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http://hdl.handle.net/10985/11316
Micromechanical modeling for the probabilistic failure prediction of stents in high-cycle fatigue
GUERCHAIS, Raphaël; SCALET, Giulia; CONSTANTINESCU, Andrei; AURICCHIO, Ferdinando
The 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.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10985/113162016-01-01T00:00:00ZGUERCHAIS, RaphaëlSCALET, GiuliaCONSTANTINESCU, AndreiAURICCHIO, FerdinandoThe 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.Micromechanical study of the loading path effect in high cycle fatigue
http://hdl.handle.net/10985/8937
Micromechanical study of the loading path effect in high cycle fatigue
GUERCHAIS, Raphaël; ROBERT, Camille; SAINTIER, Nicolas; MOREL, Franck
In this work, an analysis of both the mechanical response at the grain scale and high cycle multiaxial fatigue criteria is undertaken using finite element (FE) simulations of polycrystalline aggregates. The metallic material chosen for investigation, a pure copper, has a Face Centred Cubic (FCC) crystalline structure. Two-dimensional polycrystalline aggregates, which are composed of 300 randomly orientated equiaxed grains, are loaded at the median fatigue strength defined at 107 cycles. In order to analyse the effect of the loading path on the local mechanical response, combined tension–torsion and biaxial tension loading cases, in-phase and out-of-phase, with different biaxiality ratios, are applied to each polycrystalline aggregate. Three different material constitutive models assigned to the grains are investigated: isotropic elasticity, cubic elasticity and crystal plasticity in addition to the cubic elasticity. First, some aspects of the mechanical response of the grains are highlighted, namely the scatter and the multiaxiality of the mesoscopic responses with respect to an uniaxial macroscopic response. Then, the distributions of relevant mechanical quantities classically used in fatigue criteria are analysed for some loading cases and the role of each source of anisotropy on the mechanical response is evaluated and compared to the isotropic elastic case. In particular, the significant influence of the elastic anisotropy on the mesoscopic mechanical response is highlighted. Finally, an analysis of three different fatigue criteria is conducted, using mechanical quantities computed at the grain scale. More precisely, the predictions provided by these criteria, for each constitutive model studied, are compared with the experimental trends observed in metallic materials for such loading conditions.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10985/89372014-01-01T00:00:00ZGUERCHAIS, RaphaëlROBERT, CamilleSAINTIER, NicolasMOREL, FranckIn this work, an analysis of both the mechanical response at the grain scale and high cycle multiaxial fatigue criteria is undertaken using finite element (FE) simulations of polycrystalline aggregates. The metallic material chosen for investigation, a pure copper, has a Face Centred Cubic (FCC) crystalline structure. Two-dimensional polycrystalline aggregates, which are composed of 300 randomly orientated equiaxed grains, are loaded at the median fatigue strength defined at 107 cycles. In order to analyse the effect of the loading path on the local mechanical response, combined tension–torsion and biaxial tension loading cases, in-phase and out-of-phase, with different biaxiality ratios, are applied to each polycrystalline aggregate. Three different material constitutive models assigned to the grains are investigated: isotropic elasticity, cubic elasticity and crystal plasticity in addition to the cubic elasticity. First, some aspects of the mechanical response of the grains are highlighted, namely the scatter and the multiaxiality of the mesoscopic responses with respect to an uniaxial macroscopic response. Then, the distributions of relevant mechanical quantities classically used in fatigue criteria are analysed for some loading cases and the role of each source of anisotropy on the mechanical response is evaluated and compared to the isotropic elastic case. In particular, the significant influence of the elastic anisotropy on the mesoscopic mechanical response is highlighted. Finally, an analysis of three different fatigue criteria is conducted, using mechanical quantities computed at the grain scale. More precisely, the predictions provided by these criteria, for each constitutive model studied, are compared with the experimental trends observed in metallic materials for such loading conditions.Influence of the microstructure and defects on the high cycle fatigue strength of 316L stainless steel under multiaxial loading
