Modelling the Effects of an Inflatable Tubular Structure (ITS) on Occupant Kinematics and Injury Risk in the Rollover of a Sports Utility Vehicle (SUV)

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Nov 14, 2013 (3 years and 4 months ago)

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Modelling the Effects of an Inflatable Tubular Structure (ITS)

on Occupant Kinematics and Injury Risk in the Rollover of a

Sports Utility Vehicle (SUV)



Yuanzhi Hu, Clive E Neal
-
Sturgess, and Rong Guo


Birmingham Automotive Safety Centre
,
M
echanical and

Manufacturing Engineering
, Un
iversity of Birmingham,
Edgbaston, Birmingham, UK, B15 2TT


Abstract

The aims of this study are to

investigate the response
s

of
a Hybrid III
dummy and
a
human
body model
in rollover
crashes

of an SUV
,
and to assess the effect
of an inflatable tubular structure (ITS) on the unrestrained occupant
kinematics in rollover events.

A SAEJ2114 rollover test of a 1994 Ford Explorer with an inflatable tubular structure (ITS) is simulated for two
front row occupants, and validated in MAD
YMO. By removing the ITS, the simulation of the Hybrid III dummy
occupants without ITS is obtained. By replacing the dummy models with human body models, with and without
ITS, two other simulations are also model
l
ed. The kinematics and injury risks of the
two occupant models are
compared and evaluated. Significant differences exist in the motions, and injury levels of the dummies and human
body models with and without ITS. ITS can offer significant protection to the head by cushioning the impact of the
head

on the roof or side windows, and can mitigate against occupant ejection. The flexibility of the spine and the
neck of the human body models significantly affect the kinematics and the severity of the injuries of the occupants
modelled, and so would also a
ffect the relevance of the design of countermeasures developed from dummy tests to
real world rollover crashes of human beings.

Keywords

Inflatable Tubular Structure
, occupant kinematics, rollover, simulation, dummy model, human model

NOTATION

)
(
t
A

acceleration function

z
F


neck axial force

y
M


bending moment about the dummy’s occipital condyle


t

time



cumulative normal distribution

μ

the mean of the original normal distribution

σ

the standard deviation of original normal distribution



1 I
NTRODUCTION


Inflatable tubular structures (ITS) were first introduced as one kind of side airbags by BMW
in the 199
7

model year

for side impact h
ead and neck protection [1]
. To evaluate the effects
of side airbags on occupant protection in rollover events, NHTSA has conducted standardised
rollover tests. These test reports can be found at

t
he NHTSA Vehicle Crash Test Database

(http://www
-
nrd.nhtsa.
dot.gov/database/nrd
-
11/veh_db.html)
.

These rollover tests
have

demonstrated
the

head protection
,
and
the ejection prevention capability of
ITS
. Using

three
SAEJ2114

rollover tests and simulations
, Yaniv

et al.
[2]

also found that
the
ITS significantly
red
uced the possibility of

ejection

and reduced the vertical movement of

Hybrid III dummies.
Kompass

et al
.

[1]

estimated

that t
he effectiveness of the
ITS

wa
s 33%

in fatality reduction,
45% for AIS 3+ injuries, and 33% for

AIS 2+ injuries,

based on

the avail
able test data, and
the exposure

to injuries predicted by NASS
-
CDS 1988
-
96,

These rollover tests

were

all
based on the
Hybrid III
dumm
ies
.

The kinematics of human
body
models

is
however

quite different to that of Hybrid III dummies in rollover crashes
.

Pra
xl et al.
[3] found that
the
human body model contacted
the
side window 9ms prior to the head of the
dummy model
,

in a rollover test simulation of
a
vehicle sliding laterally against a curb
. W
hile
it

was
delayed
by
about 13ms
compared to

the
dummy model
i
n another rollover simulation
when
the
vehicle slid sideways into a gravel pit
.

