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Investigations on Fatigue Reliability of WeldedStructures with Applications to High-Speed Trains

Zhanxun Song zs1c09@soton.ac.uk - School of Engineering Sciences, UK Beijing Jiaotong University, PRC

Supervisors Prof. J. T. Xing and Dr. Y. P. Xiong

Fluid Structure Interactions

Research Group

Background

Material experiment: Fatigue performance experiment of welded structurecan be done by two methods: low frequency and high frequency.

Use the low frequency when fatigue life is short.

Use the high frequency when fatigue life is long.

Fatigue Testing

Figure 5: High frequency experiment Figure 4: Low frequency experiment

With the increasing train speed,the static and dynamic stresses intrain structures are rapidly increased.

There are a lot of welded structuresin a train. Since welded structurehas many flaws, the fatigue life of

welded structures is much shorterthan base metal . Investigations onfatigue reliability of weldedstructure is an important topic for

transportation safety.

Stress testing: Strain of welded structure in train can be measured by usingstrain gauge. The stress can be calculated and the stress spectrum can beobtained using the rain flow counting method.

Figure 6: Stress spectrum of High-speed train

( ) ( )i i c i s it X t D E Stress spectrum model:

Figure 1: China Railway High-speed (CRH)

(1 ) (1 )

(1 ) (1 )(1 )

n n pth

n q

c

K C f K da K

K dN R R K

2 2 21 1max 2min[(1 2 ) / 4 ] (1 2 ) / 4 ( )S v K v K K

k K M YS a

Fatigue FractureThere are a lot of methods for crack speed, Forman (1983) model is

very accurate for researching fatigue fracture, the crack speed formula:

There are a lot of research methods for fracture. Two methods are used very often for welded structures: stress intensity factor (SIF) and strainenergy density factor (SEDF).

SIF:

SEDF:

Fatigue Problems of welded structure

Numerical Simulation

Testing

Aim & Method

Conclusions and Future Work

Fatigue life of important parts in train structures can be estimated by using thestudied method. Simulation approach validated by the experiments could savecost for further fatigue analysis. Predict fatigue life could get the reliability of high-speed train, decrease accident.

Fatigue reliability of weld structure should be research.Fracture characteristic of welded structure must be research.Predict fatigue life should be research.

Simulation

Figure 2: Mesh model of T welded structure

Figure 3: Result of stress analysis

Numerical simulations are carried out using software of ANSYS and ABAQUS.The following two figures show the mesh structure and simulation results of aT-welded joint fixed at the two side edges of the bottom and subject to auniform pressure on the top section of the vertical plate. In the simulations, thecharacteristic of geometry and material on the welded areas must beconsidered.

Aim: Estimate flaws of welded structure, find the influence of each kind

flaw for fatigue life of welded structure. Stress influenced by arc, weld root, weld toe etc. Simulation the process of fracture of welded structure. Deal with load spectrum of welded structure in train. Predict fatigue life of weld structure in high speed train.

Method:

Stress spectrum analysis

Predict fatigue life

Beijing Jiaotong University