http://hdl.handle.net/10985/8716
Influence of the microstructure and defects on the high cycle fatigue strength of 316L stainless steel under multiaxial loading
GUERCHAIS, Raphaël; SAINTIER, Nicolas; ROBERT, Camille; MOREL, Franck
In the present study, the effects of both the microstructure and defects on the high cycle fatigue behavior of the 316L austenitic stainless steel are investigated thanks to finite element simulations of polycrystalline aggregates. The numerical analysis relies on a metallurgical and mechanical characterization. To complete the experimental study, load-controlled fatigue tests are also carried out to determine the fatigue limits at 2.106 cycles under uniaxial and multiaxial loading conditions using both smooth specimens and specimens containing an artificial hemispherical surface defect. In the finite element models, where the grain morphologies are explicitly modeled, the anisotropic behavior of each crystal is described by the generalized Hooke’s law and by a single crystal visco-plastic model. From the simulations carried out with different defect sizes and orientation sets, statistical informations regarding mesoscopic mechanical fields are analyzed. Then, using the FE results, the ability of a probabilistic fatigue criterion to predict the influence of defects and biaxiality on the average fatigue limits is evaluated thanks to a comparison with the experimental data.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10985/87162014-01-01T00:00:00ZGUERCHAIS, RaphaëlSAINTIER, NicolasROBERT, CamilleMOREL, FranckIn the present study, the effects of both the microstructure and defects on the high cycle fatigue behavior of the 316L austenitic stainless steel are investigated thanks to finite element simulations of polycrystalline aggregates. The numerical analysis relies on a metallurgical and mechanical characterization. To complete the experimental study, load-controlled fatigue tests are also carried out to determine the fatigue limits at 2.106 cycles under uniaxial and multiaxial loading conditions using both smooth specimens and specimens containing an artificial hemispherical surface defect. In the finite element models, where the grain morphologies are explicitly modeled, the anisotropic behavior of each crystal is described by the generalized Hooke’s law and by a single crystal visco-plastic model. From the simulations carried out with different defect sizes and orientation sets, statistical informations regarding mesoscopic mechanical fields are analyzed. Then, using the FE results, the ability of a probabilistic fatigue criterion to predict the influence of defects and biaxiality on the average fatigue limits is evaluated thanks to a comparison with the experimental data.Effect of defect size and shape on the high-cycle fatigue behavior
http://hdl.handle.net/10985/17241
Effect of defect size and shape on the high-cycle fatigue behavior
GUERCHAIS, Raphaël; SAINTIER, Nicolas; MOREL, Franck
This study aims to examine the effects of both material microstructure and voids on the high-cycle fatigue behavior of metals. To deal with this matter, finite element analyses of polycrystalline aggregates are carried out, for different configurations of crystalline orientations, in order to estimate the mechanical state, at the grain scale, in the vicinity of a small elliptical hole. Fatigue criteria are then applied to estimate the average fatigue limit in fully reversed tension, for different defect sizes and ellipse aspect ratios.The constitutive models and the fatigue criteria are calibrated using experimental data obtained from specimens made of 316L austenitic steel. The estimations are then compared with the experimental trends.