Th
is

study also pointed
out that “the
dummy
and human model kinematics cannot be
transferred

from one accident scenario to another

.
So d
oes ITS really provide
ejection mitigat
ion

and head protection for human being
s

during
rollover crash
es
, and what are the possible kinematic differences between the dummy and
human body models in rollover crashes?


The objectives of th
e

research
reported here are

to investigate the response of
a Hybrid III
dummy and human

body model,

and to evaluate the effect
of an
ITS on occupant kinematics
in rollover crashes from four simulations derived from a real SAEJ2114 rollover test

of a Ford
Explorer
.


2 ROLLOVER TEST
DESCRIPTIONS


A

SAE J2114 Dolly

Rollover Test

(Test No. 2553) from
t
he NHTSA vehicle crash test
database

was chosen
for the

simulat
ions
. In this test, a

1994 Ford Explorer, containing two
Hybrid III 50th percentile male dummies, was placed upon the rollover test device at 23
degrees abov
e the horizontal and was released at 30 mph.
T
he ITS devices were

inflated just
prior to the start of the test. The doors were locked and the
front side
windows rolled down
before

testing.

The vehicle made 2½ rolls and came to
rest on its roof.
Due to

the
application
of the ITS,
both dummies
remained

in the compartment. T
he HIC of the
driver
dummy was

89 at 1687.6 to 1697.3 ms while the HIC of the passenger

dummy

was

only 44 from 1300.75
to 1304.5
ms.



3

MODELLING


F
our simulations
were
derived from the rol
lover te
st

and compared
using

MADYMO.
First,
t
he rollover test and dummies’ kinematics were

reconstructed and
validated
in MADYMO, by
comparing the kinematics and accelerations of the vehicle and dummies with the test

data
.
Based on the
accurate
reconstruc
tion of the test, by removing
the
ITS
and
its

contact
characteristics
,

the

dummies


kinematics without restraints w
ere

obtained. Then

r
eplac
ing

the
dummy models with
the
MADYMO human body models, the two previous simulations were
performed again to obtain
the kinematics
of the
human

body models

with and without
the
ITS.

In the four simulations, the
crash
model

containe
d

three individual systems, i.e. the vehicle,
the interior

(
s
eats
,

steering wheel
,
front instrument panel
,

and
ITS)
, and the
occupant models
.


The
Vehicle Model



The public domain
finite element
model of a Ford Explorer, developed
by Oak Ridge National Laboratories (ORNL),
wa
s available at http://www
-
explorer.ornl.gov/flash.html. This model
provide
d

detailed finite element mesh information
exc
ept for the interior,

and was converted to a MADYMO facet surface, which then ha
d

a
relatively low computational effort compared to that of
the
finite element model. To further
save the CPU calculation time, some unimportant parts
i.e.
the rear of vehicle,

tyres, engine,
suspension, bridges, side window glass, bumpers
, transmission, etc., which di
d

not affect
occupant kinematics, were removed
.
The t
yres
were

built from solid cylindrical

models
to
assist visual comparison.

The
Vehicle Kinematics


The vehic
le
motion

wa
s the basis of the occupant simulation. Only
when the vehicle motion is validated, it is possible to obtain the correct kinematics of
occupants.
The vehicle motion was reconstructed from the recorded test data

of

the linear
accelerations (longi
tudinal, lateral, vertical) and the rotational velocities (roll, pitch, yaw).
This data was transformed from the local vehicle reference system to the inertial reference

system

using
Euler parameters or
Quaternion’s
.
Three practical factors: the gravity

ef
fect
, the
offset correction, and filter values
were

taken into consideration when the transformation
from local to global coordinate data was computed. The details of the procedure,
and the
validation were

described in the
Hu et al. [
4
]
.
T
he processing of
the sensor outputs resulted in
the vehicle kinematics in the inertial coordinate system.
In this study, the
two

simulations
used the same vehicle motion
as
shown in Figure 1.

The upper frames are from the test video,
the lower frames are the resulting sim
ulation.

