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Railroad passenger car collision analysis and
modifications for improved crashworthinessCengiz Baykasolu
a, Emin Snblolu
a, Sureyya E. Bozda
a, Fatih Aruk
a, Tuncer Topr
a& Ata Mugan
a
aFaculty of Mechanical Engineering, Istanbul Technical University, Istanbul, Turkey
To cite this article: Cengiz Baykasolu , Emin Snblolu , Sureyya E. Bozda , Fatih Aruk , Tuncer Toprak & Ata Mugan (2011)
Railroad passenger car collision analysis and modifications for improved crashworthiness, International Journal ofCrashworthiness, 16:3, 319-329, DOI: 10.1080/13588265.2011.566475
To link to this article: http://dx.doi.org/10.1080/13588265.2011.566475
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International Journal of Crashworthiness
Vol. 16, No. 3, June 2011, 319329
Railroad passenger car collision analysis and modifications for improved crashworthiness
Cengiz Baykasoglu, Emin Sunbuloglu, Sureyya E. Bozdag, Fatih Aruk, Tuncer Toprak and Ata Mugan
Faculty of Mechanical Engineering, Istanbul Technical University, Istanbul, Turkey
(Received 14 November 2010; final version received 23 February 2010)
In this study, crashworthiness assessment and suggestions for the modification of a railroad passenger car are presented. Toassess the crashworthiness, collision of the railroad passenger car onto a rigid wall is simulated by using finite element (FE)methods. A full-length, detailed passenger car model is used in FE analyses. In order to validate the FE model, simulationresults obtained for different types of static loading conditions in compliance with various scenarios defined in UIC CODEOR 577 are compared with experimental measurements before running collision analyses of the railroad passenger car.The good agreement between static tests and FE analyses results indicates that the FE model accurately represents the realstructure. Following the FE model validation, analysis of the collision behaviour of the railroad passenger car consists oftwo stages. In the first stage, the crashworthiness of the initial concept design of the railroad passenger car is analysed. Itwas observed that local buckling takes place at various points, which prevents the desired progressive damage behaviour in
the railroad car body. Having revealed the structural weaknesses, the initial design was modified and simulated again underthe same conditions. Using size optimisation, thickness of some sheet metal components is changed in order to obtain theintended progressive damage behaviour. As a resultof the modifications, the passenger car design with bettercrashworthinessproperties was obtained, in which large plastic deformations occur around the collision side of the car while mainly elasticdeformations occur in the cars body away from the bumpers.
Keywords: railroad vehicle collision; crash simulation; crashworthiness; finite element methods
Introduction
When a high speed train crash occurs, optimum occupant
protection is very important to prevent loss of life. It was
observed in many crash accidents that the traditional struc-
tural design approach, which satisfies the design require-
ments only for static loading conditions, does not provide
optimum occupant protection; thus, considerable research
has focused on structural crashworthiness of train design
in the last two decades. The most popular occupant pro-
tection approach is passive protection. According to this
approach, when a collision occurs, a passenger car deforms
and collapses in such a controlled manner that large plastic
deformations occur around the collision side of the pas-
senger car; mainly, elastic deformations occur in the other
regions and impact energy is absorbed safely outside of
passengers living regions [6].
Computational methods and validation of their results
by comparisons with experimental measurements are a
commonly used approach in crashworthiness studies of rail-road vehicles. There are some studies focusing on analysis
and improving crashworthiness capacity of railroad vehi-
cles [2,1113], crashworthiness capacity determination of
existing railroad vehicle [3] and the crashworthy design of
new railroad vehicles [4,5]. Some standards of structural
design and requirement can be found in studies by Sutton
Corresponding author. Email: [email protected]
[7] and Tyrell [8]. As experimental analyses of crashwor-
thiness are very costly in terms of time, funding and equip-
ment resources, they cannot be used at all stages of design,
which make the computational methods as important tools
in crashworthiness studies in the present times. Although
computational simulations do not have aforementioned dis-
advantages of experimental methods, to obtain realistic re-sults, they must reflect the real vehicle behaviour and crash
conditions accurately, imposing the need for any numerical
model to be verified by experiments.
Most of the studies on the crash behaviour of railroad
vehicles simulate a collision with a rigid wall. This is a
simple and ideal model to reveal the general characteristics
of impact behaviour of a full-scale car with impact test [9]
and/or computational simulations [2,12,13]. Different types
of crash tests [10] and simulations [11] can also be found
in literature.
