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Dr.-Ing. Michael Mahler

michael mahler does-not-exist.kit edu

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Beteiligte Mitarbeiter

Prof. Dr.-Ing. Jarir Aktaa 

ANSYS Creep-Fatigue Assessment (CFA) tool for EUROFER97 components

Project description

The damage caused by creep-fatigue is an important factor for materials at high temperatures. For in-vessel components of fusion reactors the material EUROFER97 is a candidate for structural application where it is subjected to irradiation and cyclic thermo-mechanical loads. To be able to evaluate fusion reactor components reliably, creep-fatigue damage has to be taken into account. In the frame of Engineering Data & Design Integration (EDDI) in EUROfusion Technology Work Programme rapid and easy design evaluation is very important to predict the critical regions under typical fusion reactor loading conditions. For this reason Özkan & Aktaa [1] developed a Creep-Fatigue Assessment (CFA) tool which is based on the creep-fatigue rules in ASME Boiler Pressure Vessel Code (BPVC) Section III Division 1 Subsection NH based on elastic analyses.

CFA tool
Fig.1: Approach of CFA tool [2]
Approach of CFA tool

The approach which is shown in Figure 1 is based on Özkan & Aktaa [1] and uses the creep-fatigue rules of ASME BPVC to calculate the fatigue and creep damage of a selected path based on elastic analysis. For fatigue damage and allowable number of cycles the total strain range

∆εt = Kv∆εmod + KΔεc  with  Δεmod = (K2Δεmax S*)/Δσmod

 

is calculated using among others a constitutive model under cyclic loading of EUROFER97 at high temperatures including irradiation effects. To figure out the creep damage the creep stress vs. time to rupture curves are necessary. Finally the fatigue and creep damage can be visualized in a creep-fatigue interaction diagram for the selected path.

Now this approach was extended [2] to be able to automatically identify the most critical path. Therefore a region of interest has to be defined for stress linearization instead of one single path only.

For each path in the selected region the allowable numbers of cycles, fatigue and creep damage are calculated to identify the most critical one. The main advantage of this extension is the automated determination of the most critical path based on the results obtained on all paths during creep-fatigue post-processing.


Benchmark
Fig.2: Benchmark on complex 3D geometry

Benchmark on complex 3D geometry

To show how the extended CFA tool is able to identify the most critical path in a selected region of interest a complex 3D benchmark example is used. Therefore a muff of EUROFER97 material with an inner pressure of 20 bar and temperature of 500°C on the inner and 450°C on the outer surface of the muff using symmetry boundary conditions have been performed with ANSYS MAPDL. Figure 2 shows the result of CFA for an irradiation dose of 15 dpa per year and hold times of zero (black), one (red), hundred (blue) and thousand (green) hours. It is clearly visible that an increase in hold time reduces the fatigue and increases the creep damage fraction.

 

 

Publications

 

[1] F. Özkan & J. Aktaa, Creep fatigue assessment for EUROFER components, Fusion Engineering and Design Volume 100 Pages 536-540, 2015

[2] M. Mahler et al., ANSYS creep-fatigue assessment tool for EUROFER97 components, Nuclear Materials & Energy, 2015, submitted