Fatigue Life Study of Bogie Framework Welding Seam by Finite Element Analysis Method
Pingqing Fan, Xintian Liu, Bo Zhao
College of Automation Engineering, Shanghai University Engineering of Science 201620, Shanghai,
Abstract
Using adaptive grid algorithm method, framework and its weld am are meshed by manual method, fillet is instead of the corner of weld am and the needed finite element model of a bogie framework and weld-am are built. Bad on the miner theory of cumulative fatigue damage and S-N curve modified, the strength and fatigue life distribution contours for welding am of the bogie framework are given; the results are basically consistent with that of the experiment, so the framework satisfies with the demand of strength and fatigue life. The thesis predicts weak location of weld am and provides basis to practical production. Keywords: FEA, Fatigue life, Welding am, S-N curve
1. Introduction
平静的海Carriage bogie bears the carbody weights and vibration from railway, and each component endures co
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ntinuous random stress in running process. At prent, there isn’t perfect norm about fatigue design, so bogie of pasnger car adopts design method of static strength, and fatigue intensity is verified by experiment. Bogie framework is produced by welding steel plates which promotes the fatigue strength of components rather than casting steel plates. Aiming at component of welding structure, welding am is area of the stress concentration and has great effect on fatigue strength of component.
Bad on a new bogie frame, the thesis analyzes strength and fatigue life of weld am, and predicts weak location.
2. Welding Seam Fatigue Life Theory
Nominal stress method is the earliest fatigue design method, which considers S-N curve of material or component as a main parameter to predict fatigue cycle numbers (total fatigue life). It is an empirical method.
Usually, S-N curve is expresd by formulas as follow:
376 P. Fan, X. Liu and B. Zhao
C N S
D (1) Where, D C are constants.
Solve logarithm of equation at both sides:
C N S lg lg lg
D (2) Obviously, cycle stress and cycle fatigue life are linear relationship in double
logarithm. Knowing fatigue limit stress 0S and corresponding cycle fatigue 0N ,
the S-N curve can be expresd as follows:
C N S lg lg lg
D (3) o S and o N are input into equation (2), equation (4) can be concluded:
C N S lg lg lg 00
D (4) According to (3) and (4):
lg lg lg lg S S N N D (5) Equation (5) is simplified as equation(6):
D (0
0S S
N N (6) When material constant D , fatigue limit stress 0S and corresponding cycle
fatigue 0N are given, cycle number under known stress amplitude is calculated
directly.
At prent, miner theory of linear fatigue cumulative damage is ud in project. For
the component under random loads, miner is not inferior to nonlinear fatigue
cumulative damage theory. If fatigue loads among random loads are almost in area
客观存在of high cycle fatigue (HCF), miner theory of linear fatigue cumulative damage is
sufficient.
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When multiple alternating amplitude value stress play a role, damage can be
expresd:
Damage caud in a circle: N D 1
(7)
Where N is fatigue life under prent stress S .
Damage caud in n circles is divided into constant-amplitude and variable-
amplitude:
Constant-amplitude force, the damage is expresd as follows:
法西斯的意思Fatigue Life Study of Bogie Framework Welding Seam 377
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N
n D
(8) Variable-amplitude force, the damage is expresd as follows: ¦ i i
i N n D (9) CR D is defined as critical damage.
Under Constant-amplitude force, if n =N , fatigue damage happens.
1 CR D (10) 3.
颈部淋巴结肿大疼痛FEA of Welding Seam 3.1 FEA Model of Welding Seam
It is necessary to deal with the corner framework welding am becau of
limitation of SEAMW module in fatigue software, so the corner of welding am is divided into as Figure 1.
Figure 1. The finite model of for the corner framework welding am
The supporting pedestal of framework contains 5880 hexahedron elements and
8100 nodes; welding position consists of 3067 quadrilateral shell elements and
5759 nodes; the framework is divided into 50330 quadrilateral shell elements and
52175 nodes.
In practical operating, framework bears complicate load, such as: vertical static
load of framework is 200KN, vertical dynamic load is 30KN, load of symmetry
along the diagonal line is 6KN, traction is 60KN, and brake force is 27KN.
The distribution of Force and torque in welding ction is showed in Figure 2.
378 P. Fan, X. Liu and B. Zhao
Figure 2. Force distribution for the corner framework weld am
Material of framework welding am is 16MnR that is low-alloy structural steel. According to GB/T1335-1996, allowed stress of material is 340MPa and elastic modulus is 2.09×105 MPa, Poisson ratio is 0.28.
3.2 FEA Result Of Welding Seam
The F EA result of weld am shows that the maximum stress value of welding am is 156MPa which is less than allowed stress of material 340MPa, and which generates inner side of weld-am junction between the bolster and side beam, and that is clo to junction of weld am and the ba. At same time, the maximum principal strain is 5.98h10-4. Moreover, inner side of weld-am junction
between side beam and cross beam is also dangerous area. Under this operating condition, the maximum displacement of the framework is 1.42mm and happens in middle part of cross beam. Deformation displacement is 1.4mm in Y direction. The result if showed in Figure 3.
Figure 3. FEA result of weld am
Fatigue Life Study of Bogie Framework Welding Seam 379
4. FEA of Fatigue Life
The ultimate purpo of fatigue life analysis ascertains fatigue life of structure. Calculation of fatigue life needs accurate loading spectra, S-N curve of material or component, proper cumulative damage theory and crack growth theory etc. Meanwhile, it also needs to consider possible defect factors. At prent, there is not preci method about calculation of fatigue life at home and abroad, so it is only estimated or predicted.
4.1 S-N Curve of Material
Usually, bad on the ction 2, S-N curve of material can be easily drawn which is showed as Figure 4.
Figure 4. Unmodified S-N curve
According to the common p-S-N curve theory, there is not fatigue damage when cycle stress is below limiting fatigue stress. Becau of structural characteristic of weld am, stress can induce crack initiation though it is below limiting fatigue stress. Therefore, p-S-N curve is in need of being modified. Aiming at the part of p-S-N curve below limiting fatigue stress, Oblique-line who slope is (
p b -
2)takes place of original horizontal line. V lg lg p p p b a N 1 t V V (12) V V V lg lg 2lg lg 11 p p p p b b a N 1 V V (13) p-S-N ˄p=95%˅modified is as Figure 5.