Question

What are the essential and desirable requirements of materials and property that might be considered to design sport helmet for riding bicycle?

Answer 1

Design Requirements:

• Maximise energy absorption/unit volume
• Load on the skull due to helmet should be considerably less than the minimum damage load.
• Lightweight
• Impact resistance
• Good visibility
• Low noise
• Easy to put on and remove
• Comfortable

Materials Requirements and Properties:

A cycle helmet must protect against the large impact received on the head during a crash. In this case, it doesn’t matter if the helmet is permanently damaged because all manufacturers recommend replacement after an accident. The most important point is that it should absorb lots of energy.

To identify materials that have high toughness and sufficient strength, we can use the selection charts. Composites, most metals, and many polymers seem good. But apart from being hard, the other requirements are that the material should be inexpensive and low weight.

Polymers best meet all these needs and are also easy to manufacture. Polymer foams should be chosen because they are easily fabricated and because, unlike honeycombs, their ability to absorb energy is omnidirectional.

The main impact absorbing material for a cycling helmet will be a molded block of polystyrene foam which could be coated with polycarbonate cover. These materials are easy to shape, which will help in structuring the helmet aerodynamically. Moreover, these foam can be made in layers with different densities to tune impact management, permitting softer layers to crush in lesser impacts and harder layers to handle the really bad hits.

Examples of advanced polymers that have the above-mentioned properties are Expanded polystyrene (EPS), Expanded Polypropylene (EPP), Expanded Polyurethane (EPU or PU).