arid damage simulation capabiliti
Contents
1. PES uis S I t ne PGFha sustenance Si ie eatin ere FZR 296 Meee Seabees EA We mrt rte ute ee yg Eo mm nc tinge te tint LE hr WISSENSCHAFTLICH TECHNISCHE BERICHTE D 120 Juli 2000 ISSN 1437 322 Possongort Archiv Ex Eberhard Altstadt and Thomas Moessner Extension of the ANSYS creep and damage simulation capabilities Herausgeber FORSCHUNGSZENTRUM ROSSENDORF Postfach 51 01 19 D 01314 Dresden Telefon 49 351 26 00 Telefax 49 351 2 69 04 61 http www fz rossendorf de Als Manuskript gedruckt Alle Rechte beim Herausgeber FORSCHUNGSZENTRUM ROSSENDORF 574 WISSENSCHAFTLICH TECHNISCHE BERICHTE FZR 296 Juli 2000 Eberhard Altstadt and Thomas Moessner Extension of the ANSYS creep and damage simulation capabilities Extension of the ANSYS creep and damage simulation capabilities Abstract The user programmable features of the finite element code ANSYS are used to generate a customized ANSYS executable including a more general creep behaviour of materials and a damage module The numerical approach for the creep behaviour is not restricted to a single creep law e g strain hardening model with parameters evaluated from a limited stress and temperature range Instea2. Page 15 5 2 Log File of the damage calls Page 15 5 3 Damage backup file Page 15 6 Examples 0 eee eee eee eee eee eee eee nnn Page 15 6 1 Tensile bar cece cence he hh rn Page 15 6 2 Disk with centre hole Page 16 6 2 1 Material behaviour cece eee ere ee eens Page 16 6 2 2 Pure creep at constant temperature Page 18 6 2 3 Creep and plasticity Page 19 References 2 0 cece cc cee cence eee teen e eee teen esse hn nn Page 19 Appendix 1 Figures 0 cece cece cece cece eee hn Page 20 Appendix 2 CRPGEN command reference Extension of the ANSYS creep and damage simulation capabilities Page 4 Nomenclature Latin C coefficients of the time hardening creep equation d d D AD K q Pa pl frac coefficients of the strain hardening creep equation damage parameter damage increment Kelvin temperature exponent for non linear interpolation Pascal stress exponent for non linear interpolation radius triaxiality function second time time increment temperature user programmable features weighting factors for interpolation of the creep strain increment coordinates strain strain rate creep fracture strain effective equivalent creep
3. Fig A7 Creep curves creep strain and creep strain rate over the time for 16MNDS at T 1373K o 10MPa Extension of the ANSYS creep and damage simulation capabilities Page 24 ANSYS 5 6 MISO Table For Material MAY 25 2000 18 32 49 Table Data TL 300 T2 475 T3 675 775 T5 875 T6 975 T7 1075 T8 1275 T9 1375 710 21475 Fig 8 Stress strain curves of 16MND5 for the temperature range from to 1475 true stress and strain based on 9 Extension of the ANSYS creep and damage simulation capabilities Page 25 ANSYS 5 6 MAY 23 2000 11 36 19 NODAL SOLUTION STEP 11 SUB 137 TIME 1000 SY BVG RSYS 1 PowerGraphics EFACET 1 AVRES Mat DMX 026037 SMN 102E 08 SMX 198E 08 102 08 690ET07 3565 07 218023 312 07 54 07 981ET07 132 08 165 08 198 08 Fig A9 Disk with hole Material 16MNDS Pure creep at 1373 and 10MPa Tangential stress after 1000 s ANSYS 5 6 MAY 23 2000 11 37 17 AVG ELEMENT SOLUTION STEP 11 SUB 137 TIME 1000 CRDMG avo DMX 026037 SMN 004353 SMX 2 167568 004353 022488 040623 058758 075893 095028 113163 131288 149433 167568 Fig A10 Disk with hole Material 16MNDS Pure creep at T 1373 and 0 10MPa Damage after 1000 s Extension of the ANSYS creep and damage simulation capabiliti
4. Extension of the ANSYS creep and damage simulation capabilities Page 13 It is not recommended to issue outres specifications other than outres all freg since element and DOF solutions need to be stored on the result file for creep damage evaluation To activate the damage accumulation and the element killing use the following commands set command name associated with UPFs begin level ucmd usr2 2 ucmd usr3 3 calculate creep damage solu set the output frequency optinal outres all freq initialize the damage procedure the calling frequency depends on the outres settings usr2 dmgcrit set fracture strains usr3 epfr_key epbr0 cltem clsig solv Table 3 ANSYS input example for the use of the creep damage module The argument dmgcrit of the usr2 command is used to select a damage criterion dmgcrit 2 triaxiality according to eq 17 dmgcrit 1 1 dmgcrit 0 no damage calculation The usr3 command provides an additional possibility to calculate the creep fracture strain or the plastic fracture strain according to epfr_ key 0 5 epbr0 cltem T clsig o 119 epfr_key 1 epbrO cltem T If the usr3 command is not entered or entered with all arguments zero the current creep fracture strain is calculated from the creep data base values see creep file example table 1 by multi linear interpolation Extension of the ANSYS creep and damage simulat
