Rissbeschreibung

FKM 2005 Issue No. 287 Project No. 263
Abstract:
Results and characteristic values determined in long-term tests for 1% CrMoNiV and 10 to 12% Cr steels and corresponding casting variants formed the basis for the summary and evaluation of calculation methods for crack initiation and crack propagation behavior under creep, creep fatigue and fatigue loading for high-temperature components of thermal machinery and plant engineering. Validity criteria are defined for the application of the C* parameter. More curves for crack initiation and crack propagation are now available from 11 melts of 1 % CrMoNiV and 10 to 12 % Cr steels and corresponding casting variants, some of which contain data up to 30,000 hours. Extrapolated curves are provided for the two-criteria diagram. The evaluation of different specimen shapes with the C* parameter resulted in some very wide scatter bands, despite observing the validity criteria. For this reason, various measures such as consideration of ductility and computational damage were investigated to reduce the scatter band of the creep crack velocity1 via the fracture mechanics parameter C*, but without significant improvement. Creep and creep fatigue crack initiation can be described in good approximation using a two-criteria method. In addition to the nominal stress in the far field, the stress intensity factor K1 (as a vehicle for describing the crack geometry) is applied to selected component geometries using available calculation rules. For creep crack initiation and creep crack propagation, documents were provided that support the application of the parameter C* to the component-relevant 3D case. For the creep fatigue crack propagation, an accumulative description was created based on a ~K1 relationship for the fatigue crack portion and a C*-dependent description for the creep crack portion. Weighting the proportions of creep and fatigue in the accumulation leads to an improvement. The comparative determination of the parameter C* for component-relevant creep cracking behavior with FE calculations and approximation methods shows that the application of approximation methods appears to be possible under reservation and is consistently on the safe side compared to the FE calculation for C*. For crack initiation and crack propagation determinations, experimentally verified values of crack initiation duration and crack propagation velocity are available. The documents and methods developed were implemented in a modularly structured HT -Riss program system suitable for application to components and validated on the basis of calculations for typical components (shaft, housing, pipeline) with assumed crack-induced defects. This provides a comprehensive calculation tool for determining crack initiation and crack propagation in hot components.

Scope of report:
286 pages, 290 figures, 34 tables, 31 pages appendix
Start of work:
01.01.2003

End of work:
31.12.2004

Funding body:
AVIF, No. A 202
Research bodies:
Materials Testing Institute University of Stuttgart (MPA) Head: Prof. Dr- lng. habil. Eberhard Roos Institute of Materials Science, Technical University of Darmstadt (lfW)
Head:
Prof. Dr.-lng. Christina Berger
Researchers:
Dr.-lng. Tongsheng Mao, Dipl.-lng. Falk Müller, Dr.-lng. Alfred Scholz, IfW Darmstadt Dipl.-lng. Magdalena Machalowska, Dr.-lng. Andreas Klenk, MPA Stuttgart

Chairman of the working group:
Dr.-lng. Jürgen Ewald, Mülheim
Chairman of the advisory board:
Dr.-lng. Jürgen Rabe, Rabe chstadt