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/10985/172412017-01-01T00:00:00ZGUERCHAIS, RaphaëlSAINTIER, NicolasMOREL, FranckThis study aims to examine the effects of both material microstructure and voids on the high-cycle fatigue behavior of metals. To deal with this matter, finite element analyses of polycrystalline aggregates are carried out, for different configurations of crystalline orientations, in order to estimate the mechanical state, at the grain scale, in the vicinity of a small elliptical hole. Fatigue criteria are then applied to estimate the average fatigue limit in fully reversed tension, for different defect sizes and ellipse aspect ratios.The constitutive models and the fatigue criteria are calibrated using experimental data obtained from specimens made of 316L austenitic steel. The estimations are then compared with the experimental trends.Influence of the microstructure and voids on the high-cycle fatigue strength of 316L stainless steel under multiaxial loading
http://hdl.handle.net/10985/10738
Influence of the microstructure and voids on the high-cycle fatigue strength of 316L stainless steel under multiaxial loading
GUERCHAIS, Raphaël; SAINTIER, Nicolas; ROBERT, Camille; MOREL, Franck
In the present study, the effects of both the microstructure and voids on the high-cycle fatigue behaviour of the 316L austenitic stainless steel are investigated by using finite element simulations of polycrystalline aggregates. The numerical analysis relies on a metallurgical and mechanical characterization. In particular, fatigue tests are carried out to estimate the fatigue limits at 2.106 cycles under uniaxial and multiaxial loading conditions (combined tension and torsion and biaxial tension) using both smooth specimens and specimens containing an artificial hemispherical defect. The simulations are carried out with several configurations of crystalline orientations in order to take into account the variability of the microstructure in the predictions of the macroscopic fatigue limits. These predictions are obtained, thanks to a probabilistic fatigue criterion using the finite element results. The capability of this criterion to predict the influence of voids on the average and the scatter of macroscopic fatigue limits is evaluated.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10985/107382015-01-01T00:00:00ZGUERCHAIS, RaphaëlSAINTIER, NicolasROBERT, CamilleMOREL, FranckIn the present study, the effects of both the microstructure and voids on the high-cycle fatigue behaviour of the 316L austenitic stainless steel are investigated by using finite element simulations of polycrystalline aggregates. The numerical analysis relies on a metallurgical and mechanical characterization. In particular, fatigue tests are carried out to estimate the fatigue limits at 2.106 cycles under uniaxial and multiaxial loading conditions (combined tension and torsion and biaxial tension) using both smooth specimens and specimens containing an artificial hemispherical defect. The simulations are carried out with several configurations of crystalline orientations in order to take into account the variability of the microstructure in the predictions of the macroscopic fatigue limits. These predictions are obtained, thanks to a probabilistic fatigue criterion using the finite element results. The capability of this criterion to predict the influence of voids on the average and the scatter of macroscopic fatigue limits is evaluated.Competition between microstructure and defect in multiaxial high cycle fatigue
http://hdl.handle.net/10985/10058
Competition between microstructure and defect in multiaxial high cycle fatigue
GUERCHAIS, Raphaël; SAINTIER, Nicolas; MOREL, Franck
This study aims at providing a better understanding of the effects of both microstructure and defect on the high cycle fatigue behavior of metallic alloys using finite element simulations of polycrystalline aggregates. It is well known that the microstructure strongly affects the average fatigue strength and when the cyclic stress level is close to the fatigue limit, it is often seen as the main source of the huge scatter generally observed in this fatigue regime. The presence of geometrical defects in a material can also strongly alter the fatigue behavior. Nonetheless, when the defect size is small enough, i.e. under a critical value, the fatigue strength is no more affected by the defect. The so-called Kitagawa effect can be interpreted as a competition between the crack initiation mechanisms governed either by the microstructure or by the defect. Surprisingly, only few studies have been done to date to explain the Kitagawa effect from the point of view of this competition, even though this effect has been extensively investigated in the literature. The primary focus of this paper is hence on the use of both FE simulations and explicit descriptions of the microstructure to get insight into how the competition between defect and microstructure operates in HCF. In order to account for the variability of the microstructure in the predictions of the macroscopic fatigue limits, several configurations of crystalline orientations, crystal aggregates and defects are studied. The results of each individual FE simulation are used to assess the response at the macroscopic scale thanks to a probabilistic fatigue criterion proposed by the authors in previous works. The ability of this criterion to predict the influence of defects on the average and the scatter of macroscopic fatigue limits is evaluated. In this paper, particular emphasis is also placed on the effect of different loading modes (pure tension, pure torsion and combined tension and torsion) on the experimental and predicted fatigue strength of a 316 stainless steel containing artificial defect.