The Interior Model


The definition of the vehicle interior compartment was needed for
evaluating the contacts between the occupants and the interior objects. Only those objects
having possible contacts with the occupants were required to be defin
ed as shown in Figure 2.
The seats
,

steering wheel

and

front instrument panel

were

constructed from several ellipsoids,
and attached to the vehicle by bracket joints. The side windows were not
modelled
.

The ITS

Model


The
ITS wa
s developed by using a fini
te element model that
wa
s expanded
with gas dynamics
.

The test

report

did

not

give
any

detail
s about the
measurements of the ITS
,
and so a
ll the sizes

of
the
ITS

were

scaled from the
photo
graphic evidence. The deployed
diameter
wa
s about 15cm, and the depl
oyed length
wa
s about 85 cm. I
n

the study
of
Yaniv

et
al. [2],
which described a s
imilar

rollover test also using a Ford Explorer, the ITS devices
measured 6 inches (about 15.3cm) in diameter when fully inflated. T
he fabric skin of the ITS
wa
s
modelled

usi
ng membrane elements (
f
our node quadrilateral element MEM4) and the
element size
wa
s 10mm. The fabric skin of the ITS model
wa
s
considered
to be

a
linear
elastic isotropic material with a mass density of 750kg/m
3
. The modulus of elasticity (Youngs
Modulus)

wa
s 250E6 N/m
2
, and Poisson's Ratio
wa
s 0.3. The thickness
wa
s 0.001m.
T
he gas
in
the model
wa
s considered
to be

a mixture of 20%
oxygen

and 80%
nitrogen
.


The Hybrid III
Dummy Model

-

the MADYMO ellipsoid model of
a H
ybrid III 50
th

percentile
male dummy
was used.

T
he joints,
relative
positioning and orientation of
the
dummy
components

(such as
the
H point, head, thorax, pelvis, elbow, wrist, knee and
ankle
) were
adjusted
to be as similar as possible to the test

The
Human
Body
Model


the MADYMO facet mode
l of a 50th percentile male human was
used.
The human body models
were

validated
in MADYMO
by b
lunt impact tests

for
component validation (
shoulder
,

thorax, abdomen,

pelvis
), sled test and vertical vibration tests
for

the full body behaviou
r

[5]
.


4 RESULT
S AND DISCUSSION



4.1 Simulation of the rollover test


1) Dummy Kinematics

The fidelity and accuracy of the
reconstruction for the rollover test

were

evaluated both
qualitatively and

quantitatively.
Q
ualitative evaluation examine
d

the visual comparison
be
tween the test

and simulation in terms of rigid body motion

of the dumm
ies
, while the
quantitative evaluation focuse
d

on the comparisons of the acceleration
s

of the dumm
ies
.
T
he
motion
s

of the dummies recorded

in

the test were compared to the corresponding

results from
the

simulation.
Figure
3

show
s

the
visual
comparison of the
simulation

and

the test at
a
number of rollover

positions. From the comparison of the motions of the arms
,

the heads, and
the
bodie
s, it

shows that the simulated motions of the dumm
y occupant models was in good
agreement with those of the actual Hybrid III dummies used.

T
he comparisons of the accelerations of the test and

the
simulation at the locations of the head
and the
thorax sensors a
r
e show
n

in Figure 4. From the comparison

of

the accelerations of the
driver and the passenger
,

b
oth
in
the test and
in
the simulation,
they
show
ed

good agreement
for the general

trend of the curves
.

The peak value, peak timing and overall signal shape for
the driver showed a good similarity. There
were however significant differences evident in
the timing, and values of some of the details of the head accelerometer outputs for the
passenger. The far side occupant, the passenger, had a wider movement than the driver. The
impact timing of the head dep
ended on the contacts between other body parts (the pelvis,
thorax, neck) and the interior. Small errors of these contacts in timing and values would
have
major
effects

on

the outputs of the head accelerations.

Overall, however, the simulation and the test

data correlated well, and the simulation
provided a good approximation of the occupants’ kinematics for the rollover test modelled.


