not protected.
• Non-Ferrous Metals: No iron here! They don't rust (but can corrode) and aren't magnetic (e.g., Aluminium, Copper).
• Alloys: A "mixture" of two or more metals to make them better. For example, Stainless Steel is an alloy that won't rust.

Memory Aid: Ferrous = Fe (the chemical symbol for Iron). If it has an F, it’s got Iron!

5. Polymers (Plastics)

In the exam, they might call plastics "polymers." There are two main types you MUST know the difference between.

Thermoplastics vs. Thermosetting Polymers

• Thermoplastics (e.g., Acrylic, HIPS, ABS): Think of Chocolate. You can melt it, shape it, let it cool, then melt it and reshape it again. This makes them recyclable.
• Thermosets (e.g., Epoxy Resin, Urea Formaldehyde): Think of an Egg. Once you "cook" it (heat it), it sets hard. If you heat it again, it just burns—it won't melt. These are heat resistant but not recyclable.

Elastomers:

These are polymers that act like rubber. They have the ability to be stretched and then return to their original shape. They are often used for ergonomic grips on tools to make them comfortable to hold.

6. Smart and Modern Materials

These are the "high-tech" materials that seem to have a mind of their own!

Smart Materials:

A smart material changes its properties in response to a stimulus (like heat, light, or pressure) and then changes back when the stimulus is gone.

• Shape Memory Alloys (SMA): If you bend it, you can return it to its original shape just by heating it up (e.g., Nitinol).
• Thermochromic Pigment: Changes color with temperature (like a mood ring or a "hot" indicator on a kettle).
• Photochromic Pigment: Changes color with light (like glasses that turn into sunglasses outside).
• Piezoelectric Material: Gives off a small electric spark when pressure is applied (used in gas lighters).

Modern Materials:

These are materials developed recently for high-performance jobs.
• Kevlar: Super strong and heat resistant. Used in bulletproof vests.
• Polymorph: A plastic that becomes moldable like clay in hot water. Great for prototyping handles.

7. Composites

Composites are "Teamwork" materials. They are made by bonding two or more materials together to create something better than the individuals.

• GRP (Glass Reinforced Plastic): Glass fibers (strong but brittle) mixed with resin (tough but soft). Together, they make a material that is lightweight, strong, and waterproof (used for boat hulls).
• CFRP (Carbon Fibre Reinforced Plastic): Like GRP but even stronger and lighter. Very expensive—used in supercars and racing bikes.

Did you know? Concrete is a composite! It's a mix of cement, sand, and stones. When we add steel rods, it becomes reinforced concrete, which is one of the strongest materials on earth.

Final Quick Review Box

1. Need it to fold? Score it first.
2. Need it to be waterproof? Use a polymer or non-ferrous metal.
3. Need it to react to heat? Use a Smart Material like SMA.
4. Remember: Thermoplastics melt; Thermosets burn!