SYNTHESIS REPORT”
FOR PUBLICATION
CONTRACT N.:
BRK?-CT94-0540 (DUMOCS)
PROJECT N.:
BE7145
TITLE:
D WY MODELLING FOR CAR <:R4SH SIM?.-JLATION
PROJECT
COORDINATOR: C. R.FIAT (Centro Ricerche Fiat)
,
.
.
PARTNERS:
PSA
(GIE PSA PEUGEOT CXTROEN)
RENAULT
(RENAULT)
VOLVO
(AB VOLVO)
MECALOG
(MECALOG S.A.R.L.)
TNo
(Netherlands Orj+nizatioxi for Applied Scientific Research - TNO)
LMS-ARMINES
(Association pour la Recherche et le d&+lo >ment des Methods et
processus Industrial)
NTUA
(National Technical University of Athens)
STARTING DATE:
*
●
.*
01/05/94
* * *
*
●
t
* * *
m
DURATION:
24 MONTHS
PROJECT FUNDED BY THE EUROPEAN
UNION UNDER Tk [E BRITE/EURAM
PROGRAMME
DATE: 11/09/96
DUMMY MODELLING FOR
CAR CRASH SIMULATION”
S. Bianco, P. Smerigiio, Centro Ricerche Fiat :;. C.p. a.,
Veicoli - Caicoli. e metodologie
Strada Torino 50
10043- ORBASSANO - ITALY
.4BSTRACT
Oriented to automotive passive safety investigations, two F~ite Elemen: models of crash test dummies and
three material models for foams and rubbers, suitable for irnplementa tion into explicit codes, have been
developed. The dummy models represent the Ilyfwid-fll dununy for fr ]ntal crash and l?utwiid-1 duminy
for side impact, which both shall be ordered in the next future by Eurapean safety regulations related to
these kind of impact. The dummy models have been modelled on the t asis of physical current version of
real dummies and successively have been subjected to three levels of ~alidation in order to furnish final
numerical tools suitable for exploitation in the crash simulation field. T} [e models have been fmtiy checked
at “certification level” test, by applying on the sevetzd body seugrnents c f the dummies the same legislative
requirements active for real crash dummies. Secondly they have been s ubjec~ed to a cycle of “component
tests” where most of their corporeal sub-parts have been physically lot .ded and correspondently tested by
means of numerical simulations, with respect to typical conditions c ccuring in crash events. The last
validation level has been focused to the reproduction of real sled test; for frontal impact (concerned to
Hybrid-III) and specific side impact tests with rigid and deformable F lates (for Eurosid-1 dummy). The
validation criteria have covered both ,kinematical and biomechanical ]erforrnances of the dummy finite
element models; the kinematical ‘output was looking at dummy displa :ements, to be compared with the
correspondent occurred in real tests, and to be marked by a numencz I-experimental agreement showing
15% error limits; the biomechanical output was oriented to all th> most significative “injury level
indicators” estimated by real crash durm-@s (HIC-head inj. criterion, 1 ‘C- viscous crit., accelerations and
forces acting on the several body parts etc.) showing an error limit of 30 Y..
The developed material models, three for foam-like materials and two for rubbers, have been devoted to
the obtainment of satisfactory numerical models for non-metallic maten ds, and have been validated on the
basis of a considerable set of experimental tests covering a Iarge range cf loading conditions and suain rate
values. The validation criterion has been guided by the requirement (fu~ illed) of showtig a 150/. error limit
between a single real tests case and the correspondent simulation per-font ,ed with a finite element technique.
Both the dummy modeIs and the material laws have been produced in order to be implemented into
RADIOSS crash explicit finite element code and to be introduced withir automotive “industrid design cycle
and scientifical academical environments oriented to perfom numerical sirmdahon of highly dynamic and
impact events.
INTRODUCTION
The current needs of passive safety investigation activity have unfoided as more and more linked to
numerical re[iab[e tools, ready and easy to use in verification and predictive phties of automotive design.
It is widely accepted that, being the current and forthcoming safety startdard regulations highly oriented to
occupant “injury level risk prediction”, the investigative actions must be pursued through numerical
anthropomorphic tools allowing the simulation of the occupant intetm:tion with the relevant automotive
environment during impact events of vm-ious type.
I
The Finite Element method for m-uctural analysis, proved to be an eficiem and reliable tool for several
technical aspecu, has then been considered to properly match the :~eea to enable speciilc numerical
investi=mtions in the passive safety iieldObjective of the project here mmmarized was the development and valit Iation of the Finite EIemem models
of two dummies widely used in crash sti”ety,tesring namely:
●
●
Hybrid-111 50th percentile dummy (in two versions, “fine” and “tom e“), to anaiyze frontal impact;
. E~osid- I dummy, to analyze side impact events.
The reason Ieading to the adoption of F.E. numerical technique for devel oping and validating >mch tools lies
in the particu.kir type of application marking some phases of modem \ chicle desi.~ which is the need of
predictive evaluation acrions, able to offer both accurate and reiiak Ie response in (mm of occupant
kinematics and biomechanical indicators norz-naily considered dwing ex]eximenzal crash acriviry, like Head
Injury cirerion (HIC), Thorzm Trauma Index (TH), Viscous Crirerion ~~C).
