Strain-gradient modelling of grain size effects on fatigue of CoCr alloy

Sweeney, Caoimhe A.; O’Brien, Barry; Dunne, Fionn P.E.; McHugh, Peter E.; Leen, Seán B.

doi:10.1016/j.actamat.2014.06.044

Cited by 72 publications

(59 citation statements)

References 52 publications

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“…Optical microscopy was first carried out to determine the grain structure in the foil. An etching solution of 100 ml HCl and 5 ml 30% H 2 O 2 was used, as described for the macro-scale CoCr material in [10,28]. Optical micrographs of the foil are shown in Fig.…”

Section: Microscopymentioning

confidence: 99%

“…1 (b), a similar grain morphology is observed for all three directions; it appears the microstructure is equiaxed. As in previous studies [10,28], an approximation of hexagonal grains is adopted to extract a grain size distribution; a hexagon-based conversion is applied to each grain measurement, whereby the grain size of a hexagonal grain (flat-to-flat dimension), with area equivalent to the measured grain area, is identified. The foil material is found to have an average grain size of 38 µm, corresponding to the average grain size for equivalent hexagonal grains.…”

Section: Microscopymentioning

confidence: 99%

“…L605 foil micro-specimens are manufactured and tested under HCF loading conditions, and microscopy is carried out on the foil to aid in generation of realistic crosssection polycrystalline models for the foil specimens. The micromechanical framework used for HCF prediction has been developed and calibrated in previous works [10,28] for the LCF fatigue behaviour of the L605 alloy, and is hypothesised to predict fatigue behaviour across both LCF and HCF regimes. Two CP models are investigated and compared within the micromechanical framework for describing the material constitutive behaviour.…”

Section: Introductionmentioning

confidence: 99%

“…Two CP models are investigated and compared within the micromechanical framework for describing the material constitutive behaviour. The first is a physically-based strain-gradient CP model, which has been calibrated against cyclic plasticity data for as-received, fine-grain (d = 32 µm) L605 material in previous work [28] and, with the same calibrated constants, has been shown to also capture the behaviour of heat-treated, coarse grain (d = 243 µm) material. A phenomenological power-law constitutive model, previously calibrated against both monotonic and cyclic plasticity data, and applied to the assessment of a stent fatigue design for the L605 alloy [10], is also investigated.…”

Section: Introductionmentioning

confidence: 99%

“…A phenomenological power-law constitutive model, previously calibrated against both monotonic and cyclic plasticity data, and applied to the assessment of a stent fatigue design for the L605 alloy [10], is also investigated. Two microstructure-sensitive FIPs, effective plastic strain, p, and crystallographic work, W, are implemented for the prediction of the number of cycles to crack initiation, N i , for HCF behaviour, based on critical FIP values calibrated and validated from macro-scale LCF test data [10,28], and the predictions are compared with the experimental stress-life data. The micromechanical framework presented and validated here for stent fatigue design addresses an outstanding predictive need, highlighted by Marrey et al [6], for HCF of CoCr alloy stents.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Microscopymentioning

confidence: 99%

Section: Microscopymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

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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Fatigue of Metallic Stents: From Clinical Evidence to Computational Analysis

et al. 2015

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The great success of stents in treating cardiovascular disease is actually undermined by their long-term fatigue failure. The high variability of stent failure incidence suggests that it is due to several correlated aspects, such as loading conditions, material properties, component design, surgical procedure, and patient functional anatomy. Numerical and experimental non-clinical assessments are included in the recommendations and requirements of several regulatory bodies and they are thus exploited in the analysis of stent fatigue performance. Optimization-based simulation methodologies have been developed as well, to improve the fatigue endurance of novel designs. This paper presents a review on the fatigue issue in metallic stents, starting from a description of clinical evidence about stent fracture up to the analysis of computational approaches available from the literature. The reported discussion on both the experimental and numerical framework aims at providing a general insight into stent lifetime prediction as well as at understanding the factors which affect stent fatigue performance for the design of novel components.

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Structural Mechanics Predictions Relating to Clinical Coronary Stent Fracture in a 5 Year Period in FDA MAUDE Database

Everett¹,

Conway²,

Desany

et al. 2015

Ann Biomed Eng

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Endovascular stents are the mainstay of interventional cardiovascular medicine. Technological advances have reduced biological and clinical complications but not mechanical failure. Stent strut fracture is increasingly recognized as of paramount clinical importance. Though consensus reigns that fractures can result from material fatigue, how fracture is induced and the mechanisms underlying its clinical sequelae remain ill-defined. In this study, strut fractures were identified in the prospectively maintained Food and Drug Administration's (FDA) Manufacturer and User Facility Device Experience Database (MAUDE), covering years 2006–2011, and differentiated based on specific coronary artery implantation site and device configuration. These data, and knowledge of the extent of dynamic arterial deformations obtained from patient CT images and published data, were used to define boundary conditions for 3D finite element models incorporating multimodal, multi-cycle deformation. The structural response for a range of stent designs and configurations was predicted by computational models and included estimation of maximum principal, minimum principal and equivalent plastic strains. Fatigue assessment was performed with Goodman diagrams and safe/unsafe regions defined for different stent designs. Von Mises stress and maximum principal strain increased with multimodal, fully reversed deformation. Spatial maps of unsafe locations corresponded to the identified locations of fracture in different coronary arteries in the clinical database. These findings, for the first time, provide insight into a potential link between patient adverse events and computational modeling of stent deformation. Understanding of the mechanical forces imposed under different implantation conditions may assist in rational design and optimal placement of these devices.

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Strain-gradient modelling of grain size effects on fatigue of CoCr alloy

Cited by 72 publications

References 52 publications

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

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

Fatigue of Metallic Stents: From Clinical Evidence to Computational Analysis

Structural Mechanics Predictions Relating to Clinical Coronary Stent Fracture in a 5 Year Period in FDA MAUDE Database

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