Energy in car design

Foamed plastics are used in helmets because of their very low density, their ability to crush and absorb energy and the possibility of economical mass production. There are many other applications of polymer foams for injury prevention, for instance the fascia padding in cars. Bicycle helmets are chosen because of the author s research experience, and because the typically 0.3 mm thick outer shell plays a minor part in energy dissipation. Consequently, the design process concentrates on the foam Hner (Fig. 14.11). In contrast, the deformation of the 4-5 mm thick thermoplastic shell of a motorcycle helmet absorbs energy of the order of 40 J, when the helmet hits a hemispherical anvil of radius 50 mm. 

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