5. curves are shown in Figure 8 A multi linear isotropic hardening is assumed and the flow rule of von Mises is used 6 2 2 Pure creep at constant temperature At first the development of stresses and damage is studied assuming pure creep no prompt plastic deformation at a constant temperature of 1370 K The creep deformation leads to a relatively quick release of the stress concentration near the hole Figures A9 and A10 show the tangential stress and the accumulated damage after 1000 s Figures A11 and A12 show the same quantities after 9900s The elements which were killed in the meantime are not shown It is remarkable that in spite of reduced cross section area the maximum stress is still lower than it was in the beginning of the calculation This is a consequence of stress relocation The development of the damage and the stress over the time for some locations on the y axis is shown in the Figures A13 and A14 In Fig A14 the effects of stress relocation and of the element killing can be clearly seen Figure A15 shows the creep strains of the two points O r and 0 1 5r over the time The element at 0 1 5r fails at a slightly lower total creep strain which is a consequence of the higher triaxiality factor at this location Extension of the ANSYS creep and damage simulation capabilities Page 19 6 2 3 Creep and plasticity In this load case creep and plasticity are combined As before the temperature is constant
6. time endtime Set maximum time for creep data generation to endtime This command is required for c 1 see crdat command and for plotting time dependent creep curves see plot 0 write fame Write generated creep data to the ASCH file fname CRPGEN for Win NT 9x Rev 1 4 Command Reference Page 37 General Shell Commands Macro Language delvar Clear all defined variables See also Definition of variables stat do dovar dostart dostop dostep Execute a do loop within a command file see The command is not possible from standard input The loop variables dostart dostop dostep can be numbers variables or expressions dostart lt dostop dostep gt 0 The loop must be closed by enddo in the same command file where it was opened The loop body must not refer to another command file Up to 10 do loops can recursively be opened at the same time echo key Switch on off command echo to standard output eof Terminate the input stream from the current input file and redirect it to the prior unit help Open help file Acrobat Reader required if expr1 op expr2 then command block elseif expr 1 op expr2 then command block else command block endif Branching within a command file not possible from standard input expr and expr2 are numerical values variables or expressions op eq ne It gt le ge The syntax is similar to the FORTRAN programming language but en
7. 152 T T o HH 0 Ta T w T Tj 6 044 Ennu 7 TaT Onn Ona Enn Eng w T T 0 054 7 Enn Ty o 9 Er The quantities without index 0 T are the actual values of the current element integration point The indexed quantities are the values from the creep data base eq 3 They form the smallest intervals which the actual quantities are enclosed in The meaning of the indices is L low bound largest data base value which is smaller than the actual integration point value and H high bound smallest data base value which is greater than the actual integration point value The first index refers to the temperature the second index to the stress and the third to the strain lt T lt T 654 Our tS 0 lt 014 047 7 pa oo erkenne S ES stresses and strains in eq 4 6 are equivalent values The components of creep strain tensor increment 7 are calculated according to the Prandtl Reuss flow rule 2 6 Extension of the ANSYS creep and damage simulation capabilities Page 10 The creep data base eq 3 has to be provided in such a way that the actual temperature and the equivalent stress of the elements do not exceed the maximum values of the creep data base If the actual temperature or stress values are smaller than the smallest values of eq 4 the
8. E en Tr _ emit o 015 E _ 0 ORL 7 e un eA 0 Ra ORL Cann 3 een e 8h o Bg 9 BL E H H H 7 E uaa e 25 7 eni o E uL Wu I UEI UR COE AY asau OL unun Evan W W W3 w 14 We W Ws with the parameters 1n 3 ME ra In 4 qe dee T T i T 15 b In 34 ug E ME ya m 0 4 1x0 It should be noted that in the above equations the index of q always corresponds to the second index of stress level and the index of always corresponds to the first index of temperature level aon Extension of the ANSYS creep and damage simulation capabilities _ Page 12 4 Damage module 4 1 Damage model The material damage due to significant creep strains is modelled by a damage measure which is incrementally accumulated at the end of a load step or substep This damage includes also the prompt plastic deformation of the structure The damage increment is eh SET 2 o T EP T T Mn with fas being the creep fracture strain of the uniaxial creep test at constant stress and temperature and er the plastic fracture strain true strain of the tensile test R is a function which considers the damage behaviour in dependance on the triaxiality of the stress t