2) Injury Analysis

Head Injury


The head injury risk was evaluated on the basis of
the
Head Injury Criterion
(HIC). HIC c
an be expressed as

[5]
:

max
1
2
5
.
2
1
2
)
(
)
(
1
2
1






















t
t
dt
t
A
t
t
HIC
t
t



[
1
]


T
he time interval (
1
2
~
t
t
) that is considered to give appropriate HIC values
can be set to
15ms or 36ms [5]. In this study, it was
set at
15ms

and
the
value of 700 of HIC was
considered as a critical value for the evaluation of the head injury.

In fact,
“NHTSA is
adopting a HIC15 limit of 700 for the small female dummy based on the fact tha
t
the

experimental population from which the HIC relationship was

derived is representative of
adult dummy

head sizes ranging from that of the small female dummy to that of the large
male dummy”
[6]
.

In this model, the HIC of the driver
wa
s 81.8 (2848.2 ms < t < 2853.5 ms)
while the HIC of the passenger
wa
s only 35.3 (15
52.9 ms< t < 1565.3 ms).
Both HIC values
were far less than the critical value
of
700.


From
the
injury criteria for front and side impact

[7,8],
the
head injury risk curve
is













)
15
ln(
)
(
HIC
Injury
Head
P




[2]


where


is the cumulative normal distribution and can be expressed as


dt
e
x
x
t





2
2
1
2
1
)
(





[3]


μ=6.96352 and σ=0.84664 for AIS 2+ head injuries, μ=7.45231 and σ=0.73998 for AIS 3+
head injuries, and μ=7.65605 and σ=0.60580 for AIS 4+ head injuries.



Based on
the Equation
2

and the simulated HIC values, the head injury risks of the driver and
the pa
ssenger shown in Table 1 were no more than
0.1
% for AIS

2. This
meant

that
both the
driver and the passenger had a
n extremely

low risk
of

serious
or

fatal head injuries.


Table
1

Probability of head injury

Probability of Head
Injury Severity

Driver

(%)

Pas
senger

(%)

AIS2

0.1

<0.003

AIS3

<0.003

<0.003

AIS4

<0.003

<0.003


The maximum resultant accelerations for the driver and the passenger were 5
2
G,
and
3
7
G
respectively. These values were also
significantly
lower than the critical value of 80G
.

Accordin
g to the study of
Schneider and Nahum
[9], the minimum
forces associated with
facial and skull fractures correspond to head accelerations of 15G~90G, which

meant

that the
driver and the passenger still had some
finite risk
of fac
ial

and skull fractures.


N
eck Injury



The neck injury risk
can be

evaluated on the basis of N
ij
, which

is a linear
combination of neck axial force (
Z
F
)

and the moment about the dummy’s occipital condyle

(
y
M
)

[5]
, as shown in Equation 4.

critical
y
critical
Z
ij
M
M
F
F
N





[4]


According to the risk

analysis published by NHTSA to support the supplemental notice of
proposed rulemaking

[6]
, t
he risk of neck injury can be calculated by the following equa
tion
s:


ij
N
e
AIS
P
185
.
2
906
.
3
1
1
)
3
(







[5]

ij
N
e
AIS
P
361
.
1
310
.
4
1
1
)
5
(






[
6
]


The

N
ij

(
N
C
F
) of
0.39
for the driver
was estimated to represent a
5
%

risk of AIS
3

neck injury,
and a
2
% r
isk of AIS
5

injury
. W
hile

t
he

N
ij

(
N
C
F
) of
0.63

for the
passenger

was estimated to
represent a
7
% risk of AIS
3

neck injury, and a
3
% risk of AIS
5

injury

as
shown in Table
2
(all figures are rounded)
.

The passenger had a slightly higher risk of AIS 3 an
d AIS 5 neck
injuries than the driver.


Table
2

Probability of Neck injury

Probability of

Neck
Injury Severity

Driver

(%)

Passenger

(%)

AIS 3

5

7

AIS 5

2

3



The risk of neck injury was higher than that of head injury for both the driver and the
passeng
er, but still very low.