Consequendy, a great importance was assi-gned to the fac~ that the Fin re Element rechnique allows to use
rook giving useful indications in general conditions of use: particularly after an iniriai phase during which
the dummy model is subjected to basic tuning and validation, it is po:;sible [o utilize it in simulations of
various impact conditions, equipped b~ different rem-aim sys~ems ar d inregmted into several vehicuktr
environmerm.
I
This fact represents a great advanrage if compared to the alternative m mental tools classifiable as partiyrigid or mukibody tvpe, which are auire efficient in terms of hardwan ~ needs and very re iiable widin tie
boundary of param&rical evaiuatio~, but require a complete ru.ning 1 ~pe.ation whenever tie general rest
layou[ is changed
I
The development of the dummy models was supported by a compieme mu-y acrivi ty, too, during which the
problem of material modeiling for foams and m,bbers, in terms of cons~itutive laws and im.mental
impiementatio~ was faced and partly solve~ relatively to the particula~ application. The impact simulation
by means of anthropomorphous rook, in fac~ had to be supported by an exhaustive and reliable material
Database on major non-convenrionai material dummy components and by a corresponded development of
new numerical packages to be implemented into WIOSS explicit F.E. code.
3. TECX3NXCAL DESCWPTTON
The project activity was performed through a research organized in d ree major Tasks, devoted to “Foam,
and rubber modeilin~’ (Task 1), “Hybrid-III dummy modei deveiopme W (Task 2) and ‘~Eu.rosid- 1 dummy
model development? (Task 3). The project structure is shown in Figu.n: i.
3.1 TASK1: FOAM AND FUJBEH3R MODEL13NG
.4s previously highlighte~ the simulation of occupant interaction with car interior and restraint system
requkes the numerical modeiling of non conventional materials, such is foanis and rubbers, characterized
by very high deformations, non linear bebaviour and srrain rate sem itivity, A proper modeiling of swch
materials, capable of reproducing the experimental behaviour at dif;erenr smin rate and at very large
smins is crucial for mode lling impacr events in which the injury risk of the occupant is the main parameter
co be evaluated
Therefore the goals of Task 1 were:
●
●
the development of a basic knowiedge about the behaviour of fo:uns and rubbers comrnoniy used in
dummies and car interiors;
the determination of proper paramerem to simulate kern with the existing material laws already
implemented in the F.E. explicit code;
~
●
the development and implementation in F.E. explicit code of new cmstitutive laws capable of improving
the accuracy of numerical simulations.
This t&k provided to tie other two the experimental background knowledge on dummy materials and the ‘
specific numerical tools in order to effectively develop and validate rht models.
From a general point of view, objective of this Task was also a deeper and better understanding of the
physical phenomena involved in foam-like material behaviour.
The objectives were not only to find proper parameters to represent t le selected materiais, but also to give
general .tidelines for studying those which show similar behaviour The results of this Task should be
considered as a basic know-how for mechanical engineers interested in understanding foam and rubber
expetimemal behaviour, and in their simulation during impact phenonerm
3.1.1 Experimental phase
The first part of the activity was devoted to tie obtainment o‘ a consistent Database concerning
experimental behaviour of foam and rubber materials commonly us td in dummies and car environments,
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I
under both static and highly dynamic ioading conditions.
The tested materials were selected considering the dummy parts wlxre an improvement in the simulation
capability is mostly desired. However, the majonry of dummy body segments were invoived in the stated
experimental phase, as it is shown in the next Table 1. The numbers in the cells comespond to the number
of tests for each material in different con.tlagnzttions.
I
MATEIUAL Code
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I
Pelvis flesh
lStemurn foam
Spine
‘ N e c k
Thorax skin
Pelvis skirt
DY NANIIC TESTS
QUASI - STATIC TESTS
TENS.
Hybrid-111
COMP.
HO 1
H02
H03
H04
EI07
FI09
X3
X3
x3
X4
x5
X4
x3
X4
x 6
x3
x4
‘H:m
x5
X4
j
.x3
EOI
E02
E03
E04
.x3
x3
x4
x2
x3
x4
x2
‘d
x5
E05
E06
X3
X5
x4
x4
‘ X 3
AO 1
X7
x4
‘::X41X31X4
X31
xj
x3
x4
Eurosid-1
Pelvis Plug
Lumbar Spine
Pelvis flesh
Upper arm
Abdo Hard
Abdo Soft
Environment
Seat foam
Seat foam 2
Knee Bar
Dashboard
x4
4
x4
x4
“x3
x3
X3
.x3
x5
x5
x3
x5
x4
x
‘
x4 - x4
x4
x9
A05
A06
A07
x4
X3
X2”
x4
x3
x3
x3
X3
x3
x4
x4
Table 1- Experimental tests on material samples.
The’, loading conditions considered in the low strain rate or quasi-stitic range were uniaxial compression
uniaxial tension and pure shear, both during loading and unloading plmses, to highiight hysteresis effect.
