Selection of Materials
Selection of Materials
Choosing the right material is a critical design skill in AQA GCSE D&T. You must consider function, aesthetics, environmental impact, availability, cost, and manufacturing processes when selecting materials.
Factors Affecting Material Selection
| Factor | What to Consider |
|---|---|
| Function | What must the product do? Load-bearing = strong material; waterproof = moisture-resistant |
| Aesthetics | How should it look/feel? Grain, colour, texture, transparency, surface finish |
| Cost | Budget constraints; material cost per unit; processing cost; waste cost |
| Availability | Can the material be sourced readily? Lead times, local vs imported |
| Environmental impact | Sustainability, recyclability, embodied energy, carbon footprint |
| Working properties | Can it be shaped using available tools/processes? Machinability, weldability |
| Physical properties | Density, strength, hardness, toughness, flexibility, conductivity |
| Social and ethical factors | Fair trade sourcing, working conditions, cultural acceptability |
| Scale of production | One-off may suit timber; mass production may require injection-mouldable polymer |
| Legislation and standards | Food-safe, fire-retardant, child-safe (BS EN safety standards) |
Matching Materials to Function
Structural / load-bearing applications:
- Mild steel — strong, tough, cheap (bridges, car chassis)
- Oak — hard, durable (furniture, flooring)
- CFRP — extremely strong-to-weight (racing car monocoque)
Transparent / optical applications:
- Acrylic (PMMA) — clear, lightweight, safer than glass
- Glass — scratch-resistant but heavy and brittle
- PET — lightweight, recyclable (drinks bottles)
Electrical / electronic applications:
- Copper — excellent conductor, ductile (wiring, PCB tracks)
- ABS — insulator, impact-resistant (plug casings)
- Urea formaldehyde — insulator, heat-resistant (plug sockets)
Outdoor / corrosion-resistant applications:
- Stainless steel — chromium oxide layer prevents rust
- Cedar — naturally rot-resistant
- HDPE — chemical and moisture resistant
Flexible / wearable applications:
- Polypropylene — fatigue-resistant, living hinges
- Elastane blends — stretch and recovery
- Silicone — flexible, heat-resistant, biocompatible
Material Testing
Designers test materials to verify their properties before committing to a design. Common tests:
| Test | Property Measured | Method |
|---|---|---|
| Tensile test | Tensile strength, elongation | Sample pulled in a tensile testing machine until it breaks |
| Hardness test (Rockwell, Brinell, Vickers) | Surface hardness | Indenter pressed into surface; indent size measured |
| Impact test (Izod, Charpy) | Toughness | Notched sample struck by swinging pendulum; energy absorbed measured |
| Bend test | Ductility, flexibility | Sample bent around a former; checked for cracking |
| Fatigue test | Resistance to repeated stress | Sample subjected to cyclic loading until failure |
| Compression test | Compressive strength | Sample crushed between plates until failure |
Material Selection for Specific Scenarios
Scenario 1 — Children's outdoor play equipment:
- Must be: tough (impact), weather-resistant, safe (no sharp edges), durable
- Suitable: HDPE (rotomoulded slides), galvanised steel (frame), stainless steel fixings
- Avoid: glass (brittle, dangerous), untreated mild steel (rusts), MDF (swells outdoors)
Scenario 2 — Portable phone charger casing:
- Must be: lightweight, impact-resistant, electrically insulating, aesthetically pleasing
- Suitable: ABS (injection moulded), aluminium (CNC machined, anodised for colour)
- Consider: recycled ABS or bioplastic for environmental benefit
Scenario 3 — Kitchen chopping board:
- Must be: food-safe, hygienic, hard-wearing, moisture-resistant
- Suitable: beech (dense, food-safe), HDPE (dishwasher-safe, colour-coded)
- Avoid: MDF (swells, glue not food-safe), softwood (too soft, absorbs bacteria)
Environmental Considerations in Selection
When selecting materials, designers should prioritise:
1. Recycled materials — reduces demand for virgin resources
2. Recyclable materials — can be recovered at end of life (thermoplastics, metals)
3. Renewable sources — timber from FSC-certified forests, plant-based polymers
4. Low embodied energy — timber requires less processing energy than aluminium
5. Local sourcing — reduces transport emissions
6. Biodegradable options — PLA instead of conventional plastic for disposable items
7. Longevity — durable materials reduce replacement frequency
Material Selection Matrix
A material selection matrix (also called a decision matrix or weighted matrix) is a systematic method for comparing material options against design criteria.
Steps:
1. List the criteria (strength, cost, weight, etc.)
2. Weight each criterion by importance (e.g. 1–5)
3. Score each candidate material against each criterion (e.g. 1–5)
4. Multiply score × weight for each cell
5. Sum the weighted scores — highest total wins
| Criterion | Weight | ABS (score × weight) | Aluminium (score × weight) | Wood (score × weight) |
|---|---|---|---|---|
| Strength | 4 | 3 × 4 = 12 | 5 × 4 = 20 | 2 × 4 = 8 |
| Cost | 3 | 4 × 3 = 12 | 2 × 3 = 6 | 5 × 3 = 15 |
| Weight | 5 | 4 × 5 = 20 | 3 × 5 = 15 | 3 × 5 = 15 |
| Aesthetics | 2 | 3 × 2 = 6 | 5 × 2 = 10 | 4 × 2 = 8 |
| Total | 50 | 51 | 46 |
In this example, aluminium scores highest overall despite being the most expensive, because strength and aesthetics compensate.
Exam Tips
- Always justify your material choice by linking specific properties to the product's requirements — generic answers score poorly
- Use the phrase "this material is suitable because..." followed by at least two relevant properties
- If asked to compare two materials, use a table format and address the same criteria for both
- Know at least one scenario where you would choose each major material from the specification
- Environmental justification is increasingly common in exam questions — always mention recyclability, embodied energy, or sustainability
- A material selection matrix demonstrates systematic thinking and scores highly in extended-answer questions
Key Definitions
- Working properties: How easy a material is to cut, shape, join, and finish using available tools and processes
- Embodied energy: The total energy consumed in extracting, processing, manufacturing and transporting a material
- FSC (Forest Stewardship Council): Certification ensuring timber comes from responsibly managed forests
- Decision matrix: A systematic tool for comparing options against weighted criteria to identify the best choice
- Food-safe: A material certified as non-toxic and safe for contact with food and drink