Is steel is the ideal material from which to make a high impact bike frame?

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Young’s Modulus

Young’s Modulus is a measure of strength and stiffness. If you get a large force over a small area then you will get a large figure for stress. And a small extension divided by a large original length will give you a small figure for strain. Divide these numbers and a large modulus results, the material extends little for a large applied force. Steel has a large modulus, meaning that it is stiff and strong. A typical modulus for steel is 1100 Mpa, whereas cfrp, titanium and aluminium have modulus’s of 2145, 900 Mpa and 400 Mpa respectively. This shows that although steel is not the strongest of the materials commonly used to construct mountain bike frames it is still very strong. Reasons why, although it is the strongest material, cfrp is not commonly used to construct frames will be discussed in the ‘cfrp’ section of this presentation.

Elongation

Elongation of a material is how much it stretches before breaking as a percentage of its overall length .The higher the percentage of elongation before a material breaks, the greater its ductility. Ductility is the ability of a material to deform without breaking. Good ductility is a desirable characteristic for a material to be used in the construction of mountain bike frames as the material will give warning before it breaks, and not just fail catastrophically, maybe leading to rider injury. Steel is a ductile material, with elongation of around 9-15%. Aluminium has an elongation before breaking of around 6-12%, titanium can have elongations of 20-30% and cfrp is below any of these materials at around 5% elongation. Steel, aluminium and titanium are all metals, and are all ductile. Cfrp, on the other hand, is a lattice carbon fibres set into plastic. This construction, whilst being very strong and lightweight, is not very ductile at all and will break without deformation, such as may be seen in the other materials, as a warning Steel has a good elongation percentage, but is beaten by titanium. Reasons that titanium, despite its good properties, is not commonly used in the production of mountain bike frames, for reasons that will be explained in the ‘titanium’ section of this presentation.

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Tensile Strength.

When considering how strong a material is, we have to think about where we are measuring this strength.

All the metals considered for the construction of bike frames are ductile. This means they stretch before they break. Steel is very strong and takes a lot of force before it yields, a good feature of a high impact bike frame. It also yields a lot, so it gives warning of impending failure. Aluminium, although it yields, is not as strong as steel and does not yield to such a degree, and so we ...

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