9. creep strain increment is zero for this step 3 2 Non linear interpolation If the temperature steps and or the stress steps in the creep data base are not sufficiently small the creep strain increment might be overestimated since the strain rate in general depends over proportionally on the stress and on the temperature respectively That s why a non linear calculation of the weighting coefficients is useful Assuming that the strain rate depends exponentially on the stress i e 8 the according interpolation between two points is et 9 i 05 07 1 05 0 the exponent can be estimated from _ _ In In In o In 0 er Similarly if it is assumed that the strain rate dependency on the temperature can be described by T 11 the appropriate interpolation between two points is e 9b _ e 7 e 9 7 12 ein ean 1 qa h vam 72 The parameter q can be estimated from 1 1 13 Of course the parameter can change with the stress level and the accumulated creep strain as Extension of the ANSYS creep and damage simulation capabilities Page 11 the parameter r may be dependent on temperature and strain Applying the above equations to the calculation of the weighting coefficients one obtains e 98 g T g ux 0 Liu 7 E e 2 8 euT Lu 07 E 55 e 35 8 _ g74n T _ Orr Erz
10. of only one element was used Fig A1 The creep data base is generated according to equation 1 with the coefficients d 69372E 23s d 3367 d 0 459 d 22392 21 1 For this hypothetical material a reference solution can be obtained using the ANSYS standard Extension of the ANSYS creep and damage simulation capabilities Page 16 creep equation So the purpose of this example is e to show that user creep module works correctly to demonstrate the influence of the interpolation method cf section 3 The load for the model in Fig A1 is a constant stress of 0 200 MPa and the temperature is 1000K The creep data base is generated for the following temperature and stress levels T 97315 0 150MPa 0 250 MPa 22 T 1073 15 150MPa Om 250 MPa The creep curves are calculated for a time range of 10 s with an integration step width of 0 025s Figure A2 shows the results for linear interpolation cf eq 6 and Fig A3 for non linear interpolation cf eq 14 With linear interpolation the creep strain is too high what is clear in view of eqs 1 and 21 whereas the results with non linear interpolation meet exactly the reference solution 6 2 Disk with centre hole The model is shown in Fig A4 The disk is loaded at its free end by a tensile stress in X direction Fig A5 shows the tangential stress of the well known elastic solution exhibiting a st
11. strain effective creep strain increment plastic fracture strain effective equivalent plastic strain effective plastic strain increment Poisson s number mechanical stress von Mises equivalent stress hydrostatic stress Extension of the ANSYS creep and damage simulation capabilities Page 5 Indices equivalent frac fracture H high hydrostatic hole L low max maximum min minimum pl plastic P primary ref reference S secondary T tertiary tan tangential Extension of the ANSYS creep and damage simulation capabilities Page 6 1 Introduction The creep behaviour of materials is usually described by analytical formulas creep laws with a number of free coefficients e g o d d 2 amp eXp 1 The coefficients c c in eq 1 are used to adapt the creep laws to creep test results performed at constant load and temperature However in practice it is often difficult to achieve a satisfying adjustment for a wide range of temperatures and stresses with only one set of coefficients Instead it appears that the coefficients itself are dependent on the temperature or on the stress level Therefore a supplementary tool is developed which allows to describe the creep behaviour of a material for different stress and temperature levels independently This is especially useful if strong stress and or temperature gradien
