Are there any implicit creep examples showing how ANSYS interpolates
temperaturedependent material properties?
Yes, please see the ANSYS 8.1 implicit creep example below. It shows how the creep constants themselves are linearly interpolated before the Norton algorithm (implicit creep material model #10) is evaluated. The input is also attached to this record as "creep_temp_int.inp". fini /clear unif_t = 100.0 ! uniform temperature (illustrates tempdependent mat props) /title, Implicit Creep #10 (Norton) with Constant Uniaxial Stress in ANSYS 8.1 /plopts,info,1 /view,,1,2,3 /prep7 et,1,SOLID185,,1 ! uniform reduced integration with hourglass control r,1 mp,ex,1,10.0e6 ! Young's modulus, psi mp,nuxy,1,0.30 ! Poisson's ratio, unitless T1 = 25.0 ! temperature 1 = 25 degrees F T2 = 150.0 ! temperature 2 = 150 degrees F T3 = 200.0 ! temperature 3 = 200 degrees F C1_T1 = 0.11e9 ! C1 at temperature T1 C2_T1 = 1.1 ! C2 at temperature T1 C3_T1 = 0.0 ! C3 at temperature T1 C1_T2 = 0.12e9 ! C1 at temperature T2 C2_T2 = 1.2 ! C2 at temperature T2 C3_T2 = 0.0 ! C3 at temperature T2 C1_T3 =0.13e9 ! C1 at temperature T3 C2_T3 = 1.3 ! C2 at temperature T3 C3_T3 = 0.0 ! C3 at temperature T3 tb,creep,1,3,3,10 ! implicit creep model #10 (Norton) tbtemp,T1 tbdata,1,C1_T1,C2_T1,C3_T1 ! C1, C2, and C3 at temperature T1 tbtemp,T2 tbdata,1,C1_T2,C2_T2,C3_T2 ! C1, C2, and C3 at temperature T2 tbtemp,T3 tbdata,1,C1_T3,C2_T3,C3_T3 ! C1, C2, and C3 at temperature T3 ! Note: Creep strain rate = C1 * (Sigma^C2) * (e^(C3/T)) ! ! Therefore, the creep strain rate dependence on temperature ! is removed (other than interpolation of constants), since ! C3 = 0 for each temperature specified ... n,1,0.0,0.0,0.0 n,2,1.0,0.0,0.0 n,3,1.0,1.0,0.0 n,4,0.0,1.0,0.0 n,5,0.0,0.0,1.0 n,6,1.0,0.0,1.0 n,7,1.0,1.0,1.0 n,8,0.0,1.0,1.0 e,1,2,3,4,5,6,7,8 ! single element (1/4 symmetry) fini /solu antype,static ! no inertia effects, so transient not needed ... nlgeom,on nsel,s,loc,x,0.0 d,all,ux,0.0 ! YZ symmetry plane nsel,s,loc,y,0.0 d,all,uy,0.0 ! XZ symmetry plane nsel,s,loc,z,0.0 d,all,uz,0.0 ! XY plane is held (pull nodes at Z=1) ... nsel,s,loc,z,1.0 sf,all,pres,20.0e3 ! constant stress as area of pressure decreases ... nsel,all tunif,unif_t! uniformtemperature toffst,460 ! Fahrenheit to Rankine conversion ... outres,all,all outpr,all,last time,1.0e8 deltim,1.0e8,1.0e9,1.0e8 rate,off solve save time,1.0e4 deltim,1.0e1,1.0e2,1.0e2 ! largest time step = 100 seconds ... rate,on,on nlgeom,on ! load drop matches cross section area decrease solve save fini /post1 /graph,full /dscale,,1 ! true scale displacement magnification set,first prnsol,epel,prin ! elastic strain (RATE,OFF result) plnsol,u,sum,2 /wait,1 set,last prnsol,epel,prin ! elastic strain (RATE,ON result) prnsol,epcr,prin ! correctly uses EFFNU=0.5 plnsol,u,sum,2 prnsol,u,comp /wait,1 fini /post26 numvar,200 file,,rst esol,2,1,,s,eqv,seqv ! average equivalent stress (constant) esol,3,1,,epcr,eqv,epcreqv ! average equivalent creep strain esol,4,1,,nl,creq,nlcreq ! average accumulated equivalent creep strain esol,5,1,,epel,eqv,epeleqv ! average equivalent elastic strain store,merge prvar,2,3,4,5 plvar,3,5 ! creep strain and elastic strain /wait,3 ! Note: Creep strain rate = C1 * (Sigma^C2) * (e^(C3/T)) const_T1 = C1_T1*exp(C3_T1/T1) ! constant part of equation ... const_T2 = C1_T2*exp(C3_T2/T2) const_T3 = C1_T3*exp(C3_T3/T3) nlog,11,2,,,C2_T1_ln_Sigma,,,,C2_T1 ! C2_T1 * ln(Sigma) nlog,12,2,,,C2_T2_ln_Sigma,,,,C2_T2 ! C2_T2 * ln(Sigma) nlog,13,2,,,C2_T3_ln_Sigma,,,,C2_T3 ! C2_T3 * ln(Sigma) exp,21,11,,,cr_rate_T1,,,,const_T1 ! const_T1*Sigma^C2_T1 exp,22,12,,,cr_rate_T2,,,,const_T2 ! const_T2*Sigma^C2_T2 exp,23,13,,,cr_rate_T3,,,,const_T3 ! const_T3*Sigma^C2_T3 solu,30,dtime,,delta_t ! time step size prod,31,21,30,,crinc_T1 ! creep strain increment for T1 prod,32,22,30,,crinc_T2 ! creep strain increment for T2 prod,33,23,30,,crinc_T3 ! creep strain increment for T3 plvar,21,22,23 ! creep strain rates at T1, T2, and T3 prvar,30,21,22,23 ! creep strain rates prvar,30,31,32,33 ! creep strain increments /eof = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Note: SLIGHT differences in the creep strain rates and creep strain increments from the POST26 calculations are due to slightly different convergence history for the different temperatures. Incidentally, by setting C3 to zero, the strain rate was not effected by the current temperature, so the temperature was only used to interpolate the creep constants, not determine the creep strain rate when the equation was evaluated. = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = For 0 degrees: (Matches 25 degree data, as expected ...) ============== THE FOLLOWING DEGREE OF FREEDOM RESULTS ARE IN GLOBAL COORDINATES NODE UX UY UZ USUM 1 0.0000 0.0000 0.0000 0.0000 2 0.29762E01 0.0000 0.0000 0.29762E01 3 0.29762E010.29762E01 0.0000 0.42090E01 4 0.0000 0.29762E01 0.0000 0.29762E01 5 0.0000 0.0000 0.63141E01 0.63141E01 6 0.29762E01 0.0000 0.63141E01 0.69804E01 7 0.29762E010.29762E01 0.63141E01 0.75884E01 8 0.0000 0.29762E01 0.63141E01 0.69804E01 ***** ANSYS POST26 VARIABLE LISTING ***** TIME 1 S EQV 71E01 0.12204 0.14516 8 0.0000 0.55571E01 0.12204 0.13410 ***** ANSYS POST26 VARIABLE LISTING ***** TIME 1 S EQV 1 EPCREQV 1 NL CREQ 1 EPELEQV seqv epcreqv nlcreq epeleqv 9695.5 20000.0 0.109704 0.109704 0.200000E02 9795.5 20000.0 0.110836 0.110836 0.200000E02 From the actual creep strain data above, we compute the creep strain increment to be: 0.110836  0.109704 = 0.001132 in/in The creep strain increment for the majority of the run is based on the maximum delta time step size of 100.0 seconds (see below). Since the stress remains constant at 20,000 psi, the following confirms that the creep strain increment for T = 100 degrees is 1.1315e3 in/in. This value is arrived at by linear interpolation of the creep constants: T1 = 25.0 C1_T1 = 0.110e9 C2_T1 = 1.10 T = 100.0 C1_T = 0.116e9 C2_T = 1.16 (60% from T1 to T2) T2 = 150.0 C1_T2 = 0.120e9 C2_T2 = 1.20 Creep strain rate = C1 * (Sigma^C2) * (e^(C3/T)) e_rate = 0.116e9 * 20,000.0^1.16 * e^(0/T) = 1.1315e5 in/in/sec e_inc = (1.1315e5 in/in/sec) * (100 seconds) = 1.1315e3in/in Note: The linear interpolation is done on the creep constants and not on the evaluated creep strain rates at the two bounding temperatures (T1 and T2 in this case) ... TIME 0 DTIM 21 EXP 22 EXP 23 EXP delta_t cr_rate_T1 cr_rate_T2 cr_rate_T3 9695.5 100.000 0.592279E05 0.173947E04 0.507322E04 9795.5 100.000 0.592279E05 0.173947E04 0.507322E04 TIME 0 DTIM 31 PROD 32 PROD 33 PROD delta_t crinc_T1 crinc_T2 crinc_T3 9695.5 100.000 0.592279E03 0.173947E02 0.507322E02 9795.5 100.000 0.592279E03 0.173947E02 0.507322E02 = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = For 150 degrees: ================ THE FOLLOWING DEGREE OF FREEDOM