CHEMISTRY · Stage 7 · Chapter 3: Metals and Non-Metals
Chemistry 3.6 Better bicycles — Materials Science and Engineering
5 min read 6 parts Lesson 6 of 7
Lesson summary
3.6 Better bicycles — Materials Science and Engineering — Alhussan International Academy — Chemistry (Stages 7–9) notes: Describe how materials are chosen for bicycles, evaluate their properties and trade-offs, and explain how science is applied in industry.Materials scientists a…
- Alternative alloys
- Carbon fibre reinforced polymer (CFRP)
- Alloy melting temperatures
- Racing cycle
- Cheap commuter bike
- Surface protection
Part 1 of 6Materials science
- Materials scientists and engineers choose or design materials to fit a purpose.
- Propertiesstrength, stiffness, density, toughness, corrosion resistance and cost.
- Trade-offsno material is perfect, so they compare materials.
Part 2 of 6History of bicycle materials
- Iron — many years ago bikes were made from iron, but the pure metal is soft and not very strong.
- Steel — an alloy of iron with carbon and other elements.
- By 1900 makers had found steel strong enough to make into tubes, so bicycles became much lighter.
- Steel is cheap and strong, bends instead of breaking in a collision and is easy to mend.
- Some steels rust if not oiled or painted, and steel is heavy for its size.
- Alternative alloys — scientists used data to work out which materials might be better, made bikes from them and tested them.
- Carbon fibre reinforced polymer (CFRP) — in the 1950s scientists placed carbon threads in a resin.
- Carbon on its own is brittle, but the new material was strong and light.
- Early CFRP bikes were not perfect, but scientists persevered, and most professional cyclists now ride CFRP bikes.
- Bamboo — a recent innovation is durable, strong, comfortable to ride and made from a sustainable material.
Part 3 of 6Comparing frame materials
| Material | Advantages | Disadvantages |
|---|---|---|
| Steel | Strong, cheap, easy to repair | Dense (heavy), can rust |
| Aluminium alloy | Light, does not rust | A little less stiff, more costly than steel, more easily damaged |
| Titanium alloy | Light, strong, rust-proof | Expensive |
| Carbon fibre composite (CFRP) | Very light and stiff, can be moulded | Expensive, can crack suddenly in a crash |
| Bamboo | Durable, strong, comfortable, sustainable | Not described in detail |
1Alloy melting temperatures1 point
— a titanium alloy melts at up to 1660 °C and an aluminium alloy at up to 652 °C.
- A lower melting temperature makes the metal cheaper to melt when making the frame.
2Composite1 point
= a material made of two or more materials combined to give better properties than either alone.
- In CFRP the carbon fibres give strength and a plastic resin holds them together.
Part 4 of 6Parts of a bicycle
| Part | Needed | Typical material |
|---|---|---|
| Frame | Strong, stiff, light | Steel, aluminium alloy, titanium or carbon fibre composite |
| Tyres | Flexible, grip, tough | Rubber |
| Brake and gear cables | Strong, flexible, do not stretch | Stainless steel wires |
| Chain | Strong, hard-wearing | Steel |
| Handlebar grips | Soft, comfortable | Plastic or foam rubber |
| Saddle | Support and comfort | Plastic with foam padding |
Part 5 of 6Evaluating choices
- Racing cyclelow mass and stiffness matter most, so carbon fibre is worth the cost.
- Cheap commuter bikecost and durability matter more, so steel or aluminium is chosen.
- Densitya low density gives a light frame.
- Surface protectionpaint or galvanising prevents rust, and anodised aluminium has a protective oxide layer.
- Good answerlink a property to the need, compare at least two materials and state the trade-off.
Part 6 of 6Sustainability and design
- Recycling — aluminium can be recycled using only about five per cent of the energy needed to extract it from its ore, steel is widely recycled using magnets, and carbon fibre composites are hard to recycle.
- Life-cycle assessment — it looks at extraction, manufacture, use and disposal to compare materials fairly.
- Design cycle — identify the need, research materials, make a prototype, test it and improve it.
- A prototype frame may be tested for fatigue by flexing it thousands of times.
- Safety — a helmet uses foam that crushes to absorb energy in a crash.
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