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In this work, stainless steel 316L obtained by Laser Powder Bed Fusion (L‐PBF) has been produced and characterized. The experimental campaign focuses on the samples in the as‐built state under cyclic tension‐compression loadings. Low cycle fatigue (LCF) and high cycle fatigue (HCF) tests are carried out. Microstructure observations are performed before and after the loadings. As‐built L‐PBF 316L has a good LCF performance despite the presence of surface defects but a low fatigue limit in the HCF regime. Removing the surface roughness has a beneficial effect but does not improve the fatigue strength to that of machined wrought 316L. Observations on the microstructure of fatigue samples indicate that LCF is dominated by the local plastic deformation, which is mostly achieved by the slip in the studied material and is not sensitive to the defect. The lack‐of‐fusion defect impairs the fatigue resistance in the HCF regime. Highlights: Monotonic tensile and LCF behavior of L‐PBF 316L are not sensitive to the surface defects.HCF behavior of L‐PBF 316L is dominated by the surface or subsurface defects.Slip planes produced during cyclic deformation are not affected by the melt pool boundaries. [ABSTRACT FROM AUTHOR]

FFT-based homogenization methods aim at calculating the effective behavior of heterogeneous materials with periodic microstructures. These methods operate on a regular grid of voxels, and hence require an appropriate spatial discretization of periodic microstructures. However, when different microstructural length scales are involved, it is not always possible to have sufficient spatial resolutions to explicitly consider the influence of fine microstructural features (e.g. voids, second-phase particles). To circumvent this difficulty, one solution consists of using composite voxel methods to define the effective properties and the effective internal variables of heterogeneous voxels. In this work, different composite voxel methods are proposed to deal with inelastic materials with multiple length scales. These methods use simple homogenization rules to calculate the effective behavior of heterogeneous voxels. The first part of this paper is dedicated to the description of the composite voxel methods, which are based either on the Voigt, laminate structure or Mori–Tanaka approximations. In the second part, these methods are used to model the elasto-plastic behavior of a pearlitic steel polycrystalline aggregate. According to the results, the Voigt approximation, which ignores morphological features, is not appropriate for treating heterogeneous voxels. When morphological information is accounted for, with either the laminate structure or Mori–Tanaka approximations, a better agreement with experimental observations is obtained. Though none of these methods is universal, they offer some possibilities to investigate the mechanical behavior of heterogeneous materials involving multiple length scales. [ABSTRACT FROM AUTHOR]

The macroscopic behavior of polycrystalline materials is largely influenced by the shape, the arrangement and the orientation of crystallites. Different methods have thus been developed to determine the effective behavior of such materials as a function of their microstructural features. In this work, which focuses on polycrystalline materials with an elastic–viscoplastic behavior, the self-consistent, finite element and spectral methods are compared. These common methods are used to determine the effective behavior of different 316L polycrystalline aggregates subjected to various loading conditions. Though no major difference is observed at the macroscopic scale, the hardening rate is found to be slightly overestimated with the finite element method. Indeed, spatial convergence cannot be guaranteed for finite element calculations, even when fine mesh resolutions, for which the computational cost is important, are used. Also, as the self-consistent method does not explicitly account for neighborhood effects, important discrepancies between the self-consistent method and the other methods exist regarding the mechanical response of a specific grain. The self-consistent method nevertheless provides a reasonable description of the average response obtained for a group of grains with identical features (e.g. shape, orientation). [ABSTRACT FROM AUTHOR]

• Microstructure-sensitive framework has been extended and applied to SLM 316L. • As-built surface roughness has been considered explicitly in the finite element model. • Textured microstructure of SLM 316L has been evaluated concerning fatigue strength. • Competitive effects of surface defect and microstructure have been distinguished. This paper aims to study the individual and competitive effects of surface defects and microstructural components in an AM 316L by numerical methods. Based on the microstructure sensitive modeling framework, numerical simulations of models in different surface states with virtual quasi-realistic explicit microstructures are performed. Problems encountered during the establishment of the numerical polycrystalline aggregate model are discussed, including the grain morphology, the strongly textured microstructure with preferential crystallographic directions, roughness and surface defect. A statistical method based on generalized extreme value distribution along with a non-local method is used to describe the stochasticity of microstructural attributes. Simulations of differently configured explicit microstructure models are analyzed and discussed. [ABSTRACT FROM AUTHOR]

• Explicit virtual microstructure is introduced to the numerical models. • Different configurations of grain size and morphology are investigated. • Stress-based fatigue criteria combined with two non-local methods are applied. • Kitagawa-Takahashi effect is reproduced and explained via the proposed framework. This study aims at investigating the effect of defect on the high cycle fatigue behavior of polycrystalline aggregates. An explicit virtual microstructure finite element model is created to conduct fatigue simulations. Different stress-based criteria frequently applied in fatigue assessment are tested with a combination of the non-local methods. Two realizations of the non-local method are used and compared. Simulation results are compared to experimental results of 316L. From the parametric simulations, better qualitative understandings on the choice of non-local method as well as its parameters are obtained. The effect of Kitagawa-Takahashi can be reproduced and explained by this proposed framework of microstructure modeling-simulation. [ABSTRACT FROM AUTHOR]

Multiaxial high cycle fatigue modeling of materials is an issue that concerns many industrial domains (automotive, aerospace, nuclear, etc.) and in which many progress still remains to be achieved. Several approaches exist in the literature: invariants, energy, integral and critical plane approaches all of them having their advantages and drawbacks. These different formulations are usually based on mechanical quantities at the micro or mesoscales using localization schemes and strong assumptions to propose simple analytical forms. This study aims to revisit these formulations using a numerical approach based on crystal plasticity modeling coupled with explicit description of microstructure (morphology and texture) and proposes a statistical procedure for the analyses of numerical results in the HCF context. This work has three steps: First, 2.5D periodic digital microstructures based on a random grain sizes distribution are generated. Second, multiaxial cyclic loading conditions corresponding to the fatigue strength at 106 cycles are applied to these microstructures. Third, the mesoscopic Fatigue Indicator Parameters (FIPs), formulated from the different criteria existing in the literature, are identified using the finite element calculations of the mechanical fields. These mesoscopic FIP show the limits of the original criteria when it comes to applying them at the grain scale. A statistical method based on extreme value probability is used to redefine the thresholds of these criteria. These new thresholds contain the sensitivity of the HCF behavior to microstructure attributes. Finally, the biaxiality and phase shift effects are discussed at the grain scale and the loading paths of some critical grains are analyzed. [ABSTRACT FROM AUTHOR]