Weiterentwicklung und Validierung eines nichtlokalen Schädigungsmodells zur Vorhersage der Bruchzähigkeit im oberen Übergangsgebiet. Teilprojekt. Weiterentwicklung von Bewertungskonzepten zum Versagensverhalten ferritischer Stähle im Übergangsbereich. Abschlussbericht
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In nuclear power engineering failure has to be excluded for components with high safety relevance. Currently, safety proofs mainly use fracture mechanics concepts. Especially in the transition area of fracture toughness where limited stable crack propagation may appear before cleavage failure the currently applied methods are limited. In the project 1501 390B of MPA Universität Stuttgart ductile crack initiation and subsequent stable crack growth in the upper transition area should be calculated using a damage mechanics model. The results of currently used local damage mechanics models depend on the element size of the numerical model. This disadvantage can be avoided using an element size depending on microstructure. With high stress gradients and small crack growth rates small elements are required. This is in conflict with an element size depending on microstructure. With so-called nonlocal damage models this is no longer a problem. By including the damage gradient as an additional degree of freedom the results depend no longer at the element size. In the project damage mechanics computations with the nonlocal Rousselier model are carried out for the evaluation of the upper transition area. An existing user element will be implemented in a commercial FEM program. The correct implementation is verified with simple sample calculations for two and three dimensions. Nonlocal damage calculations multiply the computing time. In order to reduce the computing time different approaches for the tangent module are investigated and 5 % of the computing time can be saved. For the prediction of fracture toughness from the ductile to brittle transition area the nonlocal Rousselier model is combined with the Beremin model. Thus ductile crack growth and failure by brittle fracture can be described in parallel. For the verification of the calculation model available results of fracture toughness specimens from the research project BMWi 1501 240 with the RPV steel 22NiMoCr3-7 are used. Numerical investigations of these fracture toughness specimens (C(T)-specimens and SE(B)- specimens with and without side grooves) are in compliance with experimental results. The load displacement behavior of the specimens and the developed crack front from the ductile to brittle transition area can be well calculated with the nonlocal damage model. The instability in relation to temperature calculated with the coupled damage mechanics model represents the variations of the experimental results very well.
Weiterentwicklung und Validierung eines nichtlokalen Schädigungsmodells zur Vorhersage der Bruchzähigkeit im oberen Übergangsgebiet. Teilprojekt. Weiterentwicklung von Bewertungskonzepten zum Versagensverhalten ferritischer Stähle im Übergangsbereich. Abschlussbericht
Weitere Titelangaben:
Further development and validation of a non local damage model to predict fracture toughness in the upper transition regime. subprojekt. Development of safety assessment concepts for the failure behaviour of ferritic steels in the brittle-to-ductile region. Final report