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1/2AnwenderberichteLS-DYNA Case Study
CADFEM GmbH INFOPLANER 1/2005
32
Bus Rollover Analysis
with LS-DYNA
This project, initiated by the TechNet Alliancemembers FIGES and
CADFEM, is a perfect
example for a cost-effective solution by a vir-tual company in a
network. FIGES acted as focus
point to the customer and managed the project.CADFEM trained the
customer in using LS-DYNA,
supervised the project and selected the certifica-tion agency TV
Sddeutschland. Lasso providedconsultation in proper application of
the ECEregulation.
TEMSA A.S., an important bus and coach manufacturer from
TURKEY, is currently embarking on high-technology CAE pro-jects
in cooperation with well known European CAE
consultingcompanies.
TEMSAs production facilities are located in the city of Adana
in
Turkey, and set out over a surface area of 400.000 square
meters,
including 58.500 square meters of covered areas. TEMSAs
annual
output target is 1.250 coaches, 1.500 midi-buses and 13.000
trucks. TEMSA offers new markets and customers the skills of
its
qualified workforce and advantageously low production costs.
As one of the largest, independent bus and coach producers
in
the world, with the advent of globalization TEMSA inevitably
saw
the need to integrate its product line with some of the worlds
lea-
ding component manufacturers. TEMSA collaborates with highly
esteemed European consultants in an effort to further expand
its
horizons through the continuous development and innovation
of
its range of vehicles.
If its aim is to offer coach-manufacturing solutions tailored to
cli-
ents specific needs, a manufacturing company must have a
ver-
satile, high quality production capability, as well as
state-of-the-art
technology and in-depth design experience. These are TEMSAs
main achievements. TEMSA is currently determined
to focus on achieving customer satisfaction, and
continue along its path of success by confidently
improving, innovating and developing its vehicles.
Owing to these ambitious goals, TEMSA began
using CAE technologies for its product develop-ment activities
making investments in software,
hardware and human resources.
In addition to standard Finite Element Analysis (FEA)
applications
using CAE tools such as ANSYS, TEMSA drew up and carried out
a
project in cooperation with CADFEM GmbH and TV Sddeutsch-
land in Germany which aimed to perform regulatory bus
rollover
analyses.
A rollover event is one of the most crucial hazards for the
safetyof passengers and bus drivers. In past years it was observed
that
the deforming body structure seriously threatened passengers
lives. Today, European regulation ECE R66 is in force to
prevent
the catastrophic consequences of such rollover accidents
from
occurring and thereby ensuring passenger safety for buses
and
coaches. According to said regulations, certification can be
obtai-
ned either by full-scale vehicle testing, or by numerical
simulation.
The bending deformation enables scientists to investigate
whe-
ther there is any intrusion in the passenger survival space
(residual
space) along the entire vehicle.
The non-linear explicit dynamics code LS-DYNA (solver) and
ANSA software (crash FEA pre-processor) were purchased to
usethroughout the bus rollover analysis project. Based on a
compre-
hensive agreement made between CADFEM GmbH, Figes Ltd.
and TEMSA which included software sales, on-the-job
training,
consultancy, testing and certification, two FEA engineers
from
TEMSA were assigned to start on-the-job training under the
close supervision of highly skilled staff in the CADFEM GmbH
premises in Germany and perform rollover analyses on the
TOURMALIN 12.8 vehicle.
During the first stage, the verification of the calculation
pro-cedure following regulation ECE R66 was performed. Two
separate specimens (breast knot + roof edge knot extractedfrom
the vehicle) were prepared and sent to TV Automotivefor
experimental investigations. These parts were subjected tospecific
boundary conditions and quasi-static loads at TVstesting facility.
The same test scenarios were simulated by usingLS-DYNA.
Force-deflection curves both for the experiment andsimulation were
compared, and it was observed that there wasa good correlation
between experiment and simulation. Theverification by calculation
is a compulsory requirement of theregulation, as it is the
technical services responsibility (TV Sd-deutschland in this case)
to verify the assumptions used in thenumerical analysis.
The FEA model of the full vehicle comprised 589.250 first
order
explicit shell elements, 338 beam elements and 114.605 mass
elements. Element length was assigned as 10 mm in both
criti-
cal regions (a verified assumption resulting from the
verification
of calculation) and up to 40 mm was used for those under the
floor (lower structure-chassis). The number of elements per
pro-
Result plots of rollover analysis of entire bus.
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CADFEM GmbH INFOPLANER 1/2005
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file width was at least 3 for the upper structure; the number
of
elements per width was 4 for sidewall pillars which are
significant
for rollover deformation.