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Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10985/100582015-01-01T00:00:00ZGUERCHAIS, RaphaëlSAINTIER, NicolasMOREL, FranckThis study aims at providing a better understanding of the effects of both microstructure and defect on the high cycle fatigue behavior of metallic alloys using finite element simulations of polycrystalline aggregates. It is well known that the microstructure strongly affects the average fatigue strength and when the cyclic stress level is close to the fatigue limit, it is often seen as the main source of the huge scatter generally observed in this fatigue regime. The presence of geometrical defects in a material can also strongly alter the fatigue behavior. Nonetheless, when the defect size is small enough, i.e. under a critical value, the fatigue strength is no more affected by the defect. The so-called Kitagawa effect can be interpreted as a competition between the crack initiation mechanisms governed either by the microstructure or by the defect. Surprisingly, only few studies have been done to date to explain the Kitagawa effect from the point of view of this competition, even though this effect has been extensively investigated in the literature. The primary focus of this paper is hence on the use of both FE simulations and explicit descriptions of the microstructure to get insight into how the competition between defect and microstructure operates in HCF. In order to account for the variability of the microstructure in the predictions of the macroscopic fatigue limits, several configurations of crystalline orientations, crystal aggregates and defects are studied. The results of each individual FE simulation are used to assess the response at the macroscopic scale thanks to a probabilistic fatigue criterion proposed by the authors in previous works. The ability of this criterion to predict the influence of defects on the average and the scatter of macroscopic fatigue limits is evaluated. In this paper, particular emphasis is also placed on the effect of different loading modes (pure tension, pure torsion and combined tension and torsion) on the experimental and predicted fatigue strength of a 316 stainless steel containing artificial defect.Microstructure-dependent predictions of the effect of defect size and shape on the high-cycle fatigue strength
http://hdl.handle.net/10985/10764
Microstructure-dependent predictions of the effect of defect size and shape on the high-cycle fatigue strength
GUERCHAIS, Raphaël; SAINTIER, Nicolas; MOREL, Franck
This study aims to investigate the effects of both the microstructure and void on the high-cycle fatigue behavior of metallic materials. To deal with this matter, finite element analyses of polycrystalline aggregates are carried out, for different configurations of crystalline orientations, in order to estimate the mechanical state, at the grain scale, in the vicinity of a small elliptical hole. Fatigue criteria are then applied to predict the average fatigue limit in fully reversed tension, for different defect sizes and ellipse aspect ratios. The constitutive models and the fatigue criteria are calibrated using experimental data obtained from specimens made of 316L austenitic steel . The predictions are then confronted to experimental trends .
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10985/107642016-01-01T00:00:00ZGUERCHAIS, RaphaëlSAINTIER, NicolasMOREL, FranckThis study aims to investigate the effects of both the microstructure and void on the high-cycle fatigue behavior of metallic materials. To deal with this matter, finite element analyses of polycrystalline aggregates are carried out, for different configurations of crystalline orientations, in order to estimate the mechanical state, at the grain scale, in the vicinity of a small elliptical hole. Fatigue criteria are then applied to predict the average fatigue limit in fully reversed tension, for different defect sizes and ellipse aspect ratios. The constitutive models and the fatigue criteria are calibrated using experimental data obtained from specimens made of 316L austenitic steel . The predictions are then confronted to experimental trends .The role of the microstructure and defects on crack initiation in 316L stainless steel under multiaxial high cycle fatigue
http://hdl.handle.net/10985/8903
The role of the microstructure and defects on crack initiation in 316L stainless steel under multiaxial high cycle fatigue
GUERCHAIS, Raphaël; SAINTIER, Nicolas; MOREL, Franck