Crash analyses of a railroad passenger car
FE model
A railroad passenger car called N13-type used by Turk-
ish State Railways is examined in this study. It consists of
two sidewalls, one floor, roof and end-walls. There are 22
windows on the two sidewalls. Most of the car body is made
of beams and shells. The passenger car has a maximum
ISSN: 1358-8265 print / ISSN: 1754-2111 online
C 2011 Taylor & Francis
DOI: 10.1080/13588265.2011.566475
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320 C. Baykasoglu et al.
Figure 1. Geometric model of the passenger car.
Figure 2. FE model of the passenger car.
design speed of 160 km/h. End regions of the car contain
entrance doors, corridors, water supplies, toilets and elec-
tric distribution cupboards. This layout enables the use of
these areas as energy absorption regions far away from the
main occupant area. The middle part of the car is the cabin,
from whichlargedeformations are to be kept away. Therail-
road passenger car model used in this study has a width of
approximately 2800 mm, length of 26,000 mm and height
of 3300 mm. The model has approximately 2000 different
components and 65,000 surfaces. The geometric car model
used in this study is shown in Figure 1.
The original passenger car body is made of five differ-
ent steel materials such as stainless steel, St 12, Stw 24,
St 37 and St 52. The weight of the passenger car is ap-
proximately 12.5 tons except for bogies, passengers and
other equipments. Bogies and rail tracks have not been
modelled explicitly, but corresponding point masses and
boundary conditions were applied to simulate the effect
of bogies and auxiliary equipments. The total car tare
weight is approximately 50 tons, including bogies and other
equipments.
The complete model of the passenger car contains ap-
proximately 1,650,000 elements. Approximately 95% of the
elements are linear quadrilateral shell elements, 3% of the
elements are rigid connection elements to represent weld-
ings and the rest are linear triangular shell elements andlinear 3D solid elements. A mesh view of the complete FE
model of the vehicle structure used in this study is shown
in Figure 2, and the FE model of the end region of the
passenger car is shown in Figure 3. In order to increase the
visibility, some shell elements were hidden on the sidewalls,
roof and floor areas.
To investigate the damage progress in the passenger
car, the crash speeds are chosen to be high enough to
yield the collapse of the whole vehicle end areas. Even
Figure 3. FE model of the end part of the passenger car.
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International Journal of Crashworthiness 321
Figure 4. Passenger car crash model and the rigid wall.
though various crash speeds are used in crash simulations,
mainly the results obtained for 90 km/h are examined in
this paper because of limited space. The sample crash case
is the scenario based on the passenger car crashing onto
a rigid wall with a speed of 90 km/h (25 m/s) as shown
in Figure 4. The duration of collision is selected to be 100
ms in simulations in which the software Abaqus/Explicitis used. In order to increase the stable time increment, mass
scaling method in Abaqus was applied to the model. It was
controlled by changing the mass scaling values such that
the total mass due to artificial mass scaling was not altered
more than 0.3% after trial runs. The simulation procedure
used in all collision analyses is the explicit method
implemented in Abaqus/Explicit [1] on a computer having
eight CPUs, 64 GB RAM and 2 TB hardisk capacity.
The coupler system treatment is an important issue in
the assessment of the crashworthiness of railroad vehicles,
asit isthe firstcomponent tocontact the rigid wall ina crash,
and absorbs a certain amount of impact energy. As our main
concern was to investigate the worst case to which a railroad
car is subjected, and the crashworthiness of the passenger
car would be positively affected by the the coupler system,
the coupler system is not included in the model.
The passenger car underframe is the most importantcomponent for crash energy dissipation that can be divided
into two zones by considering the crash characteristics. Fig-
ure 5 shows the end of the underfloor structure of the pas-
senger car. In this figure, the first zone starts at the end
wall and finishes 450 mm away from the end wall. The
second zone is the continuing region of the first zone as
shown in Figure 5. The first zone is the first contact re-
gion and substantially less strong than the second zone,
as most of the components are made of thin shells in this
region.
Figure 5. Bottom end structure of the passenger car.
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322 C. Baykasoglu et al.
Figure 6. Experimental setup (a) and some strain gauges (b).
Validation of the FE model by comparisons with
static tests
To validate the FE model, static FE simulation studies are
completed according to the International Standard UIC
CODE OR 577. The same tests are also been applied to
a prototype passenger car located at TUVASAS (Turkish
Wagon Industry Inc.) in Adapazari, Turkey. A total of 30
strain gauge rosettes were applied to a quarter of the car
body to capture the plane-stress behaviour of the structure,
and the simulationresults were compared withexperimental
measurements. Figure 6 shows the experimental car setup
and some strain gauges positions. The passenger car is as-
sumed to be empty in FE analyses. In addition, bogies are
not modelled explicitly, but their weights are imposed as
lumped masses at the points where the passenger car body
and the bogies are connected to. Figure 7 shows the three
experimental loading cases. Figure 8 shows the compar-
isons of the measurements with FE stress results obtained
for a symmetrical compression force of 200 tons at the
strain gauge points. Figure 9 shows the comparisons for the
measurements obtained for a tensile force of 150 tons, and
Figure 10 shows the experimental measurements and FE
results obtained for a cross-compression force of 50 tones
at various strain gauge points. In conclusion, the results of
FE model were observed to be in good agreement with ex-perimental strain gauge measurements (in brief, 27 gauge
locations demonstrate less than 10% error in von Mises
stress values).
