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@PHDTHESIS{Fischer:841494,
      author       = {Fischer, Torsten},
      title        = {{M}echanismen des {H}ochtemperaturrisswachstums in einem
                      ferritischen {S}tahl an {L}uft und in {W}asserdampf},
      volume       = {421},
      school       = {RWTH Aachen},
      type         = {Dissertation},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2017-08538},
      isbn         = {978-3-95806-326-6},
      series       = {Schriften des Forschungszentrums Jülich Reihe Energie $\&$
                      Umwelt / Energy $\&$ Environment},
      pages        = {VIII, 216 S.},
      year         = {2018},
      note         = {RWTH Aachen, Diss., 2017},
      abstract     = {Nowadays the requirements on conventional power plants have
                      fundamentally changed. Du eto an increase of renewable
                      energies proportion, e. g. wind power and photovoltaics,
                      which cannot supply energy constantly, modern power plants
                      must be able to be operated flexibly in order to compensate
                      the fluctuation in residual load. As a result of the rising
                      number of startup and shutdown processes and thus
                      temperature and internal pressure fluctuations, the
                      materialis strongly stressed. As a result of increasing
                      alternating load, the fatigue damage becomes more and more
                      important, while the influence of the creep damage caused by
                      ever shorter hold time at high operating temperatures
                      decreases. Owing to the increasing cyclic stress, the main
                      focus is on thick-walled power plant components in feedwater
                      and fresh steam systems, for e. g. spheroidal forgings,
                      fittings, collectors, pumps and turbine bypass valves (TBV).
                      Within the scope of the Federal Ministry for Economic
                      Affairs and Energy joint research project THERRI
                      (determination of characteristic parameters for the
                      evaluation of thermal fatigue crack growth in power plants),
                      two TBVs were provided after 21 years of service by
                      Kraftwerks- und Netzgesellschaft (KNG) mbH for fracture
                      mechanics experiments. The material of the TBV is
                      X20CrMoV12-1, a widespread standard 9 - 12 $\%$ Cr
                      ferritic/martensitic steel in the power industry. In the
                      present work, the influence of frequency, hold time and
                      atmosphere at maximum load on crack propagation in a
                      temperature range of 300 °C - 600 °C, which is relevant
                      for the load-flexible power plant operation, was
                      investigated. For this temperature range, data is scarce in
                      the literature. Furthermore, the combination of
                      temperature/frequency/hold time was identified, where
                      fatigue-dominated crack growth devolves to creep fatigue
                      interaction. To characterize the microstructural damage
                      mechanisms and, extensive light and electron microscopy
                      studies were performed. Extensive fracture mechanics studies
                      have shown that during the hold time test, larger crack
                      growth rates per cycle occur than in the fatigue crack
                      growth test. In comparison to pure cyclic loading, crack
                      propagation starts at significant higher $\Delta$K-values,
                      which is caused bythe hold time at maximum load. In the
                      fatigue crack growth test, the crack growth rate increases
                      slightly with decreasing frequency. Because of a dependence
                      of steam atmosphere effects on frequency (or hold time)and
                      temperature, pure atmosphere effects cannot be observed on
                      crack growth or on the start of crack growth.},
      cin          = {IEK-2},
      cid          = {I:(DE-Juel1)IEK-2-20101013},
      pnm          = {111 - Efficient and Flexible Power Plants (POF3-111) /
                      HITEC - Helmholtz Interdisciplinary Doctoral Training in
                      Energy and Climate Research (HITEC) (HITEC-20170406)},
      pid          = {G:(DE-HGF)POF3-111 / G:(DE-Juel1)HITEC-20170406},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
      url          = {https://juser.fz-juelich.de/record/841494},
}