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2 Review of Literature: Motorcycle helmet
2.4 Components of Motorcycle Helmets
The primary purpose of a motorcycle helmet is to protect the head from injuries.
Contemporary helmets protect the head against impact by having an outer shell
bonded to an impact-absorbing liner, as shown in Figs. 2.2a, b [12]. The purpose of
the outer shell is to widen the area of impact and allow the helmet to slide along the
ground.
The four main components of a motorcycle helmet are the outer shell, impactabsorbing liner, comfort padding and retention system. The outer shell is the part
that we see first and is usually made from some form of fibre-reinforced composites
or thermoplastics such as polycarbonate. This material is very tough and intended
to compress when it hits any hard object. This action disperses energy from the
impact and reduces the force before it can reach the head. More expensive helmets
are reinforced with Kevlar or carbon fibres. Thermoplastics helmets are generally
the lightest and least expensive. The thermoplastic helmet tends to have a shorter life
expectancy. Its chemical composition may be changed if it is painted or decals are
applied to its surface. Damage can occur if it is stored near gasoline, cleaning fluids
or exhaust fumes. Helmet manufacturers are constantly working to develop cheaper,
stronger and lighter materials for helmet shell construction.
The hard-outer shell of the motorcycle helmet tries to stop the penetration of
sharp objects and also acts as a safeguard for the shock-absorbing liner and prevents
the liner from disintegrating if the helmet hits the road or other objects. The helmet
liner is made of expanded polystyrene (EPS) foam of varying density and thickness
ranging from 10 to 25 mm. Lombard et al. [13] were the first to introduce expanded
polystyrene to be used in helmets. This is the important part of a motorcycle helmet,
as polystyrene is non-resilient and evenly spreads the impact in an accident and thus
reduces the shock energy that could reach the head and cause injury [14].
The impact-absorbing liner is housed inside the outer shell and is usually made
of expanded polystyrene. The liner provides a cushioning effect and absorbs the
shock in case of an accident, thus protecting the head. Both the shell and the liner
are compressed if hit hard, spreading the forces of impact throughout the helmet
material. Generally, the more the impact energy is deflected, the less it can reach the
head and cause damage. Some helmet shells are designed to delaminate in case of
impact, and others crack or break if severely hit and thus absorb the shock of the
impact.
The comfort padding that is responsible for proper fit and comfort is made of soft
foam. In some helmets, the comfort padding can be taken out for cleaning. The retention system keeps the helmet on the head in case of impact, and this is usually achieved
by chin straps that are held around the chin and clasped together by some form of
buckle. These are connected to each side of the outer shell very firmly. While wearing
the helmet, the straps should be fastened properly. Hickling [15] suggested that 12
parameters are required for the acceptability of a safety helmet to protect the head:
weather protection; thermal properties; tactile properties; absorptivity/permeability;
mass distribution; degree of fit; size and shape; retention performance and fit; helmet
2 Review of Literature: Motorcycle helmet
2.4 Components of Motorcycle Helmets
The primary purpose of a motorcycle helmet is to protect the head from injuries.
Contemporary helmets protect the head against impact by having an outer shell
bonded to an impact-absorbing liner, as shown in Figs. 2.2a, b [12]. The purpose of
the outer shell is to widen the area of impact and allow the helmet to slide along the
ground.
The four main components of a motorcycle helmet are the outer shell, impactabsorbing liner, comfort padding and retention system. The outer shell is the part
that we see first and is usually made from some form of fibre-reinforced composites
or thermoplastics such as polycarbonate. This material is very tough and intended
to compress when it hits any hard object. This action disperses energy from the
impact and reduces the force before it can reach the head. More expensive helmets
are reinforced with Kevlar or carbon fibres. Thermoplastics helmets are generally
the lightest and least expensive. The thermoplastic helmet tends to have a shorter life
expectancy. Its chemical composition may be changed if it is painted or decals are
applied to its surface. Damage can occur if it is stored near gasoline, cleaning fluids
or exhaust fumes. Helmet manufacturers are constantly working to develop cheaper,
stronger and lighter materials for helmet shell construction.
The hard-outer shell of the motorcycle helmet tries to stop the penetration of
sharp objects and also acts as a safeguard for the shock-absorbing liner and prevents
the liner from disintegrating if the helmet hits the road or other objects. The helmet
liner is made of expanded polystyrene (EPS) foam of varying density and thickness
ranging from 10 to 25 mm. Lombard et al. [13] were the first to introduce expanded
polystyrene to be used in helmets. This is the important part of a motorcycle helmet,
as polystyrene is non-resilient and evenly spreads the impact in an accident and thus
reduces the shock energy that could reach the head and cause injury [14].
The impact-absorbing liner is housed inside the outer shell and is usually made
of expanded polystyrene. The liner provides a cushioning effect and absorbs the
shock in case of an accident, thus protecting the head. Both the shell and the liner
are compressed if hit hard, spreading the forces of impact throughout the helmet
material. Generally, the more the impact energy is deflected, the less it can reach the
head and cause damage. Some helmet shells are designed to delaminate in case of
impact, and others crack or break if severely hit and thus absorb the shock of the
impact.
The comfort padding that is responsible for proper fit and comfort is made of soft
foam. In some helmets, the comfort padding can be taken out for cleaning. The retention system keeps the helmet on the head in case of impact, and this is usually achieved
by chin straps that are held around the chin and clasped together by some form of
buckle. These are connected to each side of the outer shell very firmly. While wearing
the helmet, the straps should be fastened properly. Hickling [15] suggested that 12
parameters are required for the acceptability of a safety helmet to protect the head:
weather protection; thermal properties; tactile properties; absorptivity/permeability;
mass distribution; degree of fit; size and shape; retention performance and fit; helmet