https://sam.ensam.eu:443 The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material. Fri, 10 Apr 2026 13:16:40 GMT 2026-04-10T13:16:40Z http://hdl.handle.net/10985/25282 Non local multiaxial fatigue modeling of defects: A unified approach to interpret size and shape effects MEROT, Pierre; MOREL, Franck; ROBERT, Camille; PESSARD, Etienne; GALLEGOS MAYORGA, Linamaria; BUTTIN, Paul This paper deals with the effect of defect size and shape under high cycle fatigue for metallic alloys. A large simulation campaign based on a multiaxial fatigue criterion and a non-local approach is presented. A relative defect size based on a ratio between the defect size and a characteristic length introduced by the non-local approach is defined. A normalized Kitagawa–Takahashi diagram is then obtained. A competition between the highly stressed volume size and the local maxima due to the defect is observed and seem dependent on the relative defect size. The effect of the loading mode (uniaxial and pure shear) and of the plasticity are discussed. Finally, a comparison of the simulation results with experimental data on a 316L L-PBF demonstrates the robustness of the proposed approach and explains the negligible effect of the defect morphology compared to its size. Sat, 16 Mar 2024 00:00:00 GMT http://hdl.handle.net/10985/25282 2024-03-16T00:00:00Z MEROT, Pierre MOREL, Franck ROBERT, Camille PESSARD, Etienne GALLEGOS MAYORGA, Linamaria BUTTIN, Paul This paper deals with the effect of defect size and shape under high cycle fatigue for metallic alloys. A large simulation campaign based on a multiaxial fatigue criterion and a non-local approach is presented. A relative defect size based on a ratio between the defect size and a characteristic length introduced by the non-local approach is defined. A normalized Kitagawa–Takahashi diagram is then obtained. A competition between the highly stressed volume size and the local maxima due to the defect is observed and seem dependent on the relative defect size. The effect of the loading mode (uniaxial and pure shear) and of the plasticity are discussed. Finally, a comparison of the simulation results with experimental data on a 316L L-PBF demonstrates the robustness of the proposed approach and explains the negligible effect of the defect morphology compared to its size. http://hdl.handle.net/10985/26641 Prevailing effect of residual stresses and defects on the fatigue strength of net-shape parts produced with Laser Powder Bed Fusion (L-PBF) 316L stainless steel AUFFRAY, Marion; MOREL, Franck; GALLEGOS MAYORGA, Linamaria; PESSARD, Etienne; BAFFIE, Thierry; MEROT, Pierre; BUTTIN, Paul Laser Powder Bed Fusion (L-PBF) additive manufacturing enables the production of complex-shaped parts with high mechanical resistance. Such components exhibit a multi-scale microstructure, internal, sub-surface, and surface defects, a rough surface finish and a residual stress gradient in the as-built net-shape condition. All of these factors can alter the fatigue behaviour. This study aims to improve the understanding of the combined effect of various surface parameters on the fatigue behaviour of L-PBF 316L stainless steel by conducting an extensive experimental campaign. Uni-axial fatigue tests were carried out on six batches having an as-built or heat-treated microstructure and a net-shape, pre-corroded net-shape, single-defect net-shape or polished surface condition. Results were compared with data from the literature: as-built polished, pre-corroded polished, or single-defect polished specimens. Studied defects were process-induced (e.g. lack of fusion, spatter, gas pore) and artificial (i.e. corrosion pit, electric discharge machined defect). Their sizes ranged from 10 to 700 μm. The residual stresses gradients were characterized by X-ray diffraction. A Kitagawa–Takahashi diagram was used to illustrate the effects of the various parameters on the fatigue behaviour. Residual stresses and defects were the most influential factors on the fatigue strength of net-shape specimens over surface condition and sub-surface microstructure. Financement région Pays de la Loire Sat, 05 Jul 2025 00:00:00 GMT http://hdl.handle.net/10985/26641 2025-07-05T00:00:00Z AUFFRAY, Marion MOREL, Franck GALLEGOS MAYORGA, Linamaria PESSARD, Etienne BAFFIE, Thierry MEROT, Pierre BUTTIN, Paul Laser Powder Bed Fusion (L-PBF) additive manufacturing enables the production of complex-shaped parts with high mechanical resistance. Such components exhibit a multi-scale microstructure, internal, sub-surface, and surface defects, a rough surface finish and a residual stress gradient in the as-built net-shape condition. All of these factors can alter the fatigue behaviour. This study aims to improve the understanding of the combined effect of various surface parameters on the fatigue behaviour of L-PBF 316L stainless steel by conducting an extensive experimental campaign. Uni-axial fatigue tests were carried out on six batches having an as-built or heat-treated microstructure and a net-shape, pre-corroded net-shape, single-defect net-shape or polished surface condition. Results were compared with data from the literature: as-built polished, pre-corroded polished, or single-defect polished specimens. Studied defects were process-induced (e.g. lack of fusion, spatter, gas pore) and artificial (i.e. corrosion pit, electric discharge machined defect). Their sizes ranged from 10 to 700 μm. The residual stresses gradients were characterized by X-ray diffraction. A Kitagawa–Takahashi diagram was used to illustrate the effects of the various parameters on the fatigue behaviour. Residual stresses and defects were the most influential factors on the fatigue strength of net-shape specimens over surface condition and sub-surface microstructure. http://hdl.handle.net/10985/22075 Observations on the influence of process and corrosion related defects on the fatigue strength of 316L stainless steel manufactured by Laser Powder Bed Fusion (L-PBF) MEROT, Pierre; GALLEGOS MAYORGA, Linamaria; BUTTIN, Paul; BAFFIE, Thierry; MOREL, Franck; PESSARD, Etienne Corrosive environments are known to be detrimental to the mechanical strength of metallic alloys. In the case of 316L stainless steel, the main corrosion mechanism observed