Materials in the trade: aluminium carbon fibre and steel

One of the competency objectives for the education requires that you can select and apply relevant materials based on knowledge of their properties including metals composite materials and plastics. It is not a theoretical exercise — the choice of material directly determines which tool you need to use and how careful you need to be.

§Steel — the heavy, forgiving material

Steel has been the basic material of the bicycle and motorcycle for over a hundred years. It absorbs the road's shocks and vibrations well, which provides comfortable riding on long trips, and it is relatively forgiving to repair and weld. The disadvantage is the weight and the risk of rust unless the steel is alloyed like stainless or treated against corrosion.

§Aluminum – light, stiff, and rust-free

Aluminum is lighter than steel and does not rust itself, which has made it the most common material in mid-range and cheaper chassis. On the other hand, aluminum is often stiffer and less forgiving than steel, so road bumps and vibrations are felt more clearly by the driver. Aluminum also requires its own welding technique and generally tolerates repeated repairs worse than steel.

§Carbon fibre — light and strong, but not forgiving

Carbon fibre (also called carbon or CFRP) typically weighs only about half as much as aluminium at the same strength. The material consists of thin carbon fibres that are woven or laid in layers and bound together with epoxy resin. This provides a very light and stiff structure, but carbon fibre is brittle in a different way than metal: where steel and aluminium bend before they fail, carbon fibre can crush or splinter without much warning if overloaded or overstressed.

§Epoxy and isocyanates — why the courses are mandatory

Carbon fibre components and certain adhesives/paints contain epoxy resin and in some cases isocyanates, which can cause severe skin eczema, allergies or respiratory problems if handled incorrectly. The Occupational Safety and Health Authority's rules therefore require that anyone who works with or supervises isocyanate-containing products above a certain concentration has completed work environment professional training with a valid training certificate, which must be renewed at regular intervals. This is the background for why the epoxy and isocyanate course is mandatory, even before you can move forward from the basic course.

• 01People with known asthma, eczema or lung disease should not work with isocyanate-containing products
• 02Use the prescribed personal protective equipment and extraction when working with epoxy and adhesives
• 03Know the difference between metals' and composite materials' failure mode before you clamp or repair

§Material choice is part of the trade

When you choose spare parts repair a frame or assess damage you must be able to see what material you're dealing with and what it can take. A scratch in a steel frame is often cosmetic; the same scratch in a carbon fiber frame could theoretically have cut fibers and weakened the structure invisibly. That difference is the very core of why materials science is a fixed part of curriculum not just background knowledge.