an investigation into structural failures of chinese high-speed trains

Engineering Failure Analysis 13 (2006) 427–441

www.elsevier.com/locate/engfailanal

An investigation into structural failures of Chinesehigh-speed trains

Weihua Zhang *, Pingbo Wu, Xuejie Wu, Jing Zeng

State Key Laboratory of Traction Power, Southwest Jiaotong University, Chengdu 610031, Sichuan, PR China

Received 12 July 2004; accepted 26 December 2004

Available online 7 April 2005

Abstract

This paper focuses on the structural failures of various high-speed trains in China. The reasons for the structural

failures of the trains are analyzed based on their design and service condition. Based on examples considered in the

present paper, an optimization design method and a reasonable structure are put forward. For the motor car of the

high speed train ‘‘Blue Arrow’’ dynamic stresses in service are investigated through field tests and theory analysis.

According to the dynamic stress obtained by measurement on site, some results to evaluate service life are obtained.

� 2005 Elsevier Ltd. All rights reserved.

Keywords: Structure; Failure; Stress; Bogie; High-speed train

1. Introduction

In China, railways are a major means of transportation for goods and passengers. Now the total of rail-

way lines is more than 70,000 km. In the next 15 years, 30,000 km of new railway lines will be constructed.

The speed of trains was very slow 10 years ago, about 50–70 km/h. From the last decade, a strategy to raisetrain speed was put forward by Chinese Railway Ministry. From 1997 to now, the service speed of passen-

ger trains in the main lines increases from about 60 to 150 km/h. On some special passenger transportation

lines, the train speed reaches 200 km/h. During the last few years, a prototype of EMU high-speed train was

developed. The maximum field test speed of the high-speed train reaches 321.5 km/h. But with an increase

of train speed, problems of structure reliability become very important in the running safety of the trains.

1350-6307/$ - see front matter � 2005 Elsevier Ltd. All rights reserved.

doi:10.1016/j.engfailanal.2004.12.037

* Corresponding author. Tel.: +86 28 87601068; fax: +86 28 87600868.

E-mail address: [email protected] (W. Zhang).

mailto:[email protected]

428 W. Zhang et al. / Engineering Failure Analysis 13 (2006) 427–441

The main structure failures of the trains include traction rod breaking, bogie frame cracks and suspender

disconnecting. These problems menace the service safety of Chinese high-speed trains very much now.

2. Review of structure failure

There are 35 manufacturers of railway vehicles in China. About 10 dominant manufacturers of own the

right to design new vehicles. At the beginning of the last decade, a strategy to increase train speed was put

forward by Chinese Railway Ministry. The aim of speed is 160 km/h, which is called a quasi-high speed. In

the first stage, three types of passenger cars, two types of locomotives, and one type of freight car were

developed and put into service at quasi-high speed. But up to now, the manufacturing of most of quasi-high

speed vehicles stopped because too many structure failures happened on those vehicles, which affected the

running safety. Also some serious accidents occurred due to structure failure, such as derailment, car-bodyfalling on the track and several kilometers of track destroyed. The structure failure phenomenon of bogies

and other main parts in speed-up trains are described as follows.

2.1. Passenger car bogie 209HS

The bogie 209HS was especially developed for speed-up passenger cars. Its design speed is 200 km/h.

The bogie adopts a conventional technique with swaying bolster and suspender, as shown in Fig. 1. The

car-body is supported by air springs via bolsters and the air spring supported by suspenders. The sec-ondary suspension has air springs and suspenders in series. Such a structure has a quite low stiffness of

secondary suspension in lateral direction and has good dynamic behavior. It has been widely used on

the speed-up passenger cars at the beginning of raising speed. In order to ensure the high reliability of

bogie frames in service, the strength of its frame was tested [1] and calculated [2] in the course of the

bogie study. But the bogies have been put into service two years later, structure failures have happened

very frequently. First, the linking rod which links the suspenders of the two sides is broken, after that

cracks appeared in the suspenders. Finally, cracks occurred in the pedestal of the suspender. Since the

large car-body weight is supported by the suspenders, the structure failure occurring in the suspendersaffects service safety directly. So this bogie is forbidden to be manufactured after it has been used for

two years.

2.2. Passenger car bogie CW160

The bogie CW160 was developed for the quasi-high speed passenger cars with service speed of 160 km/h.

Its secondary suspension is similar to bogie 209HS. The differences between them are:

Fig. 1. The secondary suspension of bogie 209HS.

