A new motorcycle helmet liner material: The finite element simulation and design of experiment optimization F.M. Shuaeib, A.M.S. Hamouda * , S.V. Wong, R.S. Radin Umar, M.M.H. Megat Ahmed Road Safety Research Centre, Faculty of Engineering, University Putra Malaysia, 43400 UPM, Serdang, Selangor, Malaysia Received 5 January 2005; accepted 22 April 2005 Available online 1 September 2005 Abstract This paper is devoted to study and verify the suitability of the expanded polypropylene (EPP) foam as a liner for motorcycle helmet and to perform helmet design optimization. This EPP foam has a multi-impact protection performance and also has a poten- tial for ventilation system improvement due to its resiliency. This resiliency allows for the ease of ventilation holes and channels molding without the foam breakage at the stage of mold extraction. The large scale, non-linear, dynamic finite element package LS-DYNA3D is used as a verification tool for motorcycle helmet design. Then the simulation work is carried further to provide data for helmet design analysis and optimization using the response surface methodology (RSM). The foam thickness, the foam density, and shell thickness being selected as the design factors for the response surface generation and design optimization. The results showed that the EPP satisfies the 300g headform center of gravity acceleration limit required by most of the international standards. The extended simulation output data is then used to create the response surface and determine the optimum design points. Therefore, two main contributions on motorcycle helmet design are achieved. The first is on the use of the EPP as a helmet energy absorption liner for the motorcycle helmet application, and the second is that by combining the simulation output with the design of experiment (DOE) method to study the effects of the various factors on helmet design optimization. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Design; Helmet; Simulation; Energy absorption; Foam 1. Introduction Helmets for motorcyclists are basically made form two main parts. The outer shell which is either made from thermoplastic material such as ABS or the polycar- bonate, or composite material such as GRP or Kevlar. The inner liner, which is our focus here, is generally made from the expanded polystyrene (EPS) foam. This type of foam, in spite of its excellent first impact perfor- mance, has some essential performance deficiencies, which can be formulated as follows [9,10,23–25].  EPS foam is a single impact performance and, from motorcycle crash kinematics studies it was evident that motorcycle crash is a multi-impact situation, particularly the most dangers high-speed crash.  EPS foam is brittle in its nature. This brittleness has led to two design problems, which is related to manu- facturability. The former is the helmet roll-off due to the lack of fitness of the inside helmet contour, unless additional pads made from other resilient foams such as polyurethane are added in suitable locations. The later is the difficulty in introducing ventilation chan- nels or ducts in the foam. This is important for coun- tries with tropical climate including Malaysia. The expanded polypropylene (EPP) foam shows strong potential in overcoming such problems [9,20,12]. 0261-3069/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2005.04.015 * Corresponding author. Tel.: +603 89466330; fax: +603 86566061. E-mail address: hamouda@eng.upm.edu.my (A.M.S. Hamouda). www.elsevier.com/locate/matdes Materials and Design 28 (2007) 182–195 Materials & Design