Fatigue crack initiation behaviors throughout friction stir welded joints in AA7075-T6 in ultrasonic fatigue

He, Chao; Liu, Yongjie; Dong, Jiangfeng; Wang, Hongtao; Wagner, Danièle; Bathìas, Claude

doi:10.1016/j.ijfatigue.2015.07.012

Cited by 36 publications

(33 citation statements)

References 28 publications

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“…The fatigue strength of peened specimens decreased continuously with the increasing fatigue life up to the VHCF range, while the S–N curve of un‐peened specimen exhibited a horizontal platform within the range of 10 7 –10 8 cycles. It has been found that the platform corresponded to the transition duration of fatigue crack initiation sites from the TMAZ in short fatigue life to the NZ in the VHCF . The monotonically decreasing fatigue resistance for peened specimen probably implies a different failure mechanism as compared with un‐peened specimen, and this will be explained in the following sections.…”

Section: Resultssupporting

confidence: 50%

“…The fatigue crack initiation behaviours of un‐peened FSW joint have been investigated in our previous work . It was found that fatigue crack originated from the TMAZ on the advancing side in high cycle fatigue range, because the interior particles were cracked under the intense plastic deformation during the FSW process, and fatigue cracks started propagating directly from these pre‐existing microcracks under the cyclic loading.…”

Section: Resultsmentioning

confidence: 95%

“…Generally, the fatigue strength improvement by a certain group of treating parameters remained almost consistent at different fatigue lives for parent materials . The difference of fatigue strength improvement in this work can be ascribed to microstructural and mechanical heterogeneous throughout the weld, which led to the changes of fatigue crack initiation location in different fatigue life ranges …”

Section: Resultsmentioning

confidence: 99%

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Improvement of very high cycle fatigue properties in an AA7075 friction stir welded joint by ultrasonic peening treatment

Yang

Liu

et al. 2016

Fatigue Fract Eng Mat Struct

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The present paper aims to investigate the effect of ultrasonic peening treatment on the very high cycle fatigue resistance of an AA7075 friction stir welded joint. Microscopy observation, microhardness and X‐ray diffraction measurements were carried out to characterize the treated surface of peened specimens. Fatigue crack initiation sites were investigated through scanning electron microscope, and the role of enhanced surface on fatigue resistance was analyzed. The results indicate that a sensible fatigue strength improvement can be obtained through application of ultrasonic peening treatment and that fatigue cracks can initiate from the interior of the specimen. To clarify the fatigue failure mechanism, we analyzed the microstructure characteristics, compressive residual stress profile and intermetallic inclusion distribution in the surface layers, and we discussed the capability of ultrasonic peening treatment to hinder the surface crack initiation.

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Section: Resultssupporting

confidence: 50%

Section: Resultsmentioning

confidence: 95%

Section: Resultsmentioning

confidence: 99%

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Improvement of very high cycle fatigue properties in an AA7075 friction stir welded joint by ultrasonic peening treatment

Yang

Liu

et al. 2016

Fatigue Fract Eng Mat Struct

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“…It revealed that the fatigue crack originated at the advancing side due to the effects of microstructural heterogeneity. Our previous work [12,13] also found that fatigue crack initiation sites were localized at the thermomechanically affected zone on the advancing side below 10 8 cycles. Nevertheless, the failure was prone to occur at the nugget zone in the VHCF regime.…”

Section: Introductionmentioning

confidence: 79%

“…For comparison, the data of AA 7075 FSW joint obtained from the full specimen in our previous work are also presented [13], in which the fatigue failures occurred at the TMAZ in high cycle fatigue regime and at the NZ in the VHCF. It is clear that the fatigue strength keeps going down with cyclic load increasing.…”

Section: S-n Curvesmentioning

confidence: 99%

Very High Cycle Fatigue Crack Initiation Mechanism in Nugget Zone of AA 7075 Friction Stir Welded Joint

Kitamura

Yang³

et al. 2017

Advances in Materials Science and Engineering

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Very high cycle fatigue behavior of nugget zone in AA 7075 friction stir welded joint was experimentally investigated using ultrasonic fatigue testing system (20 kHz) to clarify the crack initiation mechanism. It was found that the fatigue strength of nugget zone decreased continuously even beyond 10 7 cycles with no traditional fatigue limits. Fatigue cracks initiated from the welding defects located at the bottom side of the friction stir weld. Moreover, a special semicircular zone could be characterized around the crack initiation site, of which the stress intensity factor approximately equaled the threshold of fatigue crack propagation rate. Finally, a simplified model was proposed to estimate the fatigue life by correlating the welding defect size and applied stress. The predicted results are in good agreement with the experimental results.

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Genesis of Microstructures in Friction Stir Welding of Ti-6Al-4V

Tchein

Jacquin

Coupard

et al. 2018

Metall Mater Trans A

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This paper is focused on the genesis of microstructures in Friction Stir Welding (FSW) of the Ti-6Al-4V alloy. Several titanium joints, initially prepared with 4 different pre-heat treatments, were processed by FSW. Detailed microstructural analyses were performed in order to investigate change in the microstructure during the process. In this work, the FSW processing allows a controlled and stable microstructure to be produced in the stirring zone, regardless of the initial heat treatment or the welding conditions. The welded material undergoes a severe thermo-mechanical treatment which can be divided into two steps. First, the friction in the shoulder and the plastic strain give rise to the necessary conditions to allow a continuous dynamic recrystallization (CDRX) of the β phase. This operation produces a fine and equiaxed β grain structure. Second, once the pin has moved away, the temperature decreases and the material undergoes a heat treatment equivalent to air quenching. The material thus exhibits a β→β+α transformation with germination of a fine intergranular Widmanstätten phase within the ex-fully-recrystallized-β grains.

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Fatigue crack initiation behaviors throughout friction stir welded joints in AA7075-T6 in ultrasonic fatigue

Cited by 36 publications

References 28 publications

Improvement of very high cycle fatigue properties in an AA7075 friction stir welded joint by ultrasonic peening treatment

Improvement of very high cycle fatigue properties in an AA7075 friction stir welded joint by ultrasonic peening treatment

Very High Cycle Fatigue Crack Initiation Mechanism in Nugget Zone of AA 7075 Friction Stir Welded Joint

Genesis of Microstructures in Friction Stir Welding of Ti-6Al-4V

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