Internationally, there are two types of headforms used for impact attenuation testing of motorcycle helmets. These two types of test headforms follow specifications established by the International Standards Organization (ISO), or the US Department of Transportation (DOT). Both headforms are low resonance, rigid castings, but they differ in size, shape and weight. The headforms are supported by a rigid guide assembley that limits their motion to the vertical direction only. Different impact locations are obtained by adjustment of the headform on a spherical ball joint. Performance criteria are based on acceleration time history measurements from a uniaxial accelerometer located at the headform center of mass. A second variation on the ISO headform is found in some European helmet standards that utilize an unrestrained headform instrumented with a triaxial accelerometer. These constrained headforms respond to impact with motion in many directions and performance criteria are based on the resultant of three axis acceleration time histories. Impact attenuation tests were performed on 180 motorcycle helmets of three different designs and under environmental conditions specified by helmet performance standards. Selected tests were recorded on high-speed (1000 Hz) videotape for motion analysis. Test apparatus designs differ greatly and guided free-fall apparatus with restrained headforms produced consistently more rigorous tests than apparatus without headform guide or restraint. Significant differences were also found between DOT and ISO headforms for both peak acceleration and dwell time on flat anvil impacts when tested on the DOT-type monorail apparatus. (A)
Abstract