W
hen the head
experiences

a relative higher acceleration

than
the neck
, although the acceleration forces might not be expected to cause serious head injuries
of themsel
ves
, the compressive forces transmitted through the head would s
till have the
potential
to

injur
e

the
cervical spine.

This might be the reason why the neck had
a
higher risk
than the head

at the

same level
of indicated
injury.


Thorax

injury
-
There are several
thoracic

injury criteria available: 3ms,

v
iscous
i
njury
cri
terion (VC), t
horacic
t
rauma
i
ndex

(TTI), and c
ombined
t
horacic
i
ndex

(CTI) [5]
.

T
he

CTI
is a combination of the maximum chest deflection and the 3 ms clip maximum value of the
resultant upper spine

acceleration
[5]
.

In this study, CTI was used for
analysi
ng

the thorax
injury risk
, as injury risk curves were available.


According to the risk

analysis published by NHTSA

[6]
, t
he risk of
c
hest
injury

based on the
CTI value

can be calculated by the following equation.


CTI
e
AIS
P
431
.
6
529
.
7
1
1
)
3
(







[
7
]

CTI
e
AIS
P
201
.
5
328
.
10
1
1
)
5
(







[8]


T
he risk
s of a thorax injury of

AIS

3
were

0.5%

and 0.4% for the driver and the passenger
respectively

as shown in Table 3
. Both of them had a less than 0.02% risk of

AIS5

thoracic
injuries.

This meant that both the driver and the passenger had a
very
low risk
of

experienc
ing

AIS

2 injuries in this simulation.





Table
3

Probability of Thorax injury

Probability of

Thorax
Injury Severity

Driver

(%)

Passenger

(%)

AIS 3

0.5

0.4

AIS 5

<0.02

<0.02



From the injury risk analysis, it was found that the driver and the passenger had a very low
risk (no more than 1%) of serious to fatal injuries of the head and thorax in this simulation. It
showed that the
ITS protected the
head and the chest of the dummies by both reducing the
contact speed, and cushioning the impact of the head and the chest to roof or side windows.
However, the neck
had
a
some
what higher, but still low,

risk

(about 4
~8
%)

of
serious to fatal
injuries.


4.2

Simulation without ITS


1) Dumm
y

Kinematics

Without
the
ITS, both dummies were ejected totally from
the

side windows
, as

shown
in Figure 5.

In the period 0.0s~0.775s, because of the centrifugal effects, the head of
the dummy passenger was thrown out of t
he right side window at 0.62s. It had a
contact with the window frame at 0.645s, which resulted in a relatively high
acceleration. At the same time the dummy driver moved up and impacted the roof
,
and i
ts left arm was thrown out of the right side window.
I
n the period of
0.775s~1.69s, the passenger was completely ejected out of the window and contacted
the ground. Its head impacted the ground first at 0.85s
,

followed by the whole body.
The driver continued to move up until its pelvis was out of the side win
dow. Due to
centrifugal effects, it was thrown out from the side window at 1.41s and fell to the
ground at the front of the vehicle. Its right shoulder contacted the ground first then the
pelvis, and the head at 1.632s.
From 1.69s to 3.00s, the driver and
the passenger slid
along

the ground. The passenger stopped behind the vehicle at 2.12s, while the driver still had a
translational and rotational velocity at the end of the simulation at a time of 3.0s.


2) Injury Analysis


The values for the injury crite
ria of this simulation
a
re shown in Table 4. The
corresponding

risks of injury levels on the head, thorax and neck were shown in Table 5.
T
he critical time
for generating the potentially serious injuries was the period in which the dummies impacted
the gro
und
.
Although both dummies were ejected completely, the injury risks were quite
different.
T
he velocity, height, direction of ejection
, contact area, and contact objects

determined the severity
of
impact and hence injury. The dummy driver was ejected
upwar
dly
with a high velocity and a large

displacement
, which mea
n
t that

the driver had a higher risk
of

receiv
ing

s
o
me injury than
that of
the passenger. Moreover, the maximum head acceleration
85G of the driver
wa
s higher than the critical value 80G, which
al
so
meant that the driver had
a high risk
of

experienc
ing

fac
ial

and skull fracture.