The aim of this study is to analyse the influence of both the microstructure and defects on the high cycle fatigue behaviour of the 316L austenitic stainless steel, using finite element simulations of polycrystalline aggregates. High cycle fatigue tests have been conducted on this steel under uniaxial (push-pull) and multiaxial (combined in-phase tension and torsion) loading conditions, with both smooth specimens and specimens containing artificial semi-spherical surface defects. 2D numerical models, using a cubic elastic constitutive model, are created to determine the degree of heterogeneity of the local stress parameters as a function of the defect size. This has been done for one microstructure using several orientation sets generated from the initial texture of the material. The grains are explicitly modelled and the anisotropic behaviour of each FCC crystal is described by the generalized Hooke’s law with a cubic elasticity tensor. From the simulations carried out with different defect sizes and orientation sets that are representative of the real texture of the tested material, statistical information regarding mesoscopic mechanical fields provides useful insight into the microstructural dependence of the driving forces for fatigue crack nucleation at the mesoscopic scale (or the scale of individual grains). The results in terms of the stress fields and fatigue crack initiation conditions are determined at both the mesoscopic and macroscopic scales. The results from these FE models are used along with an original probabilistic mesomechanics approach to quantify the defect size effect. The resulting predictions, which are sensitive to the microstructure, include the probability distribution of the high cycle fatigue strength.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10985/89032014-01-01T00:00:00ZGUERCHAIS, RaphaëlSAINTIER, NicolasMOREL, FranckThe aim of this study is to analyse the influence of both the microstructure and defects on the high cycle fatigue behaviour of the 316L austenitic stainless steel, using finite element simulations of polycrystalline aggregates. High cycle fatigue tests have been conducted on this steel under uniaxial (push-pull) and multiaxial (combined in-phase tension and torsion) loading conditions, with both smooth specimens and specimens containing artificial semi-spherical surface defects. 2D numerical models, using a cubic elastic constitutive model, are created to determine the degree of heterogeneity of the local stress parameters as a function of the defect size. This has been done for one microstructure using several orientation sets generated from the initial texture of the material. The grains are explicitly modelled and the anisotropic behaviour of each FCC crystal is described by the generalized Hooke’s law with a cubic elasticity tensor. From the simulations carried out with different defect sizes and orientation sets that are representative of the real texture of the tested material, statistical information regarding mesoscopic mechanical fields provides useful insight into the microstructural dependence of the driving forces for fatigue crack nucleation at the mesoscopic scale (or the scale of individual grains). The results in terms of the stress fields and fatigue crack initiation conditions are determined at both the mesoscopic and macroscopic scales. The results from these FE models are used along with an original probabilistic mesomechanics approach to quantify the defect size effect. The resulting predictions, which are sensitive to the microstructure, include the probability distribution of the high cycle fatigue strength.Micromechanical investigation of the influence of defects in high cycle fatigue
http://hdl.handle.net/10985/8938
Micromechanical investigation of the influence of defects in high cycle fatigue
GUERCHAIS, Raphaël; SAINTIER, Nicolas; ROBERT, Camille; MOREL, Franck
This study aims to analyse the influence of geometrical defects (notches and holes) on the high cycle fatigue behaviour of an electrolytic copper based on finite element simulations of 2D polycrystalline aggregates. In order to investigate the role of each source of anisotropy on the mechanical response at the grain scale, three different material constitutive models are assigned successively to the grains: isotropic elasticity, cubic elasticity and crystal plasticity in addition to the cubic elasticity. The significant influence of the elastic anisotropy on the mechanical response of the grains is highlighted. When considering smooth microstructures, the crystal plasticity have has a slight effect in comparison with the cubic elasticity influence. However, in the case of notched microstructures, it has been shown that the influence of the plasticity is no more negligible. Finally, the predictions of three fatigue criteria are analysed. Their ability to predict the defect size effect on the fatigue strength is evaluated thanks to a comparison with experimental data from the literature.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10985/89382014-01-01T00:00:00ZGUERCHAIS, RaphaëlSAINTIER, NicolasROBERT, CamilleMOREL, FranckThis study aims to analyse the influence of geometrical defects (notches and holes) on the high cycle fatigue behaviour of an electrolytic copper based on finite element simulations of 2D polycrystalline aggregates. In order to investigate the role of each source of anisotropy on the mechanical response at the grain scale, three different material constitutive models are assigned successively to the grains: isotropic elasticity, cubic elasticity and crystal plasticity in addition to the cubic elasticity. The significant influence of the elastic anisotropy on the mechanical response of the grains is highlighted. When considering smooth microstructures, the crystal plasticity have has a slight effect in comparison with the cubic elasticity influence. However, in the case of notched microstructures, it has been shown that the influence of the plasticity is no more negligible. Finally, the predictions of three fatigue criteria are analysed. Their ability to predict the defect size effect on the fatigue strength is evaluated thanks to a comparison with experimental data from the literature.Competition between microstructure and defect in multiaxial high cycle fatigue
