scholarly journals Interior crack initiation during the very-high-cycle fatigue of railway wheel steel under axial loading and rolling contact loading

2021 ◽  
Author(s):  
Xiao-Long Liu ◽  
Pengcheng Gao ◽  
Si Wu ◽  
Guanzhen Zhang ◽  
Tao Cong
Keyword(s):  
Crack Initiation ◽  
High Cycle Fatigue ◽  
Axial Loading ◽  
Fatigue Tests ◽  
Rolling Contact ◽  
Wheel Steel ◽  
Contact Loading ◽  
Very High Cycle Fatigue ◽  
Very High ◽  
Railway Wheel Steel

In this paper, a comparative study of the very-high-cycle fatigue (VHCF) behavior of railway wheel steel under axial loading and rolling contact loading was conducted. Fatigue tests were performed with an ultrasonic fatigue test machine under axial loading, and the fracture surfaces from the fatigue tests and shattered rims taken from the failed railway wheels were observed. The wheel steel under axial loading presents a VHCF behavior with Mode I crack, and that under rolling contact loading is a VHCF behavior with mix Mode II-III crack. For the VHCF behavior with Mode I crack ,surface and interior crack initiation occurred with equal probability at both low and high stress levels and produced a dual linear S-N curve since the value of fatigue limits for the surface and interior crack initiation are close. For the VHCF behavior with mix Mode II-III crack, cracks were initiated from the interior Al O inclusion and the fatigue life was beyond 10 cycles. Fatigue bands were observed on the fracture surface under rolling contact loading. The ferrite nanograins formed due to the stress state of shear plastic strain with a large compressive stress. The formed nanograins were softer than the matrix caused by the redistribution of the carbon.

Effect of shot peening on very high cycle fatigue of 2024-T351 aluminium alloy

2020 ◽  
Vol 10 (7) ◽  
pp. 1032-1039
Author(s):  
Renhui Tian ◽  
Jiangfeng Dong ◽  
Yongjie Liu ◽  
Qingyuan Wang ◽  
Yunrong Luo
Keyword(s):  
Fracture Surface ◽  
Crack Initiation ◽  
Shot Peening ◽  
High Cycle Fatigue ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Very High Cycle Fatigue ◽  
Fatigue Strength Improvement ◽  
Ultrasonic Fatigue ◽  
Very High

To investigate the influence of shot peening (SP) on very high cycle fatigue (VHCF) performance of 2024-T351, the specimens with three surface conditions were performed under ultrasonic fatigue tests: mechanicallypolished without peening (NP), ceramic shot peening (SP1), steel and glass mixed shot peening (SP2). The roughness, microhardness, residual stress, fractography measurement and scanning electron microscopy (SEM) were applied before fatigue test to characterize the effective layer induced by the peening treatment. For the failed specimens, the fracture surface were analysed using SEM to study the mechanisms of fatigue crack propagation. In addition, the fatigue life curve in ultra-high cycle region continuously decreased in the three series of specimens. However, the experimental results revealed that fatigue strength improvement resulting from shot peening treatment was negligible in very high cycle regime. Furthermore, the stress intensity factor for the surface crack initiation (SCI) and interior crack initiation (ICI) was discussed based on quantitative analysis on the fracture surface. The average values of ΔKfish-eye for NP, SP1 and SP2 specimens are about 2.22, 1.48 and 1.61 MPa · m1/2, respectively.

Very High Cycle Fatigue and Damage Behavior of Ti6Al4V

2015 ◽  
Vol 664 ◽  
pp. 71-80
Author(s):  
Stefan Heinz ◽  
Dietmar Eifler
Keyword(s):  
Crack Initiation ◽  
High Cycle Fatigue ◽  
Phase Distribution ◽  
Fatigue Tests ◽  
Internal Crack ◽  
Cycle Fatigue ◽  
Β Phase ◽  
Very High Cycle Fatigue ◽  
Induced Defects ◽  
Very High

High frequency fatigue tests were carried out with a 20 kHz ultrasonic testing facility to investigate the cyclic deformation behavior of Ti6Al4V in the Very High Cycle Fatigue (VHCF) regime in detail. The S,Nf -curve at the stress ratio R = -1 shows a significant decrease of the stress amplitude and a change from surface to subsurface failures in the VHCF regime for more than 107 cycles. Microscopic investigations of the distribution of the α-and β-phase of Ti6Al4V indicate that inhomogeneities in the phase distribution are reasons for the internal crack initiation. Scanning electron microscopy as well as light microscopy were used to investigate the internal crack initiation phenomenon in the VHCF-regime. Beside the primary fatigue crack additional defects like micro cracks and crack clusters were observed in the fatigued specimens. SEM-investigations of specimens which were loaded up to 1010 cycles without failure show irreversible microstructural changes inside the specimens. Two step tests were performed to evaluate the influence of internal fatigue induced defects observed in specimens which did not fail within 1010 cycles.

scholarly journals Recent Advances in Very High Cycle Fatigue Behavior of Metals and Alloys—A Review

Metals ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1200
Author(s):  
Ashutosh Sharma ◽  
Min Chul Oh ◽  
Byungmin Ahn
Keyword(s):  
Crack Initiation ◽  
High Cycle Fatigue ◽  
Fatigue Testing ◽  
Fatigue Behavior ◽  
Simulation Studies ◽  
Cycle Fatigue ◽  
Future Directions ◽  
Very High Cycle Fatigue ◽  
Ultrasonic Fatigue ◽  
Very High

We reviewed the research and developments in the field of fatigue failure, focusing on very-high cycle fatigue (VHCF) of metals, alloys, and steels. We also discussed ultrasonic fatigue testing, historical relevance, major testing principles, and equipment. The VHCF behavior of Al, Mg, Ni, Ti, and various types of steels were analyzed. Furthermore, we highlighted the major defects, crack initiation sites, fatigue models, and simulation studies to understand the crack development in VHCF regimes. Finally, we reviewed the details regarding various issues and challenges in the field of VHCF for engineering metals and identified future directions in this area.

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