Concerning the tests at high strain rate, due to the greater diili xdties in achieving tests in dynamic
conditions with very soft materials at very large stmins, only uniw:ial compression WM considered. The
device used for the tests ‘was the Split Hopkinson Pressure Bar syste w suitably modified to deal with very
soft materials as foams. To test foams, low irnp,edance bars ars needed which can only be found
viscoelastic material made, requiring speciai theo~ for the 3 D wave propagation treatment. Nominal strain
rate in the range 200 s-’ - 600 S“[ were tested with this kind of device
3
In order to obtain experimental information in the dynamic range 10 s-’ - 100 s-’ with significaave
maximum strain an original new technique was adopted. the so called (‘Slow Bar technique”, developed at
LINKS Laborato~ to extend the capabilities of the Hopkinson Bar systenl.
Dynamic tests at nominal constant strain rates were also carried out b~ using a high speed testing machine
at nominal rates of 1 s-~, 10 s-i and 100 s-t.
Additional drop tests, (with different masses and impact velocities) on material samples and dummy
complete parts were also performed in order to obtain information o~l foam behaviour in more complex
loading conditions and to constitute a database of experimental tests cl xe to the real working situation for
the validation of the developed material laws.
3.1.2 lh’faterial rnodelling
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Most of the tested mawials are sensitive or very sensitive to the speed jf loading and are usually loaded up
to very large strains. .Mmost no complete 3-D constitutive law coverirg both domains can be found in the
scientific literature. Furthermore no Imown tectiques for multiaxia I testing in the dynamic range are
available.
Therefore it was decided to concentrate on 1-D modelling, knowing t lat real Ioadings in crash sirua[ions
are mostly 1-D loadings in many cases.
Furthermore limitations on tests procedures, expeciaily for dynamic loading cases, showed [hat the most
reliabie and repeatable resul~ could only be provided for simpie corr pression test in quasi-static loading
with conmoilable constant strain rates and at low impact velocities witl. variable strain rates.
Dynamic tests, preferably at relatively constmt rates, would then pro~ride usefil interpolation possibilities
as long as they remain coherent with the static test. In any case they pr ~vide a useful insight into the nature
of the foam. These tests should then be used as the basis of a one di nensional cme fitting procedure in
order to arrive at a one dimensional equation.
.4s a second step, the generalization of a unidimensional model to a ful. three dimensional formulation must
be taken into account. The implementation of a material model expr ~ssed in terms of a 1-D fommla or
experimental 1-D data Lm.rpediately poses the problem of summing tht effects of general Ioadings in terms
of a combination of equivalent pure compressions. These include unia tial mode, equibiaxial mode, planar
Qmre shear) mode&d volurnernc mode. Since no shear tests were available ( at least for high strain rates)
the natural choice of expressing the material law in the principai =es (Jf we defo~ation WM a~ctive ad
. then was been adopted.
I-D modeiling
Generally three types of material models may be considered and are of major interest to Finite Element
modelling. Either an enerb~ functiomd of some measure of the strain is available, in which case a stressstrain relationship may be obtained by deriving the functional witl. respect to the strain measures. In
different conditions a phenomenological model based on some kind of separation of the components of the
complex behaviour must be considered.
A third approach may also be adapted via direct imposition of a sre;s-strain curve obtained during some
simpIe e~erimental procedure. This approach assumes that this simple test underlies the global behaviour
of the material in a generai loading state. It may however be conside~d as a subset of the second method
and is essentially a phenomenologicd approach in the sense that the phenomena under observation is
represented by a digitalized set of values instead of a 1-D formuia fitt ?d to these data. Both the second and
the third approach, rely, heavily, of course, on the availability and reliability of the experimental data. In ail
cases the choice of the strain and stress measures is predoti,mt for a practical (and objective)
determination of the material constants.
Three different models have been developed in order to describe the utidimensional behaviour of foam-like
materials, both in static Wd dynamic unidmensional loading conditiors:
NTIJA model
LMS m o d e l
● Curve Network approach.
●
●
NTU~ modei considers foams as composite materials consisting ot a rubber-[ike structure and air. The
macroscopic behaviour is attributed to three sepamte rnechankns. mmely the confined air pressure effect
4
the elastic buckling of the poiymer structure, assumed to be a random distribution of rubber eIastic beams,
and the hyperelasric behaviour of the polymer after the densification phase. The distribution characteristic
of polymer-air contents can also be raken into account, combining with sntistical method the three effects
briefly descnbecL The NTUA method allows the imerpoIation of t?m: static and dynamic test stress-strain
cume with a formula containing S (or 11) material constants tt 1 be determined from the fitting of
experimental static and dynamic tests.
LMS model highlight the non-linear elastic behaviour of the tested fo mm, sensitive to strain rate, loaded up
to to very large strains. Studied materials are described by a Ke~vin-Voigt modeI type in which both
elasticity and viscosity are non linear. The macroscopic behaviour is the combination of three physically
simple and uncoupled contributions: a non linear elastic behaviour, a non linear viscous effect and a
buckling behaviour at low strain. The three effects are not all active for all materials and are acting in an
additive way. The resulting formuiz in the general case, contains 11 malenai consmnts to be fitted on the
experimental static and dynamic tests.