Table 4
Injury Criteria Value
s

of Dummies without ITS


Injury
Criteria

Driver

Passenger

Critical
Value

Value

Time (ms)

Value

Time (ms)

HIC

558

1625.0~1642.7

14
5

856.6
~877.6

700

A
max

of head

85G

1634.6

55G

647.7

80G

N
TE

0.31

1652.1

0.39

884.3

1

N
T
F

0.2
5

1630.9

0.07

922.9

1

N
CE

1.48

1642.7

0.4
5

887.6

1

N
C
F

0.29

424.3

0.
20

647.5

1

CTI

0.73


0.
10




Table 5
Injury Risk Dummies without ITS



Driver

(%)

Passenger

(%)

Probability of Head
Injury Severity

AIS2

23

0.9

AIS3

6

0.04

AIS4

1

<
0.01

Probability of

Neck
Injury Severity

AIS 3

34

5

AIS 5

9

2

Probability of

Thorax
Injury Severity

AIS 3

6

0.
1

AIS 5

0.1

0.0
1




4.3 Human Model Simulation with ITS


1) Human
body Kinematics


The kinematics of human
body
models with ITS
are

shown in Figure 6.
In the period
0.0s~0.775s,

t
he passenger leaned toward the driver

at first
,
and then turned to the right

due to
the centrifugal

effect
s
.

At 0.62s the right shoulder

contac
ted

the ITS.
T
he resistance from the
ITS
resisted

the outward movement of the
shoulder

and
even the whole body
, and s
o at 0.775s
the spine and the neck were
significantly bent
.
A
t
1.58s~1.81s
when the body leaned to
wards

the driver, the right arm had room
to extend out of the window. At
2.48s~3.00s,

when the
vehicle rotation
had
slowed down,

the passenger moved abruptly towards the driver.

However,

the passenger did not contact

the driver

because
its body was held by the right arm
catching the ITS
.

T
he dri
ver motion was not significant
.

I
t began to move towards the left door
. T
he body then
moved up
wards, the buttocks came off
the

seat,
and the head contacted with the roof. I
ts

left
arm was out of the side window
. From 0.49s, the driver was locked
in the sam
e
position with
its
right arm
shaking around
until the three
-
second simulation
was
over.


2) Injury Analysis


Table 6,
and
7 show the injury criteria values and injury risks of the human
body
models with
the
ITS respectively. With ITS, both occupants of
th
e
human
body
models had an extremely
low risk
of
receiv
ing

serious to fatal head injury. But both of them had about 8~9% risk
of

experienc
ing a

thora
cic

injury of AIS3, which was higher than those of dummy models with
ITS. This might because of the rigidit
y of the dummy thorax, which
gave

smaller deflection
values
than that of human body

model
.


4.4 Human Body Model Simulation without ITS


1) Human body Kinematics


Figure 7 showed the kinematics of human models without ITS.

Both

occupants had a trend to
m
ove outward, due to
the centrifugal
effect
s
.
Without ITS, the driver moved up to the roof

until

its left arm
was
out of the side window
, which resulted in t
he upward movement
being

resisted by the shoulder against the window fram
e. T
he
ejection of the
pas
senger

was also
reduced
by the right
shoulder
against the
window
, which resulted in its
head
being
maintained
in the compartment

and

resulted in the neck bending.

W
hen the vehicle rotation slow
ed

down

in the period of 2.48s~3.00s
, the driver move
d

downwar
d a little
,
the head
and the

up
per

body was out of the compartment. Without any
drastic change, the driver would be ejected totally.
While the passenger
had
a tendency

to
move to the driver,
its

right arm held
itself

by catching the side door. There was no

contact
between

the driver
and

the passenger.



