Propensities of crack interior initiation and early growth for very-high-cycle fatigue of high strength steels

Abstract

Fatigue tests of a high carbon chromium steel were performed using rotating bending and ultrasonic axial cycling. Fatigue crack initiated at specimen interior for very-high-cycle fatigue (VHCF) with fish-eye pattern embracing fine-granular-area (FGA) originated from inclusion. The fatigue life from FGA to fish-eye and from fish-eye to the critical crack size was respectively calculated, so as to estimate the fatigue life contributed by FGA. The crack extension rate within FGA was also estimated. Our results demonstrated that the formation of FGA is responsible for a majority part of total fatigue life.

Effects of loading condition on very-high-cycle fatigue behaviour and dominant variable analysis

“…A couple of statements have been made regarding the FGA formation: (1) FGA is accompanied by VHCF crack initiation from interior inclusion for high carbon steels [29], (2) FGA consumes more than 90 percent of VHCF life [12,14,17], and (3) FGA is finished when the plastic zone size of the microcrack exceeds the width of the martensite [21]. Here, we further assume that dislocations are piled up along the slip band in the martensite as described by the Tanaka-Mura model [30,31], and take into account the influence of tensile strength and FGA size on VHCF crack initiation life.…”

“…Surface defects may become non-propagating cracks [12], and sometimes grain boundary could also become a crack origin for high carbon chromium steel under low tempering temperature [5,13]. It is also revealed that fatigue crack initiation within FGA is dominated for high cycle fatigue (HCF) and VHCF, and FGA consumes more than 90% fatigue life [14,15]. Thus, microstructure barriers near the fatigue crack origin are responsible for crack initiation and determine the fatigue life scattering.…”

Effect of Tempering Temperatures on Tensile Properties and Rotary Bending Fatigue Behaviors of 17Cr2Ni2MoVNb Steel

“…Fatigue strength of 1 × 107 cycles is usually defined as the fatigue limit. All specimens were tested at room temperature at a frequency of 6000 r/min and under load control at stress ratios R = −1, and the regarded load was taken as the control variable [13][14][15]. The dimensions of fatigue specimens are shown in Figure 1b.…”

A two-parameter model to predict fatigue life of high-strength steels in a very high cycle fatigue regime

“…It was shown that the stress intensity factor range at the front of the FGA was a constant and was close to the threshold value of the crack propagation K th . In crack initiation and early growth stage of VHCF, the crack growth rate is much lower than 10 −10 m/cycle [13,[17][18][19][20], and more than 90 % of fatigue life is consumed to form the FGA [21][22][23][24][25]. Therefore, it is essential to develop a model to predict the fatigue life in relation to FGA.…”

“…Hong et al [25] developed the dislocation model proposed by Tanaka and Mura [32]. By introducing a fraction of an irreversible dislocation, the number of cycles related to crack initiation N i at inclusion was expressed as:…”