W. Zhang et al. / Engineering Failure Analysis 13 (2006) 427–441 429

(1) There is no linking rod between the suspenders of the two sides in CW160.

(2) The suspension structure of the suspenders at two ends is different. 209HS uses the rubber pad struc-

ture and CW160 uses the knife-edge type structure.

The structure failure happening on CW160 includes cracks in the pedestal of the arm shape axle-box (pri-mary suspension) and breaking of the suspender. The suspender breaking led to an accident of the car-body

falling on the track during train running and so the sleepers of several kilometers of line were destroyed.

2.3. Passenger car bogie 206WP

The bogie frame of bogie 206WP is a U type welded structure. The secondary suspension spring is in-

stalled in the middle of the side beam of the bogie frame. It is different from the two bogies with swaying

bolster and suspender mentioned above. It is unnecessary to worry that the car-body may fall in on thetrack due to the failure of the swaying suspension system. But an unexpected accident takes place. The bo-

gie frame was torn and the train derailed due to side bearing pad failure. Therefore, the manufacture of

bogie 206WP also was ceased after this bogie came into service for a few years.

2.4. Freight car bogie ZK2

In China, an important freight car bogie consists of three pieces called a Z8 bogie. The design speed of

this bogie is 120 km/h. In order to match the speed of speed-up passenger trains, the freight car speed in-creased from 50 to 90 km/h in 1998. Unfortunately the speed-up freight car derailed frequently at tangent

lines. The reason for derailment is the hunting motion due to the low warp stiffness. In order to increase the

warp stiffness, a cross rod framework is used between the two side frames of the bogie and the modified

bogie is termed ZK2. Two cross rods connect the two sides of the frame via a welded pedestal. Such a mod-

ification is very effective to increase the critical hunting speed, and the freight could run at speed of 130 km/

h in field tests. Fatigue of the cross rods and connecters occurred frequently after ZK2 came into service.

2.5. Locomotive bogie SS8

Bogie SS8 is specially designed for an electric locomotive of speed-up trains. The traction motor

equipped with the bogie is of DC type. It is rigidly suspended from the bogie frames. Since the DC motor

is heavier than AC motor, the dynamic force became much more violent as the running speed increased. So

the motor suspension seat at the end of the tube beam of the frame cracked.

2.6. ‘‘Blue Arrow’’ high speed train

‘‘Blue Arrow’’ design speed is 200 km/h. The train consists of two electric locomotives and nine trailer

passenger cars. The structure failure mainly appeared on the connecting parts between the bogie and the

body of electric locomotives. The serious problems are as follows:

(1) Cracks initiated and grew in the suspension pedestal of driving motor and the bolts were broken.

(2) Fatigue cracks appeared in the traction base at the bottom of the car-body.

2.7. ‘‘Pioneer’’ high speed train

‘‘Pioneer’’ is the first generation of high speed trains developed in China. It is an EMU train with dis-

tributed traction power. Its design speed is 250 km/h. The train had excellent dynamic behavior in the first 6


months in the course of field tests. But the pedestal of the anti-hunting damper cracked after 6 months and

the anti-hunting damper was defective. This situation caused a hunting of the vehicles at a speed of 200 km/

h and the ride comfort index in the lateral direction is more than 3.0.

During the test, another accident of ‘‘Pioneer’’ is the burning of a traction motor. It is because the bear-

ing of the motor was damaged, which leads to the rotor contacting and scratching the stator.

2.8. ‘‘Star of China’’ high speed train

‘‘Star of China’’ is a recently developed high-speed train. Its design speed is 270 km/h. The maximum test

speed is 321.5 km/h (see Fig. 2). Since the train is the most advanced in China, its structure design is given

close attention. Structure failures became less. But the skirt plate of the car-body of one trailer car was still

broken due to the air-dynamic effect at 290 km/h during the test.

3. Analysis of structure failure

Through the above description and analysis of the structure failures of speed-up trains, it is clear that

those structure failures should be attributed to some design mistakes. They can be classified as follows:

3.1. Mistakes in estimating the service condition

The structure design of the trains is based on the design standard, the structure function expected and the

service condition. The service condition includes the forces, vibration, environment, etc. For the design,

strength analysis and testing of the structure, its service condition has to be taken into account. The sim-

ulated external loads for the strength analysis and testing of the structure are determined according to its

practical service condition. Probably a small mistake in estimating the service condition could lead to a fail-

ure of a whole design and a low quality of structure performance.