12. the log file lt jobnam gt crlg can be created jobnam defaults to file This ASCII file contains the base name of creep data files the number of temperature levels the number of stress levels per temperature the number of strain rate strain pairs for each level and the first twenty of such pairs The file is written if the third argument of the ucri command is set to 1 for example usr1 testcrp 5 1 5 2 Log File of the damage calls This ASCII file is named lt jobnam gt dmg and contains information on current load step substep time number of elements and number of nodes Moreover for each element the average temperature stresses creep strains plastic strains and accumulated damage is recorded The log information is appended each time the dmg routine is called The file is newly created in the first loadstep if the analysis is not a restart 5 3 Damage backup file This binary file is named lt jobnam gt dsav and contains the accumulated damage This file is necessary if a restart analysis is performed In the case of a restart the creep data base must be input in the same way as in the first analysis since the creep data base is not stored in the db file cf usr1 command Additionally the previously accumulated damage must be input from the dsav file This is automatically initialized if a restart analysis is performed 6 Examples 6 1 Tensile bar For verification of the creep module a simple model which consists
13. 1370 and the stress load is 0 10 MPa The Figures A16 and A17 show the tangential stress and the accumulated damage after 1000 s Figures A18 and A19 show the same quantities after 4800s The development of the damage and the stress over the time for some locations on the y axis is shown in the Figures A20 and 21 Figure A22 shows the equivalent creep strain and the equivalent plastic strain of the two points 0 r and 0 1 5r over the time The stress near the hole exhibits a slightly different behaviour compared to the pure creep case ref Fig A21 red curve It starts with a lower value since a prompt plastic deformation occurs and the maximum stress is limited to the initial yield stress After that the stress is increasing due to the plastic hardening of the material After some 8005 a stress relocation starts to develop as a consequence of the increasing creep deformation The progress of damage looks also somewhat different than in the pure creep case ref Fig A20 The damage value at t 0 s is not zero but up to 0 29 This is the result of the prompt plastic deformation The contribution of the plastic strain to the damage leads to a shorter time at which the first element fails 4300 s vs 8400 s in the pure creep case Fig A13 The failure of the first element causes a prompt increase of the damage in the neighbouring elements since the stress relocation leads to another prompt plastic strain increment This effect can al
14. Ca NIVHIS 6 1OMPa Equivalent creep strain over time at points 1 and 2 see Figure A13 Fig 15 Disk with hole Material 16MND5 Pure creep at T 1373 and Extension of the ANSYS creep and damage simulation capabilities Page 29 ANSYS 5 6 JUL 6 2000 12 52 44 NODAL SOLUTION STEP 11 SUB 134 TIME 1000 sy RSYS 1 PowerGraphics 103E 08 200 08 103E 08 6956 07 3598 07 221048 3158 07 651E 07 9886 07 132 08 1668 08 200 08 Fig A16 Disk with hole Material 16MND5 Creep and plasticity at T 1373 and 0 10MPa Tangential stress after 1000 s ANSYS 5 6 JUL 6 2000 12 53 19 AVG ELEMENT SOLUTION STEP 11 SUB 134 TIME 1000 DMG DMX 027558 SMN 004256 SMX 656388 004256 076715 149174 NH 221633 204092 206551 Cad 139011 51147 LI 583929 WB oos Fig A17 Disk with hole Material 16MNDS Creep and plasticity at T 1373 and 6 10MPa Damage after 1000 s Extension of the ANSYS creep and damage simulation capabilities Page 30 ANSYS 5 6 JUL 6 2000 13 05 52 NODAL SOLUTION STEP 53 SUB 145 TIME 4800 AVG RSYS 1 PowerGraphics EFACET 1 184 08 108Ht08 752b5 t07 428 07 1046 07 2206707 544 07 868 07 119 08 152 08 1846 08 Fig A18 Disk with hole Material 16 5 Cre
15. PGEN for Win NT 9x Rev 1 4 Command Reference Page 34 CRPGEN for WIN NT 9x Revision 1 4 Command Reference clear Delete all preceding settings of the erdat time epmax sigma temp commands erdat stloc cl c2 c3 c4 c5 c6 Set the creep parameters c c C C and select creep law STLOC refers to the first creep parameter to be input e g crdat 4 c1 c2 c3 reads the constants c and c If c 0 use strain hardening model according to x C 20 80 ex a is unused If c 1 use time hardening model according to 5 C4 i c0 0 t ex is unused If c 2 use time hardening model according to 5 c Cc t c C Fe Un exp is unused envsig sigfac sigoff Convert a creep function to another stress unit system e g from Pa to MPa This command can be used to change existing creep data files to use them in different engineering unit systems The stress level in a creep data file is changed according to new Sigfac 0 44 sigoff The command should only be used in connection with read and write Example read file1 c01 envsig 1 0e 06 write file2 c01 epmax epmax Define the maximum strain up to which the creep curve is to be generated Command is required for 0 see erdat CRPGEN for Win NT 9x Rev 1 4 Command Reference Page 35 exit Terminate the program The data base is not automatical
