Research on high cycle fatigue damage characterization of FV520B steel based on the nonlinear Lamb wave

2021 ◽  
pp. 030932472110384
Author(s):  
Pengfei Wang ◽  
Qiwen Zhou ◽  
Bingbing Chen ◽  
Sanlong Zheng ◽  
Chao Wang ◽  
...  
Keyword(s):  
Fatigue Damage ◽  
Room Temperature ◽  
High Cycle Fatigue ◽  
Lamb Waves ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
High Strength ◽  
Cycle Fatigue ◽  
Initial Stage

In this study, high-strength steel FV520B sheets were subjected to high-cycle tensile-tension fatigue experiments at room temperature in order to obtain fatigue-damaged specimens. Then Lamb waves were used to perform nonlinear ultrasonic testing on them to obtain the normalized relative nonlinear coefficients, β′/ β0. The corresponding relationship between β′/ β0 and the percentage of fatigue life was obtained. Finally, the microstructural changes of the damaged samples were observed by a scanning electron microscope in order to explore the correlation mechanism between β′/ β0 and the degree of micro-defects and fatigue damage. The experimental results showed that as the number of fatigue cycles increased, β′/ β0 first slowly rose, then quickly rose to reach a peak, and finally declined, which was consistent with the generation and propagation of dislocations and cracks during fatigue damage. As the length and number of microcracks increased, β′/ β0 also increased, especially in the initial stage of fatigue crack initiation. β′/ β0 was very sensitive to the size of fatigue cracks, so the change of β′/ β0 can be used to detect the degree of early fatigue damage of the material.

Micromechanics of an Extrusion in High-Cycle Fatigue With Creep

1990 ◽  
Vol 57 (4) ◽  
pp. 815-820 ◽  
Author(s):  
T. H. Lin ◽  
S. R. Lin ◽  
X. Q. Wu
Keyword(s):  
Crack Initiation ◽  
Tensile Strain ◽  
High Cycle Fatigue ◽  
Elevated Temperatures ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Tensor Component ◽  
Shear Stresses ◽  
Cycle Fatigue ◽  
Thin Slice

Extrusions and intrusions often are sites of fatigue cracks. The extent of extrusions is important in fatigue crack initiation. Metals often are subject to fatigue loadings at elevated temperatures. At temperatures below one half of the melting temperature slip is the main mechanism of inelastic deformation. In this study, an aluminum polycrystal loaded in this temperature range is considered. A most favorably oriented crystal located at a free surface of a f.c.c. polycrystal subject to creep under cyclic tension and compression of high-cycle fatigue is considered. An extrusion in this crystal is shown to be produced by a positive slip in one thin slice “P” and a negative slip in a closely located slice “Q”. An initial tensile strain εααI in the thin slice “R” sandwiched between P and Q causes a positive initial shear stress ταβI in P and a negative one in Q. It is shown that the extrusion growth causes a tensile strain in R, which can activate a second slip system giving a creep strain with a tensor component εαα. It has the same effect as the initial strain εααI in causing this difference in shear stresses in P and Q and gives much additional extrusion growth. The extent of intrusion and extrusion is important in this study of crack initiation.

Characterization of the Welded-Joint of High-Strength High-Toughness Seamless Steel Pipe under High-Cycle Fatigue Condition

2017 ◽  
Vol 896 ◽  
pp. 202-208
Author(s):  
Qing Chao Tian ◽  
Xian Ping Dong ◽  
Hai Chao Cui ◽  
Ke Xu
Keyword(s):  
High Cycle Fatigue ◽  
Welded Joint ◽  
Weld Zone ◽  
High Strength ◽  
Cycle Fatigue ◽  
Steel Pipes ◽  
Fine Grain ◽  
The Matrix ◽  
Bainite Microstructure

The welded joint of a S890QL grade steel pipes containing 1.2% Ni have been prepared to characterize the use performance under high cycle fatigue test. It has been found that the fatigue strength of the welded joint is 290MPa with a fatigue life of more than 10 million cycles, and the obtained Basquin equation is σa=488*(2N)-0.02758 . It is found that the steel exhibits the whole bainite microstructure when the cooling rate is less than 1°C/s. The welded joint is divided into the weld zone, the coarse grain zone, the fine grain zone, the softening zone and the matrix. The fine grain characteristic in the welded area determines the good anti fatigue performance of the investigated steel.

