7/25/2019 Helmet Pm32

1/86

Design of Motorcycle Helmets

Puneet Mahajan

Indian Institute of Technology Delhi

INDIA.

7/25/2019 Helmet Pm32

2/86

Helmet Components and Principle

7/25/2019 Helmet Pm32

3/86

More than 80 percent of all motorcycle crashes result in injury or death to the

motorcyclist.

Per mile driven, a motorcyclist is 16 times more likely to die in a crash than an

automobile driver.

Wearing a motorcycle helmet reduces that risk by almost one-third (29

percent).

Wearing a helmet is the single most critical factor in preventing or reducing

head injuries among motorcycle drivers and passengers.

Some facts about helmets (from a US study)

7/25/2019 Helmet Pm32

4/86

First, about half of all serious motorcycle accidents happen when a car pulls

in front of a bike in traffic. These accidents typically happen at very low

speeds, with a typical impact velocity, after all the braking and skidding,below 40 kmph.

Actual crash speeds are slow, but the damage isn't. These are serious,

often fatal crashes. Most of these crashes happen very close to home.

Some facts about helmets Hurt Report, (1981)

7/25/2019 Helmet Pm32

5/86

The next-biggest group of typical accidents happens at night, often on a

weekend, at higher speeds.

They are much more likely to involve alcohol, and often take place when a

rider goes off the road alone.

These two groups of accidents account for almost 75 percent of all seriouscrashes.

So the accident we are most afraid of, and the one we tend to buy our

helmets forcrashing at high speeds, out sport ridingis relatively rare.

Some facts about helmets Hurt Report, (1981)

7/25/2019 Helmet Pm32

6/86

A vast majority of head impacts occur when the rider falls off his bike and

simply hits his head on the flat road surface.

The energy is proportional to the height from which the rider fallsnot hisforward speed at the time.

Going faster when you fall off does not typically result in your helmet taking a

harder hit.

90 % of the head impacts were equal to or less than the force involved in a 2.2

m drop (23 km/hr). 99% of the impacts were at or below the energy of a 3.3 m

drop (29 km/hr).

A high-speed crash may involve a lot of sliding along the ground, but all modern

full-face helmets do an excellent job of protecting you from abrasion.

Some facts about helmets (Hurt Report and a similar study in Thailand )

7/25/2019 Helmet Pm32

7/86

Helmets hit a flat asphalt surface (75-85%)

Helmets do hit curbs a small percentage of the time, but usually after slidingalong on the road first.

Some facts about helmets

7/25/2019 Helmet Pm32

8/86

Helmets don't obscure vision.

All helmets provide a field of vision of more than the 140 degree standard that

state driver licensing agencies use to identify vision problems.

Helmets don't impair hearing.

for someone without a helmet, the wind and sound of the engine are very

loud, and any other important sounds must be even louder to be heard over

all that noise. With a helmet on, surrounding sounds are quieter, but in equal

proportions.

Technically speaking, the signal to noise ratio stays the same.

Visibility.

Although black helmets are popular among motorcyclists, they offer the leastvisibility to motorists. A rider wearing a plain white helmet rather than a black

one reduces his or her chance of collision by 24% because it is so much more

visible day or night. Nevertheless, black helmets outsell white ones by

20:1.

Some other facts about helmets

7/25/2019 Helmet Pm32

9/86

Sagittal view of Human head and Meninges (Ref. Nucleus Medical art, 2001)

7/25/2019 Helmet Pm32

10/86

Brain basically floats inside the skull, within a bath of cervical-spinal fluid

(CSF)and a protective cocoon called the dura.

When the skull stops suddenlyas it does when it hits something hardthe

brain keeps going, and has its own collision with the inside of the skull.

If that collision is too severe, brain injuries such as shearing of the brain tissue

bleeding in the brain, or between the brain and the dura, or between the dura

and the skull can occur.

When the brain is injured internally, bleeding and inflammation make it swell

and it presses harder against the inside of the skull and tries to squeeze

through any opening, bulging out of eye sockets and oozing down the base of

the skull.

Brain Injury

7/25/2019 Helmet Pm32

11/86

When the helmet hits the road or a curb, the outer shell stops instantly.

Inside, the head keeps going until it collides with the liner. When this

happens, the liner brings the head to a gentle stop.

t

vmF

=

more t less impact force on the head

How does it work ?

Kinetic energy of head Strain energy of liner

7/25/2019 Helmet Pm32

12/86

F F

FOAM STEEL

(x)foam(x)steel

Deformations

7/25/2019 Helmet Pm32

13/86

t t

( ) ( )2

foamfoammv

2

1av XF = ( ) ( )

2

steelsteelmv

2

1av XF =

XX steelfoam >

FF avav steelfoam