Fatigue crack initiation in as forged Ti–6Al–4V bars with macrozones present

Zhang, Kai; Yang, Kun; Huang, Aijun; Wu, Xinhua

doi:10.1016/j.ijfatigue.2015.05.020

Cited by 74 publications

(24 citation statements)

References 25 publications

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“…Jha et al proposed a model that the deviation of fatigue life of (α + β) titanium alloy results form a heterogeneity between the facet and the surrounding matrix . In addition, in Ti‐6Al‐4V, the so‐called macrozone is believed to behave like a large single crystal because of the similar orientation of plural grains . These ideas seem to be reasonable to explain the results obtained by μCT imaging.…”

Section: Discussionmentioning

confidence: 95%

Initiation and growth behaviour of small internal fatigue cracks in Ti‐6Al‐4V via synchrotron radiation microcomputed tomography

Yoshinaka

Nakamura

Takeuchi

et al. 2019

Fatigue Fract Eng Mat Struct

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Small internal fatigue cracks initiated in Ti‐6Al‐4V in the very high cycle regime were detected by synchrotron radiation microcomputed tomography (SR‐μCT) at SPring‐8 in Japan. The initiation and growth behaviours of the cracks were nondestructively observed, and the da/dN‐ΔK relationship was measured and compared with that obtained in a high vacuum environment. SR‐μCT revealed that more than 20 cracks were initiated in one specimen. The crack initiation life varied widely from 20% to 70% of the average fatigue life and had little influence on the growth behaviour that followed. The initiation site size of each internal crack detected in one specimen was comparable with the size of the fracture origins obtained in ordinary fatigue tests. These results suggest that the surrounding microstructures around the initiation site are likely a dominant factor on the internal fracture rather than the potential initiation site itself. The internal crack growth rates were lower than 10−10 m/cycle, and extremely slow rates ranging from 10−13 to 10−11 m/cycle were measured in a lower ΔK regime below 5 MPa√m. The internal crack growth rate closely matched that of surface cracks in a high vacuum, and the reason for the very long life of internal fatigue fractures was believed to result from the vacuum‐like environment inside the internal cracks.

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Section: Discussionmentioning

confidence: 95%

Initiation and growth behaviour of small internal fatigue cracks in Ti‐6Al‐4V via synchrotron radiation microcomputed tomography

Yoshinaka

Nakamura

Takeuchi

et al. 2019

Fatigue Fract Eng Mat Struct

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“…A macro-zone, which is badly oriented for slip adjacent to a softer unit well-oriented for slip, provides the potential for load shedding from soft to hard grains during dwell and for the formation of a large basal facet across the entire α unit. This has been argued to be of particular significance in dwell fatigue and in driving the 'dwell debit' [39], [40], [41].…”

Section: Application To Cold Dwellmentioning

confidence: 99%

The effect of the beta phase on the micromechanical response of dual-phase titanium alloys

Ashton

Jun

Zhang

et al. 2017

International Journal of Fatigue

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This paper investigates the role of beta phase on the micro-mechanical behaviour of dual-phase titanium alloys, with particular emphasis on the phenomenon of cold dwell fatigue, which occurs in such alloys under room temperature conditions. A strain gradient crystal plasticity model is developed and calibrated against micro-pillar compression test data for a dual-phase alpha-beta specimen. The effects of key microstructural variables, such as relative beta lath orientation, on the micromechanical response of idealised alpha-beta colony microstructures are shown to be consistent with previously-published test data. A polycrystal study on the effects of the calibrated alpha-beta crystal plasticity model on the local micromechanical variables controlling cold dwell fatigue is presented. The presence of the alpha-beta phase is predicted to increase dwell fatigue resistance compared to a pure alpha phase microstructure

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“…More recent modelling work by Phung et al [23] used the Schmid criterion to predict preferential sites of persistent slip marking (PSM) only to conclude that the prediction of the two different types of PSMs they considered could not be achieved. Understanding local slip behaviour in micro-volumes [25] or macrozones in Ti 6Al 4V [26] from macroscopic stress states also remains problematic. To date, local stress effects and their role in Schmid factor determination have not been thoroughly investigated.…”

Section: Introductionmentioning

confidence: 99%

An HR-EBSD and computational crystal plasticity investigation of microstructural stress distributions and fatigue hotspots in polycrystalline copper

et al. 2016

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High resolution EBSD studies on a deformed copper polycrystal have been carried out to quantify the microstructural residual stress distributions, and those of stress state including triaxiality of importance in defect nucleation studies. Crystal plasticity analysis of a representative, similarly textured, model polycrystal has been carried out showing that the experimental distributions of microstructural residual stress components, effective stress, hydrostatic stress and stress triaxiality are well captured.The crystal model enables point-wise microstructural Schmid factors to be calculated both globally (ie with respect to the macroscopic remote loading) and locally from full knowledge of the grain-level stress state. Significant differences are demonstrated such that global Schmid analysis tends to overestimate slip activity and the frequency of high Schmid factors, indicating that the local microstructural heterogeneity is significant and caution is necessary in interpreting polycrystal behaviour using global Schmid factors. A stored energy criterion for fatigue crack nucleation indicates that preferential sites for fatigue crack nucleation are local to grain boundaries (as opposed to triple junctions), and that hard-soft grain interfaces where high GND densities develop are preferable.

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Fatigue crack initiation in as forged Ti–6Al–4V bars with macrozones present

Cited by 74 publications

References 25 publications

Initiation and growth behaviour of small internal fatigue cracks in Ti‐6Al‐4V via synchrotron radiation microcomputed tomography

Initiation and growth behaviour of small internal fatigue cracks in Ti‐6Al‐4V via synchrotron radiation microcomputed tomography

The effect of the beta phase on the micromechanical response of dual-phase titanium alloys

An HR-EBSD and computational crystal plasticity investigation of microstructural stress distributions and fatigue hotspots in polycrystalline copper

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