is pitting, which leads to localized rough defects. As for other materials submitted to cyclic loadings and prone to pit, corrosion defects tend to be at the core of crack initiation leading to failure. The work here-by presented will thus focus on the relationship between the fatigue performance and the presence of process or corrosion related defects for a 316L stainless steel manufactured by Laser Powder Bed Fusion (L-PBF). To do so, cylindrical samples were produced vertically, then machined to fatigue specimens in as-built state (no heat treatment). Specimens were polished in order to only characterize the bulk material and not its raw surface. The fatigue responses of three batches corresponding to three configurations of surface integrity (polished, pre-corroded and with an Electric Discharge Machined (EDM) defect) were investigated. For the polished batch, fracture surface observations showed that initiation started from a lack of fusion (LoF) surface pore in all specimens. The pre-corroded batch was prepared under potentiodynamic anodic polarization conditions in a neutral NaCl solution. On those samples, some cracks initiated on corrosion pits, depending on the severity of the corrosion applied to each sample and its initial population of defects. For the EDM batch, a hemispherical defect, at the source of all failures, was machined in the middle of the gauge length. A good correlation between Murakami’s square root of the area parameter and the fatigue strength was observed on a Kitagawa-Takahashi diagram for all tested specimens. This correlation showed an independence of the defect type (LoF, pit, machined defect) on the specimens fatigue strength. Defect morphology doesn’t seem to be an important driving force for crack initiation as ellipsoidal corrosion pits, hemispherical EDM defects and flat lacks of fusion, although very different in terms of shape, are just as harmful at equivalent sizes. Wed, 06 Oct 2021 00:00:00 GMT http://hdl.handle.net/10985/22075 2021-10-06T00:00:00Z MEROT, Pierre GALLEGOS MAYORGA, Linamaria BUTTIN, Paul BAFFIE, Thierry MOREL, Franck PESSARD, Etienne Corrosive environments are known to be detrimental to the mechanical strength of metallic alloys. In the case of 316L stainless steel, the main corrosion mechanism observed is pitting, which leads to localized rough defects. As for other materials submitted to cyclic loadings and prone to pit, corrosion defects tend to be at the core of crack initiation leading to failure. The work here-by presented will thus focus on the relationship between the fatigue performance and the presence of process or corrosion related defects for a 316L stainless steel manufactured by Laser Powder Bed Fusion (L-PBF). To do so, cylindrical samples were produced vertically, then machined to fatigue specimens in as-built state (no heat treatment). Specimens were polished in order to only characterize the bulk material and not its raw surface. The fatigue responses of three batches corresponding to three configurations of surface integrity (polished, pre-corroded and with an Electric Discharge Machined (EDM) defect) were investigated. For the polished batch, fracture surface observations showed that initiation started from a lack of fusion (LoF) surface pore in all specimens. The pre-corroded batch was prepared under potentiodynamic anodic polarization conditions in a neutral NaCl solution. On those samples, some cracks initiated on corrosion pits, depending on the severity of the corrosion applied to each sample and its initial population of defects. For the EDM batch, a hemispherical defect, at the source of all failures, was machined in the middle of the gauge length. A good correlation between Murakami’s square root of the area parameter and the fatigue strength was observed on a Kitagawa-Takahashi diagram for all tested specimens. This correlation showed an independence of the defect type (LoF, pit, machined defect) on the specimens fatigue strength. Defect morphology doesn’t seem to be an important driving force for crack initiation as ellipsoidal corrosion pits, hemispherical EDM defects and flat lacks of fusion, although very different in terms of shape, are just as harmful at equivalent sizes. http://hdl.handle.net/10985/22986 Fatigue strength and life assessment of L-PBF 316L stainless steel showing process and corrosion related defects MEROT, Pierre; MOREL, Franck; PESSARD, Etienne; GALLEGOS MAYORGA, Linamaria; BUTTIN, Paul; BAFFIE, Thierry The present work focuses on the modelling of the fatigue behaviour of a 316L produced by laser powder bed fusion containing various defect populations : Lacks of fusion, corrosion pits and one electric discharge machined hemispherical defect. As shown in previous experimental studies, the crack leading up to failure systematically initiated on a single surface defect. The nature and morphology of the critical defect did not show any influence on the fatigue strength, and only its size seemed to matter. To take into account the critical defect size, models based on linear elastic fracture mechanics were implemented and identified. A modified Paris propagation law was used to model the short crack regime. This approach was used to predict S–N curve domains based on critical defects size range. Fri, 21 Oct 2022 00:00:00 GMT http://hdl.handle.net/10985/22986 2022-10-21T00:00:00Z MEROT, Pierre MOREL, Franck PESSARD, Etienne GALLEGOS MAYORGA, Linamaria BUTTIN, Paul BAFFIE, Thierry The present work focuses on the modelling of the fatigue behaviour of a 316L produced by laser powder bed fusion containing various defect populations : Lacks of fusion, corrosion pits and one electric discharge machined hemispherical defect. As shown in previous experimental studies, the crack leading up to failure systematically initiated on a single surface defect. The nature and morphology of the critical defect did not show any influence on the fatigue strength, and only its size seemed to matter. To take into account the critical defect size, models based on linear elastic fracture mechanics were implemented and identified. A modified Paris propagation law was used to model the short crack regime. This approach was used to predict S–N curve domains based on critical defects size range.