http://hdl.handle.net/10985/16495
Competition between microstructure and defect in multiaxial high cycle fatigue
GUERCHAIS, Raphaël; SAINTIER, Nicolas; MOREL, Franck
This study aims at providing a better understanding of the effects of both microstructure and defect on the high cycle fatigue behavior of metallic alloys using finite element simulations of polycrystalline aggregates. It is well known that the microstructure strongly affects the average fatigue strength and when the cyclic stress level is close to the fatigue limit, it is often seen as the main source of the huge scatter generally observed in this fatigue regime. The presence of geometrical defects in a material can also strongly alter the fatigue behavior. Nonetheless, when the defect size is small enough, i.e. under a critical value, the fatigue strength is no more affected by the defect. The so-called Kitagawa effect can be interpreted as a competition between the crack initiation mechanisms governed either by the microstructure or by the defect. Surprisingly, only few studies have been done to date to explain the Kitagawa effect from the point of view of this competition, even though this effect has been extensively investigated in the literature. The primary focus of this paper is hence on the use of both FE simulations and explicit descriptions of the microstructure to get insight into how the competition between defect and microstructure operates in HCF. In order to account for the variability of the microstructure in the predictions of the macroscopic fatigue limits, several configurations of crystalline orientations, crystal aggregates and defects are studied. The results of each individual FE simulation are used to assess the response at the macroscopic scale thanks to a probabilistic fatigue criterion proposed by the authors in previous works. The ability of this criterion to predict the influence of defects on the average and the scatter of macroscopic fatigue limits is evaluated. In this paper, particular emphasis is also placed on the effect of different loading modes (pure tension, pure torsion and combined tension and torsion) on the experimental and predicted fatigue strength of a 316 stainless steel artificial defect.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10985/164952015-01-01T00:00:00ZGUERCHAIS, RaphaëlSAINTIER, NicolasMOREL, FranckThis study aims at providing a better understanding of the effects of both microstructure and defect on the high cycle fatigue behavior of metallic alloys using finite element simulations of polycrystalline aggregates. It is well known that the microstructure strongly affects the average fatigue strength and when the cyclic stress level is close to the fatigue limit, it is often seen as the main source of the huge scatter generally observed in this fatigue regime. The presence of geometrical defects in a material can also strongly alter the fatigue behavior. Nonetheless, when the defect size is small enough, i.e. under a critical value, the fatigue strength is no more affected by the defect. The so-called Kitagawa effect can be interpreted as a competition between the crack initiation mechanisms governed either by the microstructure or by the defect. Surprisingly, only few studies have been done to date to explain the Kitagawa effect from the point of view of this competition, even though this effect has been extensively investigated in the literature. The primary focus of this paper is hence on the use of both FE simulations and explicit descriptions of the microstructure to get insight into how the competition between defect and microstructure operates in HCF. In order to account for the variability of the microstructure in the predictions of the macroscopic fatigue limits, several configurations of crystalline orientations, crystal aggregates and defects are studied. The results of each individual FE simulation are used to assess the response at the macroscopic scale thanks to a probabilistic fatigue criterion proposed by the authors in previous works. The ability of this criterion to predict the influence of defects on the average and the scatter of macroscopic fatigue limits is evaluated. In this paper, particular emphasis is also placed on the effect of different loading modes (pure tension, pure torsion and combined tension and torsion) on the experimental and predicted fatigue strength of a 316 stainless steel artificial defect.