Study on small fatigue crack initiation and growth for friction stir welded joints

Sun, Guo-Qin; Wang, Chongwen; Wei, Xinhai; Shang, De‐Guang; Chen, Shujun

doi:10.1016/j.msea.2018.10.002

Cited by 38 publications

(18 citation statements)

References 29 publications

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“…Aluminum alloy has ductility characteristics; however, in the instant fracture zone, it exhibited a large number of cleavage steps (marked with white arrows in Figure 16), showing the characteristics of brittle fracture. This is also different from the mixed brittle and ductile fracture feature when undergoing fatigue in an inert environment [22]. This indicates that the brittle feature of the instant fracture zone was caused by hydrogen embrittlement occurred in corrosion environment.…”

Section: Corrosion Fatigue Transient Crackmentioning

confidence: 77%

“…The microstructure of the aluminum alloy changed during the FSW process. Three distinct zones, namely, WNZ, TMAZ, and HAZ, were generated due to the nonuniform heating and plastic flow [ 22 , 23 , 24 ]. The macrostructure of the FSW joint cross-section is shown in Figure 6 , and the microstructure of the FSW joint is shown in Figure 7 .…”

Section: Resultsmentioning

confidence: 99%

“…When these two kinds of damages coexist, the corrosion effect of the corrosive medium on the crack-tip metal significantly increases the corrosion fatigue crack growth rate of the welded joint surface, leading to the premature failure of the FSW joint. However, current research on the corrosion fatigue of FSW joints mainly focuses on the corrosion fatigue study of samples after pre-corrosion combined with fatigue behavior [ 19 , 20 , 21 , 22 , 23 ], which is different from the coupled effect of the corrosion environment and the fatigue of structures under alternating loads in the oceanic environment. At present, there are few reports on the corrosion fatigue of FSW joints under the coupled effect of corrosion and fatigue, which is not enough to provide significant guidance for the improvement of the corrosion fatigue performance of welded joints.…”

Section: Introductionmentioning

confidence: 99%

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Corrosion Fatigue Fracture Characteristics of FSW 7075 Aluminum Alloy Joints

Shao

Bai

et al. 2020

Materials

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The corrosion fatigue properties and fracture characteristics of friction stir welding joints of 7075 aluminum alloys were studied via corrosion fatigue tests, electrochemical measurements, and corrosion fatigue morphology and microstructure observations. The results show that the corrosion fatigue crack of the friction stir welding (FSW) joint of 7075 aluminum alloys originated in the junction zone between the thermomechanically affected zone and the weld nugget zone. The corrosion fatigue life of the joint decreased with increasing stress amplitude, with an S–N curve equation of lgN = 5.845 − 0.014S. Multiple crack sources were observed in the corrosion fatigue fracture. The main crack source originated from the corrosion pits at the interface between the thermomechanically affected zone and the weld nugget zone due to the influence of the coarse microstructure and the large potential difference between both zones. Corrosion morphologies of a rock candy block and an ant nest appeared in the crack propagation zone and the grain boundary of the weld nugget zone. In addition, fatigue speckles and intergranular fractures were observed, as well as brittle fracture characterized by cleavage steps and secondary cracks in the final fracture zone.

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Section: Corrosion Fatigue Transient Crackmentioning

confidence: 77%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Corrosion Fatigue Fracture Characteristics of FSW 7075 Aluminum Alloy Joints

Shao

Bai

et al. 2020

Materials

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“…The tests were paused at a predetermined cycle number to make a replica of the specimen surface. To facilitate the replicating process, a static tensile load of 80% of the maximum test load was manually applied to ensure that the cracks were fully open [17]. A cellulose acetate film softened by acetone was pasted on the surface of the specimens to record the initiation and propagation of the cracks.…”

Section: Methodsmentioning

confidence: 99%

“…To solve the unknown parameters, G 0 can be moved to the left side of the equation, and then take the logarithm of both sides, Equations (16) and (17) can be converted into the following:…”

Section: Experimental Verification Of the Multiaxial Short Cracks Gromentioning

confidence: 99%

Study on Short Fatigue Crack Behaviour of LZ50 Steel Under Non-Proportional Loading

et al. 2020

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The low cycle fatigue tests using the replica technique for LZ50 steel under non-proportional cyclic loading were carried out, and eight groups of effective test data were obtained. The evolution behaviour of short cracks was studied based on the effective short cracks criterion. The results show that short cracks generally originate in the grain or along the grain boundary. At the microstructural short crack stage, the crack propagation is influenced strongly by the microstructure of the material, and the growth rate of the short crack slows down several times according to the number of obstacles encountered. At the physical short crack stage, the crack propagation breaks through the banded structure of pearlite. Thus, the dominant effective short fatigue crack is formed, and the crack growth rate increases rapidly. Based on the modified parameters of the uniaxial short crack model, an approach is presented to calculate the growth rate of short cracks under multi-axial non-proportional loadings, and the new model can consider the non-proportional factor F. The fitting results of the multi-axial microstructural obstacles model are compared with test data. The comparison results show that this model can reflect the trend of short fatigue crack propagation rate under non-proportional loadings.

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Review on fatigue life prediction models of welded joint

Kang

Luo

2020

Acta Mech. Sin.

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Study on small fatigue crack initiation and growth for friction stir welded joints

Cited by 38 publications

References 29 publications

Corrosion Fatigue Fracture Characteristics of FSW 7075 Aluminum Alloy Joints

Corrosion Fatigue Fracture Characteristics of FSW 7075 Aluminum Alloy Joints

Study on Short Fatigue Crack Behaviour of LZ50 Steel Under Non-Proportional Loading

Review on fatigue life prediction models of welded joint

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