Crash progress in the passenger car body
Figure 11 shows the crash progress in the passenger car
structure for eight different time instants. Only the end
region of the passenger car structure is shown in this figure
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International Journal of Crashworthiness 323
Figure 7. Three loading cases: (a) Symmetrical compression force of 200 tons, (b) tensile force of 150 tons, (c) cross-compression forceof 50 tons.
for clarity. It can be seen in Figure 11 that the deformation
of the initial concept passenger car structure does not fol-
low the desired progressive damage form; zone 1 collapsedfully at a time instant of 18 ms, then plastic deformation
started in zone 2 and undesired local buckling occurs in
the cabin area. At 100 ms, the end area of the passenger car
fully collapsedand plastic deformation occurred in thelocal
buckling areas. Thus, structural modifications are necessary
to prevent this local buckling, achieve the desired progres-
sive deformation form and enhance crashworthiness.
Figure 12 shows the relationship between the reaction
force and time. The progress of the collision force can be
divided into two phases. In the first phase, taking place in
the first 18 ms, it can be seen that the maximum value of
the collision force looks like a pulse when the passenger
car first comes into contact with the rigid wall. Althoughthe coupler system is not included in the model, zone 1
(which is the weakest area of the passenger car) behaves
like the coupler system and reduces the peak value of the
first contact force. In this phase, the reaction forces are in
the range of 0.82.8 MN except for the impulses in the
beginning of the crash zone 1. In the next phase between18 and 100 ms time interval, when deformation starts at
the first support beams in zone 2, a high impulse force ap-
pears at the time instant of 18 ms due to the first support
beam deformation. At the time instant of 22 ms, another
peak in collision force appears again due to the deforma-
tion of second support beams. During the time interval of
22100 ms, the reaction forces are in the range of 1.03.1
MN except for the impulses in the beginning of the crash
zone 2.
Figure 13 shows the history of the crash energy
absorption during crash simulation at the speed of 90
km/h. After the first deformation phase (from 0 to 18 ms),
variation of the absorption energy shows an almost lineartrend in time. Thus, it can be concluded that although some
local bucklings occur in the cabin areas shown in Figure 11,
collision energy absorption continues in a stable fashion
Figure 8. Results of symmetric compression force of 200 tons.
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324 C. Baykasoglu et al.
Figure 9. Results of tensile force of 150 tons. (Gauge number 30 is not shown due to scale; its test measurement is 516 MPa and FEanalysis result is 571 MPa.)
and the passenger car end structure absorbs a considerableamount of crash energy. Over the total 100 ms period, total
collision energy of 7.4 MJ is absorbed by the car body.
About 16% of this energy is absorbed by zone 1.
Figure 14 shows the time history of the longitudinal
displacement of the two nodes, with labels 643516 and
783617, which are located on the borders of front and rear
cabin areas, respectively. The displacement at node 783617
indicatesthe deformation of thepassenger carend structure.
The considerable difference between the displacements of
these two nodes shows that large amount of plastic defor-
mation occurs in the passenger cabin. It can be seen in
Figure 11 that the side sill buckling causes this difference.
Elastic deformation of the cabin is observed in the first 20
ms, but after this time interval, plastic deformation starts
in the cabin due to side sill buckling. At the time instant of
100 ms, the difference between displacements of the two
nodes is about 250 mm.
It is concluded that the passenger car end structure ab-sorbs a certain amount of collision energy in contact with
a rigid wall, but the desired progressive deformation form
is not observed due to the plastic deformation in the pas-
senger cabin. Thus, modifications are needed to prevent
plastic deformation in the cabin to ensure optimal occupant
protection.
Structural weak points and crashworthiness
enhancement
It is already observed that the side sill buckling occurs
during the crash and structural improvement is needed tostabilise the process. The side sills shown in Figure 15 are
long and thin components in the passenger car. So, they can
be easily bent in the lateral plane. Several support beam
and side sill thickness values are taken into consideration
in order to adjustthe relative stiffness of differentunderfloor
Figure 10. Results of cross-compression force of 50 tons.
