Abstract
High-cycle and very-high-cycle fatigue tests via rotary bending (52.5 Hz), electromagnetic resonance (120 Hz) axial cycling, and ultrasonic (20 kHz) axial cycling were performed for a high-strength steel with three heat treatment conditions, and the effects of loading frequency and loading type on fatigue strength and fatigue life were investigated. The results revealed that the loading frequency effect is caused by the combined response of strain rate increase and induced temperature rise. A parameter η was proposed to judge the occurrence of loading frequency effect, and the calculated results were in agreement with the experimental data. In addition, a statistical method based on the control volume was used to reconcile the effect of loading type, and the predicted data were consistent with the experimental results.
Highlights
The research of very-high-cycle fatigue (VHCF), which is fatigue failure beyond 107 cycles of loading, is a hot topic in structural integrity because engineering structures require greater than 107 cycles of safe performance [1,2,3,4,5,6]
Due to the fact that the fine-granular area (FGA) region consumes a dominant part of total fatigue life, the formation mechanism of FGA has been extensively investigated [3,12,13,14,15,16,17,18,19], and the recently proposed model of numerous cyclic pressing [18,19] is capable of explaining the formation mechanism of FGA regions for the cases subjected to different stress ratios, which is validated by new results on titanium alloys [20]
Several experimental devices have been used for the testing of VHCF, such as rotary bending (RB), servo-hydraulic (SH), electromagnetic resonance (ER), and ultrasonic loading (UL) machines
Summary
The research of very-high-cycle fatigue (VHCF), which is fatigue failure beyond 107 cycles of loading, is a hot topic in structural integrity because engineering structures require greater than 107 cycles of safe performance [1,2,3,4,5,6]. The influencing variables on internal fatigue crack initiation include stress level, microstructure, inclusion size, etc., and the effect of stress concentration factor and corrosive environment on VHCF behavior was investigated [11]. Due to the fact that the FGA region consumes a dominant part of total fatigue life, the formation mechanism of FGA has been extensively investigated [3,12,13,14,15,16,17,18,19], and the recently proposed model of numerous cyclic pressing [18,19] is capable of explaining the formation mechanism of FGA regions for the cases subjected to different stress ratios, which is validated by new results on titanium alloys [20].
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