Fatigue crack nucleation: Mechanistic modelling across the length scales

Dunne, Fionn P.E.

doi:10.1016/j.cossms.2014.02.005

Cited by 77 publications

(43 citation statements)

References 58 publications

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“…These GND and residual stress hot spot observations agree well with reported preferential fatigue crack sites observed by optical or scanning electron microscopy as well as predicted mechanistic modelling on various length scales as summarised by recent reviews of fatigue crack nucleation by Sangid [59], Dunne [60] and McDowell and Dunne [61]. Although a detailed fatigue crack mechanism is not yet clear, it is evident that strong correlations have been found between dislocation density and stress hot spots and microstructural features favoured for crack nucleation.…”

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confidence: 78%

Evolution of intragranular stresses and dislocation densities during cyclic deformation of polycrystalline copper

2015

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We have used the cross-correlation based high resolution electron backscattering diffraction (HR-EBSD) technique to evaluate at high spatial resolution the spatial patterning of the type III intragranular residual stresses and geometrically necessary dislocation (GND) density within polycrystalline Cu after cyclic deformation. Oxygen free high conductivity (OFHC) polycrystalline copper samples were cyclically deformed under stress-control at a load ratio of 0.1 and EBSD measurements were made at points throughout the early stages of fatigue when strain amplitudes and cyclic creep rates are changing most significantly, namely at 0 cycles, 2 cycles, 200 cycles and 2000 cycles. Statistical analysis is presented showing that moderate correlations exist between stored GND density, residual intragranular stress and distance from the nearest grain boundaries or/and triple junctions. Ref: Ms.No.A-15-232Manuscript: "Evolution of intragranular stresses and dislocation densities during cyclic deformation of polycrystalline copper" Dear Prof MahajanWe are very pleased to submit our revised manuscript to Acta Materialia for considering publication. Each of referee's comment and suggestion has been carefully addressed. Detailed explanations are included in the 'Response to Reviewer' file. All changes and corrections to our original manuscript have been highlighted in the revised manuscript.We would be very grateful for Editor's effort and time to process our manuscript and very look forward to hearing from you soon. Authors are very grateful to Reviewer's time, effort and constructive comments. In order to comprehensively revise our manuscript and give most appropriate response, we address Reviewer's comments one by one in detail in the following section. (Reviewer's comments are marked using red colour, correction to the manuscript are marked as yellow and Authors responses are marked as blue.Editor's/Reviewer's comments: This paper gives some interesting insights into dislocation and stress development during cyclic testing. Overall the analysis is appropriate, although I was surprised about two things: the correlations reported in the paper are pretty low; I was surprised that the authors did not pursue this a little further to factor out some of the issues (such as substructure development) that appear to play an important role in causing this. Relating to the previous point, the authors mention dislocation substructure development in an extremely cursory and handwaving fashion. They mention correlations with orientation and different types of structure, but in an almost off-handed way that does not even connect with the wealth of literature on the subject. Issue 2. should certainly be fixed, and it would be nice to improve issue 1. a little if possible. I have made comments on the manuscript that I hope will be helpful (including pointing out a few typos).1. These coefficients are low. The correlation coefficients are generally not very high (~-0.2) (That's a bit of a stretch) This is a sensible suggestion and ...

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supporting

confidence: 78%

Evolution of intragranular stresses and dislocation densities during cyclic deformation of polycrystalline copper

2015

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“…As mentioned previously, crack initiation is expected to dominate over propagation in HCF, particularly in the case of micro-scale components, and it has been firmly established that FCI is a microstructurally-driven phenomenon [15][16][17]. Sangid [18] provides a comprehensive description of the build-up of dislocations and development of energy minimising dislocation structures leading to the formation of persistent slip bands, and subsequent crack initiation at the slip band-matrix interface.…”

Section: Introductionmentioning

confidence: 95%

Micro-scale testing and micromechanical modelling for high cycle fatigue of CoCr stent material

Sweeney

O’Brien

Dunne

et al. 2015

Journal of the Mechanical Behavior of Biomedical Materials

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This paper presents a framework of experimental testing and crystal plasticity micromechanics for high cycle fatigue (HCF) of micro-scale L605 CoCr stent material.Micro-scale specimens, representative of stent struts, are manufactured via laser micromachining and electro-polishing from biomedical grade CoCr alloy foil. Crystal plasticity models of the micro-specimens are developed using a length scale-dependent, strain-gradient constitutive model and a phenomenological (power-law) constitutive model, calibrated from monotonic and cyclic plasticity test data. Experimental microstructural characterization of the grain morphology and precipitate distributions is used as input for the polycrystalline finite element (FE) morphologies. Two microstructure-sensitive fatigue indicator parameters are applied, using local and non-local (grain-averaged) implementations, for the phenomenological and length scale-dependent models, respectively, to predict fatigue crack initiation (FCI) in the HCF experiments.

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“…Many recent reviews have outlined the importance of understanding of fatigue crack formation, and propagation mechanisms at the microstructure scale are critical to facilitate quantitative prediction of fatigue lifetime as a function of microstructure [2][3][4][5][6][7]. These reviews highlight the need to deliver new experimental insight into deformation processes and failure in fatigue to drive modelling that can accurately capture microstructurally-sensitive effects and use geometrically faithful models.…”

Section: Introductionmentioning

confidence: 99%

On the mechanistic basis of fatigue crack nucleation in Ni superalloy containing inclusions using high resolution electron backscatter diffraction

et al. 2015

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This is an authors' copy of a manuscript published in Acta Materialia Volume 97, 15 September 2015, Pages 367-379. http://dx.doi.org/10.1016/j.actamat.2015.06.035 AbstractA series of interrupted three-point bend low-cycle fatigue tests were carried out on a powder metallurgy FHG96 nickel superalloy sample containing non-metallic inclusions. High resolution electron backscatter diffraction (HR-EBSD) was used to characterize the distribution and evolution of geometrically necessary dislocation (GND) density, residual stress and total dislocation density near a non-metallic inclusion. A systematic study of room temperature cyclic deformation is presented in which slip localisation, cyclic hardening, ratcheting and stabilisation occur, through to crack formation and microstructurally-sensitive propagation. Particular focus is brought to bear at the inclusion-matrix interface. Complex inhomogeneous deformation structures were directly observed from the first few loading cycles, and these structures were found not to vary significantly with increasing number of cycles. A clear link was observed between crack nucleation site and microstructurally-sensitive growth path and the spatially-resolved sites of extreme values of residual stress and GND density.

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Fatigue crack nucleation: Mechanistic modelling across the length scales

Cited by 77 publications

References 58 publications

Evolution of intragranular stresses and dislocation densities during cyclic deformation of polycrystalline copper

Evolution of intragranular stresses and dislocation densities during cyclic deformation of polycrystalline copper

Micro-scale testing and micromechanical modelling for high cycle fatigue of CoCr stent material

On the mechanistic basis of fatigue crack nucleation in Ni superalloy containing inclusions using high resolution electron backscatter diffraction

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