Table of Contents
MPC Project Omega model
The MPC Project Omega creep model is described in the standard “API 579-1/ASME FFS-1 2007 Fitness-For-Service” chapters 10.3.5.3 a F.7.1.1.
The creep strain rate is defined in (10.1) as $$\dot\varepsilon_c = \dot\varepsilon_{c0}\exp(\Omega_m\varepsilon_c),$$ where $\dot\varepsilon_{c0}$ is the creep strain rate in the beginning of the time interval, $\Omega_m$ is the multiaxial damage parameter, and $\varepsilon_c$ is the accumulated creep strain. The values of $\dot\varepsilon_{c0}$ and $\Omega_m$ are determined accoring to the section F.7.1.1 of the standard.
Input quantities
The MPC Project Omega model is activated by the parameter $\mathtt{KCRP}=5$ in the file name.iP.
All materials used must be assigned to the elements using the file name.DAT.
The material parameter files have the following structure:
* * Comments *
AKONSTANTY $A_0$ $A_1$ $A_2$ $A_3$ $A_4$
BKONSTANTY $B_0$ $B_1$ $B_2$ $B_3$ $B_4$
BETA_OMEGA $\beta_\Omega$
ALFA_OMEGA $\alpha_\Omega$
SR_DELTA $\Delta_\Omega^\text{sr}$
CD_DELTA $\Delta_\Omega^\text{cd}$
- The number of initial comment lines is unlimited.
- There must be an empty line before each block.
- The blocks
AKONSTANTY,BKONSTANTY,BETA_OMEGA,ALFA_OMEGA,SR_DELTAaCD_DELTAcontain all 14 parameters of the model.
| Model parameters | ||
|---|---|---|
| $A_0$ to $A_5$ | material constants defined in table F.30 of the standard | |
| $B_0$ to $B_5$ | ||
| $\beta_\Omega$ | the parameter of the MPC project | |
| $=0.33$ | (constant) | |
| $\Delta_\Omega^\text{cd}$ | the correction parameter for creep toughness | |
| $=-0.3$ | ductile material | |
| $=+0.3$ | brittle material | |
| $\alpha_\Omega$ | the parameter of the MPC project | |
| $=3.0$ | a sphere or spherical bottom of a pressure vessel with an internal overpressure | |
| $=2.0$ | a cylinder or cone with an internal overpressure | |
| $=1.0$ | other shapes and loadings | |
| $\Delta_\Omega^\text{sr}$ | the corection parameter for creep properties dispersion | |
| $=-0.5$ | lower bound | |
| $=+0.5$ | upper bound | |
Example
There is only one matterial used in the creep problem.
- name.iP
; KREST NLC NCYC KMOD KCRP KLARG KCNT IP 1 11 1 0 5 0 0 3*0 11*2 RP 10*0 0 1 100 1000 10000 30000 80000 120000 160000 200000 250000 EN EN
- name.DAT
number 1 mpcpo.dat
- mpcpo.dat
************************************************************************ * * * API 579-1 * * * * parameters description * * * * A(0) - A(4) model constants from the table F.30 * * B(0) - B(4) model constants from the table F.30 * * BETA_OMEGA parameter (always 0.33) * * ALFA_OMEGA parameter of the MPC project * * 3.0 sphere or spher. bottom w/ int. overpressure * * 2.0 cylinder or cone w/ internal overpressure * * 1.0 other * * SR_DELTA correction par. for the creep properties dispersion * * CD_DELTA correction parameter for the creep toughness * * * ************************************************************************ AKONSTANTY -16.3 38060.0 -9165.0 1200.0 -600.0 BKONSTANTY -1.0 3060.0 135.0 -760.0 247.0 BETA_OMEGA 0.33 ALFA_OMEGA 1.00 SR_DELTA -0.5 CD_DELTA -0.3