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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

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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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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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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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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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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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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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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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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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