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 Engi- neering Data and 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. The presented Creep-Fatigue Assessment (CFA) tool is based on the creep-fatigue rules in ASME Boiler Pressure Vessel Code (BPVC) Section 3 Division 1 Subsection NH which was adapted to the material EUROFER97 and developed for ANSYS. The CFA tool uses the local stress, maximum elastic strain range and temperature from the elastic analysis of the component performed with ANSYS. For the as- sessment design fatigue and stress to rupture curves of EUROFER97 as well as isochronous stress vs. strain curves determined by a constitutive model considering irradiation influence are used to deal with creep-fatigue damage. As a result allowable number of cycles based on creep-fatigue damage interaction under given hold times and irradiation rates is obtained. This tool can be coupled with ANSYS MAPDL and ANSYS Workbench utilizing MAPDL script files

Aktaa, J.

Mahler, M.

Özkan, F.

Nuclear Materials and Energy

English

AbstractThe 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 and 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. The presented Creep-Fatigue Assessment (CFA) tool is based on the creep-fatigue rules in ASME Boiler Pressure Vessel Code (BPVC) Section 3 Division 1 Subsection NH which was adapted to the material EUROFER97 and developed for ANSYS. The CFA tool uses the local stress, maximum elastic strain range and temperature from the elastic analysis of the component performed with ANSYS. For the assessment design fatigue and stress to rupture curves of EUROFER97 as well as isochronous stress vs. strain curves determined by a constitutive model considering irradiation influence are used to deal with creep-fatigue damage. As a result allowable number of cycles based on creep-fatigue damage interaction under given hold times and irradiation rates is obtained. This tool can be coupled with ANSYS MAPDL and ANSYS Workbench utilizing MAPDL script files

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ANSYS Creep-Fatigue Assessment tool for EUROFER97 components 

