A computational investigation into energy absorption characteristics of multicomponent facing-foam systems of helmets

The strategic utilization of facing layers is investigated as a mechanism to increase the energy absorption in foam liner systems for improving the protective performance of helmets. Energy absorption applications extensively use foams because of their ability to efficiently absorb large amounts of strain energy at low stress levels; however, many deformations are localized to a small volume of the foam available in the system thereby reducing the material system effectiveness. One of these cases occurs as the result of poor fit of helmets. This paper details a systematic computational investigation characterizing the energy absorption of multi-layer material constructions consisting of foam combined with a relatively stiff facing layer. Results obtained reveal that facings provide a mechanism to alleviate the effects of a small deformation area caused by both poor fit and thick comfort foam in helmets, though the facings must have substantial flexural rigidity of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mo>~</mml:mo> <mml:mn>0</mml:mn> <mml:mo>.</mml:mo> <mml:mn>01</mml:mn> <mml:mi>P</mml:mi> <mml:mi>a</mml:mi> <mml:mo>×</mml:mo> <mml:msup> <mml:mi>m</mml:mi> <mml:mn>3</mml:mn> </mml:msup> </mml:mrow> </mml:math> to improve the energy absorption of the pads. Energy absorption efficiency of the foam-facing system for multiple loading curvatures have been used to quantify the energy absorption improvements of the system provided by the use of higher facing rigidity, especially when the impact is near or past the edge of the pad system.