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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.