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Nuclear Materials and Energy 9 (2016) 535–538 Contents lists available at ScienceDirect Nuclear Materials and Energy journal homepage: www.elsevier.com/locate/nme ANSYS Creep-Fatigue Assessment tool for EUROFER97 components M. Mahler ∗, F. Özkan, J. Aktaa Karlsruhe Institute of Technology (KIT), Institute for Applied Materials, 76344 Eggenstein-Leopoldshafen, Germany a r t i c l e i n f o Article history: Received 22 October 2015 Revised 29 March 2016 Accepted 28 May 2016 Available online 24 June 2016 Keywords: Creep damage Fatigue damage ASME BPVC EUROFER97 a b s t r a c t 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 Engi- neering Data and 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. The presented Creep-Fatigue Assessment (CFA) tool is based on the creep-fatigue rules in ASME Boiler Pressure Vessel Code (BPVC) Section 3 Division 1 Subsection NH which was adapted to the material EUROFER97 and developed for ANSYS. The CFA tool uses the local stress, maximum elastic strain range and temperature from the elastic analysis of the component performed with ANSYS. For the as- sessment design fatigue and stress to rupture curves of EUROFER97 as well as isochronous stress vs. strain curves determined by a constitutive model considering irradiation influence are used to deal with creep-fatigue damage. As a result allowable number of cycles based on creep-fatigue damage interaction under given hold times and irradiation rates is obtained. This tool can be coupled with ANSYS MAPDL and ANSYS Workbench utilizing MAPDL script files. © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ). 1 P  f  a  c  w  i  F  u∑ d  b  s  r  t  a  i  a  t  d  A  b  e  S  I  f  c  W2 A  i  h2. Introduction The creep-fatigue evaluation based on the rules in ASME Boilerressure Vessel Code (BPVC) [1] is often used to identify creep andatigue damage. In contrast to ASME BPVC similar rules are avail-ble in RCCMRx code [2] where EUROFER97 is proposed to be in-luded to this code [3] . The procedure mentioned in ASME BPVCas adapted to the ferritic-martensitic steel EUROFER97 [4] andmplemented in a program written in FORTRAN named Creep-atigue Assessment (CFA) tool [5] . This tool uses the following fail-re criterion of ASME BPVC:  [ n N d ] + ∑ [ t T d ] ≤ D (1) The first part on the left side of Eq. (1) represents the fatigueamage with the number of applied repetitions n and the num-er of design allowable cycles N d for the specific cycle type. Theecond part on the left side shows the creep damage with the du-ation t and the allowable time duration T d for a specific time in-erval. On the right hand side of the equation the variable D is the∗ Corresponding author. Tel.: + 49 721 608 28388. E-mail address: Michael.Mahler@kit.edu (M. Mahler). y  p  i  a  ttp://dx.doi.org/10.1016/j.nme.2016.05.017 352-1791/© 2016 The Authors. Published by Elsevier Ltd. This is an open access article ullowable total damage in case of creep-fatigue interaction whichs not constant. The damage D is given by a creep-fatigue dam-ge envelope as bi-linear curve [1] . The CFA tool is able to identifyhe design allowable numbers of cycles, the creep and the fatigueamage fraction on a defined path which is picked by two nodes inNSYS MAPDL. Özkan and Aktaa [6] used this tool on complex testlanket module (TBM) of future fusion reactor components [7] tovaluate the creep and fatigue damage on specific paths using AN-YS MAPDL post-processing of thermo-mechanical elastic analysis.n addition they extended the CFA tool to consider irradiation ef-ects into account [8] . Now the present paper shows how the mostritical path can be identified in ANSYS MAPDL as well as in ANSYSorkbench using an extension of this CFA tool. . Approach of CFA tool and required data for Eurofer97 The approach which is shown in Fig. 1 is based on Özkan andktaa [5] where the creep and fatigue damage is calculated accord-ng to the creep-fatigue rules in ASME BPVC based on elastic anal-sis for a path which must be defined by the user in finite elementrogram ANSYS during post-processing by hand. This selected paths then used for stress linearization to identify primary, secondarynd peak stresses. The most important steps of this approach arender the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ). 