One of the structure failures of ‘‘Pioneer’’ high speed train is taken as an example. A driving motor of

Pioneer burned due to bearing damage during its test. Through checking the design document of Pioneer, itis found that a mistake in the design was made, namely, 0.1 g was selected as a design impact acceleration of

Fig. 2. The high speed train ‘‘Star of China’’.


the driving motor. This value is too small. In fact, when the motor works on the high speed train, its accel-

eration in the vertical or in the horizontal direction is as large as 3–5 g. So the bearing originally used could

not bear such a large horizontal dynamic force. After the bearing is replaced by a deep groove ball bearing,

the bearing and motor work quite well up to now.

A similar failure happened on a ‘‘Blue Arrow’’ electric locomotive. It has a half car-body suspensionstructure for the driving motor. So the motor is suspended from the car-body and bogie frame. According

to the original design, the designed impact acceleration of the motor is 0.3 g. So the suspension force of

motor should equal 1.3 g times the mass of the motor, which is taken into account in the design of the sus-

pension structure of motor. It is obvious that the suspension force is considered too small and the designed

suspension structure is too weak. Accordingly, the suspension pedestal of the driving motor cracked and

the bolts broke.

3.2. False structure restricting part compatible motion

Usually a bogie consists of many parts, such as motors, wheelsets, car-body suspensions, brake system

and so on. It is necessary that relative motions occur among them when the train is running. Such a

motion (or freedom) of each part is not only advantageous to the dynamic performance of the vehicle

and track, but also reduces stresses in the restrained parts and dynamic stresses. But the false structure

resists the part motion and leads to restriction stress. Structure failure may occur in a short time of

service.

One typical example is taken from bogie 209HS of passenger car. The structure of bogie 209HS withparts of suspension system is shown in Fig. 1. The two parallel suspenders, linking rod and bogie frame

constitute a parallelogram structure, as shown in Fig. 3. Rubber pads are used at the joints of the sus-

penders and the linking rod in order to keep linking flexibility of the suspenders and the linking rod.

During vehicle running, as a lateral movement of the car-body happens, the suspender will tilt, and

the angles between the suspenders and the linking rod will change since the linking rod has only a par-

allel movement. Due to using unavailable stiffness rubber pads at the joints, a bending stiffness forms at

the joints. Therefore the tilting motion of the suspenders is restricted and large bending stresses occur in

the suspenders and the linking rod. Such a dynamic bending stress leads to the cracking of the suspendersand linking rod.

There are two ways to improve the service condition. One is to reduce the joint stiffness of the suspenders

and the linking rod. The other is to use a flexible linking rod.

A similar failure occurs in the bogie CW160. For the bogie suspenders are also used, but a knife-edge

type structure is used instead of the rubber pads at the suspension joints (see Fig. 4). An advantage of

the knife-edge is that the suspender sways freely in the lateral and vertical planes. But the swaying of

the suspender in the longitudinal and vertical plane (cross of knife-edge) is restricted. The bending stress

in the suspender is easily caused due to bogie vibration in the longitudinal direction and the suspenderscracked after about three years of use. This problem can be settled by using ball joints at the end of the

suspender. So the suspender sways freely in the longitudinal and lateral directions.

Fig. 3. Sketch of sway system.

Fig. 4. Sketch of suspension of CW160.


3.3. Unreasonable structures

Through the analysis of the structure failures happening in speed-up trains in China, it can be found that

most structure failures are caused by unreasonable structure directly.

3.3.1. Unreasonable pedestal structures

There are a lot of pedestals on a bogie, which are welded on the bogie frame. They are usually used for

connecting the traction rod, damper, etc. The pedestal shown in Fig. 5(a) is an unreasonable typical struc-

ture used on bogie 209HS. The pedestal is welded on the side plate of the bogie frame. When a force acts on

the pedestal, the force will be transferred to the side plate through the pedestal. Since the side plate is thin(about 10 mm), it deforms very much. The weld line between the pedestal and the side plate is easily

cracked. As mentioned above for 209HS, the pedestals of the suspender cracked after a few service years.

This problem was analyzed by field stress measurement and the results obtained indicate that the service life

of the pedestals of the suspender is only 2.47 years [3]. As the reasonable design, the clapboard has to be

used to fill in the beam frame in order to enhance the stiffness of the side plate, as shown in Fig. 5(b). The

top plate of the pedestal is an extended part of the cover plate of the frame and its support plate is extended

from the cover plate of the frame to the bottom plate. For this structure, it is not necessary to worry about

the large deformation of the side plate and cracking of the weld line.Fig. 6(a) shows an unreasonable pedestal structure used in ‘‘Pioneer’’ high speed trains. It is a seat for a

pedestal of an anti-hunting damper. The seat is constituted by three parallel steel plates. Such a structure is

Fig. 5. Pedestal structures. (a) Unreasonable structure. (b) Reasonable structure.