Tension tests were carried out on several specimens at
TVSddeutschland facilities in order to obtain material data.
Thetrue stress-strain curves were obtained and imposed in
LS-DYNAaccordingly. The material model for the deformable structure
inLS-DYNA is the so-called MAT Type 24, Piecewise Linear Iso-
tropic Plasticity model. This is an elastic model made of
plasticwhich applies the Youngs Modulus if the stress is lower
thanthe yield stress, and measured stress-strain-curves if the
stress isgreater than the yield stress. Rigid parts (engine, gear
box, fueltank, axles, etc) are modeled using the so-called Rigid
Material,MAT Type 20. MAT Type 9, Null Material was used to
definethe survival space (residual space).
Upon completion of the mesh generation of the bare
structure,masses were imposed according to a structured
methodology.Firstly, a list of TOURMALIN Vehicle masses was
prepared. Theengine, gearbox and fuel tank were roughly 3D modeled
as
rigid parts. Inertias were calculated analytically, and mass
andinertia were imposed on a representative node (on the
appro-ximate center of gravity points for the relevant part) of
theseparts. The axles were modeled using rigid truss elements
andthe mass and inertias imposed using the same method. Thefixed
masses were imposed by using mass elements. The dis-tributed masses
were imposed by changing the density of therelated region.The
Center of Gravity (CoG) of the vehicle was measured by
test in TEMSA. The measured values were in a good agreement
with the ones coming from the FEA model. To exactly match
the
measured and calculated CoGs, the CoGs of engine, gearbox
and
the axles were fine tuned in the FEA model.
When it came to the definition of survival space, the
statementin the regulation ECE R66 was used to form the basis of
thesurvival space model. It was introduced 500 mm above thefloor,
under the passengers feet, 300 mm away from the insidesurface of
the side of the vehicle, throughout the entire vehicle(trim lengths
were also considered and added to these values).The model of the
survival space consists in rigid beam frames ineach section (10
sections), rigidly mounted in the hard regionunder the floor. There
is no stiffness connection between theserigid beam frames as these
shell elements are modeled usingNull material, for visual purposes
only.
At the final stage, non-linear explicit dynamic solutions were
per-
formed in LS-DYNA software.
The total energy according to the formula indicated in the
ECE
R66 regulation was as follows:
E*= 0.75 Mgh (Nm) was applied to the structure by a
rotational
velocity to all the parts of the vehicle. h is the vertical
distance
between the vehicle CoG at free fall position, and the vehicle
CoG
which is kinematically rotated up to the ground contact
position.
The hardware resources utilized were 2 PCs running with
Linux
Suse O/S for the generation of FE mesh in ANSA Software, and
a
LINUX cluster with 6 XEON processors (to perform the
solutions)located in CADFEM GmbHs premises in Grafing near
Munich.
The multiple analyses were carried out until the final design
which
met the requirements of the ECE R66 regulation was
eventually
obtained. The entire project was supervised by TV and
certifi-
cation granted to TEMSAs TOURMALIN 12.8 following a final
meeting in Germany.
The simulation project was initiated in CADFEM GmbH subsi-
diaries in Chemnitz and Leinfelden, Germany and continued at
TEMSA A.S. in Adana, Turkey. The final stage, and the
simulations
in LS DYNA were performed in Chemnitz. Both CADFEM GmbHand TEMSA
A.S. were consulted by LASSO Ingenieurgesellschaft
mbH and TV Sddeutschland during the various stages of the
project.
Finally, very special thanks go to the CADFEM GmbH staff,
espe-
cially Dr. Ulrich Stelzmann for his patience, dedication,
expertise,
and effort during the entire duration of the project. Also
many
special thanks to Dr. Ulrich Hindenlang of LASSO and Mr.
Franz
Bartl of TV Sddeutschland for their precious, constructive
coo-
peration.
AuthorsKadir Elitok, FEA Engineer TEMSA A.S.Fatih Han Avci, FEA
Engineer TEMSA A.S.Contacts
TEMSA A.S.www.temsa.com.tr
Crash Analysis with LS-DYNADr. Ulrich Stelzmann, CADFEM GmbH
E-Mail: [email protected]
LS-DYNA (international sites)www.lstc.com .
www.lsdyna-portal.com
Figes (LS-DYNA distributor in Turkey)www.figes.com.tr
TV Sddeutschlandwww.tuev-sued.de
Testing and simulation results of a roof component show high
correlation.
