Overview
This lecture reviews essential materials and their properties for GCSE and A-level Design & Technology exams. It covers definitions, categories, and detailed examples of woods, composites, metals, papers, boards, textiles, smart materials, and polymers. The content overlaps between GCSE and A-level, but always check your exam board specification for required materials.
Physical vs. Working Properties
- Physical properties: Characteristics a material has before use.
- Examples: density (mass per volume), weight, moisture content, shrinkage, thermal/electrical conductivity, grain direction (in wood), color, texture, transparency, chemical resistance, absorbency.
- Working properties: How a material behaves when manipulated or under force.
- Examples: workability (ease of cutting/shaping/finishing), machinability, stability (resistance to warping/twisting), abrasion resistance, flexibility, tear/crease resistance, printability, hardness (resistance to scratching/indentation), toughness (resistance to shock), tensile/compressive strength, elasticity, permeability, malleability (shaped by hammering), ductility (drawn into wires), reliability, moldability.
- Exam questions often ask for one physical or working property of a material.
Woods (Timbers)
- Hardwoods: From broadleaf deciduous trees; denser, slower-growing, generally stronger, closer grain (less likely to split).
- Examples:
- Oak: Hard, resistant to wear, attractive grain, contains tannic acid (can corrode steel), strongest and densest hardwood, used in furniture and barrels.
- Mahogany: Dark red, durable, stable, used in musical instruments and cabinets.
- Jelutong: Softer, spongy texture, easy to work, low density and durability, tight grain.
- Balsa: Very lightweight, straight grain, low density, used in model making, easy to carve.
- Beech: Straight grain, fine texture, easy to work, used in mallets, toys, chopping boards.
- Acronym: "BOMJB" (Balsa, Oak, Mahogany, Jelutong, Beech).
- Softwoods: From coniferous trees (needle-like leaves); lighter, faster-growing, more knots, less dense.
- Examples:
- Redwood: Lightweight, good strength, used in structural components and decorative mouldings.
- Larch: Hard, tough, waterproof, prone to splitting, used in boat building and fences.
- Pine: Straight grain, knotty, lightweight, susceptible to rot (needs finishing), used in furniture and construction.
- Cedar: Darker color, natural resistance to decay and insects, used in outdoor cladding and furniture.
- General timber properties: Hardness, workability, various strengths (tension, compression, shear, torsion, bending).
Composites
- Timber-based composites:
- MDF (Medium Density Fibreboard): Smooth, dimensionally stable, not moisture-resistant, dense, takes paint well, comes in large sheets.
- Plywood: Layers with odd numbers, strong and stable, high strength-to-weight ratio, visible layers, used in furniture and construction.
- Blockboard: Solid wood strips sandwiched between veneers, strong, used in construction.
- Hardboard: Thin, tough, smooth, used for wardrobe backing.
- Chipboard: Made from wood chips, strong in all directions, unattractive, used in flat-pack furniture, available in various grades and densities.
- Polymer-based composites:
- Carbon fiber reinforced plastic (CFRP): Carbon fiber and polyester resin, lightweight, corrosion-resistant, tough, stiff, used in cars and sports equipment, made by layup lamination.
- Glass reinforced plastic (GRP): Glass fiber and polyester resin, lightweight, tough, electrical insulator, transparent to radio waves, used in boats and water tanks, also made by layup lamination.
Metals & Alloys
- Ferrous metals: Contain iron, magnetic, can rust.
- Mild steel (low carbon steel): ~0.3% carbon, ductile, high tensile strength, tough, malleable, poor corrosion resistance, used in bolts, car bodies, appliances.
- Medium carbon steel: ~0.7% carbon, harder than mild steel, less ductile, malleable, tough, used in tools and machine parts.
- Cast iron: Hard outer skin, good under compression, brittle, used in bench vices and manhole covers.
- Note: Increasing carbon content increases strength/hardness but also brittleness.
- Alloys: Mixtures of metals to enhance properties.
- Brass: 65% copper, 35% zinc, corrosion-resistant, good conductor, hard, malleable, ductile, used in fittings.
- Stainless steel: Contains chromium, nickel, silicon, manganese; tough, hard, corrosion-resistant, smooth, nonporous, used in cutlery and kitchenware.
- Duralumin: Aluminum, copper, magnesium; lightweight, strong, used in aircraft and vehicles.
- Non-ferrous metals: Do not contain iron, non-magnetic, do not rust.
- Aluminum: Lightweight, ductile, malleable, used in cans, bike frames.
- Copper: Tough, malleable, ductile, good conductor, used in wires and pipes.
- Tin: Ductile, malleable, used in solder and as a coating for food cans.
- Zinc: Corrosion-resistant, used in coatings (galvanizing), buckets, street lamps.
- Acronym: "ACTZ" (Aluminum, Copper, Tin, Zinc).
Papers & Boards
- Papers:
- Layout paper: Thin, translucent, for tracing and sketching, ~50 gsm.
- Tracing paper: Thicker, for copying images, 60–90 gsm.
