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Modelling of IGSCC mechanism

This study focuses on developing a computational model for IGSCC, integrating fracture mechanics, diffusion, and electrochemistry to understand the oxide penetration and weakening of grain boundaries. The model includes cohesive elements and oxidation processes. The results show good agreement with experimental tests under different conditions. Ongoing experiments aim to further validate the model's predictions.

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Modelling of IGSCC mechanism

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  1. Modelling of IGSCC mechanism Michal Sedlak, Bo Alfredsson, PålEfsing Solid Mechanics Royal Institute of Technology (KTH)

  2. Introduction • Stress Corrosion Cracking(SCC) • Intergranular (IG) Materials Reliability Program: Proceedings of the 2005International PWSCC of Alloy 600 Conference and Exhibit Show (MRP-154)

  3. Assumedmodel • At water exposure the oxide grows at the grain boundaries • The rate is determined by stress, path, ions… • Oxide penetration for long cracks is governed by diffusion of species to the crack-tip. • The oxide weakens the grain boundaries mechanical strength

  4. Schematic model Diffusion Cohesive elements Oxidation Oxide penetration

  5. Model • Developing a computational model for IGSCC • Multi-physics problem • Fracture mechanics • Diffusion • Electrochemistry • …… • …… • Using ABAQUS *UEL

  6. Fracture mechanics model • 2D cohesive element • PPR potential K. Park, G. H. Paulino, “Cohesive Zone Models: A Critical Review of Traction-Separation Relationships Across Fracture Surfaces” , Applied Mechanics Reviews, Vol. 64

  7. Diffusion model Diffusion equation Diffusivity Reaction

  8. Coupling Damage parameter Coupling of energies L M. Sedlak, B. Alfredsson, P. Efsing. A cohesive element with degradation controlled shape of the traction separation curve for simulating stress corrosion and irradiation crackingEngFractMech2017;193(2018):172–196.

  9. Results CT model

  10. Results – Cold Work M. Sedlak, B. Alfredsson, P. Efsing. Coupled diffusion and cohesive zone model to simulate the intergranular stress corrosion cracking in 316L stainless steel exposed to cold work ,Sent-In

  11. Results – Stress intensity factor K

  12. Quasi-static testing in controlled environment • Test setup

  13. Specimen 1 • Specimen 1, CT specimen • Material 304L • Temperature 180 ° C • 30 days in the oven • Solution sodium thiosulfate (1.8%) and sodium chloride (3%). • Loaded with bolt , force 25 kN

  14. Specimen 1 • Specimen 1 , CT specimen • Remaining force = 9,85 kN. • SCC crack, 500 μm • Transgranular Images on the fracture surface, with optic microscope

  15. Specimen 1 Pictures on tangential cracks, with optic microscope

  16. Specimen 1 Pictures on the cracking surface, with SEM

  17. Specimen 2 • Specimen 1, CT specimen • Material 304L • Temperature 180 ° C • 30 days in the oven • Solution sodium thiosulfate (1.8%) and chloride 13 ppm (tap water) • Loaded with bolt , force 25 kN • Potential Drop used, with current switching • Transgranular crack

  18. Specimen 2 Pictures on tangential cracks, with optic microscope

  19. Summary • A coupled model for simulating SCC, with diffusion as main mechanism was constructed • Change in yield stress fits experiments. • Stress intensityfactor results are fitting the experiment well. • Experimentsareongoing

  20. Thanks for your attention.

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