536 M. Mahler et al. / Nuclear Materials and Energy 9 (2016) 535–538 Fig. 1. Approach of CFA-Tool for critical path identification. (For interpretation of the references to osc           t  t  u  i  s  t  D  E  A  t  h  a  F  c  f  t  c o  s  h  a  1  s  r  c d  t  t  s  t  t  t  A t  t  b  h  r  F  f  a  t  tNomenclature n number of applied repetitions (–) N d number of design allowable cycles (–) t duration (s) T d allowable time duration (s) D total damage (–) ɛ t total strain range to determine number of design allowable cycles (–) K v Multiaxial plasticity and poisson ratio adjustment factor (see ASME BPVC) (–) ɛ mod modified maximum equivalent strain range (–) K local geometric concentration factor (–) ɛ c creep strain increment (–) ɛ max maximum local equivalent strain range from elastic analysis (–) S ∗ stress indicator determined at ɛ max (see ASME BPVC) (MPa) S m allowable stress (MPa) σ mod modified stress range at ɛ max (see ASME BPVC) (MPa) Abbreviations BPVC Boiler Pressure and Vessel Code CFA Creep-Fatigue Assessment EDDI Engineering Data and Design Integration MAPDL Mechanical ANSYS Parametric Design Language TBM Test Blanket Module the ratcheting rules mentioned in ASME code like 3 S m rule includ-ing primary and secondary stress parameters ( X, Y ), the calculationof total strain range and calculation of the relaxation stress. Thesemain steps are highlighted in Fig. 1 as blue boxes. To check the ratcheting rules and calculate total strain rangeand stress relaxation for EUROFER97 in a temperature range be-tween room temperature and 650 °C different material specificcurves are mandatory like design fatigue, stress to rupture andisochronous stress vs. strain curve, see gray box in Fig. 1. For EUROFER97 the design fatigue curves at different temper-atures in Fig. 2 (a) by Aktaa et al. [9] are used to get informationabout fatigue behavior. For a given total strain range [1] ε t = K v ε mod + K ε c with ε mod = K 2 ε max S ∗σ(2)mod he design allowable number of cycles N d can be identified. Theotal strain range in Eq. (2) is determined according to ASME BPVCsing the values ɛ mod , ɛ c and σ mod which are calculated us-ng the Creep-Fatigue Assessment tool. Considering only the elastictrain range ɛ max from finite element analysis instead of the to-al strain range ɛ t is underestimating the creep-fatigue damage.ue to the lack of available isochronous stress vs. strain curves forUROFER97 in ASME code a constitutive model for RAFM steels byktaa and Schmitt [10] considering irradiation effects [11] is usedo calculate required stress and strain values for consideration ofold time effects. For the creep behavior stress to rupture curvest different tem peratures in Fig. 2 (b) by Tavassoli [12] on EURO-ER97 are used to get the minimum time to rupture T d of a givenreep stress which is based on the total strain range identified be-ore and the use of the constitutive model for RAFM steels by Ak-aa and Schmitt [ 10 , 11 ] in terms of isochronous stress vs. strainurves. Fig. 2 (c) shows examples of isochronous stress vs. strain curvesn EUROFER97 at 450 °C. These curves are predicted using the con-titutive model [ 10 , 11 ] and show the influence of irradiation andold time on EUROFER97. For the non-irradiated state two curvesre visible. One without hold time and one with a hold time of0 0 0 h which results in a reduction of stresses in the stress vs.train curve. For this hold time another curve with an irradiationate of 15 dpa is given. Compared to the non-irradiated curve thisurve is shifted to higher stresses due to irradiation hardening. All details and requirements on calculation of creep and fatigueamage are explained in ASME BPVC Section 3 Division 1 Subsec-ion NH including a lot of steps to be taken into account. Due tohe huge number of steps to be followed in ASME code and inome cases due to lack of available material data for EUROFER97he Creep-Fatigue Assessment tool was initially developed [5] . Athis development stage the main disadvantage of this tool was thathe path for Creep-Fatigue Assessment must be selected by hand inNSYS post-processing. Now in the present paper the approach is extended to be ableo automatically identify the most critical path. With this extensionhe disadvantage of selecting a specific path within a componenty the user itself can be avoided. Therefore a region of interestas to be defined in ANSYS MAPL or Workbench post-processing,espectively. The general idea is shown with the green boxes inig. 1 . One region must be on the inner and one on the outer sur-ace of the component. Based on this selection the attached nodesre extracted to create paths for stress linearization and to identifyhe elastic strain range based on the thermal and the two struc-ural analyses for primary and primary + secondary loads. M. Mahler et al. / Nuclear Materials and Energy 9 (2016) 535–538 537 Fig. 2. Design fatigue curves [9] (a), stress to rupture curves [12] (b) and isochronous stress vs. strain curves [5] including hold time and irradiation effects (c). a) thermal loads b) primary loads c) primary+secondary loads450 500 3.6·10-6 4.6·10-5 1.6·10-5 5.3·10-4Fig. 3. Thermo mechanical elastic finite element analysis in ANSYS MAPDL.  