RESULTS ARE IN GLOBAL COORDINATES NODE UX UY UZ USUM 1 0.0000 0.0000 0.0000 0.0000 2 0.83849E01 0.0000 0.0000 0.83849E01 3 0.83849E010.83849E01 0.0000 0.11858 4 0.0000 0.83849E01 0.0000 0.83849E01 5 0.00000.0000 0.19238 0.19238 6 0.83849E01 0.0000 0.19238 0.20985 7 0.83849E010.83849E01 0.19238 0.22599 8 0.0000 0.83849E01 0.19238 0.20985 ***** ANSYS POST26 VARIABLE LISTING ***** TIME 1 S EQV 1 EPCREQV 1 NL CREQ 1 EPELEQV seqv epcreqv nlcreq epeleqv 9695.5 20000.1 0.168651 0.168651 0.200001E02 9795.5 20000.1 0.170390 0.170390 0.200001E02 From the actual creep strain data above, we compute the creep strain increment to be: 0.170390  0.168651 = 0.001739 in/in The creep strain increment for the majority of the run is based on the maximum delta time step size of 100.0 seconds (see below). Since the stress remains constant at 20,000 psi, the following confirms that the creep strain increment for T2 (150 degrees) is 0.173948E02 in/in. TIME 0 DTIM 21 EXP 22 EXP 23 EXP delta_t cr_rate_T1 cr_rate_T2 cr_rate_T3 9695.5 100.000 0.592281E05 0.173948E04 0.507323E04 9795.5 100.000 0.592281E05 0.173948E04 0.507323E04 TIME0 DTIM 31PROD 32 PROD 33 PROD delta_t crinc_T1 crinc_T2 crinc_T3 9695.5 100.000 0.592281E03 0.173948E02 0.507323E02 9795.5 100.000 0.592281E03 0.173948E02 0.507323E02 = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = For 200 degrees: ================ THE FOLLOWING DEGREE OF FREEDOM RESULTS ARE IN GLOBAL COORDINATES NODE UX UY UZ USUM 1 0.0000 0.0000 0.0000 0.0000 2 0.22452 0.0000 0.0000 0.22452 3 0.22452 0.22452 0.0000 0.31752 4 0.0000 0.22452 0.0000 0.22452 5 0.0000 0.0000 0.66420 0.66420 6 0.22452 0.0000 0.66420 0.70112 7 0.22452 0.22452 0.66420 0.73619 8 0.0000 0.22452 0.66420 0.70112 ***** ANSYS POST26 VARIABLE LISTING ***** TIME 1 S EQV 1 EPCREQV 1 NL CREQ 1 EPELEQV seqv epcreqv nlcreq epeleqv 9695.5 20000.8 0.491894 0.491894 0.200008E02 9795.5 20000.8 0.496967 0.496967 0.200008E02 From the actual creep strain data above, we compute the creep strain increment to be: 0.496967  0.491894 = 0.005073 in/in The creep strain increment for the majority of the run is based on the maximum delta time step size of 100.0 seconds (see below). Since the stress remains constant at 20,000 psi, the following confirms that the creep strain increment for T3 (200 degrees) is 0.507345E02 in/in. TIME 0 DTIM 21 EXP 22 EXP 23 EXP delta_t cr_rate_T1 cr_rate_T2 cr_rate_T3 9695.5 100.000 0.592303E05 0.173955E04 0.507345E04 9795.5 100.000 0.592303E05 0.173955E04 0.507345E04 TIME 0 DTIM 31 PROD 32 PROD 33 PROD delta_t crinc_T1 crinc_T2 crinc_T3 9695.5 100.000 0.592303E03 0.173955E02 0.507345E02 9795.5 100.000 0.592303E03 0.173955E02 0.507345E02 = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = For 250 degrees: (Matches 200 degree data, as expected ...) ================ THE FOLLOWING DEGREE OF FREEDOM RESULTS ARE IN GLOBAL COORDINATES NODE UXUY UZ USUM 1 0.0000 0.0000 0.0000 0.0000 2 0.22452 0.0000 0.0000 0.22452 3 0.22452 0.22452 0.0000 0.31752 4 0.0000 0.22452 0.0000 0.22452 5 0.0000 0.0000 0.66420 0.66420 6 0.22452 0.0000 0.66420 0.70112 7 0.22452 0.22452 0.66420 0.73619 8 0.0000 0.22452 0.66420 0.70112 ***** ANSYS POST26 VARIABLE LISTING ***** TIME 1 S EQV 1 EPCREQV 1 NL CREQ 1 EPELEQV seqv epcreqv nlcreq epeleqv 9695.5 20000.8 0.491894 0.491894 0.200008E02 9795.5 20000.8 0.496967 0.496967 0.200008E02 = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = 

