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Effet des défauts de fabrication et de corrosion sur le comportement en fatigue d'un acier 316L obtenu par fabrication additive.

Abstract : Laser Powder Bed Fusion (L-PBF) is a booming additive manufacturing process in many industrial sectors. For renewable marine energies applications, mechanical and corrosion properties of components and structures operating under chemically aggressive environment conditions must be known to ensure optimized design. This thesis work falls within this scope with a focus on the fatigue, corrosion and atmospheric corrosion-fatigue of a L-PBF 316L stainless steel. The as-built L-PBF 316L microstructure is very different from its wrought counterpart. The L-PBF process is also at the origin of defects, such as Gas Pore (GP) or Lack of Fusion (LoF). The main purpose of this study is to get a better knowledge of the influence of these defects on the corrosion and fatigue behaviours. It is observed that for corrosion in a neutral saline solution or under salt-spray, inherent defects do not affect the corrosion pit nucleation. In high cycle fatigue and without any pre-corrosion, LoF near the surface are almost systematically at the origin of the crack initiation. The introduction of corrosion pits before the fatigue loading reveals a competition between L-PBF related defects and corrosion pits populations. More precisely, the uniaxial fatigue behaviours of three distinct batches are studied. Polished samples, precorroded samples and samples with artificial hemispherical defects are tested. A correlation between the defect at the origin of the crack initiation size and the fatigue strength is observed independently of the critical defect type. Various factors that could affect the defect criticality (morphology, local microstructure) are discussed. In order to model the impact of defects of different types, two different approaches are developed and compared. The first one, based on linear elastic fracture mechanics, takes into account the position and size of the defect. The second one is a non-local approach using finite element simulations and a multiaxial fatigue criteria. In this approach, some morphologic parameters of the critical defects are considered, in addition to its size and position.
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https://pastel.archives-ouvertes.fr/tel-03688021
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Submitted on : Friday, June 3, 2022 - 4:18:18 PM
Last modification on : Friday, August 5, 2022 - 2:54:00 PM
Long-term archiving on: : Sunday, September 4, 2022 - 7:48:15 PM

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  • HAL Id : tel-03688021, version 1

Citation

Pierre Merot. Effet des défauts de fabrication et de corrosion sur le comportement en fatigue d'un acier 316L obtenu par fabrication additive.. Mécanique des matériaux [physics.class-ph]. HESAM Université, 2021. Français. ⟨NNT : 2021HESAE076⟩. ⟨tel-03688021⟩

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