Helmet Liner Research Articles

DYNAMIC CHARACTERIZATION OF MOTORCYCLE HELMETS: MODELLING AND COUPLING WITH THE HUMAN HEAD

Research into the protection of the human head calls for accurate modelling of both the protection system and the head. This study proposes a model incorporating both lumped parameters of the helmet and the head and their coupling during impact. The mechanical characteristics of the shell and of the helmet liner are determined by modal analysis and dynamic compression tests respectively. The coupling of these two components of the helmet is explored using numerical optimization methods based on impact tests which are also used to validate the model. A new dummy head, developed in a previous study and capable of simulating the relative brain–skull displacement was used in the parametric study of the helmet to optimize the density of the polystyrene liner. The ultimate purpose of the study is to devise methods of evaluating the protective aspects of the helmet and then to provide less-expensive methods for optimizing new products on the basis of biomechanical criteria. So far, the study has shown that the optimum density of the liner can be determined not only empirically but also theoretically. It has also shown that optimum helmet parameters depend on the mechanical properties of the dummy head used.

Shock Mitigating Foams, 1. Structure and Property Relationships

As a precursor to the custom manufacture of shock mitigating foams for helmet liners, assessments are required of the essential structure and property inter-relationships. This paper establishes a rationale for developing such systems in the context of using them for minimising the destructive forces resulting from single heavy impact (crash) and/or repeated light impact (buffeting). The basic chemistry of polyurethane foam is reviewed, along with physical structure and mechanical property aspects. Methods of predicting impact behaviour from static/dynamic tests are highlighted, including a review of how continuum theory may be applied in practical situations.

Load-Deflection Analyses of Shock Mitigating Polyurethane–Silicone Foams

Three types of polyurethane-silicone foam are analysed in terms of their compression load-deflection, static load-deflection, recovery time and matrix transition temperature characteristics. The information produced is used to discuss their suitability as shock mitigating helmet liner materials. The rate of deflection during mechanical testing is shown to be highly significant at values <400% min-1 and the compression-deflection ‘plateau’ characteristics analysed in terms of a 10% load differential. Foam type 1085–47 is demonstrated to be of potential use in single impact shock absorption contexts and types 101–38 and 1085–41 of use where repeated impacts are anticipated and there is limited time available for recovery.

Head Protection in Sport with Particular Application to Ice Hockey*

A mathematical model for studying head protection in static is presented and its application to the design of ice hockey helmets is discussed. Static load and dynamic impact tests indicate that dynamic tests are to be preferred when estimating the stiffness of the materials used ns helmet liners. Solutions to the differential equations governing the linear motion of the head under a sideboard collision provide information regarding the thickness of the energy absorbing helmet liner and the tolerance level to which the helmet can be expected to perform. The model also provides a useful estimate of the angular velocity of the head imparted by the rebound from the sideboard. Although the helmet cannot prevent angular motion of the head, an estimate of the expected angular velocity may indicate that additional measures must be taken to prevent head injury from such angular motion. The study also indicates that the problem of providing head protection in ice hockey is of such magnitude that a helmet alone cannot be expected to provide total protection and additional modification to the playing environment must also be undertaken.

Evaluation of a water-cooled helmet liner : Kissen, A.T., et al. Nov 1974, 27 pp; abstr in Government Reports Announcements (Report No AD/A-004 776/1GA)

Evaluation of a water-cooled helmet liner : Kissen, A.T., et al. Nov 1974, 27 pp; abstr in Government Reports Announcements (Report No AD/A-004 776/1GA)

Tracking with Head Position Using an Electrooptical Monitor

An electrooptical head-position monitoring system was designed and built and is used in single-axis and three-axis ``hands-off'' control tasks. The monitor consists of a transparent plexiglass body-fixed helmet provided with a set of eight silicon photodetectors sensing pitch, roll, and yaw motions of the head. Two light-emitting diodes, attached to the pilot's helmet liner, provide the ac modulated near infrared radiation. Head control is compared with conventional manual control for single-axis and three-axis tracking tasks. Both performance curves and describing functions are presented.