The Curve Network approach is more a technique for the exploitati~ m of experimental data, rather than a
material law by itself It is based on the direct use of the ex~erimentzl compression curve from quasi-static
and dynamic tes~s, instead of forrnuling a relationship between stress strain and strain rate. The strain rate
dependence is introduced by interpolating the experimental curves a; different strain rates. This method is
quite straightf~mztrd if all the experimental curves are available, if they show good coherency and if the
tested strain mtes cover an appropriate range of dynamic condit: ens, relatively to the actuai Ioading
co ndltio n.
I
Generalization to 3-D
The same generalization method was used to extend the different m modimensional formulations to a fill
‘i.hree dimensional formulation. The genet@ loading condition was considered as a combination of
equivalent pure compression conditions. Basic assumption is the isc tropy of the material: foam materials
are supposed to have no directionality, so that the same srress-stmin curve is valid for all directions.
The aIgorithm used for the generaiizatioti to 3-D can be briefly summ tized iri the following manner:
— at each computation cycle the principal engineering strains and the corresponding skin rates are
computed
– the uncoupled phcipal stresses are computed by means of the cmve network approach or by means of
a 1-D interpolation formula ( NTUA or LIMS), as a function of pr ncipal nominal strain and strain rate
— if necessary, the uncoupled stresses can be coupled by introducing a Poisson effect
– the Cauchy stresses are finally computed in the giobal axis.
Due to the lack of dynamic multia.xial experimental tests, the validiq~ of the method used to generalize the
1-D formulation to a 3-D one could only be evaluated by the t:orrelation achieved in the drop test
simulations and in the ftdl scale tests involving more complex loading pattern than the, simple uniax.ial
compression.
3.13 lMatenal models validation
,.
The developed material laws, after development and impIementatiart as prototype in IMDIOSS explicit
code, were tested through an additional speciilc experimental prog~ composed of both drop tests on
material samples and component tests on some dummy segments. T le originality of these tests is that the
strain rate is not constant during the experiment and that the velocity and the energy involved is of the same
order of magnitude than in the actual crash tests on dummies.
An additional evaluation of the performance of the new material laws could come also ffom the Ml scale
simulations on the compiete dummies, even if in these cases the K aterial law is not the only parameter
affecting the nurnericaf experimental correlation and many other unlalowns can affect the results.
A correspondent simulation program was set on, exactiy covering the experimental activity previously
mentioned.
In a first phase, the new material laws were tested by means of :. simple compression procedure, thus
allowing to detetmine the proper parameters for the different forrmiation for most of the tested materials,
to verifi the stress-strain relation with respect to experimental tes~s m samples and to comp~e the results
from different formulations. [n a second phase drop tests and comporent tests have been simulated.
5
3.2 TASK 2: HYBRID-HI DUMMY MODELLING
In order to increase car safety within acceptable time-schedules new d~:sign tools are neede~ as mentioned.
The numerical Hybrid-HI, which was developed in Task 2, is intendec to offer a deeper understanding on
human surrogates and safety systems behaviour during impact conditions. It has to be remarked that the
peculiarity of such numerical tools is to be individuat?d in the capab: lity to fulfd the specifications of an
industrial calculation center, which are accuracy of results and low ?rofile in hardware needs. For these
reasons, the dummy model was developed in IWO versions:
1. a coarse model (2500 elements), to be used as a loading device i 1 structural analysis on restraint
systems, for qualitative predictive investigations on occupant kim matics and interaction with seat
and restraint system itself
7-.
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a second ref”med version (6000 elements, Figure 2), developed with the puqose to accurately predict
injury criteria and enabIe to study detailed phenomena in safety Sys< ems.
*
The deveioped FEM models were also requested to be effective for jafety engineering: they must be
suitable, in terms of user-friendliness and computational compie> ity, to tie time scale and the
procedures currently leading the automobile design.
This means that the dummy FEM models have to be detailed e lough to simulate sophisticated
phenomen% but also suitable for massive inuoduction into car design tycle.
The quali~ level needed for the new generation of FEh4 dties can be expressed considering that the
majority of dummy models currently available allow to perform crash simulations in terms of kinematic
behaviour only, and that the desired objective is the capability to repr >duce an automotive impact with
~ good reliabi]i~ also in te~ of biomechanics, which means “inj~ 1 :vel risk prediction”.
This capability, - for an acceptable industrial expioitahon, should -w: uantee”a numencab’experirnental
agreement marked by a 3 0°/0 error limit.
3.2.1 Technical approach
Basic aspect of the general method used in the development of the dm u-ny model was the validation of each
important part of the dummy, or of the sled environment separa! e]y, before assembling them into a
complete model.
Second aspect was the development of the model through sevezd steps, from the fmt fictional
validations, ftig numerical and stability problems and verifjing ; I global satisfactory behaviour, to a
cycle of intermediate validations, comparing numerical and experime:md resuIts and inputting at each time
improved-knowledge and experience into the models, towards the fma validation in which the performances
of the models with respect to the planned objectives were verified.
The acquired knowledge in dummy modelhng clearly suggested t lat, for an effectively and accurate
development of the NVO mode Is, it was convenient to start the mo delling phase focusing on a cietaiIed
version of the dummy and to derive the simplified version SUIX equently, through a rationai modei
simplification.