16. ab 1 s23b Floating point variables are truncated to integer If for example a 3 25E 01 then the result of a is 32
17. d N the number of strain rate strain pairs for the m th stress level within the k th temperature level The routine user01 1 is used to realise the creep data input into ANSYS The data must be provided by the user as a set of ASCII files for each temperature stress level one file The structure of a creep data file is demonstrated in the following example 73150 02 00000 05 50000 01 00000 02 Temperature Stress kPa creep fracture strain number of strain sets in this file NPR POF WW 00000 00 97257 04 16640 03 92061 03 73599 03 16071E 01 56547E 01 99738E 01 00000E 05 55093 05 85600E 05 72162 05 03866E 04 83579E 03 16142E 03 50632E 03 Table 1 creep data file example 1 n seti 1 depsi set2 eps2 deps2 set3 eps3 deps3 eps4 deps4 eps5 deps5 eee set98 eps98 deps98 set99 eps99 deps99 set100 epsi00 depsi00 The creep data files must be named according to the pattern basename c where stands for the sequent file number 01 nfiles To read the creep data files use the following ANSYS commands 3 4 Extension of the ANSYS creep and damage simulation capabilities Page 8 set command name associated with user01 ucmd usrl i specify the names and the number of the creep data files usrl filename nfiles log key intp key instruct ANSYS to use the user defined creep law
18. d of this strain rate strain relations can be read from external creep data files for different temperature and stress levels The damage module accumulates a damage measure based on the creep strain increment and plastic strain increment of the load step and the current fracture strains for creep and plasticity depending on temperature and stress level If the damage measure of an element exceeds a critical value this element is deactivated Examples are given for illustration and verification of the new program modules Extension of the ANSYS creep and damage simulation capabilities Page 3 Contents Nomenclature 00 cece cee cece rece eee hh et Page 4 1 Introduction 6 2 Input of the creep data of the materials Page 6 3 Calculation of the creep strain increment Page 8 3 1 Linear interpolation 0 cece cece ence ee ren Page 8 3 2 Non linear interpolation 0 ccc eee eee cece eee eee Page 10 4 Damage module 0 ccc cece eee eth en Page 12 4 1 Damage model 0 ccc Page 12 4 2 Calling the damage procedure Page 12 4 3 Plotting the damage Page 14 5 Additional files created Page 15 5 1 Log File of creep data base input
19. dif and then are required Recursive if statements are possible CRPGEN for Win NT 9x Rev 1 4 Command Reference Page 38 Anput fname Directs input stream to file fname Recursive switches are possible If files with extention mac macros are existing in the current working directory these macros files can be input by simply typing the basename of the macro file e g type mac01 to input the command file mac01 mac Jout Switch program printouts from standard output to file fname If fname is not input switch back to standard output stat Print all defined variables See also Definition of variables delvar Definition of variables Variables can be defined by var value where value can be a number a name of a variable a numerical expression or a character string The name of the variable var must begin with a letter and can consist of 8 characters Expressions can be assembled from numbers and numerical variables Valid operators are left opening bracket right closing bracket plus addition minus subtraction multiplcation division power operation The defined variables are global ones The character equivalents of variable values can be used in command strings by str varname str2 vamame is replaced by its character value For example the following commands are equivalent vari xyz read file var1 read filexyz vnum 23 siglab 1 s vnum b sigl
20. ensor 8 2 s 50 20 2a 17 3 O ogv where is the hydrostatic stress and O is the von Mises equivalent stress Alternatively the triaxiality function can be set to 1 The damage increment is calculated for each element by averaging its nodal equivalent creep and plastic strains The accumulated damage is ldstep D IAD 18 If the element damage reaches the value of D 1 the element is killed by setting its death flag to 1 refer to the element birth and death section of 3 4 2 Calling the damage procedure The creep damage module is realized in the subroutine dmg 01 and a number of supporting routines The invocation of this module is initialized by the user routine USERO2 Once this initialization has been done the creep damage routine is automatically called after each substep or after each loadstep depending on the settings with the outres command This is realized by the UPFs USOLBEG USSFIN and USOLFIN respectively If all substeps are written to the result file outres all all the damage routine is called after each substep Otherwise the damage routine is called after each loadstep default If the analysis is a restart analysis the previously accumulated damage values are resumed from the binary file lt jobnam gt dsav Notes It is not necessary to invoke usrcal command the initialization for USOLBEG USSFIN ULDFIN USOLFIN and USEROU is done automatically
