Other physical properties
Picking properties
Whenever you build an engineered product you have to be sure every material has the right properties for the job. Depending on the product, there are several things to consider. Will the material be strong enough? What happens to it when the temperature or pressure changes? Does it conduct heat well, or is it a good insulator? Is it dense? Are parts of it very heavy? Is it waterproof? Will it be able to resist corrosion? The list can go on and on.
Often we can find the properties of a material in a data book or an electronic database. However, properties can only be found in this way for pure substances or known materials. Sometimes we have to carry out tests to find their properties.
The properties of some materials depend on the treatments they receive during processing. This might include adding other materials to make an alloy, for example, or modifying the composition of a polymer.
On your bike
During the Athens Olympics, the British Cycling team won four medals. Chris Hoy – who won gold for the one kilometre time trial – did it on a bike that weighed just less than 7 kg.
The frame was made from high grade carbon-fibre with super tough epoxy resin ACG MTM28.
It’s a great example of how modern technology is used to find the right mix of properties. Bikes need to be strong and light. They also need to be a bit flexible so the ride’s comfortable.
Most bike frames are made from steel because it's strong, cheap and easy to shape. By adding other materials the frames can be made stronger and more flexible.
Aluminium is popular – it’s light and strong, it doesn’t rust easily and it’s recyclable. Sometimes magnesium, silicon, zinc, copper or chromium is added.
Titanium is the expensive option. It has all the properties of aluminium and it doesn’t suffer from “metal fatigue”. That’s when metals get weakened from constant vibrations or bending. But pure titanium is too flexible. Oxygen has to be added.