Modelling and validation of motorcyclist helmet with composite shell

Abstract

The aim of this paper is to propose a new helmet finite element model of a commercial helmet with a composite outer shell and to validate it under normative conditions against experimental tests. After a meshing of the helmet based on the computer-aided design (CAD) provided by the manufacturer, the mechanical properties of each component of the helmet (the outer shell and the foam) have been implemented under LS-DYNA FE code. The composite outer shell has been modelled with a non-homogeneous law by taking into account characteristics of each ply composing the laminate in terms of elastic behaviour as well as rupture behaviour. The foam characteristics are based on literature data. After coupling of the helmet model with the headform model, the novel helmet model has then been validated against experimental data under normative conditions as prescribed by standard ECE 22.05. IntroductionMotorcyclists' helmets for motorcyclists are basically made from two main parts, the outer shell and the foam liner. The main function of the outer shell is to distribute impact loads over a large area and to protect the head from the penetration of sharp objects. There are essentially two different types of outer shells: thermoplastic and composite outer shells. Thermoplastic outer shells can be made either of ABS (acrylonitrile butadiene styrene) or polycarbonate. Composite outer shells are usually made of fibrereinforced plastics. The type of plastic commonly used is epoxy resin and the type of reinforcement is glass fibre due to its relatively low cost and fairly good mechanical performance. Carbon and Kevlar are also used, but only for the most advanced or competition helmets. The main advantage of using composite outer shells lies in their capability of absorbing more energy by rupture in comparison with thermoplastic outer shells.The main function of the energy-absorbing liner is to provide a stopping distance for the head during an impact. The material commonly used for the foam liner is expanded polystyrene (EPS) as it has excellent performances, lightweight characteristics and low cost.In order to better understand the helmet behaviour in case of impact, a number of authors have proposed helmet models. The first helmet models that can be found in the literature are lumped-mass models. Köstner and Stöcker in 1987 [7] and Mills and Gilchrist in 1988 [9] proposed lumped-mass models of helmet with a symmetrical outer shell and whose foam was based on springs and dampers.

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