Each dummy parts had to be accurately defined in terms of georreuy, inernai properties and material
properties, with a detail level balancing the two conflicting requirements on model size and accuracy. All
the measurement capabilities cumently implemented in the real &mmies had to be reproduced in the
numerical models, as head, chest and pelvis accelerometer, fe:nur, tibia, neck and lumbar spine
forces/moments and fiially chest deflection measurement.
As prescribed by the US regulation FMVSS-208, all the certification tests that are regularly performed and
verified on the physical Hybnd-[11 dummies, or on its parts, had :0 be numerically simulated. For the
detailed version of the dummy model, all the certification tesrs (heat. drop test. knee impact. chest impact
and neck pendulum test) Were fulfilled, except limited situations ( i.e neck extension test) that in any c’me
6
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seemed not to affect global behaviour and accuracy in the full scale val dation tests. The coarse dummy,
which was required to work ordy as a“ loading device and did nor have to idfil the re=gdations requirements
in terms of certification tesu. was actually capable of respecting most oft lem.
From the evaluation of the first dummy validation tests, it clearly appeared thatthe simple fidflrnent of the
certification requirements would not be Suficient to obtti a good corre ation o.n mosr of Pagers in a.
full scale sled test simulation- For that reason addkionaJ experiment tests on dummy se~ents were
carried out in order to further validate the dummy model segments on an mlarged experimental database of
more complex and realistic component tests. The fine version of the dut amy was therefore also vaiidated
with respect to the following supplementary component tests:
—
—
—
—
drop test of a single rib
drop test of ribcage onto rigid rim with different speeds, angle and pot It of impact
dynamic test on pelvis and lumbar spine alone
impact of rigid piate onto the pelvis
belt-pelvis intemction test.
In order to create a large and consistent database of experimental dat i on the Hybrid-III behaviour in
different worl@ng conditions. a variety of sled tests on the complete dun-u IY were c~ied out in such a way
that they represented several possible resmaint systems and crash speeds. Five different con@rations were
examinate~ creating a car interior surrogate representative of a medium car environment:
– rigid seat simplified belt geometry, high velocity (CASE 1)
– rigid seat, s~and~d belt hiSh velocity (CASE ~)
- rigid sea~ standard belt, low velocity (CASE ~)
–– figid seat, s~dmd belt, high ve]bcity witi head impact onto dwhbo~ d (CASE 4)
–. rigid sea< ~belted dummy wirh airbag and [eg impact onto kneebar (2ASE 5).
lri order to remove as many as possible urdmown parameters in the final sled test vaiidatiori of the Hybnd111 model, some, additional tes~ were needed to characterize the component used in the sled test
environment (head impact onto dmhboard, knee impact onto kneehr, ai -bag drop test. and beh static test).
The validation of the numerical models of such components was m mly achieve& with a numerical
experimental correlation marked by a 15 / error limit0
0
33 TASK 3: Eurosid-1 DUMMY MODELLING
The nature of the European nonpative on the side impact has not c1 anged since the beginning of the
project This regulation will come into force on 1998 and will be based o I biomechanicil criteria.
During a full scaIe side impact there is a strong interaction between he sn-ucture, the padding and the
dummy. The understanding of the behaviour of the dummy and the h!teraction with its environment by
using numerical tools e~erimentally validated is still one of the kc!’ of success to satisfi the future
European normative.
The objective of this Task was to develop a Finite Element model of the ElJROSID- 1 dummy (Fi=we 3),
which was requested to be :
1. a ‘detailed model in order to take into account the. complex interactions occuming in a real side impact
context. The measurement sensors used in the real dummy and thy biomechanical criteria had to be
imp lemented into the model.
2. cxpen”mentally fully vaiidated it had to be coherent in presence of the biomecharical and structural
phenomem occurring in the side impact. The series of tests to be performed must reflect the different
situations observed in a fklt scale side impact.
3. numerically robust and smbfe : the model had to be tailored acct)rding to the current and expected
capabilities of the explicit numerical codes used for automotive crash simulations.
7
3.3.1 Technical approach
The nurqerical dummy involves all corporeal segments: Head, Neck Shoulder, Thorax, .%bdomen, Pelvis,
Legs, Arms and outer skin.
Each part of the dummy had to be geomeuically defined with actitte 3D description, and the matetia~
prope~ies had to be correctly modeiled- The ma~enals used in the Ewosid dummy had to be characterized
by using three different approaches:
— some material models, mainly in the pelvis were defined by using tke new constitutive law, results of the
activity of Task 1;
– the most important part of rubber materials in the peIvis, abdomt n and spine were modelled with the
standard material law implemented in the explicit code, taking int J account the results obtained in the
experimental tes~ on material samples;
— a third. group of materiais were modelled with the standard matent.1 law, with the parameters chosen in
such a way that the dummy segments fuifiIl the certification and tlx additional component resrs.
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The measurement sensors currendy used in the real dummy had to b~ reproduced in the numerical model.