2) Injury Analysis


The injuries of both occupants were
analysed

in Table 8,
and
9. Although both
human body
models
were not ejected totally, the driver still had some risk
of

receiv
ing

serious to fatal
inju
ry.
Its

thorax had about
a
73% risk to receive
an
injury of AIS 3. The maximum

head
acceleration
of
11
1
G was
significantly

higher than the critical value 80G. It indicated that the
head had high risk
of
experienc
ing

fac
ial

and skull fracture. The passenger

did not show any
significant possibility of

experienc
ing

serious to fatal injuries
to

the head, neck
or

thorax.


4.5 Simulation Comparison


Occupants
(both the
dummy or human
body models)

had the tendency to move outward and
upward in the four
r
ollover si
mulations, due to centrifugal effect
s
. The application of ITS and
the difference between
the dummy

and
human body model

changed their kinematics
and also
changed their injury risks
in the same rollover test
.


When the vehicle rolled over, the passenger m
oved towards the driver at first, and then moved
back, due to centrifugal effects. But because of the flexibility of the human spine in the
human body model, the kinematics of the passengers was quite different. When the passenger
moved back with
the
ITS
a
s
shown in Figure 8, the movement included two

components
, the
lateral movement and the upward movement. Because of the flexibility of human spine in the
human body model, the lateral movement of the human passenger was delayed compared to
that of the dumm
y passenger. This mean
t

that the human passenger move
d

up more than the
dummy, but also move
d

to the right a little. Whereas the human passenger
had already moved
up and
impacted

the roof before the
head

arrived the ITS
, and the shoulder contacted the ITS
not the head. But for the dummy passenger, the head was just in the ‘right position’ and was
protected by the ITS. Apparently, the head of the dummy passenger was protected better than
that of the human passenger in this simulation. Although both of them h
ad a low risk of
receiving serious to fatal injuries, the maximum head acceleration of the human passenger
was higher than that of the dummy passenger, which means that the human passenger had a
higher risk of experiencing facial and skull fractures than t
he dummy passenger.


The case without ITS is shown in Figure 9, the passenger
s

continued to move outward. The
human passenger moved up until its neck contacted the roof rail which prevented it from
ejection, while for the dummy passenger, the head passed
through the side window, and the
whole body was ejected completely. Although the ejected dummy passenger did not show any
absolutely higher risk of experiening serious to fatal injuries than the human passenger, the
ejection
would result in contusion and a
brasions to the whole body, and also
increased the
risk of impacting with other objects, such as other vehicles, trees, curbs etc. in real world
crashes.


The driver
s

also tried to move outward. When the
driver

s
head

contacted the roof rail, the
force wa
s transfer
r
ed to the upper body with a force and a moment shown in Figure 9. For
the
dummy driver, because of the rigidity of the neck, the forces and the moments were larger
than those for the human driver. It forced the dummy driver to be rotated towards

the
passenger, whereas the human driver continued to move outward until the shoulder contacted
the window frame which prevented it from ejection.


4.6:

OTHER CONSIDERATIONS


Roof Intrusion
-

In the four simulations

shown
, the vehicle was considered as a r
igid body
without

any deformation and

so

no
roof intrusion. Intruding surface
s

can change
the

occupant
contact location, body shape or stiffness
,
the contact acceleration,
and also

the injury level

[11].
Researchers

have tried to find, but have not
found,
a relationship between roof crush and
head/neck injury [12
-
15]. The most significant limitation is
the definition

of the
rollover crash
severity,
I
t is reasonable to assume that the likelihood of injury in a rollover accident
increases as the accident seve
rity increase [11]
, and i
t is

also

reasonable to think that the
injury risk would increase if the vehicle
were

deformable
,

in these simulations
the HIC value
s

w
ere

only 89 for driver dummy,
and
44 for the passenger dummy
in

this

test.
These values
only rep
resented less than
a
0.1% head injury risk
at

AIS2. So these rollover simulations
,

without considering the vehicle deformation
,

have value
as a

reference.


