The shear properties of the foam cushioning material in a bicycle helmet can be correlated to the resulting rotational acceleration of the head during impact. This rotational acceleration is known to cause significant brain injuries, and should be minimized. It is therefore important to study the shear behavior of helmet foams. Bicycle helmet foam, however, never experiences purely shear or compression deformation. Impacts are generallyoriented at oblique angles and result in foam deformation with both a shear and a compressive component. A test method to apply a combination of shear and compressive displacements to a foam sample has been developed. Furthermore, it is possible to analyze the shear and compressive components of deformation separately so that thecoupling between shear and compressive behavior in cellular materials can be observed.
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