You can input other creep expressions using the user programmable feature and setting TBOPT = 100.
You can define the number of state variables using the TB command with Lab = STATE. The following
example shows how five state variables are defined.
TB,STATE,1,,5You can simultaneously model creep (TB,CREEP) and isotropic, bilinear kinematic, and Hill anisotropy
options to simulate more complex material behaviors. See Material Model Combinations for the com-
bination possibilities. Also, see Material Model Combination Examples (p. 216).
To perform an implicit creep analysis, you must also issue the solution RATE command, with Option
= ON (or 1).The following example shows a procedure for a time hardening creep analysis. (See Fig-
ure 8.11:Time Hardening Creep Analysis (p. 212).)
Figure 8.11: Time Hardening Creep Analysis
TimeStr ssThe user applied mechanical loading in the first load step, and turned the RATE command OFF to bypass
the creep strain effect. Since the time period in this load step affects the total time thereafter, the time
period for this load step should be small. For this example, the user specified a value of 1.0E-8 seconds.
The second load step is a creep analysis. The RATE command must be turned ON. Here the mechanical
loading was kept constant, and the material creeps as time increases.
/SOLU !First load step, apply mechanical loading
RATE,OFF !Creep analysis turned off
TIME,1.0E-8 !Time period set to a very small value
...
SOLV !Solve this load step
!Second load step, no further mechanical load
RATE,ON !Creep analysis turned on
TIME,100 !Time period set to desired value
...
SOLV !Solve this load stepThe RATE command works only when modeling implicit creep with either von Mises or Hill potentials.
For most materials, the creep strain rat e changes significantly at an early stage. Because of this, a gen-
eral recommendation is to use a small initial incremental time step, then specify a large maximum in-
cremental time step by using solution command DELTIM or NSUBST. For implicit creep, you may need
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