m  t  a  t  T  a  r3 p  a  n  4  a  s  p  t  t  s  m  o  s  (  a  F i  n  r  p  o  f  i  3  f  s  Fig. 4. Selection of inner and outer regions of interest. (For interpretation of the references to osc w  t  i  p  h  T  c  d  l  a i  F  A  w  a  After determination of allowable number of cycles and mini-um time to rupture of each path in the selected region the CFAool identifies the most critical one to finally calculate the fatiguend creep damage for this path based on Eq. (1) . As a result the to-al damage and the allowable number of cycles can be carried out.he main advantage of this approach shown in this paper is theutomated determination of the most critical path based on theesults obtained on all paths during creep-fatigue post-processing. . Benchmark on a complex 3D geometry in ANSYS MAPDL To show how the CFA tool is able to identify the most criticalath in a selected region of interest a complex 3D benchmark ex-mple is used. Therefore a muff of EUROFER97 material with an in-er pressure of 20 bar and temperature of 500 °C on the inner and50 °C on the outer surface of the muff using symmetry bound-ry conditions have been performed with ANSYS MAPDL. Fig. 3 (a)hows the result of the steady state thermal analysis with the tem-erature distribution between the inner and the outer surface ofhe muff. This temperature distribution is used for the first elas-ic structural analysis considering the primary loads (inner pres-ure). The distribution of the equivalent total elastic thermal andechanical strain is shown in Fig. 3 (b) with its maximum valuef 4.6 ×10 −5 on the inner surface of the muff. The second elastictructural simulation considering the primary + secondary loadsinner pressure and thermal expansion) yields a maximum equiv-lent total elastic thermal and mechanical strain of 5.3 ×10 −4 , seeig. 3 (c)). Based on these three elastic analyses the CFA tool is able todentify the most critical path by post-processing. Therefore an in-er and outer region must be defined. Fig. 4 shows the selectedegions of the muff. In this example the green surface in Fig. 4 isicked for the inner (GEOM-INNER) and the purple surface for theuter (GEOM-OUTER) region, respectively. Based on these two sur-aces the nodes adjacent to them are selected to result in a set ofnner (N_L1) and outer nodes (N_L2). In case of the green surface135 nodes are lying on this surface. Next an algorithm searchesor the minimum distance between inner and outer region andelects all elements which are on that minimum distance pathshich results in 3135 paths based on the number of nodes at-ached to the surface. Using only the minimum distances betweennner and outer region is an acceptable assumption, because otherossible distance combinations are in practice in rare cases andowever the tool provides realistic results for the chosen distances.he CFA tool linearizes the stresses along all that paths and cal-ulates the allowable number of cycles, the creep and the fatigueamage. The computation time is about 8 min for post-processingike stress linearization and extraction of additional informationnd 1 min for CFA tool executable itself. After that calculation the minimum allowable number of cycless identified to figure out the most critical path and its position.ig. 5 shows the result of CFA for an irradiation dose of 15 dpa.NSYS MAPDL shows on screen the position of the critical pathithin the finite element mesh highlighted in red ( Fig. 5 , left) andlso the creep and fatigue damage visualized in the creep-fatigue538 M. Mahler et al. / Nuclear Materials and Energy 9 (2016) 535–538 Table 1 CFA results for different hold times and irradiation rate of 15 dpa. Hold time (h) Allowable cycles (–) Fatigue damage (–) Creep damage (–) 0 > 10 0 0 0 0 1 0 1 65418 0 .065 0 .411 100 2370 0 .002 0 .979 10 0 0 323 0 .0 0 0 0 .997 Fig. 5. CFA results for 15 dpa. (For interpretation of the references to osc                     A E  r  a  dR               damage interaction diagram ( Fig. 5 , right). A prompt on screenshows in addition the maximum allowable number of cycles forthis critical path which is equal to 65,418 cycles under 1 h holdtime. The results of other hold times at same irradiation rate arelisted in Table 1. Due to the used shape of interaction diagram for calculation ofcreep and fatigue damage it is clearly visible that an increase inhold time reduces the fatigue and increases the creep damage. Asa result the allowable numbers of cycles decrease with increasinghold time on the most critical path. The main advantage of thistool extension is that the user does not have to select the criticalregion by hand. As it is well known due to creep not the region ofmaximum stress must be the critical one. In some cases the regionof maximum temperature is critical. 