- Copier paper: Inexpensive, general-purpose, can be colored, ~80 gsm.
- Cartridge paper: Heavy, off-white, textured, for sketching, 120–150 gsm.
- Boards:
- Mounting board: Compressed cotton fibers, used for picture mounting and modeling.
- Corrugated board: Cardboard with fluted middle layer, strong in one direction, used in packaging.
- Folding box board: Multiple layers, printable, can be embossed, used in packaging.
- Foil-lined board: Board with foil for water resistance, used in food and drink packaging.
- Solid white board: High-quality, smooth both sides, good for printing, used in greeting cards and packaging.
- Foam board: Foam core with card outer layers, lightweight, used in displays and presentation boards.
Textiles
- Natural fibers:
- Cotton: From cotton plant, high absorbency, dyes easily, breathable, used in towels, bedding, clothing.
- Linen: From flax, durable, lightweight, crisp texture, stiffer than cotton, used in suits and home furnishings.
- Wool: From sheep fleece, warm, flame-resistant, self-extinguishing, used in clothing and environments needing fire safety.
- General properties: Breathable, absorbent, biodegradable.
- Man-made fibers:
- Polypropylene: Quick-drying, lightweight, draws sweat away, used in sportswear.
- Nylon: Not absorbent, durable, high elasticity, tear-resistant, used in industrial fabrics.
- Polyester: Durable, retains shape, crease-resistant, used in trousers, jackets, waterproof clothing.
- Textile treatments:
- Fire retardants: Delay spread of fire.
- PTFE coating: Provides stain resistance.
- Water resistance: Chemical coating reduces absorbency, used in outdoor products.
- Common textile properties:
- Tensile strength: High in man-made fibers.
- Elasticity: High in man-made fibers.
- Absorbency: High in natural fibers.
- Crease resistance: High in man-made fibers.
Smart Materials
- Thermoceramics: Mixture of metallic and ceramic powders, hard, stable at high temperatures, used in automotive parts and cutting tools (e.g., tungsten carbide).
- Shape memory alloys: Return to original shape when heated (e.g., nitinol in dental braces).
- Thermochromic pigments: Change color with temperature (e.g., color-changing mugs, thermometers).
- Photochromic pigments: Change color with light intensity (e.g., welding goggles).
- LCDs (Liquid Crystal Displays): Change from light to dark with electric voltage, used in screens.
- Quantum Tunneling Composites (QTCs): Change electrical conductivity under pressure, used in touch screens and sensors.
- Reactive glass: Changes tint with external stimulus (e.g., windows that darken in sunlight).
Polymers (Plastics)
- Thermoplastics: Can be reheated and reshaped; no cross-links between polymer chains.
- Acrylic: Tough, hard, chemical-resistant, translucent/transparent, used in car lights, line bending, bathtubs.
- ABS: Tough, used in rigid suitcases and casings, can be pigmented.
- LDPE (Low Density Polyethylene): Flexible, used in plastic wrap and bags.
- PET: High tensile strength, used in bottles for detergents and shampoos.
- Polypropylene: Used in ring binders, good fatigue resistance (can be bent repeatedly).
- PVC: Flexible, chemical-resistant, used in hoses, book protectors, food trays.
- uPVC: Opaque, weather-resistant, rigid, used in pipes, window frames, doors.
- HDPE (High Density Polyethylene): Weatherproof, translucent/transparent, used in bottles, toys, buckets, good for blow molding.
- Thermosets: Cannot be reshaped after curing; have cross-links between polymer chains.
- Urea formaldehyde: Hard, heat-resistant, electrical insulator, brittle, used in plug sockets.
- Polyester resin: Rigid, heat-resistant, brittle, used in layup for GRP and CFRP.
- Epoxy resin: Rigid, clear, hard, tough, used for casting and encapsulation (e.g., surfboards).
- Melamine formaldehyde: Hard, stable, electrical insulator, used in laminate countertops.
- Elastomers: Can be deformed under pressure and return to original shape.
- Natural rubber: High tensile strength, low elongation, electrical insulator, good cold resistance, used in tires and balloons.
- Neoprene: Tough, oil/chemical/abrasion-resistant, used in wetsuits.
Key Terms & Definitions
- Density: Mass per unit volume.
- Malleability: Ability to be shaped without breaking.
- Ductility: Ability to be stretched into a wire.
- Toughness: Resistance to impact or shock.
- Thermoplastic: Plastic that can be reshaped with heat.
- Thermoset: Plastic that cannot be reshaped after curing.
- Composite: Material made by combining two or more materials for improved properties.
- Ferrous: Metals containing iron.
- Alloy: Mixture of two or more metals.
- Absorbency: Ability to take in moisture.
Action Items / Next Steps
- Review your exam board specification or revision list to identify which materials you need to study.
- Memorize key properties and uses for each material category.
- Practice explaining the difference between physical and working properties for exam questions.
- Be able to give examples of materials and their typical applications.
- Understand the main advantages and limitations of each material type.