21. ep and plasticity at T 1373 and 6 10MPa Tangential stress after 4800 s Fig A19 Disk with hole Material 16MNDS5 Creep and plasticity at T 1373 and 6 10MPa Damage after 4800 s Extension of the ANSYS creep and damage simulation capabilities Page 31 ERE Ej EU LLL BENA TIME Fig A20 Disk with hole Material 16MND5 Creep and plasticity at T 1373 K and 0 10MPa Damage over time at four points DMG 1 at x 0 y r DMG 2 at 0 1 5 DMG 3 at 0 2 5 r4 DMG 4 at 0 b E ILS BEI AT I E EUR STRESS T EE d ELLEN EST EE Setan i CEEELEEEEELEE x1Ox 2 52 TIME s Fig A21 Disk with hole Material 16MND5 Creep and plasticity at T 1373 K and 6 10MPa Tangential stress over time at four points see Figure A13 Extension of the ANSYS creep and damage simulation capabilities Page 32 Cx 1084 4 woe HH EPPL 1 1 1 2 Fig A22 Disk with hole Material 16MND5 Creep and plasticity at T 1373 and 6 10MPa Equivalent creep strain and equivalent plastic strain over time at points 1 and 2 see Figure A13 Extension of the ANSYS creep and damage simulation capabilities Page 33 Appendix 2 CRPGEN command reference CR
22. es Page 26 ANSYS 5 6 MAY 23 2000 12 16 59 NODAL SOLUTION STEP 103 SUB 439 TIME 9900 sy AVG RSYS 1 PowerGraphics EFACET 1 AVRES Mat DMX 107927 SMN 126E 08 SMX 182 08 126E 08 915E 07 572 07 230E 07 1128 07 455E 07 7975 07 1148 08 148 08 182 08 Fig 11 Disk with hole Material 16MND5 Pure creep at T 1373 and 6 1OMPa Tangential stress after 9900 s ANSYS 5 6 MAY 23 2000 12 17 46 AVG BLEMENT SOLUTION 962179 Fig A12 Disk with hole Material 16MND5 Pure creep at 1373 and 10MPa Damage after 9900 s Extension of the ANSYS creep and damage simulation capabilities Page 27 Fig A13 Disk with hole Material 16MNDS5 Pure creep at 1373 and 0 10MPa Damage over time at four points DMG 1 at x 0 y r DMG 2 at 0 1 5 DMG 3 at 0 2 5 r4 DMG 4 at 0 b EIE RUE MINI REL le RU m 7 Lumen ei Fig 14 Disk with hole Material 16MNDS Pure creep at T 1373 and 10 Tangential stress over time at four points see Figure A13 Page 28 Extension of the ANSYS creep and damage simulation capabilities Cx 10333 SN 5 CLEEENEKLELS EIE a ELI NC o o o o o M N lt
23. escription of the standard non summable miscellaneous element output NMISC The UPF USEROU was employed to realize the additional nmisc output The damage value is automatically stored on the first place after the last standard NMISC output The graphical output during the postprocessing can easily be realized with the commands etable pletab esol 4 The output frequency to the result file depends on the settings of the outres command 4 Table 4 shows an ANSYS input example post processing posti set etable crdmg nmisc 26 26 if element is plane42 pletab crdmg avg Table 4 ANSYS input example for plotting of the creep damage Note The creep damage calculated with the stresses and strains of the n th result set is stored in the n 1 st result set of the result file This unintended shift is due to the fact that the USEROU routine is called before USSFIN damage calculation after a substep and ULDFIN Extension of the ANSYS creep and damage simulation capabilities Page 15 damage calculation after a loadstep This cannot be influenced by the UPF programmer However in the additional file lt jobnam gt dmg see section 5 the assignment between the element results and the calculated damage is correct The command macro pldmg mac can be used as a work around for this problem 5 Additional files created 5 1 Log File of creep data base input To verify the input of the creep data files