4. Conclusion Based on the results the following conclusions can be deducted:• A powerful Creep-Fatigue Assessment tool for EUROFER97 wasdeveloped as post-processing for ANSYS MAPDL and also avail-able for ANSYS Workbench. • Preliminary thermo-mechanical elastic analysis for stress lin-earization is based on three finite element analysis: → thermal,primary and primary + secondary loads. • CFA tool can be used for any complex 3D structures. • Automated identification of the most critical path in the com-ponent by selecting areas of interest is realized. • CFA results for different hold times have been presented for anirradiation rate of 15 dpa. • Application to real structures and further developments of re-sulting needs for optimization are ongoing. cknowledgments This work has been carried out within the framework of theUROfusion Consortium and has received funding from the Eu-atom research and training programme 2014-2018 under grantgreement no. 633053 . The views and opinions expressed hereino not necessarily reflect those of the European Commission. eferences [1] ASME, Boiler Presssure and Vessel Code, Section III, Division 1, Subsection NH,Appendix T, 2004. [2] Afcen, RCCMRx Code 2012, 2012. [3] F. Tavassoli , Eurofer steel, development to full code qualification, Procedia Eng.55 (2013) 300–308 . [4] R. Lindau , A. Möslang , M. Schirra , Thermal and mechanical behaviour of re-duced-activation ferritic-martensitic steel EUROFER, Fusion Eng. Design 61–62(2002) 659–664 . [5] F. Özkan , J. Aktaa , Creep fatigue assessment for EUROFER components, FusionEng. Des. 100 (2015) 536–540 . [6] F. Özkan , J. Aktaa , Creep-fatigue design rules for EUROFER97, ICFRM-16 PosterID 16-170 Beijing, China, 2013 . [7] F. Cismondi , S. Kecskes , G. Aiello , HCPB TBM thermo mechanical design: as-sessment with respect codes and standards and DEMO relevancy, Fusion Eng.Des. 86 (2011) 2228–2232 . [8] F. Özkan , J. Aktaa , Creep fatigue assessment macro in MAPDL for EUROFER,SOFT-2014 Poster ID P2.124 San Sebastian, Spain, 2014 . [9] J. Aktaa , M. Weick , M. Walter , High Temperature Creep-Fatigue StructuralDesign Criteria for Fusion Components Built from EUROFER 97, FZKA 7309Forschungszentrum Karlsruhe (2007) . [10] J. Aktaa , R. Schmitt , High temperature deformation and damage behavior ofRAFM steels under low cycle fatigue loading: experiments and modeling, Fu-sion Eng. Des. 81 (2006) 2221–2231 . [11] J. Aktaa , C. Petersen , Modeling the constitutive behavior of RAFM steels underirradiation conditions, J. Nuclear Mater. 417 (2011) 1123–1126 . [12] F. Tavassoli , Fusion Demo Interim Structural Design Criteria (DISDC) TechnicalReport TW4-TTMS-005-D01, CEA, 2004 . 

ANSYS Creep-Fatigue Assessment tool for EUROFER97 components

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 and 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. The presented Creep-Fatigue Assessment (CFA) tool is based on the creep-fatigue rules in ASME Boiler Pressure Vessel Code (BPVC) Section 3 Division 1 Subsection NH which was adapted to the material EUROFER97 and developed for ANSYS. The CFA tool uses the local stress, maximum elastic strain range and temperature from the elastic analysis of the component performed with ANSYS. For the assessment design fatigue and stress to rupture curves of EUROFER97 as well as isochronous stress vs. strain curves determined by a constitutive model considering irradiation influence are used to deal with creep-fatigue damage. As a result allowable number of cycles based on creep-fatigue damage interaction under given hold times and irradiation rates is obtained. This tool can be coupled with ANSYS MAPDL and ANSYS Workbench utilizing MAPDL script files

M. Mahler

F. Özkan

J. Aktaa

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ANSYS Creep-Fatigue Assessment tool for EUROFER97 components

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