Chin strap forces in bicycle helmets

Abstract

The objective of this experimental investigation was to find out what dynamic forces a bicycle helmet' retention system is subjected to when head impact accidents take place. Different helmet models were subjected to simulated accidents, of the type with the head first (with vertical and horizontal velocity) against a rigid asphalt surface. The chin strap forces developed in the accident simulations of the present study were low compared to the requirements of most of the existing standards for bicycle helmets. The arithmetic mean of the chin strap peak forces of all impacts was 4² N.

Three types of helmets were investigated, one hard-shell helmet, one non-shell helmet and one ribbed helmet (large ventilation holes) with hard shell. A six-year-old child test dummy and a car-crash test facility with a piece of inclined asphalt road on the carriage were the main attributes of the study. The test dummy was suspended from the ceiling and was hit by the piece of asphalt road mounted on the stiff car-crash track carriage. Several different single-type accidents were simulated. All impacts were carried out with the helmeted dummy's head impacting the asphalt layer first. The types of accidents simulated were all meant to simulate the case in which the bicycle is blocked in one way or another and the rider continues with a certain horizontal and vertical velocity.

As a subsidiary result it was discovered that the rotational effects of the tested helmets differed appreciably. The shell helmets did not grip the asphalt layer at all and did not rotate, which implies that the headform did not rotate either. The non-shell helmets gripped the asphalt layer in each impact, rotated and transferred this rotation to the headform.

The stability of children's helmets should be considered more important for the helmet's ability to stay on the wearer's head than buckles that withstand high force levels. The helmet design in itself could result in different chin strap forces in accidents. One of the key factors is probably the helmet's area of coverage and its fit to the head. This study of the chin strap forces developed in bicycle retention systems in single-type accidents indicates that chin strap buckles with a self-release function are applicable to children.

Key words:

• bicycle helmet
• chin strap
• head rotation
• oblique impact
• helmet testing
• force
• acceleration

Additional information

Notes on contributors

Torbjörn Andersson

Correspondence to: Mr, Torbjörn Andersson, Swedish Natl. Testing & Research Inst., Box 857. S-501 15 Borȧs, Sweden, Telephone [phone], Telex 36252 Testing S, Telefax'46 33 13 55 02