Fig. 6. The seat for a pedestal of anti-hunting damper. (a) Unreasonable structure (b) Reasonable structure.


very weak in the lateral direction. In fact, a simple way to enhance the seat strength is to add clapboards

between parallel steel plates, as shown in Fig. 6(b).

3.3.2. Unreasonable structure bolted joints

Bolts are widely used in bogies to fasten one part to another through tension force. Generally the bolt isnot suitable for bearing shear load and bend load. Fig. 7 describes two examples of a new bogie used in a

210 km/h EMU train. Fig. 7 (a) indicates a safety holder for a motor. The left structure of the safety holder

is an unreasonable structure, which makes bolts suffer shearing load. Structures at the right of the motor are

reasonable in that they use a pin or hook to suffer the shearing load. In the reasonable structures, the bolts

should work in a simple forcing situation. Example 2 is another unreasonable structure for a safety holder

for an axle box (Fig. 7 (b)), in which the bolt is not only to suffer a tension force, but also a bending load.

The easy way to enhance seat strength is to use two bolts to fix the safety holder.

3.3.3. Unreasonable structure of spring house

In bogies, most of the primary suspensions use coil springs. Generally the coil spring is set on an axle box

and the bogie frame is put on the top of the coil springs. In order to reduce the height of the bogie frame, a

special structure for primary suspension spring is that the coil spring is fitted into a housing on the frame, as

shown in Fig. 8. The spring force Fz acts on the cover plate of the housing, and the cover plate deforms. It is

very easily that the cover plate is torn. So in real design, the cover plate of the spring housing should be

thick enough to avoid tearing [4]. But the reasonable design is not to let the spring force Fz act directly

on the cover plate.Table 1 lists the main structural failures and their causes.

Fig. 7. Examples of unreasonable structures in using bolts. (a) Example 1. (b) Example 2.

Fig. 8. Unreasonable structures of spring housing.

Table 1

Structure failure and reason in speed-up trains

Type of car or bogie Speed ( km/h) Structure failure Cause

Bogie 209HS 160 Linking rod, suspenders and

pedestal of suspender cracked

False structure restricting part motion

Bogie CW160 160 Suspender broken False structure restricting part

Bogie 206WP 160 Side bearing pad failure Unreasonable side bearing material

and structure

Bogie ZK2 120 Cross rod and connecter cracked False structure restricting part

compatible motion

Bogie SS8 160 End beam of frame broken Unreasonable pedestal structures

‘‘Blue Arrow’’ motor car 200 Pedestal of driving motor and traction

base on bottom of car-body racked

Unreasonable pedestal structures

and mistake in estimating the

service condition

‘‘Pioneer’’ high speed train 250 Pedestal of anti-hunting damper cracked

and traction motor burned

Unreasonable pedestal structures

and mistake in estimating the

service condition

‘‘Star of China’’ high speed train 270 Skirt plate of car-body broken Unreasonable pedestal structures

210 km/h EMU train 210 Safety holders Unreasonable structure in using bolt


4. Study on structural failures of locomotive ‘‘Blue Arrow’’

Following is a study on the structural failures of locomotive ‘‘Blue Arrow’’ as an example. As mentioned

above, the design speed of ‘‘Blue Arrow’’ high speed trains is 200 km/h. The train is composed of two elec-

tric motor cars and nine trailer passenger cars. The structure failures mainly occurred on the motor cars.

Serious fatigue cracks initiated and developed in the traction base and in the suspension pedestal of driving

motor on the bottom of the car-body. The study on the above structure failures and fatigue cracks was car-

ried out in detail.

4.1. Theory analysis

The whole Finite Element model of the motor car-body was put forward [5]. The car-body under the

frame, the cover plate of car roof, the end wall and side wall are meshed with triangular and rectangular

plates, and shell elements, respectively. The pillars of side wall and end wall, the longitudinal sill of side

wall, the longitudinal sill and bent beam of car roof are treated as beam elements. Thus, the mesh of the

car-body includes 74110 nodes, 83909 plate elements and 5932 beam elements. The mesh is shown inFig. 9.

