Safer Vehicle Design

S. MukherjeeS. Mukherjee

TRIPP

IIT Delhi

Why a risk

• Five horsepower

• Kinetic energy of

about 1 KiloJoules

• 100 to 600 horsepower

• At at 40 kmph and 800

kg without load

kinetic energy is 100 • The operator

– undergoes three years

of fulltime training

– wear helmets

eyeglasses

– their skills are

constantly upgraded by

retraining programs.

kinetic energy is 100

KiloJoules.

• The operators

– mostly untrained

– operating them part

time for maybe 1 hr. a

day.

Safety cannot be cognitive

• We can convert a typical speed of 40 km/hr.

to the more engineering 11 m/s.

• If the dashboard is 1m away

• If the car comes to a dead halt, • If the car comes to a dead halt,

distance covered in 1/11 sec.

• Flick of an eyelash or three human

synapse

• Three synapse cycles is too small

for any cognitive action.

Safety cannot be reflex• The 5 kg baby has a kinetic energy of

approximately 300 Joules.

• 300 Joules is equivalent to lifting a 60 kg

mass by half a meter against gravity.

• Doing that in tenth of a second is beyond • Doing that in tenth of a second is beyond

the capacity of most humans.

• Parental instinct will just not be backed by

parental muscle power.

• Must be engineered.

Newton and Safety

• Equivalent impact when travelling

in a vehicle at 40 km/hr.

• Velocity attained by a body under

free fall through a height of 6.2 m.

(two floors)

• Vaulting record of Sergei Bubka.

• As a kid, I have jumped down from

one floor height and am still

healthy, but not two floors.

Wear a cushion

• For Mr. Bubka, the IOC

recommends a cushioning of

28” depth.

• Most car users would not like

to strap a cushion the moment to strap a cushion the moment

they sit inside vehicles.

• The cushion appears only when

there is an impact, and is called

an airbag.

• Stringent requirements make

airbags cost $1000.

Slow it down

• If the vehicle speed is halved, the survival height

becomes 1.5 m in place of 6 m

• The bonnet of a car is about a metre.

• If the bonnet compress on impact, then the • If the bonnet compress on impact, then the

dashboard of the vehicle does not stop

instantaneously but travels forward.

• This gives additional space to the designer of the

airbag and seatbelt to bring the rider to rest.

• It is not sufficient to have a crush zone. The

crushing must be supported by appropriate seat

belt design to save lives

Honeycomb

• Honeycomb materials used to design crush

zones as they have good energy absorption

characteristics.

• They can be designed to fit stress corridors

on demand and are lightweight structural on demand and are lightweight structural

materials.

VRU• There are many more people outside the vehicle

than inside in developing countries.

• The principles used in protecting the riders are

applicable in protecting the road user as well.

• One design would be to mandate a crush boundary • One design would be to mandate a crush boundary

layer of half a meter.

• Bonnets that fold on impact, rounding of front

profile, sinking hard pivots of windscreen wiper

below the bonnet are some of the measures

• Present-day bumper and bonnets with small

clearance to engine are not VRU friendly.

VRU Simulation

Car MC Crash

Airbags

• Airbags have to deploy fully within 5 ms to

avoid ‘slapping’ the rider.

Very effective in

protecting riders

avoid ‘slapping’ the rider.

• The airbag mass is about 200 gm. and

moves at a peak speed of around 100m/s !

• Energy content is about 1000 Joules!

• A slap good enough to break a jaw.

• Plus avoid hot gases scalding the rider.

Airbags

2 ms

48 ms

Nature of Standards

• Common basic methodology for assessing systems

• Standards are based on existing proven technology

• Should be updated whenever necessary.

• Research standards need quantitative measures

• Legislative standards require pass/no-pass evaluations.• Legislative standards require pass/no-pass evaluations.

• Establish the simplest procedures that give standardised,

repeatable, reproducible, realistic, and representative test

conditions

• Inferences’ concerning the relevance of the sample results for

the overall population can be made using statistical or

simulation techniques

Outcome

Injury risk

Injury severity

Inp

ut

Outcome

Exposure

Dosage

Cra

sh s

everity

Injury risk

Injury severity

Outcome

Injury risk

Injury severity

Inp

ut

Outcome

Head A

ccele

ratio

n

Chest C

om

pre

ssio

n

Fem

ur C

om

pre

ssiv

e L

oad

Injury risk

Injury severity

WHAT LEVEL OF INJURY IS

ACCEPTABLE?

