S. Agostinetto⁽¹⁾, E. Rossini⁽²⁾, L. Fumagalli⁽³⁾, A. Coda⁽³⁾

 ⁽¹⁾AGV S.p.A. - 15050 Rivalta Scrivia (AL) - ITALY
⁽²⁾eXtreme Materials S.r.l. - 23845 Costamasnaga (LC) - ITALY
⁽³⁾SAES Getters S.p.A. - 20020 Lainate (MI) - ITALY

Typical structures and materials for motorcycle helmets have to guarantee user safety. A helmet is designed to protect the rider in case of accident by absorbing impact energy and reducing the load to the head.

In order to keep the high load-carrying properties while improving toughness of composite structures of the helmet shells, many approaches have been proposed such as fibre and matrix toughening, interface toughening, through-the-thickness reinforcements, and hybridizing. Among them, hybridization with high strain-to-failure fibres, like thin shape memory alloy wires (SMAs), seems to be a promising technology. The high strain capability of SMA fibres associated to the stress-induced recoverable martensitic phase transformation, with a typical plateau region in the stress-strain curve, enables SMA wires to absorb much more strain energy than other fibres before their failure thus allowing toughening of the composite structure besides keeping unaltered its high load-carrying properties.A patented fabric produced by eXtreme Materials using superelastic thin wires (diameter of about 0.2 mm) supplied by SAES Getters was mounted in different areas of helmets. The transformation temperatures and superelastic properties on shape annealed wires have been measured. The helmet prototypes have been tested according to current European regulation ECE E2205.