The concerned parameters are :
–
–
–
–
–
–
–
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Head acceleration
Rib deflections
Rib accelerations
Thorax accelerations TI ( lS’ thoracic vertebra) and T12 (12ti thora :ic)
Abdomen forces
Sacrurn acceleration
Pubic symphysis force.
The first validation of the model consisted in sitm-dating the certificate on t~sts. These tests (head drop tes~
neck pendulum tei~, shoulder test, thorax certification, Iumbar spine test. abdomen impact test and pelvis
certification) are dynamic tests involving the most important corporea segments which provide corridors of
response to be fi.dfilled by a certified real dummy. In the same way, ‘he behaviour of the numerical model
had to respect these regulations.
Since the corridor of response of the certification tests are quite Wiile and they concern few parameters,
from the beginning of the project it appeared clear that these tesm were not sufficient to constitute a
complete validation of the different dummy segments. A set of addi :ional tests focused on some dummy
components, with specific measurements were performed in order to extend the data and ensure a reliable
and complete validation on the main segmerms of the Eurosid mode. The supplementary tests taken into
account were:
angle drop tests on a singIe rib;
— impact tests on arm and shoulde~
— impact tests on isolated abdomen;
— impact tests on isolated pelvis at different speeds,, angle and point of impact.
These additional tests alIowed to improve in a large range the dynamic behaviour of the dummy part
models, taking into account the influence of impact velocity and the sm.sitivity direction of loading.
An experimental sled test program with a complete dummy had to bc defined in order to establish the data
reference for the global validation of the dummy model. These tests represent realistic side impact loadings
on the dummy and take into account the car environment. Different impact velocities, load directions, side
structure shapes and material paddings were investigated.
The validation of the dummy model towards the experimental sled tests was the last step of the Eurosid- 1
Task. The representative and exhaustive aspects of the tests a.llowe i to establish a consistent validatio~
giving biomechanical riumerical-experimental agreement within 25 M. error limit.
The use of paddings in some experimental sled tests implies that the:/ had to be specified and mode[led. [t
required the development of a numerical model and the characterization of the material propernes. To
succeed in this work it w& considered essentizd that during the validation of foam and rubber models (in
Task 1) the numerical-experimental a&eement showed a 15!A0 error lirrit.
4. R E S U L T S
4.1 Task 1: material modelling
The results achieved by Task 1 can be briefly summarized in the foilow @ points:
— development of a basic knowiedge on foam and rubber behaviot r, relatively to their application in
impact events;
— determination of a quite large Database of experimental data on fo uns and rubbers commordy used in
dties;
. development and, implementation in RADIOSS F.E. explicit code o:’ three new material laws for foanis,
suitable for the simulation of such materials in crash events (NT JA model, LIMS model and Curve
Network approach);
development aiid implementation in RADIOSS F.E. explicit cod{ of two material laws’ for rubbers
(NTUA formula and Ogden modei);
— identification of the material parameters necessary for the modelling of the mosl relevant dummy parts.
I
Due to the objective dit%culties in performing the experimental actit ity, the results of the Task 1 were
transferred to Task 2 and 3 with certain time delay with respect to k itial pianning, so that they could be
effectively utilized oniy partly in the development of the dummy r lodeis. In any case the knowledge
developed within the tlarn.ework of Task 1 will constitwe the basis fi lr further future improvement in the
dummy model performances.
I
1
4.2 Task 2: EIybrid-IU dummy model
The Finite Ele.mem model of Hybrid-HI was obtained in two versi ms, each of them characterized by
different targets, with respect to validation phase and relevant final performances.
t
The Hybrid-HI dummy, “coarse version” (2500 elements), developed :0 serve as a loader for the occupant
restraint system was properly teste~ showing satisfactory performar ces, both in terms of CPU time and
numerical accuracy.
I
The Hybrid-III dummy, “free” version (6500 deformable elements J, developed to be utilized in filly
detailed simulations, was validated against a cycle of sled tests [ rganized into 5 impact cases, by
comparing all the experimental biornechanical outputs with the respel:tive numerical ones, as .suminarized
in the following table.
I
!
CASE 1.
I
CASE 2
1
CASE 3
I
CASE 4
Diagcmal belt load
‘<z Q/o
-i- 5 Q/o
<2 O/.”
<2 o/Q
Lap belt load
-8!Xo
-5
<z
~ 2 0/0
Head acceleration
-8 ‘/o
< 5 0/0
HIC 36
ms
+7%
+ 18.5 Q/.
Chest acceleration
-12 ‘?40
<5
yo”
0/0
+
Q/o
2 5 O/.
+ 23 ~Yo
+ 20 (y”
CASE 5
I
\
-----
+ 20 Q/m
-22
?40
+ 29010
-41
‘Yo
~ 5 0/0
~ 5 0/0
+ 20 0/0
+ 28 %,
I
Femur axial force
---
+ 20 ‘yo
-20 ‘?4
(2d
!
,
I
peak)
-30 ‘A
-12 %
-13 oh
-8’?40
Chest deflection
-20 ‘A
-29 ?40
-23 0/0
-28!4
- 17V0
Pelvis acceleration
-20 ‘?40
- 1 7 ‘h
<10 %
:15 Yo
+ 15 0/0
Note: the percentage here expressed for each variable is based on the con .parison berween the numerical peak
value and the experimental one.
