Mechanisms of interior crack initiation in very-high-cycle fatigue of high-strength alloys

Strain controlled tests were performed on a high strength steel to investigate the influence of tension mean stress to the crack initiation process at the very high cycle fatigue regime. It is supposed that the variation of stress the state in the vicinity of a non-metallic inclusion results in a change to the energy transferred to the surrounding metallic matrix. To prove this, incremental step tests on cylindrical specimen were realized in which the tension mean stress was stepwise increased. It could be verified that the hysteresis area, which is a criterion of the work transferred to the specimen, decreases with increasing tension mean stress. The test results provide a reasonable physical model to estimate the influence of tension mean stress to the crack initiation process in the very high cycle fatigue regime.

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Very High Cycle Fatigue Behavior and Thermographic Analysis of High Strength Steel

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.118-120.948 ◽

2010 ◽

Vol 118-120 ◽

pp. 948-951

Author(s):

Chuang Shao ◽

Claude Bathias ◽

Danièle Wagner ◽

Hua Tao

Keyword(s):

Crack Initiation ◽

High Strength Steel ◽

High Cycle Fatigue ◽

Fatigue Testing ◽

Fatigue Behavior ◽

High Strength ◽

Cycle Fatigue ◽

Subsurface Crack ◽

Very High Cycle Fatigue ◽

Very High

Very high cycle fatigue behavior of high strength steel, were investigated using ultrasonic fatigue testing equipment at 20 kHz up to 109cycles. S-N curves at room temperature with different stress ratio (R=0.01 and R=0.1) was determined. The experimental results show that fatigue strength decrease with increasing number of cycles between 105 and 109. SEM examination of fracture surface reveals that fatigue damage was governed by the formation of cracks, and subsurface crack initiation was in the very long life range. The results shown that the portions of life attributed to subsurface crack initiation between 107 and 109 cycles are 99%.

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Study on Very High Cycle Fatigue Fracture of High Strength Steel with CFB/M Complex Microstructure

Materials Science Forum ◽

10.4028/www.scientific.net/msf.638-642.3839 ◽

2010 ◽

Vol 638-642 ◽

pp. 3839-3845 ◽

Cited By ~ 3

Author(s):

Y. Yu ◽

B.Z. Bai ◽

Jia Lin Gu

Keyword(s):

Crack Initiation ◽

High Purity ◽

High Cycle Fatigue ◽

High Strength Steels ◽

High Strength ◽

Inclusion Size ◽

Cycle Fatigue ◽

Very High Cycle Fatigue ◽

Very High ◽

Production Conditions

The influence of production conditions and Nb microalloy on the very high cycle fatigue (VHCF) behaviors of different Carbide-free bainite/martensite (CFB/M) steels was studied, which include steels produced in laboratory and steelworks. Results show the Nb-microalloy can strengthen the microstructure including the soft bainite plate and improve the VHCF property evidently. In addition, the high purity of steels can avoid inclusion induced crack initiation, but can not improve the VHCF property unless the microstructure possesses favorable uniformity. The critical inclusion size is suggested to be 10-15μm and the CFB/M complex microstructure may be less sensitive to inclusions than other high strength steels.

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