24. ion capabilities Page 14 T T 0 4 7 0 81x Ty 0 0 4 58 Ty TL us Ty Tj py 014 T 0 2 T T 0 pn T T T o H H Ty 7 0 HH fa L0 20 For the meaning of the indices see sections 2 and 3 The plastic fracture strain is calculated from the last strain stress point of the MISO table or of the MKIN table interpolation between the temperatures Refer to the tb tbpt tbtemp commands 3 4 The usr2 and usr3 commands can also be used with an ANSYS standard creep law c6 100 however in this case the creep fracture strain must be entered via usr3 since it is otherwise not available After the solv command the scalar ANSYS parameter dmgmax is available which represents the maximum creep damage of all elements at the current loadstep Note an element is killed the stress distribution may promptly and significantly change So it is recommended to observe the process of element killing after each load step using the standard ANSYS commands esel get If one or more elements are killed during the load step the time increment for the next step should be sufficiently small 4 3 Plotting the damage The damage D is calculated for each element whenever the cr dmg routine is invoked section 4 2 To make this quantity available for the postprocessing it is written it to the NMISC records of the elements refer to 5 for the d
25. ly saved Use the write command plot pikey Plot creep curves If plkey 0 plot t and t if plkey 1 plot amp e prdat Print creep parameters to standard output read fname Read a creep data file fname is the file containing a creep curve amp e o const T const rsolve Continue the solution after the change of creep parameters This command can be used to generate creep curves which are governed by different creep equations e g primary secondary and tertiary creep stage A solve command must have been entered before the first rsolve command An additional time or epmax command is also required where the endtime or epmax argument must be greater than that of the previous solve or rsolve process Stress and temperature must not be changed after the solve command Example sigma 100 temp 800 crdat 1 1 0e 16 2 2 0 14 9860 0 1 time 3000 steps 200 solve crdat 1 3 0e 15 2 2 0 01 9860 0 1 time 5600 steps 150 rsolve write crpdat c01 sigma sigma Define the stress level for the creep curve CRPGEN for Win NT 9x Rev 1 4 Command Reference Page 36 solve Start generation of creep data Command requires creep parameters to be input see crdat time epmax steps steps nstep Define the number of time strain steps nstep pairs are to be generated temp temp Define the temperature level for the creep curve to be generated
26. nsion of the ANSYS creep and damage simulation capabilities Page 20 Appendix 1 Figures Extension of the ANSYS creep and damage simulation capabilities Page 21 Fig A1 Model of the tensile bar N LI creep strain NLLLLLI LAN Fig A2 Tensile bar creep curves axial strain and lateral strain vs time linear interpolation and reference solution inii Se EEE creep strain SIG 200MPA T 1000K DELTA_SIG 100 DELTA_T 100 Fig A3 Tensile bar creep curves axial strain and lateral strain vs time non linear interpolation and reference solution Fig A4 Model of the rectangular disk with a centre hole uniform stress at red symmetry conditions at 0 and 0 blue ANSYS 5 6 MAY 22 2000 09 58 14 NODAL SOLUTION STEP 1 SUB 1 TIME 100E 04 AVG SMNB 109E 08 SMX 308 08 SMXB 3225 08 PRES 1008408 103 08 5738407 117E407 3398 07 B 7058407 20s 1718 08 LI 2168 08 L 2628 08 308 08 Fig 5 Tangential stress elastic solution Extension of the ANSYS creep and damage simulation capabilities Page 23 Fig Scheme of a creep curve with primary secondary and tertiary creep stage 6 100 1 373 03 sig 9 998E406 e IE n M 5 00 03 1 006404 1 50 04 2 00E404 2 50E404 3 00E 04 CTI A time
27. prep7 tb creep mat tbdata 1 1 100 Table 2 ANSYS input example for using the user defined creep data base If log 1 a control output file lt jobnam gt crlg is written If the argument intp_key 1 the non linear interpolation scheme is activated section 3 For the generation of the creep data files the supporting program CRPGEN is available command reference in Annex 2 3 Calculation of the creep strain increment To realize the calculation of the creep strain increment according to the non standard creep law the UPF usercr f was modified and linked to the customized ANSYS executable 1 In this routine the scalar creep strain increment Ae amp At is determined from the creep data input see section 2 by multi linear interpolation T Ae w Epa t War 5 tW t Wr Emm We Een At 3 1 Linear interpolation Assuming that the strain rate depends linearly on stress and temperature between two data base points the weighting factors in eq 5 are Extension of the ANSYS creep and damage simulation capabilities Page 9 Ty T 0 4 7 0 Erun 8 ue Ty T py 915 Enna 5 Ty 0 4 0 144 Ty T 0547 05 uua 7 i wy DO Oa T4 TL 65 47 911 u w Ty T Orn E Ty T 0 47 95 nus Erz T T yay 7 0 Ey 8 W z n 6 Ty 7 T yay 7951 Era
