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Research Papers

Computational Assessment of Stent Durability Using Fatigue to Fracture Approach

[+] Author and Article Information
Gordana R. Jovicic

Professor
Faculty of Engineering,
University of Kragujevac,
Sestre Janjic 6,
Kragujevac 34000, Serbia
e-mail: gjovicic.kg.ac.rs@gmail.com

Arso M. Vukicevic

Faculty of Engineering,
University of Kragujevac,
Sestre Janjic 6,
Kragujevac 34000, Serbia
e-mail: arso_kg@yahoo.com

Nenad D. Filipovic

Professor
Faculty of Engineering,
University of Kragujevac,
Sestre Janjic 6,
Kragujevac 34000, Serbia
e-mail: fica@kg.ac.rs

Manuscript received August 22, 2013; final manuscript received May 10, 2014; published online xx xx, xxxx. Assoc. Editor: Keefe B. Manning.

J. Med. Devices 8(4), 041002 (Aug 19, 2014) (8 pages) Paper No: MED-13-1198; doi: 10.1115/1.4027687 History: Received August 22, 2013; Revised May 10, 2014

Stents are metal scaffold devices used to maintain lumen and restore blood flow of diseased artery. Despite they brought care of coronary diseases to a new level of efficacy, problem of stent fracture remains unclear even after global needs reached number of 5 × 106 devices yearly. For projected work-life of 10 years, rate of fracture occurrence in stents varies from 5% up to 25% for different designs. Analysis of such miniature devices and long-term events in realistic in vivo conditions remains impossible while experimental in vitro measurements provide limited results consuming much time and expensive equipment. The principal aim of this study was to propose procedure for numerical estimation of coronary stents durability assuming the hyperphysiological pulsatile pressure conditions. The hypothesis was whether the stent durability would be achieved safely for the projected work-life of 10 yr? The procedure was carried out within three phases: (a) initial fatigue analysis based on S-N approach; (b) fatigue lifetime assessment based on fatigue crack growth simulation using Paris power law, and (c) safe-operation, i.e., no-fatigue failure (based on Kitagawa–Takahashi diagram) as well as immediate predictions of the fracture event in the stent. For considered generic stent design, results showed that the stent durability would be achieved safely. Since special diagrams were used, the fatigue risk assessment was clearer compared to the conventional fatigue lifetimes. Moreover, it was found that crack growth was stable for both small and large scale sizes of the crack. Besides the fact that the presented procedure was shown as suitable for numerical assessment of the generic stent durability under hyperphysiological pulsatile pressure conditions, it was concluded that it might be applied for any other design as well as loading conditions. Moreover, it could be efficiently combined with experimental procedures during the process of the stent design validation to reduce manufacturing and testing costs.

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References

Figures

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Fig. 1

Procedure overview

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Fig. 2

Fatigue crack growth rate diagram

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Fig. 3

KT diagram for safe-operation assessment

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Fig. 7

Crack growth simulation: (a) Initial sharp crack form and (b) contour of effective stress in 8th step of crack growth simulation with flaw depth of 83μm

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Fig. 6

Mesh refinement: (a) FEM mesh before and after remeshing, (b) and (d) original elements, (c) and (e) refinement patterns, and (f) and (g) elements after refinement

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Fig. 9

KT-diagram and numerical values of flaw propagation in the stent

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Fig. 5

Contours of: (a) mean stress, (b) amplitude stress, (c) principal stress σ1, and (d) reciprocal FSF

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Fig. 4

Crack propagation: (a) volume integration around crack front and (b) angle crack growth in plane x1-x2 normal to the crack front

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Fig. 8

Predicted residual lifetime of the stent following Paris law for various cyclic stress ranges and flaw sizes

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