• Prevent Death?

• Prevent Permanent Disabilities?

• Prevent AIS 3+ Injuries?• Prevent AIS 3+ Injuries?

• Prevent AIS 3+ to X% of Population?

• Prevent AIS 2+ to Y% of Population?

Injury CriteriaHead Injury Criteria (HIC)

< 1000Max

F + M

F + Mc c< 1Nij=

( )( )

HIC t tt t

a dtt

t= -

-.

2 1

2 1

251

1

2

∫

.

Compression Criteria s(t) < 7.5 cmAcceleration Criteria a(t) < 65 g’sViscous Criteria (V*C) V(t)*s(t)/D < 1 m/s

F < 8 kN

Knee Shear

x < 15 mm

F + M

F + Mc c<1TI =

Force CriteriaF(t) < 10 kN

“Censored” Biomechanical Test Data

Injury X X XXXXXX X X XX X X X X1

TransitionRegion

No InjuryRegion

InjuryRegion

Parameter

No Injury X X X XXXXXX X XX X X X X0

Inju

ry R

isk F

un

ction

.1

.00

Cumulative Frequency Distribution

0.5

0

Pa

ram

ete

r

0.0

0

Cumulative Frequency Distribution

0.5

0

0.4

0.6

0.8

1

P(i

nju

ry)

P(AIS 2+)

0

0.2

0.4

0 5 10 15 20

Femur Force (kN)

P(i

nju

ry)

0.4

0.6

0.8

1

P(inju

ry)

P(AIS 2+)

P(AIS 3+)

P(AIS 4+)

P(AIS 5+)

0

0.2

0.4

0 20 40 60 80 100

Maximum Chest Compression (mm)

P(inju

ry)

0.4

0.6

0.8

1P

(in

jury

)

P(AIS 2+)

0

0.2

0.4

0 50 100 150 200

Peak Chest Acceleration (g)

P(in

jury

)

P(AIS 2+)

P(AIS 3+)

P(AIS 4+)

P(AIS 5+)

Who is an

average

adult adult

person?

50th percentile adult male

• The 50th percentile is the smallest number for which at least 50% of the numbers are less than or equal to it.

• So a dummy with all dimensions, weight • So a dummy with all dimensions, weight and moment of inertia such that 50% of the US population are less than or equal to that measure.

• What are the implications for your safety?

Converting Injury Risk vs. Crash Severity

Crash

Injury Risk

P(1/x)P(1/x)

Crash

Severity

Dummy Response

Volvo Car Corporation

P(1/x)

What was achieved

• Data reveals that occupants travelling in cars manufactured between 1978 and 1982 are 28% more likely to be seriously injured than those in cars manufactured between 1992 and 1997.

• Newer cars perform even better in crashes.

• Analysis undertaken by the Monash University Accident • Analysis undertaken by the Monash University Accident Research Centre has shown that there is a good correlation between the ANCAP crash test results and the vehicle's actual real world performance as measured in the Used Car Safety Ratings.

• This accords with overseas studies such as a survey by the United States National Highway Traffic Safety Administration which showed that cars that did well in US NCAP crash tests experienced a lower occupant fatality rate in real world crashes than those that did poorly.

The road forward for India

• Establish safety standards with emphasis

on:

– type A and smaller vehicles.

– Vans and other utility vehicles

– Three wheelers

• Pedestrian impact standards irrespective of

what the rest of the world does.

• Include buses and trucks in the standards.

– Include under run protection for two wheelers

• Investigate helmet standards to make it

more suitable to Indian conditions.

• Set up 2 - 3 multidisciplinary crash research

teams.

– The mandate of the teams will be to understand

special conditions and needs in India.special conditions and needs in India.

– Establish epidemology of crashes.

• This data is essential for estimating the

effect of safety systems and change in

standards

Good luck !