School of Mechanical Engineering, Shenyang Jianzhu University, Shenyang 110168, China
Cite this article:
ZHANG Xiaochen, MENG Weiying, ZOU Defang, ZHOU Peng, SHI Huaitao. Effect of Pre-Cyclic Stress on Fatigue Crack Propagation Behavior of Key Structural Al Alloy Materials Used in High Speed Trains. Acta Metall Sin, 2019, 55(10): 1243-1250.
The complex cyclic loading is a "potential killer" affecting the service security of high speed trains. It is necessary to investigate the influence of cyclic loading on vehicle structures and explore potential methods to improve the service strength and life of structural materials. In this work, the mechanical property tests for key structural materials (Al alloy) that experienced years of service were described, the fatigue crack propagation (FCP) behavior at different stages were analyzed, and the changing pattern of mechanical behavior of material was demonstrated over time. Since the specimens showed turning characters on FCP behavior, the mechanical property tests for materials that subjected to different levels of pre-cyclic stress (PCS) were further carried out to analyses the "coaxing" effects of PCS and establish a more reasonable life prediction model for materials. It is found that a turning phenomenon or "turning" point is clearly shown in the early stage of the fitted curves for the specimens with service experience, which is mainly due to the delayed extension behavior in the region near the threshold; the curves of crack propagation rates and stress intensity factor (da/dN-ΔK) of specimens subjected to PCS show a similar turning phenomenon at the initial stage of steady-state crack growth to that of specimens with service experience; the "coaxing" effect of PCS on material is different for different PCS levels, and there is an optimal PCS for the "coaxing" effect; the model proposed in this study has higher accuracy in FCP life prediction for the da/dN-ΔK curves with "turning" character.
Fund: National Natural Science Foundation of China(51705341);National Natural Science Foundation of China(51675353);Natural Science Foundation of Liaoning Province(20180540137);Natural Science Foundation of Liaoning Province(2019-BS-198)
Fig.1 Photo of the chassis of high speed train (a) and finite element method (FEM) stress analysis and schematic diagram of sampling method (b) (1—sheet material, 2—anti-snake movement damper seat, 3—section bar, 4—draw beam)
Fig.2 Dimensional drawing of standard three-point bend specimen (unit: mm)
Fig.3 Fitted curves of crack propagation rates vs stress intensity factor range (da/dN-ΔK) in the steady growth zone
Fig.4 da/dN-ΔK curves considering the range near fatigue crack propagation (FCP) threshold
Fig.5 da/dN-ΔK curves in the steady growth zone subjected to pre-cyclic stress (PCS)
Fig.6 The increase of da/dN with different PCSs at different ΔK
Fig.7 Experimental data and the Paris fitted curves (a) and drawing of partial enlargement (b)
Fig.8 Fitted curves of the experimental data-piecewise curve fitting
PCS
MPa
ΔK at the turning point
MPa·m1/2
Whole fitting
Piecewise fitting (curve 1)
Piecewise fitting (curve 2)
lgC
m
lgC
m
lgC
m
0
-
-7.39186
3.44199
-7.39186
3.44199
-7.39186
3.44199
30
10.41
-7.75152
3.59695
-9.41163
5.33065
-7.52036
3.41039
60
11.55
-8.16278
3.89175
-9.95825
5.72909
-7.79621
3.60007
90
10.81
-7.58924
3.49789
-9.77501
5.77199
-7.30743
3.27054
120
10.22
-7.41945
3.38241
-8.92749
5.00362
-7.12119
3.14091
Table 1 Material constants based on Paris' law
Fig.9 PCS life prediction based on whole curve fitting and piecewise curve fitting
[1]
Jin X S, Guo J, Xiao X B ,et al. Key scientific problems in the study on running safety of high speed trains [J]. Eng. Mech., 2009,26(Suppl.II):8
Schijve J. Fatigue damage in aircraft structures, not wanted, but tolerated? [J]. Int. J. Fatigue, 2009, 31: 998
[6]
Beretta S, Ghidini A, Lombardo F. Fracture mechanics and scale effects in the fatigue of railway axles [J]. Eng. Fract. Mech., 2005, 72: 195
[7]
Regazzi D, Beretta S, Carboni M. An investigation about the influence of deep rolling on fatigue crack growth in railway axles made of a medium strength steel [J]. Eng. Fract. Mech., 2014, 131: 587
[8]
Liu Y M, Stratman B, Mahadevan S. Fatigue crack initiation life prediction of railroad wheels [J]. Int. J. Fatigue, 2006, 28: 747
[9]
Zhao Y X, Yang B, Feng M F ,et al. Probabilistic fatigue S-N curves including the super-long life regime of a railway axle steel [J]. Int. J. Fatigue, 2009, 31: 1550
[10]
Zhao Y X, Yang B, Sun Y F,et al. Probability-based cyclic constitution models for LZ50 axle steel [J]. Chin.J.Mech.Eng., 2004, 40(9): 48
Gough H J. The Fatigue of Metals [M]. London: Scott, Greenwood & Son, 1924: 15
[14]
Hironobu N, Ken-Ichi T. Fatigue crack acceleration and closure in rotating bending tests of 0.54% carbon steel [J]. Eng. Fract. Mech., 1978, 10: 855
[15]
Hironobu N, Ken-Ichi T. Significance of initiation, propagation and closure of microcracks in high cycle fatigue of ductile metals [J]. Eng. Fract. Mech., 1981, 15: 445
[16]
Ishihara S, McEvily A J. A coaxing effect in the small fatigue crack growth regime [J]. Scr. Mater., 1999, 40: 617
[17]
Metal Materials and their strength laboratory of Xi'an Jiaotong University. Special Issue for Materials of Metal and Their Strength (2) [M]. Xi'an: Xi'an Jiaotong University Press, 1972: 76
Lu X, Zheng S L. Strengthening and damaging under low-amplitude loads below the fatigue limit [J]. Int. J. Fatigue, 2009, 31: 341
[20]
Zheng S L, Xu H H, Feng J Z ,et al. Lightweight design of automobile drive shaft based on the characteristics of low amplitude load strengthening [J]. Chin. J. Mech. Eng., 2011, 24: 1111
[21]
Zheng S L, Liang G Q, Wang Z R, et al. Compilation of automotive lower control arm spectrum based on the low-amplitude training load [J]. J. Mech. Eng., 2014, 50(16): 147
The Quality and Technology Supervision Bureau. GB/T 6398-2000 standard test method for fatigue crack growth rates of metallic materials [S]. Beijing: Standards Press of China, 2001
Paris P C, Gomez M P, Anderson W E. A rational analytic theory of fatigue [J]. Trends Eng., 1961, 13: 9
[24]
Paris P C, Erdogan F A. A critical analysis of crack propagation laws [J]. J. Basic. Eng., 1963, 85: 528
[25]
Chen Y L, Bian G X, Yi L ,et al. Research on fatigue characteristic and fracture mechanics of aluminum alloy under alternate action of corrosion and fatigue [J]. J. Mech. Eng., 2012, 48(20): 70
Yan Y, Lu M, Li X W. Effects of pre-fatigue deformation on the uniaxial tensile behavior of coarsegrained pure Al [J]. Acta Metall. Sin., 2013, 49: 658