On Fatigue Crack Initiation in the Matrix in Very High Cycle Fatigue Regime

2014 ◽  
Vol 783-786 ◽  
pp. 2266-2271 ◽  
Author(s):  
Guo Cai Chai
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Fatigue Damage ◽  
Strain Localization ◽  
High Cycle Fatigue ◽  
High Strain ◽  
Fatigue Crack Initiation ◽  
Cycle Fatigue ◽  
Very High Cycle Fatigue ◽  
Very High

In very high cycle fatigue, VHCF, regime, fatigue crack initiation can occur at subsurface defects such as inclusion or subsurface non-defect (matrix) origin. This paper provides a study on the fatigue crack initiation mechanisms at subsurface non-defect (matrix) origin in two metallic materials using electron backscatter diffraction and electron channeling contrast imaging. The results show that the strains in the material in the VHCF regime were highly localized, where the local maximum strain is greatly higher than the average strain value. This high strain localization can lead to the formation of fine grain zone and also fatigue damage or fatigue crack initiation at grain boundaries or twin boundaries by impingement cracking. High strain localization is caused by strain accumulation of each very small loading, and also increases the local hardness of the material. This may start quasi-cleavage crack origin, and consequently the formation of subsurface fatigue crack initiations. The results also show that fatigue damage and crack initiation mechanisms in the VHCF regime can be different in different metals due to the mechanisms for local plasticity exhaustion.

Micro Mechanical Behaviors and Damage in Nickel Base Alloy and Steels during Very High Cycle Fatigue

2016 ◽  
Vol 258 ◽  
pp. 506-513
Author(s):  
Guo Cai Chai
Keyword(s):  
Fatigue Damage ◽  
High Cycle Fatigue ◽  
Base Alloy ◽  
Fatigue Crack Initiation ◽  
Cycle Fatigue ◽  
Nickel Base Alloy ◽  
Very High Cycle Fatigue ◽  
Nickel Base ◽  
Cyclic Plastic Deformation ◽  
Very High

Fatigue damage in a metallic material during very high cycle fatigue can strongly be correlated to the microstructure. This paper provides a review and a discussion on the micro damage behaviors in a nickel base alloy and three steels during very high cycle fatigue using micro plasticity and material mechanics. The results show that cyclic plastic deformation in these materials can occur very locally even with an applied stress that is much lower than the yield strength. The fatigue damage occurs mainly at grain or twin boundaries due to local impingement and interaction of slip bands and these boundaries. The crystallographic properties, Schmid factors and orientations of grain and boundaries have very important roles to the fatigue damage. Subsurface fatigue crack initiation in the matrix is one of the mechanisms for very high cycle fatigue. In the fine granular area, high plastic strain localization and cyclic plastic deformation can lead to dislocation annihilation and consequently formation of vacancies, or eventually nanopores at the subcell boundary that leads to fatigue crack initiation and propagation.

scholarly journals Microstructural mechanisms of cyclic deformation, fatigue crack initiation and early crack growth

2015 ◽  
Vol 373 (2038) ◽  
pp. 20140132 ◽  
Author(s):  
Haël Mughrabi
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Crack Growth ◽  
Fatigue Damage ◽  
Cyclic Deformation ◽  
Damage Evolution ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Cycle Fatigue ◽  
Cubic Metals

In this survey, the origin of fatigue crack initiation and damage evolution in different metallic materials is discussed with emphasis on the responsible microstructural mechanisms. After a historical introduction, the stages of cyclic deformation which precede the onset of fatigue damage are reviewed. Different types of cyclic slip irreversibilities in the bulk that eventually lead to the initiation of fatigue cracks are discussed. Examples of trans- and intercrystalline fatigue damage evolution in the low cycle, high cycle and ultrahigh cycle fatigue regimes in mono- and polycrystalline face-centred cubic and body-centred cubic metals and alloys and in different engineering materials are presented, and some microstructural models of fatigue crack initiation and early crack growth are discussed. The basic difficulties in defining the transition from the initiation to the growth of fatigue cracks are emphasized. In ultrahigh cycle fatigue at very low loading amplitudes, the initiation of fatigue cracks generally occupies a major fraction of fatigue life and is hence life controlling.

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