Vehicle Movement


In rollover crashes, the kinematics of the vehicle and the occupants can
affect e
ach other.
The o
ccupant motion
s

have an effect on the
mass distribution of the
vehicle
-
occupant
system
, and so
can
change the vehicle motion. E
qually
, the vehicle motion also
affect
s

the occupant movements.
The
four
simulations
used the same
vehicle

moveme
nt.
Therefore, the occupants


movements derived from the test were not exactly the
same as the
actual ones. There should be some differen
ce
, although the degree of change was not clear.

T
he ratio of the mass of two dummies (154kg) to the vehicle mass (1729
.5kg) was less than
10%
, and so it is concluded that t
he simulations using the same vehicle motion
were

reasonable.


6
CONCLUSIONS


The four rollover simulations
of a Ford Explorer derived from the SAEJ2114 rollover test
investigated the kinematics of Hyb
rid III dummy model and a human body model
with and
without
the
ITS
, and analysed the injury risks indicated.

The simulations
demonstrated

some
significant
differences between
the dummy

model
and
the
human
body model
.
The main
difference was because of the

flexibility of human spine and neck in the human body model
as compared to the dummy model, this

affected the
comparative

kinematics, contact area
, and

injury level
.

Without
the
ITS, both dummy models were ejected completely from their own side window
s,

a
nd so were exposed to the
possib
i
l
ity

of

receiv
ing contusion and abrasions over the whole
bod
ies.
T
he dummy driver had about
a
23% risk
of an

AIS 2+ head injury
,
and a
34%
risk of

AIS3 neck injuries.

For the human model occupants, they were both contained

within the compartment, as the
kinematics was different. Compared to that of the dummy passenger, the outward lateral
movement of the human passenger was delayed, due to the flexibility of human spine, and
this resulted in the human passenger being contai
ned in the compartment. While for the
human driver, because of the flexibility of the human neck model, the forces/moments
transferred from the head were small which affected its initial kinematics
,

and resulted in the
human driver not being ejected comple
tely in the three
-
second simulation conducted.

The
human driver had about
a
73.1% risk
of

AIS 3 thorax injuries. Both drivers (
the
dummy
model and
the
human model) had
a
high risk
of

experienc
ing

fac
ial

and skull fracture.
Although the ejected dummy passen
ger did not show any absolutely higher risk of
experiencing serious to fatal injuries than the human passenger, the ejection would result in
contusion and abrasions over the whole body, and also an increased the risk of impacting
other roadside objects suc
h as other vehicles, trees, curbs etc. in real world crashes.


With ITS, the occupants
, both
dummy models and human models stayed in the compartment
.

ITS
significantly
reduced
the
occupants outward movement, and
to some extent

it also
mitigate
d the upward
movement if the shoulder was under the ITS. It
protect
ed

the head by
reducing the contact speed, and cushioning the impact of the head to the roof or side
windows.

Due to the
presence

of
the
ITS, the heads of
the
occupants had an
extremely

low
risk
of

seri
ous to fatal injuries
, however the compressive forces transmitted through the head
would have the potential
to

injur
e

the cervical vertebrae.
With ITS, the head of the dummy
passenger was protected by the ITS, while for the human passenger, it protected th
e shoulder.

This
indicated that some
of the
countermeasures
in rollover crashes,
developed
from

dummy
test
s,

should

be re
-
examined from the perspective of human body modelling, to give optimum
protection to
human being
s in real world rollover crashes
.



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E
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Fig. 1

Vehicle Motion


Fig.

2 Interior Model


Fig.
3

Comparison of

Occupant Kinematics in the Test and the Simulation


Fig.
4

Comparison of the Accelerations of the Head and the Thorax


Fig.
5

The kinematics of
Dummies without ITS


Fig.
6

The kinematics of
Human models with ITS


Fig.
7

The kinematics of
Human
body
mo
dels without ITS


Fig.

8

Comparison of human body model and dummy with ITS


Fig.

9

Comparison of human and dummy without ITS