The design of a cycle safety helmet requires a lining that will crush at a stress of 8-12 MPa and be as light as possible. Use the \(\sigma_{f}-ho\) chart of Fig. 3.4 to select an appropriate class of material to meet this need.

Fig. 3.4

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10,000 T Strength-density Metals and polymers: yield strength, a Ceramics, glasses: modulus of rupture, MOR Elastomers: tensile tear strength, 1000 Composites: tensile failure, o Strength, of (MPa) 100 10 0.1 Foams Rigid polymer foams. Ceramics Composites Diamond Si3N4 SIC Al alloys CERP Al2O3 Ti alloys Steels Metals Ni alloys Tungsten alloys Polymers and elastomers Mg alloys, GFRP PEEK Tungsten carbide PMMA -Copper. alloys Woods, Il- Natural materials Flexible polymer foams 0.01 10 100 PP- PE Woods, Zinc alloys Lead alloys Cork Butyl rubber Silicone elastomers Concrete Guidelines for minimum mass design 1000 Density, p (kg/m) 10,000 MFA 15