Crack initiation characteristics and fatigue property of a high-strength steel in VHCF regime under different stress ratios
Crack initiation characteristics and fatigue property of a high-strength steel in very-high-cycle fatigue (VHCF) regime under different stress ratios were investigated in this paper. Fatigue tests were performed at stress ratios of -1, -0.5, 0.1 and 0.3 by using an ultrasonic fatigue testing machi...
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| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Gruppo Italiano Frattura
2016-01-01
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| Series: | Fracture and Structural Integrity |
| Subjects: | |
| Online Access: | http://www.gruppofrattura.it/pdf/rivista/numero35/numero_35_art_11.pdf |
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| Summary: | Crack initiation characteristics and fatigue property of a high-strength steel in very-high-cycle
fatigue (VHCF) regime under different stress ratios were investigated in this paper. Fatigue tests were
performed at stress ratios of -1, -0.5, 0.1 and 0.3 by using an ultrasonic fatigue testing machine. The difference
of S-N data and the characteristics of crack initiation under different stress ratios were examined. It is shown
that the magnitude of stress ratio has a substantial effect on the fatigue strength that decreases with the increase
of stress ratio. However, the variation tendency of the S-N data from low-cycle fatigue to VHCF regime is
similar for the four cases. SEM observations of the fracture surface indicate that fatigue crack initiates from the
surface of specimen in low-cycle regime and initiates mostly from the inclusion in the interior of specimen in
high-cycle and VHCF regimes, which is irrespective of the state of stress ratio. By means of Focused Ion Beam
technique, the samples of crack initiation region were prepared then observed via TEM. The observations show
the microscopic morphology of the crack initiation region, showing the different crack initiation characteristics
and revealing the mechanism of crack initiation for different stress ratios. Moreover, the effect of inclusion size
on fatigue life is discussed with the results showing that the effect of stress ratio and inclusion size on fatigue
strength is well described by our proposed formula. |
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| ISSN: | 1971-8993 1971-8993 |