The vertical force of the car-body acts on the frame through the secondary suspension. Fourty-eight

spring elements are used on the bearing plates of the coil springs, the stiffness of the elements equals that

of the secondary suspension. At the place of the buffer seat, longitudinal constraint is added. According to

the Chinese standard 95J01-M and UIC Code 615-4 [6], the vertical force, lateral force, damping forces,

braking force and traction force are taken into account in the calculation. The weight of the motor car

is 78t and the axle load is 19.5t, the maximum traction force of the motor car is 211 kN.

For the materials of 09CuPTRe and Q345 used for the car-body, the Von Mises stress should be lessthan their allowable stresses of 184 and 216 MPa, respectively.

From the calculation results for the car-body strength under traction, the maximum stress of the car-

body reaches 285 MPa on the bottom surface (270 MPa on the top surface), which appears in the strength-

ening plate between the traction rod seat I and the lower frame, as shown in Figs. 10 and 11. The local

Fig. 9. Finite element model of motor car-body.

Fig. 10. Equal Von Mises stress contours of motor car-body.


maximum stress in the traction rod seat II is 195 MPa, which appears in the strengthening plate between

traction seat and the lower frame, as shown in Fig. 12. The local maximum stress of body bolster I and

II are 177 and 136 MPa, respectively, which occur in the lower cover plate of the bolster, as shown in Figs.

13 and 14.

The strength calculation results show that the maximum stress in normal service exceeds the allowable

stress, the strength of the traction seat of motor car is not quite enough to bear the dynamical loads. So the

car-body structure should be further improved.

Fig. 11. Local Von Mises stress of traction rod seat I.

Fig. 12. Local Von Mises stress of traction rod seat II.


Fig. 13. Local Von Mises stress of body bolster I.

Fig. 14. Local Von Mises stress of body bolster II.



4.2. Field tests

The dynamic stress measurement for the motor car of the ‘‘Blue Arrow’’ AC train was carried out on the

line from Guangzhou to Shenzhen [7]. Because the main problems of the motor car occurred on the

car-body structure when running on tracks, the key measurement points were arranged on the car-body.According to the finite element analysis results, measurement points with relatively large stresses were cho-

sen, such as the place near the traction rod seat, the car-body bolster and the bottom parts of welding of

other main supporting seats. The test results were used to evaluate the strength of the motor car, and can

provide useful data for necessary structure modification.

Figs. 15 and 16 show part of measurement points on the car-body. It is seen in Figs. 17–20 that the max-

imum stress amplitude of the car-body is 284.3 MPa at point No. 6, which appears on the position of the

body bolster thick plate in the car-body vertical direction. The maximum stress amplitude of No. 29 point

reaches 253.1 MPa. This point is near the sill inner vertical plate of the body bolster end. The maximumstress amplitudes of these two points exceed the value of the fatigue limit, for an un-welded steel part spec-

ified by the Goodman fatigue limit curve. Thus, the fatigue strength of these locations are low. The max-

imum stress amplitudes at points No. 47, No. 49, No. 51 and No. 52 near the traction seat are higher than

130 MPa, which exceeds the limit values of angle welding specified by the Goodman fatigue curve.

Through field tests, the fatigue strength problems of the motor car are found and the finite element anal-

ysis results are validated. Then the car-body structure can be modified according to the test results.

Fig. 15. Measuring points on body bolster.

Fig. 16. Measuring points near car-body traction rod seat .

Fig. 17. Fatigue evaluation of body bolster seat points.

Fig. 18. Fatigue evaluation of traction rod seat points.



5. Conclusions

Through an investigation into structural failures of speed-up trains in China, it can be found that struc-

tural failure has happened on every type of speed-up trains. Through the failure statistics and analysis of

structures of the speed-up trains, the causes for the structure failure are attributed to the following aspects:

(1) Errors exist in using the service condition in the fatigue test and numerical calculation of the bogie

frames, such as loading, acceleration.

(2) Unreasonable structure parts restrict their motions and additional large dynamic stresses occur in the

parts.

(3) Unreasonable structures often lead to steel plate distortion, let the bolts suffer large shear and bending

loads, and leads to structural failure finally.

(4) Existing standards for strength tests and strength calculations are not suitable for speed-up trains.They only examine the main frame. But most structural failures occurred at the pedestal, connector,

etc, in small parts. So it is necessary to develop a new strength standard which fully considers the ser-

vice condition of speed-up trains.

Acknowledgement

This work is supported by the National Science Foundation of China (NSFC).

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an investigation into structural failures of chinese high-speed trains

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