Overview of fatigue life assessment of baffles in Wendelstein 7-X
| Autor: | Joris, Fellinger, Citarella, Roberto Guglielmo, Giannella, Venanzio, Lepore, MARCELLO ANTONIO, Raffaele, Sepe, Michael, Czerwinski, Friedemann, Herold, Reinhold, Stadler, Sepe, Raffaele |
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| Přispěvatelé: | W7-X Team, Max Planck Institute for Plasma Physics, Max Planck Society, Fellinger, Jori, Citarella, Roberto, Giannella, Venanzio, Lepore, Marcello, Sepe, Raffaele, Czerwinski, Michael, Herold, Friedemann, Stadler, Reinhold |
| Jazyk: | angličtina |
| Rok vydání: | 2018 |
| Předmět: |
Materials science
Baffle 02 engineering and technology Bending 01 natural sciences 7. Clean energy 010305 fluids & plasmas Wendelstein 7-XFirst wallFatigueCracksFEMBEMThermo-mechanics 0203 mechanical engineering 0103 physical sciences Heat shield Wendelstein 7-X General Materials Science Composite material Stress intensity factor Fatigue Civil and Structural Engineering FEM Mechanical load Crack First wall BEM Mechanical Engineering Thermo-mechanic Paris' law Finite element method 020303 mechanical engineering & transports Nuclear Energy and Engineering Materials Science (all) |
| Zdroj: | Fusion Engineering and Design |
| Popis: | Wendelstein 7-X (W7-X), the world’s largest nuclear fusion experiment of modular stellarator type, started operation in 2015 and will be upgraded with a water cooled first wall for steady state operation in 2020. The first wall consists of a CFC armored island divertors, adjacent baffles, heat shields, and stainless steel wall panels. Baffle and heat shield segments consist of graphite tiles, bolted with low pre-stress onto heat sinks of CuCrZr that are in turn brazed onto water cooled steel pipes. Cracks were detected before installation in the baffles in the root of the brazed seam in over 100 locations. Such cracks are attributed to the imposed plastic deformation of the pipes to bring them into the final shape following the complex 3D geometry of the plasma vessel. This paper gives an overview of the experimental and numerical work using finite element method (FEM) and dual boundary element method (DBEM), including sub-modeling to assess the risk of a water leak during operation. Details of the numerical work is published in Giannella et al. (2017), Lepore et al. (2017) and Citarella et al. (2018). First fatigue crack growth experiments were carried out on pipe material and thermal-mechanical crack growth predictions were made with FEM and DBEM. It appeared that the Stress Intensity Factor (SIF) threshold of the ductile steel is only reached when large plastic strains occur, thus violating the field of application of linear elastic fracture mechanics to forecast crack growth. Afterwards, representative brazed pipe samples were manufactured and subjected to initial plastic deformation causing cracks in 11 out of 12 samples. Some samples were tested up to 60,000 bending load cycles. Two out of four samples failed after ∼35,000 cycles. Before and after the test, the shape of the cracks was measured using 3D computer tomography scans. Equivalence between thermal load in W7-X and the mechanical load in the cyclic test was determined with the numerical models to allow for a prediction of the fatigue life in W7X. Additional modeling showed that also plastic zones away from the cracks can limit the fatigue life. |
| Databáze: | OpenAIRE |
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