In this study the effect of the stiffness sequence of the padding materials of sports equipment, and in particular helmets, on absorbing the impact to the head has been investigated. Specifically, for each arrangement of the padding materials, the strain in the brain has been calculated. In addition, for each impact, the acceleration of the centroid of the head and the Head Injury Criterion (HIC) has also been obtained. As the first preliminary study a simple spherical model of head/brain, including the skull and the brain and three layers of the padding have been generated. The materials of the three layers of padding vary from viscoelastic, soft elastic to a hard elastic material. Then the head was impacted to the padding with the speed of 2 m/s. Finally the sequence of the padding layers was rearranged and the head was impacted to the padding with the same speed. For each case, the HIC value of the impact was determined.
The results revealed that when the viscoelastic materials was in the middle (the first case) the HIC was 143.5 and the strain in the brain at the center corresponding to corpus callosum was 0.192%. Also for, the second case, where the viscoelastic materials was directly the contacting layer with the head, the HIC value was 46.8 and the brain strain was 0.15%. The reason that the strain in corpus callosum has been determined in this analysis is due to the fact that the literature reflects that the strain in corpus callosum is a good predictor for the onset of concussion due to an impact.
It was concluded that when the viscoelastic padding is located on the outer surface of the protective padding device, the HIC value and the strain in the brain are lower, i.e. it is safer. This study can be employed to analyze head impacts with different layered barriers, i.e., composite materials, sandwich panels, glass, and also the interior trim of a car and as well as many other protective paddings.