28. ress maximum of 0 max 30 at the 90 position 6 2 1 Material behaviour The material of the disk is assumed to be the French reactor pressure vessel steel 16MND5 The creep behaviour of this material at high temperatures was investigated within a extensive experimental program funded by the European Commission 9 Based on the experimental data the ANSYS creep data base is generated The creep curves are subdivided into three sections cf Fig A6 I primary creep range t lt tp I secondary creep range ty t t tertiary creep range t t t4 The creep curves were generated at different temperature and stress levels according to the following equations I T Cop T t T CO Cop T t T 1 Pe 1 Cap Ik TY 0 tos Ss D cas T 1 _ i DH Q3 P Cu T 6 N t D 2 D terry Extension of the ANSYS creep and damage simulation capabilities Page 17 For the primary creep stage an equivalent strain hardening representation is Dip T dap T T with 1 Cap D C 1 es d d 1 Cap 1 Cp 24 The coefficients of the primary creep stage were taken from the work of IKONEN 9 who summarized a couple of creep test performed in a temperature range of 600 1300 C According to the experimental data in 9 it was assumed that the transition between prima
29. ry and secondary creep takes place at a creep strain of p 0 1 and the transition between secondary and tertiary creep at a creep strain of 0 2 The fracture strain is about pa Er 08 The times for the creep stages can be calculated by cf eq 23 _ Otca Ep PL Ceo 1 ET 1 Cas Es 7 Ep C3g 1 ix 25 ts x g 95 tp n 1S 1 1 Es tort dico Cy To get a smooth transition between the stages of the creep curve the coefficients C and must fulfill the relations C3p C3s Cis m Ci tp C Cg nen 26 Cap Cag Cor Table 5 shows the parameters for the creep curves The coefficients D p dj and d are parameters fitted to the experiments by IKONEN 9 the other coefficients follow from these fitted parameters by using the above equations The coefficients are related to the stress unit MPa and the time unit sec Extension of the ANSYS creep and damage simulation capabilities Page 18 0 304 TY 2 Cop Cap Cis Cos is foo loo oo joo oo joo joo TT L5 P er qe p p p p p p Table 5 Parameters of the creep curves for the steel 16MND5 Figure A7 shows the creep strain and the creep strain rate at 1373 ando 10MPa example In some load cases creep and prompt plasticity occur simultaneously Therefore the temperature dependento
30. so be seen in the strain curves Fig A22 Contrary in the pure creep case the killing of the first element only causes a steeper gradient in the damage curves of the neighbouring elements Fig A13 Comparing the damage Fig A20 with the plastic strains and creep strains Fig 22 it can be stated that the relative contribution of the plastic strain to the damage is larger than that of the creep strain This is due to the fact that in the case of the 16MNDS steel the plastic fracture strain is smaller than the creep fracture strain see also eq 16 References 1 ANSYS Programmers Manual ANSYS Inc 1998 2 ANSYS User s Manual Theory Rev 5 5 ANSYS Inc 1998 3 ANSYS User s Manual Analysis guide Rev 5 5 ANSYS Inc 1998 4 ANSYS User s Manual Command reference Rev 5 5 ANSYS Inc 1998 5 ANSYS User s Manual Elements manual Rev 5 5 ANSYS Inc 1998 6 Becker A A Background to Material Non Linear Benchmarks NAFEMS report R0049 International Association for the Engineering Analysis Community i Azodi D P Eisert U Jendrich W M Kuntze GRS Report GRS A 2264 8 Lemaitre 1 A Course on Damage Mechanics ISBN 3 540 60980 6 2nd edition Springer Verlag Berlin Heidelberg New York 1996 9 Ikonen K 1999 Creep Model Fitting Derived from REVISA Creep Tensile and Relaxation Measurements Technical Report MOSES 4 99 VTT Energy Espoo Finland Exte
31. ts are present and if both primary and secondary creep are to be considered in the analysis Additionally it is possible to calculate the creep damage and deactivate elements whose accumulated damage is greater or equal to one The user programmable features available on the ANSYS distribution media were used to develop the tools The Compac Visual Fortran Compiler Rev 6 1 was used for programming and for generating the customized ANSYS executable on a Windows NT platform 2 Input of the creep data of the materials The creep behaviour of a material can be described by the strain hardening representation f 0 T 2 The time hardening representation or the work hardening representation can in general be transformed into eq 2 The relation eq 2 is transferred into the ANSYS database by means ofa number of discrete pairs of the form En 3 n T const o const x Several of such sets for different temperature and stress levels can be combined The complete creep data base then is as follows Extension of the ANSYS creep and damage simulation capabilities Page 7 p c LEN c c K MK N K MK N The first index refers to the temperature the second index to the stress and the third to the strain K is the number of temperature levels Mk the number of stress levels within the k th temperature level an
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