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International Journal of Crashworthiness 325
Figure 11. Crash deformation progress in the initial concept passenger car at 90 km/h.
zones, enhance the structural stability of zone 2 and avoid
lateral bending of the side sill.
Subsequently, collision of the modified railroad passen-
ger car onto a rigid wall is simulated and the results of the
modified and original structures are compared. In Figure
16, the modified passenger car crashes into a rigid wall at
an initial speed of 90 km/h. It is concluded from Figure 16
that the end structure of the passenger car undergoes pro-
gressive deformation, and the problems that appeared in the
original passenger car body were overcome as a result of
the modifications. Desired large plastic deformation occurs
at the end region of the passenger car and small elastic de-
formation occurs in the passenger cabin. Zone 1 collapses
fully at the time instant of 18 ms (similar to that of the orig-
inal model), and then zone 2 undergoes the deformation of
about 2200 mm at 100 ms.
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326 C. Baykasoglu et al.
Figure 12. Collision force versus time.
Figure 17 shows the relationship between the reaction
force and time for the modified car crashing at 90 km/h.
The progress of the crash force is similar to that of the
original passenger car. Reaction force increases and energy
absorption capability of the end structure is enhanced due
to structural modifications. No weakness or deficiency is
observed in the modified passenger car.
Figure 18 shows the energy absorbed by both the mod-
ified and original passenger cars. Over the total 100 ms
Figure 13. Collision energy absorbed by the passenger car struc-ture.
Figure 14. Displacement of the two reference nodes located atthe two ends of passenger cabin.
period, the modified passenger car absorbed a total energy
of 8.35 MJ, which is 13% more than that of the original pas-
senger car. Similar to the original case, 1.2 MJ of energy is
absorbed by zone 1 (from 0 to 18 ms). It can be deduced
from Figure 18 that the energy absorption of the modified
passenger car structure shows a stable trend similar to that
of the original passenger car body.
Figure 19 shows the displacement history of thelongitu-
dinal displacements of the two reference nodes of the mod-
ified car structure, with labels 643516 and 783617, whichare located on the front and rear of the cabin, respectively.
In Figure 19, it can be seen that there is no considerable rel-
ative displacement between node 643516 and node 783617.
The displacement at node 783617 indicatesthe deformation
of the passenger car end structure and it is about 2200 mm.
On the basis of these observations, it is concluded that the
cabin has undergone only elastic deformations while the
passenger car end area collapsed progressively.
Figure 15. View of the side sill.
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International Journal of Crashworthiness 327
Figure 16. Crash deformation progress of the end of the modified passenger car at 90 km/h.
Figure17. Collisionforceversus time forthe modified passengercar.
Figure 18. Collision energy absorbed by the modified and origi-nal passenger car structures.
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328 C. Baykasoglu et al.
Figure 19. Displacements of two reference nodes of the modified passenger car.
Conclusion
The energy absorption capability of the full-scale originaland modified railroad passenger cars is examined during a
crash into a wall. This is evaluated by simulating the crash
of the railroad car onto a rigid wall at 90 km/h. It was shown
that the original passenger car structure absorbs the colli-
sion energy in a stable trend, but the deformation of the
car body does not follow the desired progressive form and
local buckling occurs. These undesired deformation char-
acteristics occur due to the side sill buckling and too stiff
behaviour of zone 2 components, that is, support beams.
Side sill buckling causes plastic deformation of the passen-
ger cabin region and destroys the stability of the structure.
In addition, excessively stiff components do not deform in
the desired manner, which in turn transmits the crash forceinto the interior regions and prevents the structural stability
as well. In order to improve the progressive deformation
feature and enhance the energy absorption ability of the
car structure, the thickness values of the side sill and var-
ious zone 2 components were modified to adjust relative
stiffness of different underfloor regions. As a result of the
size optimisation of the thickness values of these compo-
nents, the plastic deformation of the cabin is prevented and
desired progressive deformation of the passenger car end
regions is satisfied. The modified passenger car absorbs
about 13% more energy than that of the original passengercar structure.
In these analyses, only rigid wall crash scenarios were
considered. This is the simplest and most ideal crash sce-
nario,but it is very usefulto obtaingeneral characteristicsof
crash behaviour of railroad vehicles. In future, crash study
of two trains can be completed on the basis of the models
presented in this paper.
Acknowledgements
The authors would like to thank Dr. Erdal Aba, Orhan Aydemir,Yusuf Aldemir,TanzerOzturk,Cemil Uslu, Gokhan Ylmaz,TanerSaruhani and Halil Ersoy from Turkish Wagon Industry (TU-VASAS). This research is supported by The Scientific and Tech-nologicalResearch Council of Turkey (TUBITAK) under the grantnumber 105G123.
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