Energy Absorbing Characteristics of Ice Hockey Helmets
AbstractThere is little doubt that existing ice hockey helmets decrease the severity and incidence of head injuries ( Dick, 1993). Helmet designers arc faced developing a design that optimizing a number of safety features. Energy absorption qualities of' the head gear is generally considered the primary characteristic of the helmet. The weight, moment of inertia, overage, heat dissipation and cut resistance are other safety issues that have to be considered. The present study was designed to try and better understand the energy absorption characteristics or different helmet materials. Two fundamental technologies are used lo protect the head 'The first can he described as a single impact material and the second a multiple impact material. They differ in a number of respects, however the most important distinguishing feature is the ability of the latter material to absorb more then one impact in the same location. Such sports as American football and ice hockey involve contact resulting in repeated impacts absorbed by the helmet. In activities such n bicycling that do not encounter repeated impact to the head the helmet is designed to absorb a single impact and then be replaced. In an attempt to understand the effect of material composition, thickness a d density we undertook a study comparing the effect of these variables on energy absorbing capacity. We compared Rubatex,Dertex, expanded polypropylene and expanded polyethylene ( 1.27 to 1.59mm ) at 20,30,40 and 60joules of energy with material densities ranging from 3.03 to 6.58 pounds per square feet. While there were expected trends between the independent variables an interaction was observed. The energy absorbing characteristics was specific to the type or the material . At lower energies the vinyl nitrile based foams of lower densities performed better. The expanded bead materials of high density were the worst performers. However - at very high energies the expanded bead materials performed better. These result.. raise questions concerning whether the same energy absorbing criteria should be used to design helmets for young children as are used fur adults. It also brings into question as whether certification requiring higher energies necessarily result in safer helmets for ice hockey.
Equipment / Instrumentation
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