1. Modelling of IGSCC mechanism
Michal Sedlak, Bo Alfredsson, Pål Efsing
Solid Mechanics Royal Institute of Technology (KTH)
-LWR Light water reactor

2. Introduction Stress Corrosion Cracking (SCC) Intergranular (IG)
-SMALL part but big
-Typical in material you dont want to crack, austenitic ss
-difference to cast iron , uniform corrosion
-nuclear buisness
Materials Reliability Program: Proceedings of the 2005 International PWSCC of Alloy 600 Conference and Exhibit Show (MRP-154)

3. Assumed model
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
MODEL
-- Water
-- Diffusion
-- Adsorbtion
--oxide grows virgin material
-- oxide cracks new virgin
--- repeting (slip - oxidation)

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
Many more physics
Modula softwere

6. Fracture mechanics model
2D cohesive element
One of two parts
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
-explain diffuion equation
h(c,ny) equation adsorbtion, show arrows
-small figure ,big figure
-- big figure ,diffusion, BC osv

8. Coupling Damage parameter Coupling of energies
Fracture energy loss is due to adhesive integral
-newton rhapson is used
-du to path depedency in cohesive elemetn
M. Sedlak, B. Alfredsson, P. Efsing. A cohesive element with degradation controlled shape of the traction separation curve for simulating stress corrosion and irradiation cracking Eng Fract Mech 2017;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 intensity factor results are fitting the experiment well.
Experiments are ongoing

20. Thanks for your attention.