Micromechanical modeling for the probabilistic failure prediction of stents in high-cycle fatigue

Abstract

International audienceThe present paper introduces a methodology for the high-cycle fatigue design of balloon-expandable stents. The proposed approach is based on a micromechanical model coupled with a probabilistic methodology for the failure prediction of stents. This allows to account for material heterogeneity and scatter, to introduce a fatigue criterion able to consider stress gradients, and to perform a probabilistic analysis to obtain general predictions from a limited number of realizations of microstructures investigated. Numerical simulations have allowed to highlight the noteworthy characteristics of the mechanical response in the stent as well as the heterogeneity of the mechanical fields due to stress concentrations in the unit cell geometry and to strain incompatibilities between the grains induced by the anisotropy of their mechanical behavior. The predicted survival probability of the stent is in accordance with the experimental data from the literature. Moreover, the influence of the amplitude of the arterial pressure on the fatigue strength of the stent has been evaluated

A Critical Review on Metallic Glasses as Structural Materials for Cardiovascular Stent Applications

“…Hence, long-term structural integrity of stents, especially their fatigue behaviour, must be one of the major design considerations. In the HCF regime, where typically more than 10 5 cycles at low stresses are required for failure, the deformation is primarily elastic [ 155 , 156 ]. If the process-induced material defects, e.g., surface roughness, inclusions, porosity, etc., are minimized by optimization of the processing parameters and engaging in repeated elastic deformation of the material sample to remove the ‘softer’ sites in the BMGs, the HCF behaviour of BMG-based stents could be improved.…”

Effect of defect size and shape on the high-cycle fatigue behavior

“…where s s is the resolved shear stress acting on the slip system s; r 0 is the initial critical shear stress, v s and r s are respectively the kinematic and isotropic hardening variables associated to the slip system s; K and n are the parameters controlling the viscosity. The The material parameters of the single crystal viscoplaticity model have been calibrated from low-cycle fatigue tests conducted in several loading conditions: tension, torsion and combined outof-phase tension and torsion [13]. These parameters are summarized in Table 1.…”

“…The determination of the macroscopic fatigue strength requires specific fatigue criteria to accurately estimate the detrimental effect of a small notch. In order to address this issue, two multiaxial fatigue criteria, previously discussed, are used in the present work: a probabilistic fatigue criterion based on a distribution of the crack initiation threshold [12], a deterministic criterion relying on a fatigue damage process zone [13].…”

“…The deterministic criterion discussed in this section has been presented in a previous study [13]. Summarily, this criterion relies on the assumption that the fatigue crack initiation occurs if an equivalent stress r eq averaged over a given grain set G PZ exceeds a threshold c:…”

“…The objective of the present work is to analyze this issue from a numerical point of view, in the continuation of previous works [11][12][13] where fatigue design methodologies based on finite element analyses (FEA) of polycrystalline microstructures have been proposed. More precisely, FEAs of two-dimensional polycrystalline aggregates, loaded in fully reversed tension, are conducted in order to estimate the mechanical behavior, at the grain scale, in microstructures containing a small elliptical hole.…”