Table 2- Hybrid-HI fme model validation. Synoptic tab[e on numericaI / exFerimemal correlation
For the vet-y majority of the variables, as shown in Fig. 4 and 5, the ac :uracy targets initially planned were
achieved:
●
●
15 ?4 error limit concerning the occupant kinematics
30 ‘/0 error limit concerning the occupant biomechanics
Furthermore, a good agreement was reached for many other significa’ ive outputs. as shown in Fig. 6 for
example for the neck-chest bending moment.
[t is to be remarket too, that a complete set of component valida~ion t ;sts and numerical simulations were
perfonne~ focused to the modelling of ~vo important car interior part i: dashboard and bee-bar. Also for
this phase the initial planned objective (15 % error limit for mm xical-experirnemal agreement) was “
achieved.
I
I
43 Eurosid-1 dummy modeI
1
\
In this cask a 3D deformable F.E. model of the Eurosid-1 dummy was developed and validated. The model,
containing 9000 deformable elements, is a detailed numerical repr{ :sentation of the geomeuy and the
material propernes. All tie .standaid and additional instrumentatiu~s existing in the real dummy are
implemented in the model as well as the biomechanical criteria.
The dummy model is vaiidated at three levels:
1.
>
at level of material propernes
● at level of durnrny segments (thorax, shoulder, abdomen, etc.)
● at level of the global dummy model.
I
The robustness of the model is established in the most cases of 1 Jading. The experirnentahumencal
correlation is summarized in the following table and some output curv x are shown as exampIe in Fi~e 7
for one particular reference test.
●
Test Nb. - Test layout
D943620
D943611
D943608
D943614
D943616
RIB deflection
upper middle lower
RIB Viscous Criterion
upper mi~ ‘die lower
v= 7 ds
50/0/0
0° impact angle
no arm involved
=
v 7 In/s 50/0/0
0° impact angle
arm involved
=
v 5 rn)s 50/0/0
+20° impact angle
no arm
v=5rn/s 50/0/0
-20° impact angle
no arm
‘v=7rn/s ()/50/()
0 ° ,impact angle
no arm
Pubic
Force
Abdomen
Force
12 ?40
11 Yo
11 Yo
6 ‘%
3 Y.
-14 %
---
-18 ?Jo -21 %
-1?40
-21 Yo
3 Yo
4 “/0
-8.5 %
---
‘ 16 %
-6Y0
- 5 %
2 ‘h
-29 “h
1 v.
-8Y0
- 1 9 Vo
---
-6Y.
-10 “A
-4’%
- 9 %
-1: ‘Yo
-7Y0
1 %0
---
3 0/0
14 %
26 ‘/o
5%
12 ‘!40
9 %0
-24 %
- 3 2 “L)
10
D943615
—
=
5 m / s 0/5010
0° impact angte
v
13’70
12 Yo
33 ‘x.
9 ‘Y.
-1 0/0
12940
13 “/0.
lno arm
D943605 { V = 9 mh 0/50/50
11 “/0
8 7.
-t-
—
T
-i–”
I
“1
I
i
I
12 %
1 Yo
-19(0
80 %
2.5 0/0
60 ‘Yo
32 ‘h
5 %0
2%
70 %
10 Y.
-14 %0
38 “h
8 %0
47 “/0
10070
10 %
-1 “!0
45 0/0
1
17 9’!0 17 “/0
6 ‘?4.
7 Y.
T30 arm
}
D952S03 I V = 7 rII/S 50/0/0
deformable seaf
-14 % 8 ?40
17 Y.
arm involved
D952806 v = 7 m/s 0/50/50
padding on impact.
1 %
1 Y.
-3 “/0 3 Q/o
arm involved
D952S07 v = 7 U-JS ()/50/50
srd. car posi [i on
13 Q/o 11 0/0
21 9’0 20 0?0
arm involved
~—
Note: the percentage here expressed for ea( injury indicator is norrmlii ed I
tolerance level
Table 3- Eurosid-I model valida~ion. Synoptic table on numerical / expen nental
I
‘m
h respect to the respective injury
correlation.
The evaluation of the dummy model showed that the quality level of the numerical results is not
homogeneous from a segment to another one.
The thorax segment reached the wished quali~ within 25 ‘X. for the bi ]mechanical criteria.
The peIvis model is cumently the most critical dummy part wit!! nur ~erical-experimental agreement above
25 ‘Y. for some of the biomechanichal criteria. This situation is probably due to a criticity of-m ateri al
coupling effect between the pelvis foam and the ruboer skin. Thi; situation affects also the abdomen
perform~ces in the cases where it is not primarily impacte~ due to an unrealistic loading distribution
among the body segments involved by’ the impact. The points to be improved have been determined with .
accuracy and source of improvements exists in the complete expIoitat ion of Ewosid materkd data produced
by Task 1.
5. CONCLUS1ONS
The project took consistency around the need of giving new in} estimation instruments to automotive
calculation and design departments in increasing the levels of occupalt protection during impact.
In this context the finite element objects which have been developed set a fixed point in human surrogates
simulation and impact studying of foam-like materials.
Concerning Hybrid-III, the finite element frontal impact dummy dew:loped in two versions, the majority of
initialIy planned objectives have been achieved.
The “coarse version” of the model, composed by 2500 deformable elements, ~marantees a satisfactory
kinematic behaviour, validated against a specific experimental prog~atn. Three kinematic indicators (hea&
thorax and pelvis Ievels) have been monitonzed for five test cases, thich indicate an error with respect to
test results limited to 15 ‘Yo in four of these test cases.
The “free version”, composed of 6500 deformable elements, offess the same performance in kinematic
terms, added to the capability to estimate the injwy level risk !hrough the so caIled %iomechanical
outputs”: in 38 of the total of 40 indicators (for all the. five tmt cases) the numerical-experimental
agreement is below the limit of 30 Y., which still has to be considered a significative mkget for such a kind
of numerical investigation.
For as regards Eurosid- 1 dummy model (for side “mpact) the final p xformances shown J global behaviour
matching with most of the targets initially set, meaning this a satisfa :Iory functioning of the whole dummy,
11
and the very major part of the biomechanicai indicators giving ‘eliable results with respect to the
experimental data. However it is to be mentioned that the Eurosid- 1 c.~y is requested to be utilized in
harder working conditions if compared to Hybrid-HI case, because of the direct loading acting on the
dummy applied by the moving intruding suucturai part of the vehicle. “his particular situation cause, when
using a corresponding numericaI model, a decreasing in quality and rt:liabilhy of results. In synthesis, for
Eurosid- 1 dummy model still some criticities exist in terms of reprodu(:ing the behaviour of the peIvis part,
where the biomeckm.ical shown response is above the 25’ZO error ~irnit .watanteed by the other body
segments. The possible actions in order to f~ these problems have been already focused and result in a
reasonable amount of activity worthwhile to be carried on by a potentizl extension of the research.
I
The development of new constituhve modeis for foams and rubbe -s allowed to overcome the border
represented by the metallic matenais, whose cons~itutive laws have bec n utilized for a long time to simulate
also crushing of foam-like materiais, just adapting some pam.rneter; to take care of the general basic
assumptions originally tailored around materials like steel and similar.
A considerable and consistent Database containing the complete outt :ome of the e.xperirnentai activity is
currently avaiIabIe, thus allowing to refer to a valid characterization] [ pkitfonn in order to complete the
currenr l-D formulation of the developed models, to be necessarily e> .tendied to a 3-D one. This phase is
now possible. thanks also to the basic knowiedge developed in the sp~ :cific fiel~ mostly deriving from the
fruitful cooperation between industrial and academical scientific envirc nments.
I
I
6. ACKNOWLEDGEMENTS
I
The research activity performed during this project has been allowed by the support of the EUROPEAN
COMMUNITY under the Brite-Euram project. organization, which ed to the signature of the Contract
n.BRE2-CT94-0540 (D UMOCS) related to project n.13E-7 145.
I
/
i
I
Task 1
1
FOAM AND RUBBER
MODELLING
* Modelling at low
Task 2
DEVELOPMENT
OFNIJMERICAL
HYBRIDI!IMODEL
I
1
strain rates
‘
* Dummy part modelling
according to
certification
tests
●
Material modelling
Car interior modelling
validation of the
numerical procedure
according to sied tests
* Padding modelling
*
1“*
1-
Experimental sled
Deliverables:
* Validation of dummy
according to
certification
tests
I
* Validation of dummy
*
* Dummy part modelling
+’
and dummy assembly
* lrnplementation of
material law in
explicit code
●
*
I
DEVELOPMENT .
OF NUMERICAL
EUROSID MODEL
* Modelling at high
strain rates
and dummy assembly ~
* Validation of dummy
Task 3
r
Validation of dummy.
according to sled tests
Experimental sied
tests
..-,
+
v
E%EIEHZIEEEI
Milestones:
1) Results of experimental tests at low and high strain rates (:nonth 13)
2) Results of experimental sled tests on HYBRID iii and EUR 3SID
(month 19)
3) New materiai iaw implemented in expiicit code (month 19)
. .
Figure 1- Project flow chart
I
Figure 2- Eiybrid-IU fine model. Compiete and expioded view.
Figure 3- Eurosid- 1 model. Complete and exploded view
fim mcdd
H@rid–HI
validation
ibXWZl!iCS
500
400
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‘
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Figure 4- Hybrid-UI fine model wdidation. Sle(i test CASE 2
Numerical / experimental correlation on hlematics
120
J ----~
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Figure 5- Hybrid-111 fine model
Sled test CASE 2
Numerical / expetiental corre~ation on bio] nechanics
160
Hylrid–III@e model vdidatbt
Neck–
momnt
chm$.benditg
SW [Nm].
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Figure 6- Hybrid-KII @e model valickition
Neck / chest bending moment
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50
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acceleration - lateral cnmpmwnt
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[
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40
35
30
25
20
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Figure 7- Eurosid-1 validation. Sled test on defornw,ble fixun cushion
Numerical/ experimental correlatioi(
I
40
1
50
60